VATIC Associates
VAT-E-05 Circuit Breakers and Switches
Circuit Breakers and Switches
VAT-E-05
Contents
Overview................................................................................................................ 3
1. Circuit Breaker Design Characteristics ........................................................3
Common Breaker Terms ..........................................................................................................3
Ratings .....................................................................................................................................4
Classes......................................................................................................................................4
Live Tank vs. Dead Tank Circuit Breakers..............................................................................6
2. Circuit Breaker Components......................................................................... 7
Interrupting Chamber ...............................................................................................................7
Contacts..................................................................................................................................10
Operating Mechanism ............................................................................................................14
Bushing and Connection Terminals .......................................................................................15
Control Cabinet ......................................................................................................................20
Indications ..............................................................................................................................21
Racking Mechanisms .............................................................................................................27
Safety Locks ...........................................................................................................................28
3. Types of Circuit Breakers............................................................................ 28
Oil - 2.4 kV to 220 kV ...........................................................................................................28
Air Magnetic - 16 kV And Below ..........................................................................................32
SF6 Gas – 66 kV to 500 kV ....................................................................................................35
Vacuum – 16 kV And Below .................................................................................................41
Self-Contained .......................................................................................................................43
4. Types of Operating Mechanisms ................................................................. 46
Manual ...................................................................................................................................46
Solenoid .................................................................................................................................48
Pneumatic...............................................................................................................................49
Motor Spring ..........................................................................................................................52
Hydraulic ................................................................................................................................54
Gas .........................................................................................................................................60
5. Circuit Switches............................................................................................ 61
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Common Suppliers.................................................................................................................61
Construction ...........................................................................................................................61
Operation................................................................................................................................61
Alarms and Indications ..........................................................................................................62
Application .............................................................................................................................62
Configurations........................................................................................................................62
Interlocks................................................................................................................................62
Malfunctions ..........................................................................................................................62
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Overview
This section of the operator’s manual will provide the reader with the
information that is needed to answer what, how, and when of circuit
breaker/switches operation, application and system interrelationship.
The discussion within this section will revolve around introducing the
operator to the two categories of switching equipment (circuit breakers
and switches) commonly used within a typical transmission system. In
addition, this section addresses the methods developed for the operating
mechanisms to perform their function.
1. Circuit Breaker Design Characteristics
The circuit breaker is one of the most important pieces of electric utility
equipment and has the most severe duty cycle imposed on it. Circuit
breakers are the only current interrupting devices that combine full fault
current interrupting capability with the ability to be manually or
automatically opened or closed.
During abnormal conditions, the function of the circuit breaker is to
disconnect and electrically isolate equipment and lines in the electrical
system that are in trouble or have failed. During normal conditions, the
circuit breaker carries and switches load currents from zero to rated
current on a continuous basis.
Circuit breakers are designed to interrupt either normal or fault currents.
They behave as large switches that may be opened or closed by local
control switches or remotely. Furthermore, circuit breakers will
automatically open a circuit whenever line current exceeds a preset
limit. Circuit breakers can be set more accurately than fuses and, unlike
fuses, they do not require replacement after each fault.
Common Breaker Terms
Breaker Speed
The speed at which a circuit breaker operates is very important. The
speed of the circuit breaker is measured in feet per second between the
two points, which has been determined as necessary by the
manufacturer to extinguish the arc in the arcing zone.
Arc Zone
The area that is used to measure breaker speed. It is usually a few
inches after where the contacts part on opening and before the contacts
make closing.
Closing Time
The time that the closing coil is energized until the main contacts touch.
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Expressed in cycles.
Opening Time
The time that the trip coil is energized (0 line) to the point where the
main contacts part. Expressed in cycles.
Ratings
Rated Voltage
Rated voltage is the maximum operating voltage for which the circuit
breaker is designed. Voltage ratings are given in terms of three-phase
line-to-line voltage.
Impulse Withstand Impulse withstand voltage designates the strength of the circuit breaker
to resist sudden, short-duration voltage stresses, such as those imposed
Voltage
by lightning strikes. This rating is also called the basic insulation level,
or BIL, and is generally 3 to 4 times the rated voltage.
Short Time
Current
The short time current rating is the maximum amount of current in
amperes which the circuit breaker contacts and internal conductors can
carry, without damage, for a short time period (typically, three seconds).
This rating also accounts for permanent stress to insulation, heat, and
electromagnetic effects.
Continuous
Current Rating
Continuous current is the maximum value of steady state amperes that
the circuit breaker contacts and internal conductors are designed to
carry.
Rated
Interrupting
Current
Rated interrupting current is the maximum current at the time the
contacts part that the circuit breaker is designed to interrupt.
Duty MVA
Duty MVA is the maximum power at the time the contacts part that the
circuit breaker is designed to interrupt.
Duty Cycle
The duty cycle is the minimum amount of time necessary after a closing
and tripping operation before the circuit breaker can be closed and
tripped again. The duty cycle is listed on the circuit breaker nameplate.
A typical duty cycle listed on the nameplate may be CO-15 sec.-CO,
which means close and open, wait 15 seconds, and then close and open
again.
Classes
Air-Magnetic
An air magnetic circuit breaker operates on the principle that an arc can
be interrupted in air by sufficiently elongating and cooling it. This is
accomplished by means of a strong magnetic field that lengthens the arc
and forces it into a cool dielectric material. Extinguishing of the arc
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takes place in a device called an arc chute, which is mounted on the
circuit breaker above the contact.
Air-Blast
An air blast circuit breaker uses high-pressure dry air for arc
interruption. The air blast circuit breaker is a two-pressure system
breaker, which is of a live tank design. When an air blast circuit
breaker opens, a jet of high-pressure air is blown through the arcing
zone, constricting the arc by pressure and cooling it by diffusion and
absorption of heat.
Oil Circuit
Breakers (OCB)
An oil circuit breaker (OCB) is one of the most common breakers in a
typical transmission system. This breaker uses oil of high dielectric
strength as an insulating and interrupting medium. When the oil circuit
breaker opens the oil around the contacts is vaporized into a gas by the
arc. To control the expansion of the gas formed by the arc a device
called an interrupter is used. The containment of the gas expansion
tends to cool the arc, which increases the dielectric strength of the gas.
When the circuit breaker opens and the contacts separate, the moveable
contact passes toward the open end of the interrupter, passing by a
series of openings or ports built into the interrupter. The pressure inside
the interrupter blows the elongated arc through the ports into the cooler
oil outside thus extinguishing the arc.
Vacuum Circuit
Breakers
Vacuum circuit breakers can interrupt high voltage power with the
contacts moving only 1/4 to 1/2 of an inch. The reason that vacuum
breaker contacts have this capability is that a vacuum is an excellent
insulator. Electrical current cannot flow across a gap between two
conductors unless there is present, between the conductors, some source
of ions or electrons. Obviously, if the gap is in a perfect vacuum, there
is nothing in the gap. This includes ions or electrons.
If two contacts which are butting and carrying current in a vacuum can
be parted in the vacuum and the vacuum maintained as they part, the arc
will be quickly extinguished. Because of the design of vacuum
breakers, small mechanisms with low power requirements can do the
job previously requiring large mechanisms with huge springs and large
operating power requirements.
SF6
Another method of arc interruption uses sulfur hexaflouride gas. Gas
circuit breakers, frequently used in the system, come in many styles and
designs. There is a two-pressure, and a single-pressure design. Though
the design may vary, they all have several common elements. These
elements are:
•
They all utilize SF6 (sulfur hexaflouride) gas as an insulating and
interrupting medium.
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•
•
SF6 gas is:
•Highly stable
•Odorless
•Inert
•Colorless
•Non-toxic
•Tasteless
•Non-poisonous
•Electro-negative
•Nonflammable
•Heavier than-air
They all operate as a closed gas system where no gas is vented to
atmosphere.
At 30 to 45 psig of pressure, it is superior to the dielectric strength of
transformer oil. Because of its superior properties, this style of circuit
breaker is smaller in size and faster in interrupting than most oil circuit
breakers.
Single-Pressure
For a single-pressure SF6 breaker, also known as a puffer breaker, the
gas fills the void within the breaker’s tank. Depending on the design of
the breaker, the SF6 that is in the area of the arc or an internal
mechanical bellows will place the SF6 gas in contact with the arc. The
SF6 combines with the arc to produce a relatively immobile ion. The
loss of conducting electrons causes the arc to be easily extinguished at
current zero.
Dual-Pressure
When the gas blast circuit breaker opens, a blast of SF6 gas is blown
into the arc. Because SF6 gas is electronegative, it combines with the
arc and produces a relatively immobile ion. The loss of conducting
electrons causes the arc to be easily extinguished at current zero.
The important difference between the single and dual pressure breakers
is the single-pressure breaker does not have a compressor and storage
tank to store the SF6 gas. The single-pressure breaker generally relies
on the extinguishing properties of the SF6 gas to quench the arc.
Live Tank vs. Dead Tank Circuit Breakers
A live tank is a circuit breaker tank that is energized at the same
potential as the line. A dead tank is a circuit breaker tank that is at the
same potential as ground.
Due to the inherent greater safety of a dead-tank circuit breaker, most of
the circuit breakers are of the dead tank design. The system has very
few live tank circuit breakers left in the system. Only a few air blast
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circuit breakers employ the Live tank design. Even these should be
replaced by the end of the year 2000.
2. Circuit Breaker Components
This part of the section describes and identifies through text, pictures,
and line drawings the major subassemblies that make up a circuit
breaker.
Interrupting Chamber
Dielectric Medium
The dielectric medium is one of the most significant physical properties
that affect the interrupting properties of the circuit breaker. The gas or
liquid that fills the interrupting chamber and occupies the space
between the breaker contacts is called the circuit breaker dielectric or
dielectric medium. The dielectric medium of circuit breakers must
have excellent insulating capabilities and only electrically breakdown
during very high voltages. Circuit breakers use dielectric mediums of
oil, air, gas, or vacuum.
Dielectric mediums are used in circuit breakers for arc extinction and
electrical insulation. Dielectric mediums provide electrical insulation
between the contacts when the contacts are open. Dielectrics also
provide electrical insulation between the contacts and other non-current
carrying metal components of the circuit breaker such as the tank of the
interrupting chamber.
A medium’s dielectric strength is a measure of how well the medium,
or material can withstand voltage without conducting electricity. For
example, insulating oil has a higher dielectric strength than air.
Therefore, oil can withstand a higher voltage without conducting
electricity than air. In addition, a medium is sometimes pressurized. In
general, pressurizing a dielectric increases its dielectric strength.
Air
Air is used in air circuit breakers for arc extinction and electrical
insulation in the interrupting chamber. An air gap of 0.3 inches can
withstand 25 kV at normal pressure and ambient temperature (40°C).
The air used to extinguish the arc is usually compressed to very high
pressures (2000 - 4000 pounds per square inch) to attain the dryness
required for arc quenching. Since water is a good conductor of
electricity, the less moisture that the air contains the better the dielectric
strength of the air.
Oil
In an oil circuit breaker, oil provides electrical insulation in the
interrupting chamber, while hydrogen gas is used for arc extinction. Oil
decomposes under the influence of extreme arc heat into carbon and
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hydrogen creating a high-pressure arc bubble. The arc bubble consists
of a mixture of metal vapors and ionized gases having hydrogen content
of approximately 70 percent. The hydrogen has the effect of
de-ionizing and extinguishing arcs at a rapid rate by cooling them.
SF6
SF6 gas is used in gas circuit breakers for arc extinction and electrical
insulation in the interrupting chamber. SF6 gas has remarkable arc
quenching abilities that are attributed to its ability to recover its
dielectric strength quickly after arc passes through a current zero.
Vacuum
In a vacuum circuit breaker, the dielectric medium in the interrupting
chamber is a vacuum. Ideally, a vacuum would provide perfect
insulation because there would not be anything to fuel an arc. In
practice, however, gases are absorbed onto the contacts within the
vacuum, and there is an emission of charged particles from the contact
surfaces during arc interruption.
Arc Interruption
Mechanisms
In a circuit breaker, a number of factors work together to extinguish an
arc and interrupt a circuit. These factors include:
•
Speed
•
Distance
•
Cooling
•
Dielectric strength
•
Current zero
Speed
The speed at which a circuit breaker's contacts separate is important
because the faster the contacts open, the less time there is for the space
between the contacts to heat up and become a conductor. Slower
separation allows more time for an arc to form and maintain itself.
Distance
When the distance between the contacts increases, the arc must stretch
in order to maintain current flow. In addition, as the distance increases,
more voltage is required to sustain current flow.
Cooling
Generally, when air and gases are heated, they become electrical
conductors: as they get hotter, they conduct better. Consequently,
cooling plays an important role in helping to extinguish arcs. The term
"cooling” refers to any physical effects that take heat away from an arc.
Some common cooling methods include directing a blast of air or gas at
an arc as shown in Figure E-05-A-1. Forcing the arc against cold metal
or insulating materials, as illustrated in Figure E-05-A-1. Submerging
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the circuit breaker contacts and the arc in insulating oil as pictured in
Figure E-05-A-2.
Figure E-05-A-1 Air/Gas Blast Elongating Arc
Insulating Material
Figure E-05-A-1 Arc Forced Against Cold Metal Or Insulating
Material
Oil
Figure E-05-A-2 Contacts and Arc Submerged In Insulating Oil
Dielectric Strength
Circuit breakers also use mediums of different dielectric strengths to
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help extinguish arcs. A medium's dielectric strength is a measure of
how well the medium, or material, can withstand voltage without
conducting electricity. Because of differences in dielectric strength,
some materials conduct electricity less readily than others do.
Current Zero
Another factor that helps to extinguish arcs is current zero. Alternating
current constantly changes polarity from positive to negative or negative
to positive in recurring cycles, as indicated in Figure E-05-A-3. Current
zero occurs at the exact time that the polarity changes. At that time,
there is no current flow. Circuit breakers are designed to take
advantage of these momentary absences of current flow to extinguish
arcs.
Figure E-05-A-3 Current Zero
Contacts
The primary purpose of the interrupting chamber of a circuit breaker is
to house the insulating gases or liquids of a sufficient dielectric strength
to extinguish the arc formed when the circuit breaker contacts open.
To aid in arc interruption, interrupting chambers use the principles of
arc elongation, arc constriction, and de-ionization of the conductive arc
path. Arc elongation simply means making the arc path longer, thereby
increasing cooling and de-ionization by diffusion. Arc constriction
reduces the cross sectional area of the arc; thereby increasing the
voltage required to maintain it. De-ionizing the conductive gas created
by the arc path reduces the free electrons available in the gas, which, in
effect, changes the conductivity.
Multiple interrupting chambers in series per phase increases the
interrupting capacity of the circuit breaker. By placing multiple
interrupting chambers in series, the voltage across each interrupting
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chamber is reduced proportionally; therefore the dielectric strength of
the interrupting medium exceeds the ability of the arc to recover at the
applied voltage. Recovery voltage is the rapid rise of voltage across the
opening contacts after the arc first extinguishes and the current flow
goes to zero.
A circuit breaker may use multiple interrupters. However, if the voltage
distribution is not evenly divided between each set of contacts, the
dielectric strength of the insulation between contacts may not prevent
re-ignition of the arc. The placement of capacitors in parallel with the
interrupting chamber ensures equal voltage distribution across the
contacts. These capacitors are referred to as switching or grading
capacitors.
Resistors that shunt the arc gap increase the interrupting capacity and
decrease the rate of rise of the arc's recovery voltage. When a shunt
resistor is used, a part of the arc’s current is diverted through the
resistor. The resistor will drop voltage across it, which leaves less
voltage to re-strike the arc.
All circuit breakers have at least one set of contacts per phase, which
are responsible for closing or opening the high voltage circuit through
its pole. The force required to open or close these contacts is supplied
by the circuit breakers operating mechanism.
The contacts for carrying load current are typically made of copper or
copper coated with silver since copper has a low resistance and is well
suited for carrying current continuously without excessive heating. On
the down side, copper has a low melting point (1,083°C) and has a
tendency to weld when subjected to considerable amounts of arcing.
A pair of contacts made of tungsten is sometimes provided to carry
current only during the closing or interrupting process. Tungsten is used
because it has a high melting point (3,380°C) and little tendency to
vaporize or burn during arcing as copper does. The copper contacts that
carry current continuously are referred to as the "main" contacts and the
tungsten contacts between which the arc is drawn are referred to as the
"arcing" contacts.
There are five principal types of circuit breaker contacts:
•
Butt
•
Wedge
•
Brush
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Butt
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•
Bayonet
•
Finger
Butt contacts, as shown in Figure E-05-A -4, consist of two conductors
with flat or curved faces that butt together when the circuit breaker is
closed. The mating surfaces are usually silver-plated to reduce heating
and pitting. A spring held tight by a latch or other restraining device
holds the moving butt contact solidly against the stationary butt contact.
When the circuit breaker trips the latch is released and the spring pulls
the contacts apart rapidly. These types of contacts are primarily used on
low voltage (13.8 kV) and low current applications.
Figure E-05-A -4 Butt Contact
Wedge
Wedge contacts, also known as finger and blade contacts, are commonly
used for circuit breakers. The wedge, the moving contact, is forced into
a set of flared contact fingers, the stationary contacts, as illustrated in
Figure E-05-A-5. These contacts are usually arranged in pairs and
provided with reinforcing springs to increase contact pressure. Steel
supporting springs align the fingers on the wedge.
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Figure E-05-A-5 Wedge Contacts
Brush
Brush contacts, as shown in
Figure E-05-A-6, are used on lower voltages. The stationary contact
consists of solid copper stud. The moving contact consists of
laminations and has a main contact and one or more secondary contacts.
Figure E-05-A-6 Brush Contact
Bayonet
Bayonet contacts consist of a rod for the moving contact that is forced
into a stationary sheath contact. The stationary sheath contact usually
consists of one or more spring sleeves, which provide the contact
pressure during operation. Bayonet contacts are made of copper and
used for the main current carrying contacts. An arcing contact of a
tungsten alloy is usually provided to prevent main contact surface
damage during circuit interruption. Figure E-05-A-7 is an illustration of
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bayonet contacts.
Figure E-05-A-7 Bayonet Contacts
Finger
Finger contacts shown in Figure E-05-A-8, is used on almost all
voltages, SF6 puffer type and oil circuit breakers. When the finger
contact is closed, eight to ten stationary contact fingers make the current
connection to the main moving contact. As the main moving contact
separates from the stationary contact fingers, the arcing contacts still
make the current connection. An arc is formed as the arcing contacts
begin to separate. The movement of the contact forces SF6 gas over the
arcing contacts to extinguish to the arc.
Figure E-05-A-8 Finger Contacts
Operating Mechanism
The operating mechanism provides the mechanical force that opens and
closes the circuit breaker contacts. There are six types operating
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mechanisms, distinguished by how they close the circuit breaker main
contacts. The six types are manual, solenoid, pneumatic, motor spring,
hydraulic, and gas. For each, the method of opening the main contacts
is the same: the contacts fall open under the influence of gravity and
accelerating springs following the operation of a trip coil.
All of these circuit breaker mechanisms have a mechanical flag, called
the semaphore, which shows whether the circuit breaker contacts are
open or closed. The different operating mechanisms are covered in
more detail later in section 3.1.4.
Bushing and Connection Terminals
Bushings are used as the entrance leads or connection terminals into
circuit breakers. In addition to providing the point of connection, the
bushing provides insulation to the conductor and seals the circuit
breaker from the harmful effects of the environment. Bushings may
also contain bushing current transformers (BCTs) for measuring current
flow through the circuit breaker as shown in Figure E-05-A-9. Figure E05-A-10 illustrates where the bushing current transformers are normally
located on a circuit breaker.
POLARITY MARK
POLARITY MARK
TRANSFORMER
LEADS
X1
X2
X3
X4
X5
BUSHING TYPE
Figure E-05-A-9 Bushing Current Transformer
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Normal
BCT
Location
Figure E-05-A-10 Normal BCT Location On The Bushing
Five major types of bushings are used on circuit breakers. These five
types are:
Solid Porcelain
•
Solid porcelain bushings
•
Oil filled bushings
•
Condenser bushings
•
SF6 bushings
•
Composite and Silicone
Solid porcelain bushings, shown in Figure E-05-A-11, are solid
porcelain cylinders that surround the conductors. Solid porcelain
bushings are used for lower-voltage circuit breakers (up to about 20 kV)
of relatively small interrupting capacity.
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Figure E-05-A-11 Solid Porcelain Bushing
Oil-Filled
Oil-filled bushings are used on circuit breakers operating at voltages up
to 230 kV. In the example shown in Figure E-05-A-12, the conductor is
mounted inside cylindrical porcelain insulators filled with oil. Thin
insulating cylinders of special materials, like plastics, may divide the oil
space with an oil gauge or sight glass at the top to indicate the oil level
in the bushing.
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Figure E-05-A-12 Oil Filled Bushing
Condenser
Condenser bushings, as shown in Figure E-05-A-13, are used on higher
voltage circuit breakers (usually over 75 W). Conductors may be
insulated with concentric layers of oil-impregnated paper, with metal
foil inserted at several locations among the layers. This insulation
arrangement is similar to placing a voltage across several series
connected capacitors.
If the capacitors or layers have equal
capacitance, the voltage is equally divided between them. The
capacitances of each layer are made equal by using metal foil of equal
area. As the radius of the layers increases further from the conductor,
the length of metal foil must decrease to obtain the same area. The
division of voltage among capacitance layers of insulation allows a
reduction in the overall amount of insulation required.
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Figure E-05-A-13 Condenser Bushing
SF6 Bushings
In SF6 circuit breakers, the hollow porcelain bushing is opened to the
main breaker tank and filled with SF6 gas to serve as insulation as
shown in Figure E-05-A-14.
SF6 bushings are not generally
interchangeable with other types of bushings.
Figure E-05-A-14 SF6 Bushing
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Composite and
Silicone
VAT-E-05 Circuit Breakers and Switches
Composite and silicone bushings are a recent development in the
electrical industry. Their construction is similar to the solid porcelain
bushings. However, instead of using fired porcelain, a silicone and
resin composite is used. The bushing is not ridged like a solid porcelain
bushing, but is more like a firm rubber. The concept is that these new
bushings will provide a better service life since they will not be as
susceptible to environmental and physical damage like the porcelain
material.
Control Cabinet
The circuit breaker control cabinet, shown in Figure E-05-A-15, is
mounted on the circuit breaker and contains the important control
devices for the circuit breaker. The control cabinet also serves as the
termination point for control and indication cables wired to the control
house.
The circuit breaker control and indication circuits provide the necessary
capability to operate the circuit breaker safely. The control circuitry
enables the operator of the circuit breaker to trip or close the breaker
manually or automatically. The indication circuitry notifies personnel
of the status of the breaker, i.e., opened or closed, and alarm conditions.
Newer circuit breakers have alarm indication boards inside the control
cabinet.
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Figure E-05-A-15 Three Phase Circuit Breaker
Every circuit breaker has a control circuit associated with it. The
control circuit combines the switches, relays, control contacts, alarm
circuits, and indicating lights that enable the circuit breaker to be
controlled.
Control circuits are primarily powered by DC power. Compared to AC
control circuits, DC control circuits are more reliable. DC control
circuits can operate from station batteries during an outage while AC
control circuits may not.
The control circuit can be divided into three parts according to the
function each part performs. These three parts or functions are:
•
Opening or tripping
•
Closing
•
Indication
Indications
Sight gages
Sight gauges provide the Substation Operator with a visual indication of
the oil level in an oil bushing or the humidity of the air in an air circuit
breaker.
Oil circuit
breaker’s bushings
The Substation Operator may come across two different types of sight
gauges at the substation. They are:
Sight Level -provides a visual reference level of the oil in the bushings.
A sight level is shown in Figure E-05-A-16.
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Sight Level
Figure E-05-A-16 Sight Level
Gauge – provides a mechanical level indication of the oil in the
bushings. Figure E-05-A-17 is a typical example of an oil level gauge in
the TYPICAL system.
Oil Level
Gauge
Figure E-05-A-17 Oil Level Gauge
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Oil circuit
breaker’s - tanks
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As with the sight gauges of the oil bushings, the oil circuit breaker level
indications provide the Substation Operator with a visual indication of
the oil level in tank of the oil circuit breaker. There are three common
level indicators used to provide a indication of the oil level in the circuit
breaker tank, they are:
Sight Level – (or Sight glass) provides a visual reference as to the oil
level in the circuit breakers tank. A sight level is shown in Figure E-05A-18.
Figure E-05-A-18 Oil Tank Sight Glass
Gauge – provides a mechanical level indication of the oil in the tank,
using some type of mechanical level detection such as displacement of
or pressure/weight on the detecting device.
Float – similar to the gauge but provides the level indication from a
simple float connected to the meter through magnets.
Air circuit
breaker’s – Litmus
Paper
Provides a visual indication, a bull’s eye at the control cabinet, of the
humidity of the air inside the air circuit breaker. The paper will turn red
if the humidity within the circuit breaker is too great. Due to the
construction of the circuit breaker in service in the TYPICAL system,
for example a live tank circuit breaker, all air circuit breakers are
scheduled for replacement by the end of the year 2000.
Pressure Gauges
SF6 breakers, whether single or dual pressure, require the monitoring of
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the SF6 gas in the tank and the bushing so that the dielectric medium
meets design specifications to allow the breaker to operate as designed.
This is even more critical for the dual pressure systems since its proper
operation and its ability to extinguish the arc is dependent on the
pressurized SF6 gas in the high-pressure cylinder. Figure E-05-A-19 is a
typical example of pressure gauges used in the system for a dual
pressure SF6 breaker.
Highpressure
Gauge
Lowpressure
Gauge
Figure E-05-A-19 Pressure Gauges
Hydraulic Gauges
Hydraulic gauges are used to monitor the pressure of the hydraulic fluid
in hydraulic operating mechanisms. The pressure is monitored to
ensure the breaker operates as designed. Figure E-05-A-20 is a typical
example of a hydraulic pressure gauge used in the system.
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Hydraulic
Pressure
Gauge
Figure E-05-A-20 Hydraulic Gauge
Temperature
Gauge
Only dual pressure SF6 breakers monitor gas temperature. The
temperature is monitored to ensure that the breaker operates as
designed. Figure E-05-A-21 is a typical example of the temperature
gauges used in the system for its dual pressure SF6 breakers.
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Temperature
Gauges
Figure E-05-A-21 SF6 Temperature Gauges
Counters
Counters are used to measure the number of opening operations that the
breaker has performed. It is used by maintenance to determine what
work or repairs may need to be performed on the breaker or as a
troubleshooting aid. A typical counter is shown in Figure E-05-A- 22.
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Counter
Charging
Spring
Indicator
Semaphore
Figure E-05-A- 22 Counter and Semaphore
Semaphore
The circuit breaker’s semaphore provides the operator or the
maintenance individual with a visual indication of the breaker’s
operating state, i.e. open or closed. Most circuit breakers’ semaphore
indications are a mechanical type, which provides positive indication of
the position of the breaker. ABB uses a micro switch to detect the
position of the breaker so its semaphore indication does NOT provide
positive indication of the breaker’s position. Figure E-05-A- 22 is a
photo of a typical semaphore flag indicator that is commonly used in the
system. The semaphore indicates that the breaker is closed / shut.
Racking Mechanisms
When some of the smaller circuit breakers need to be worked on by
maintenance, the breaker is removed from its normal operating position
to a position that allows for the breaker to be worked on safely and
accessibility. This position is called the racked out position. When
maintenance needs to be performed on a breaker, such that it will need
to be racked out, the racking mechanism will have to be installed on to
the breaker. The racking mechanism provides maintenance personnel
with the necessary tools, supports and leverage to withdraw the breaker
from its normal operating position to its maintenance position and then
return it to its operating position after completion of the maintenance.
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Safety Locks
Safety locks provide some rudimentary level of protection for the
breaker. They may be electrical or mechanical interlocks to prevent
damage to the breaker from an improper action.
3. Types of Circuit Breakers
A particular type of circuit breaker is called by the type of interrupting
medium used. This section will provide a more detailed examination of
the various circuit breaker types used in a power delivery system.
There are five major types of circuit breakers to be discussed. They are:
•
Oil
•
Air Magnetic
•
SF6 gas
•
Vacuum
•
Self-contained
Oil - 2.4 kV to 220 kV
Oil circuit breakers are one of the most commonly used circuit breakers
on the system.
Common Suppliers The following is a list of commonly found oil circuit breakers used in
the typical system. They are:
•
ABB
•
GE
•
ITE
•
Westinghouse
•
Kelman
•
Mcgraw Edison
Basic Construction Oil circuit breakers use three types of arc interrupters to extinguish an
arc:
And Operation
Arc Extinction In
•
De-ion grid arc interrupters
•
Explosion oil blast interrupters
•
Impulse oil blast interrupters
The "de-ion grid" consists of a stack of insulated U-shaped iron plates
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and sheets of insulating material shaped to form pockets as illustrated in
Figure E-05-A-23. The moving contact passes through a slot at the
opening of the U. Vents are located between this slot and the exterior
of the interrupter.
Figure E-05-A-23 De-ion Grid Arc Interrupter
When the moving contact moves downward, an arc is formed in the slot
between the two contacts. Magnetic lines of force are set up around the
arc. The magnetic lines of force follow the iron path and force the arc
to do likewise.
The arc is forced through and confined to the grid area between the iron
plates. Oil in the grid area is vaporized by the heat of the arc, which
forms a gaseous mixture more than 70% hydrogen gas.
The specific heat of hydrogen is relatively high; meaning hydrogen
requires relatively large quantities of heat to raise its temperature. This
property has the effect of cooling and de-ionizing arcs at a rapid rate.
Therefore, the hydrogen in the path of an arc recovers its dielectric
strength rapidly.
In escaping through the vents, the hydrogen-endowed gas passes
through the center of the arc. As the hydrogen gas is relatively cooler
than the ionized gas in the center of the arc stream, it tends to de-ionize
the ionized gas.
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The shape of the interrupter towards the bottom of the U is such that a
longer arc path is formed. Thus, the de-ion grid interrupter works on a
combination of all three arc interruption methods previously referred to:
Arc Extinction In
Explosion Oil Blast
Interrupters
•
Forcing the arc into a confined space, thus decreasing its area
•
Causing the arc to travel through a longer path
•
De-ionizing the gas
The principle of operation of explosion oil blast interrupters differs
from the de-ion grid type in that oil is forced across or into the arc,
rather than the arc forced into the oil.
In explosion oil interrupters, two sets of butt contacts in series form the
circuit. Each is in a confining chamber as shown in Figure E-05-A-24.
The main moving contact consists of a hollow rod as shown in the
figure.
Figure E-05-A-24 Explosion Oil Blast Arc Interrupter
When the circuit breaker opens, two arcs are formed, one between each
set of contacts. The two arcs break down the oil between the contacts,
creating high-pressure gas bubbles. As with the de-ionized grid
interrupters, these gas bubbles consist mainly of hydrogen. The upper
arc and gas bubbles cause a great pressure on the oil in the upper
chamber. This forces the oil through openings in the plate between the
two chambers. These openings are located so that the stream of oil is
directed against the arc in the lower chamber.
The only path of escape for the expanding gas bubble in the lower
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chamber is through the hollow rod that forms the lower contact. The oil
forces the gas that forms in the lower arc down the hollow rod into the
breaker tank.
Although there is an initial lengthening of the arc when the contacts
move apart, this type of interrupter works mainly on the principle of
decreasing the cross sectional area of the arc path. When the gas is
forced out of the lower chamber, this area is zero.
Interrupters of this type differ widely in appearance and design.
However, the principle is same in that pressure generated by one arc
forces oil through or across the path of another arc.
Arc Extinction In
Impulse Oil Blast
Interrupters
The impulse oil blast type interrupters differ from the explosion type in
that the oil pressure is caused by mechanical means rather than by an
arc. Please refer to Figure E-05-A-25. The lower contact, in closing,
forces a piston to the top of a separate oil chamber against a spiral
spring. When the breaker opens, the spring forces the piston downward,
causing a blast of oil to flow across the arc path. Extremely fast arc
interruptions can be obtained by the proper use of this principle.
Figure E-05-A-25 Impulse Oil Blast Interrupter
Alarms And
Indications
The commonly found alarms and indications for this type of breaker
are:
•
Oil level – by sight glass, or gauge
•
Low air pressure alarm
Applications
This breaker type is generally used in the 2.4 kV to 220 kV range.
Typical
Malfunctions
Any of the following indications are tattle-tail that a problem is
occurring within the breaker. Be observant of any of the following
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conditions and inform the necessary personnel:
•
Signs that oil has been expelled from the breaker, from the rupture
disk or a seal
•
Inspect the breaker for any damage that might be apparent to the
circuit breaker’s bushings
•
Verify oil level on an oil-filled bushing
•
Listen for any unusual noises coming from the circuit breaker
•
Inspect the breaker for any abnormalities, such as unusual smells or
broken parts.
•
Continuous motor operation indicates that there has been a failure of
the circuit breaker mechanism or control circuit.
•
Check pressure gauges.
Air Magnetic - 16 kV And Below
Introduction
The dielectric strength of air is not very high. Air circuit breakers,
however, have features that make up for the relatively low dielectric
strength of air.
There are two major types of air circuit breakers:
•
Air magnetic
•
Air blast
Basic Construction Air magnetic circuit breakers are used in low voltage distribution
applications. They are mounted in a metal protective cabinet. The
And Operation
design and physical features of an air magnetic circuit breaker can vary
depending on the manufacturer, but they all share common features that
are used to break the circuit and extinguish the arc.
Arc Extinction In
Air Magnetic
Circuit Breakers
Air magnetic circuit breakers have two sets of contacts, a set of main
contacts and a set of arcing contacts as shown in Figure E-05-A-26.
When the breaker is closed the main current path is through the main
contacts. When the circuit breaker trips and the main contacts open,
arcing does not occur between the main contacts since the circuit is still
completed through the arcing contacts. After the main contacts
separate, the arcing contacts separate creating an arc between the arcing
contacts.
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Figure E-05-A-26 Air Magnetic Circuit Breaker Interrupter
The arcing contacts are designed to withstand the intense heat of the arc
but only for a very short period. To quickly extinguish the arc between
the arcing contacts a number of features in the circuit breaker work
together. These features include:
•
A puffer
•
Arc runners
•
Magnetic blow out coils
•
Pole pieces
•
Arc fins
The puffer includes:
•
Cylinder
•
Piston
•
Hollow tube and nozzle
As the circuit breaker contacts separate, the puffer piston is moved
through the cylinder. Please refer to Figure E-05-A-27. Air in the
cylinder is compressed and forced through the hollow tube and nozzle.
The nozzle directs the air at the arc, helping to cool the arc. At the
same time, the air from the nozzle forces the arc away from the arcing
contacts and towards arc runners.
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Figure E-05-A-27 Air Magnetic Circuit Breaker Interrupter With
Contacts Open
Arc runners are conductors that help carry the arc away from the arcing
contacts. As the arcing contacts continue to separate, the distance
between the arcing contacts becomes greater than the distance between
the arc runners. The arc will try to maintain itself over the shortest
possible distance. Since the distance between the arc runners is shorter
than the distance between the opening arcing contacts, the arc, assisted
by the puff of air, will jump from between the arcing contacts to
between the arc runners.
The arc runners are connected to magnetic blow out coils. A blow out
coil is a conductor that is wound around an iron core. When the arc
current flows through the arc runners it also flows through the blow out
coils and creates a magnetic field. The cores of the blow out coil are
connected with pole pieces that are metal plates. The plates concentrate
the magnetic fields between the arc runners. They also help dissipate
heat to cool the arc.
The magnetic field created by the blow out coils forces the arc into arc
fins. Arc fins are insulated plates that provide greater arc interruption
ability than air alone.
Arc fins do not readily conduct electricity. Consequently, they obstruct
the path of the arc. As the arc is forced into the fins, it has to travel a
longer distance in order to sustain current flow. They also absorb and
dissipate heat, helping to cool the arc.
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Eventually, the arc is stretched and cooled until finally, at current zero,
the arc is completely extinguished and the circuit is open.
Alarms And
Indications
There are no alarms associated with this type of breaker. The only
indication available to the operator is the semaphore. Relays should be
checked for circuit breaker fault interruption.
Applications
This breaker type is generally used for 16 kV and below.
Typical
Malfunctions
Any of the following indications are an indication that a problem is
occurring within the breaker. Be observant of any of the following
conditions and inform the necessary personnel:
•
Signs of damage to the breaker.
•
Be alert for any unusual odors.
•
Listen for any unusual noises coming from the circuit breaker.
•
Inspect the breaker for any abnormalities.
•
Verify that after maintenance, the breaker is properly aligned and in
its normal operating position after the breaker is racked in.
SF6 Gas – 66 kV to 500 kV
Introduction
SF6 gas is a very efficient dielectric, and due to its physical properties
SF6 gas breakers are generally used in higher voltage situations. There
are two major types of SF6 gas circuit breaker. They are grouped by the
SF6 gas pressure that they use to extinguish the arc.
Common Suppliers The following is a list of commonly found SF6 gas circuit breakers used
in the typical system, they include:
Of This Type:
Types Within This
•
ITE
•
Kelman
•
GE
•
Westinghouse
•
Siemens
•
ABB
•
Mitsubishi
There are two major types of SF6 gas circuit breaker: dual-pressure (gas
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Category
blast) and single-pressure (puffer).
Dual Pressure Type
As the name implies, there are two different pressure areas in a dual
pressure SF6 circuit breaker, a low-pressure area and a high-pressure
area. The low-pressure area insulates the contacts from the interrupting
chamber cover and serves as a receiving tank during a breaker tripping
operation. When the circuit breaker is tripped, high-pressure gas vents
through the contacts and extinguishes the arc. Dual-pressure circuit
breakers typically use the dead tank design.
Single-Pressure
Type
In single-pressure SF6 circuit breakers, SF6 gas is maintained at a
constant pressure in the interrupting chamber. At 230 kV and below,
single-pressure SF6 breakers generally use the dead tank design.
Basic Construction Both types of SF6 gas breakers will be discussed here.
And Operation
Arc Extinction In
Dual-Pressure
Circuit Breaker
The interrupting mechanisms of a dual-pressure circuit breaker are
enclosed in a tank of low-pressure SF6 gas as shown in Figure E-05-A29. The main arc extinguishing features include:
•
Main and arcing contacts
•
A reservoir of high-pressure SF6
•
A blast valve
•
Blast tubes
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Figure E-05-A-28 Dual Preassure SF6 Circuit Breaker
The main features of the set of contacts are:
•
Hollow moving contacts
•
Stationary contact fingers which grip either end of the hollow
moving contacts
•
An arcing horn
•
A blast tube
When the V is closed, the current path is through the conductors
insulated by bushings and through the contacts. The contacts are
enclosed in low-pressure SF6 gas. When the breaker trips, the contacts
separate and an arc forms.
The arcing horn protrudes farther than the contact fingers that encircle
it. Since an arc takes the shortest path between conductors, it transfers
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from the stationary contact fingers to the arcing horn. Then it transfers
from the outside surface of the movable contact to the inside surface.
This minimizes burning of the contact fingers. In addition, the arcing
horn is designed to withstand the intense heat of the arc for a very brief
period.
As the circuit breaker contacts continue to separate, the distance the arc
must travel to sustain itself increases. At the same time, the contacts
begin to separate, pressurized SF6 gas blasts through the blast tubes,
through the arc, and through the hollow moving contact. The blast
further lengthens the arc as well as cools it until the arc extinguishes at
a current zero.
Arc Extinction In
Single-Pressure
Circuit Breaker
In single-pressure SF6 circuit breakers, SF6 gas is maintained at a
constant pressure in the interrupting chamber. As the circuit breaker
contacts open, a puff of gas is forced across the arc path quenching the
arc as the contacts continue to separate. At 230 kV and below, singlepressure SF6 breakers generally use the dead tank design.
Use Of Capacitors
To Increase
Interrupting
Rating
Capacitors are used to distribute the voltage equally to each set of
contacts allowing greater interrupting capability of the breaker.
Lightning
Arrestors
Lightning arrestors are used to protect normally opened system parallel
point in the system. All normally opened circuit breakers are protected
from the potential damage that could occur to the internals of a circuit
breaker from a Lightning strike. Normally closed breakers generally do
not receive the same amount of Lightning strike protection since the
lines that they are connected to are, themselves, connected to protecting
arrestors. Furthermore, if a Lightning strike should happen, the line
itself would tend to dissipate the energy over the whole line and not
allow the discharge to affect only one item.
Synchronous
Switching
In the past, most of the electrical load on the system was motors
(inductive) and restive loads, these types of loads are not very sensitive
to short term voltage transients. Today, with modern electronic devices
these transients can be very damaging to the internal components of the
electronic devices. With the common use by business and homes of
these devices, companies must be sensitive to how maintaining the
system in proper operation parameters affects our end user and strives to
minimize the effect of system operation on our customer.
To limit transients on the system utilities use a new device, a
Synchronous Control Unit (SCU) shown in Figure E-05-A-29. These
units are being in installed in the breaker’s control cabinet, at the
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factory, of some ABB SF6 200 kV and 66 kV breakers.
Figure E-05-A-29 Synchronous Control Unit
The SCU is a microprocessor-based control device that enables
synchronized closing or opening of an Independent Pole Operated
breaker. Synchronized closings reduces transients over-voltages and
currents associated with switching operations of:
•
Shunt capacitor banks
•
Shunt reactors
•
Transformers
•
Transmission lines
Utilities are using these devices with shunt capacitor banks when
additional reactance (kVAR) is needed on the system. Simply put, the
SCU monitors a number of parameters and shuts the breaker, when
called to so that the breaker shuts at a zero current point. Thus, voltage
transients on the system are minimized. Figure E-05-A-30 shows
voltage and current effects on a worst case compared to a synchronous
closing.
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Figure E-05-A-30 Switching Transients (ABB –Synchronous Control Unit Operation)
Alarms And
Indications
Common alarms associated with this type of breaker are:
•
Low-pressure alarm on the low-pressure side informs the Operator a
problem exists with the low-pressure side of the SF6 breaker.
•
High-pressure cutout on the high-pressure side informs the Operator
a problem exists with the high-pressure side of the SF6 breaker that
will prevent its proper operation. The high-pressure cutout will trip
the breaker if closed and will prevent its closing if opened.
•
Low-pressure cutout on the compressor shuts the compressor off
when the low side becomes dangerously low.
Common indications include:
•
High-pressure side gas pressure gauge
•
High-pressure side gas temperature gauge
•
High-pressure side gas pressure gauge
•
High-pressure side gas temperature gauge
•
Semaphore indication
Applications
This breaker type is generally used for higher voltage applications such
as 66 kV to 500 kV.
Typical
Malfunctions
Common problems are:
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•
Blown diaphragm
•
Gas leaks
•
Air compressor failure
•
Low gas
•
Gas temperatures
•
Excessive compressor run time
Vacuum – 16 kV And Below
Common Suppliers Common suppliers of this type of breaker to the system include:
Of This Type
• ABB
•
Square D
•
IEM
•
YIN
•
GE
•
Westinghouse
Basic Construction The vacuum interrupter has been developed for voltages up to 36 kV.
However, in the system they are only used up to 16kV. They can
And Operation
interrupt high voltage power with the contacts moving only 1/4 to 1/2 of
an inch. The reason that vacuum breaker contacts have this capability is
that a vacuum is an excellent insulator. Electrical current cannot flow
across a gap between two conductors unless there is present, between
the conductors, some source of ions or electrons. Obviously, if the gap
is in a perfect vacuum, there are no ions or electrons.
If two contacts which are butting and carrying current in a vacuum can
be parted in the vacuum and a vacuum maintained as they part, the
current will stop. Because of the design of vacuum breakers, small
mechanisms with low power requirements can do the job previously
requiring large mechanisms with huge springs and large operating
power requirements.
Some vacuum circuit breakers that are rated for operation at continuous
current levels above 2000 amperes will employ two blowers. One is
mounted on either side of the high voltage compartment to circulate air
over the primary current carrying components (Vacuum Bottles) and
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their respective heat sinks. The added cooling capacity provided by the
blowers is required only for current levels that exceed 2000 amperes.
The automatic mode of operation is designed to initiate the operation of
the blowers when the primary current reaches or exceeds 2000 amperes.
Furthermore, the system will secure blower operation when the primary
current levels drops below the 2000 amperes level.
It would seem that the vacuum breakers are an ideal process for highperformance circuit breakers. However, the interrupting chamber,
commonly called a vacuum jar or jar seen in Figure E-05-A-31, is sealed
porcelain or vitrified glass vessel, and maintenance of the contacts is not
possible. The life, governed by contact erosion, is expected to be about
20 years, if the vacuum is maintained.
Figure E-05-A-31 Vacuum Bottle
Alarms And
Indications
Alarms:
•
Loss of fan power. In the event of a loss of fan power the operator
must devalue the circuit breakers rating.
Indications:
•
Semaphore
Applications
This breaker type is generally used for 16kV applications and below.
Typical
Malfunctions
As an operator, you should inspect a vacuum breaker for the following,
and take the appropriate action:
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•
Look for signs of insulator damage
•
Look for signs of heating
•
Listen for any unusual noises which might indicate any abnormal
conditions
•
Looks at the indicating ammeters to be certain all three phases are
open or closed depending upon the desired operation
Self Contained
Basic Construction Self-contained circuit breakers, or commonly referred to as reclosers,
incorporate features of conventional oil or vacuum circuit breakers with
And Operation
other auxiliary systems such as relays, battery and charger, and
metering. The auxiliary systems are housed in a separate cabinet from
the circuit breaker mechanism housing. Self-contained circuit breakers
are generally used in customer's service substations where installation
and maintenance costs must be kept to a minimum.
Bushing current transformers on the source side of the self-contained
circuit breaker are used as the source for metering and relaying current.
Figure E-05-A-32 shows a typical control panel for a self-contained
circuit breaker.
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Figure E-05-A-32 Typical Control Panel for a Self-Contained
Circuit Breaker
The major components of self-contained circuit breakers are listed
below:
•
Circuit breaker mechanisms
•
Battery and charger
•
Control Switch
•
Meters
•
Relays
•Minimum trip resistors determine the load current value that will
trip the circuit breaker
•Timing plugs: set the "time curve" characteristic
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•
Selectors: set the speed of phase and ground current relay operation
•
Lockout selector: sets the number of automatic re-close operations
•
Re-closing interval plugs: set the time interval between the relay
operation and actual re-closing
•
Reset delay plug: sets the reset time for a sequence of operations
•
Relay targets: indicate relay operation by buttons (pop-out type) or a
counter
•
Trip operation counter: operates (advances) each time the circuit
breaker operates
•
Lockout indicator lamp: provides visual indication that the circuit
breaker has completed all relaying and re-closing cycles and has
locked out.
•
Re-closing relay switch: allows the re-closing function to be cut in
or cut out
•
Ground trip blocking disables ground relay tripping to prevent
unintentional operation of the circuit breaker during bypass
switching
Arc Extinction In
self-contained
Circuit Breakers
The interrupting unit of self-contained circuit breakers is very similar to
those found in other oil or vacuum circuit breakers of similar voltage
classes. All three phases are contained in a single vacuum or oil-filled
tank. Arc extinction in self-contained circuit breakers is also similar to
the arc extinction in oil or vacuum circuit breakers discussed earlier.
Alarms And
Indications
Alarms and indications in self-contained circuit breakers are also
similar to the alarms and indications in oil or vacuum circuit breakers
discussed earlier.
Applications
Applications of self-contained circuit breakers are the same as
applications of oil or vacuum circuit breakers discussed earlier.
Typical
Malfunctions
Typical malfunctions in self-contained circuit breakers are the same as
those of oil or vacuum circuit breakers discussed earlier with the
addition of control circuit problems of the self-contained unit.
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4. Types of Operating Mechanisms
There are six different types of circuit breaker mechanisms that are
commonly used in the system, they are:
•
Manual
•
Solenoid
•
Pneumatic
•
Motor Spring
•
Hydraulic
•
Gas
Each will be reviewed in this section, covering the way it operates, any
associated alarms and indications, and its application. Furthermore, any
problems that the mechanisms are prone, to which the operator should
be sensitive, are covered as well.
Manual
Basic Construction The first type of circuit breaker mechanism is the manual device. It
requires the Operator to supply the closing force through a handle
And Operation
connected to an operating arm and mechanical linkages to the main
circuit breaker contacts. A manual operator is pictured in Figure E-05A-33 and illustrated in Figure E-05-A-35. This type of mechanism is
seen mostly in older substations in the Station Light and Power circuit.
Manual operating mechanisms are available to close small circuit
breakers. They use a lever-operated toggle mechanism that releases
energy from a relatively small spring. They may or may not have
tripping capability. If they cannot trip, a back up protective device is
applied.
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Figure E-05-A-33 Manual Operator
Figure E-05-A-34 Manual-Type Operating Mechanism
Alarms And
Indications
Alarms:
•
There are no alarms associated with the manual operating
mechanism.
Indications:
•
Applications
The manual operating mechanism has only a semaphore
There are very few of these mechanisms left in the system. This type of
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mechanism may be found in older substations in the Station Light and
Power circuit.
Typical
Malfunctions
Be observant of the following possible problems with the manual
operating mechanism:
•
Poorly operating hinge or lever points
•
Linkages that do not operate freely
Solenoid
Basic Construction The solenoid mechanism, shown in Figure E-05-A-35 and Figure E-05A-37, incorporates a large solenoid or coil that produces a strong
And Operation
magnetic field when a DC current flows through it. An armature or iron
bar, which is connected by mechanical linkages to the breaker’s
contacts, will be attracted into the solenoid by the magnetic field. The
components are shown in the positions they would be in when the
breaker's contacts are open. The components involved in closing the
breaker are a solenoid (which consists of a coil, a plunger, and a push
rod), and an arrangement of links and levers, and an operating rod.
The device that provides the force to close the circuit breaker is the
solenoid. To close the breaker, the energized solenoid, or closing coil,
creates a magnetic field. The magnetic field pulls the plunger into the
solenoid, causing the push rod to push against the links and levers. The
connected links and levers then move the operating rod. The operating
rod causes the circuit breaker to close.
Figure E-05-A-35 Solenoid Operating Mechanisms
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Figure E-05-A-36 Solenoid Operating Mechanism
Alarms And
Indications
Alarms:
•
There are no alarms associated with the solenoid operating
mechanism.
Indications:
•
The solenoid operating mechanism has only a semaphore.
Applications
This type of circuit breaker mechanism is found on circuit breakers at
voltages from 440 V to 66 kV.
Typical
Malfunctions
Know how to tell if the closing coil remains energized after a closing
operation. The coil will burn out if continuously energized; it is not
designed for continuous duty.
Know what to do if the closing coil or closing circuit malfunctions.
Damage to the coil may result.
Know where the DC knife switch is located, so the operator can restore
normal configuration if the switch is left open after performed
maintenance. This prevents unnecessary issuance of a maintenance
request if the breaker is not properly restored after a maintenance
operation.
Recognize broken components inside the mechanism compartment.
Prevents further damage to a breaker.
Pneumatic
Basic Construction Pneumatic operating mechanisms use a piston driven by compressed
high-pressure air to apply closing and tripping forces to the mechanism.
And Operation
Since high-pressure air is used, an air compressor and storage tank is
necessary. The controls on the compressed air lines, however, are
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electrically operated.
Most pneumatic circuit breakers use a solenoid to trip the circuit
breaker however, some Mitsubishi and Westinghouse 220 kV breakers
use air for tripping. A variation of pneumatic operation is pneumatic
closing with a tripping spring being compressed during the pneumatic
closing operation. The pressure varies from a few hundred to several
thousand psi. Figure E-05-A-38 shows a simplified pneumatic operating
mechanism.
To Close
To close the circuit breaker, an electrically operated air valve is opened
between the air storage tank and the closing piston. When the close coil
valve is energized, the control valve opens and permits pressurized air
from the air reservoir tank to flow into a cylinder with a piston. This
drives the piston and closes the circuit breaker by means of a
mechanical linkage. The circuit breaker has a latching mechanism to
hold it closed. Through a series of auxiliary contacts, the air valve coil
is de-energized, closing the air valve, and allowing the piston to return
to its normal position.
To Open
To open the circuit breaker contact, the trip coil is energized. A plunger
releases the latch, permitting the circuit breaker contacts to open. The
spring, not shown, compressed during the closing sequence, releases
and speeds the opening of the circuit breaker contacts. For this type of
circuit breaker mechanism, the control cabinet contains the compressor
and motor, the air valve, the air storage facilities, the closing and
tripping coils, and the control devices.
Advantage
The advantage of this design is that relatively low power is demanded
when initially pressurizing or maintaining established system pressure
in a pneumatic cylinder. However, once the circuit breaker operational
sequence begins, the energy stored in the pneumatic cylinder will be
released and generate a tremendous amount of closing power. This
closing power will be of a magnitude much greater than possible with
the maximum output of the low energy pneumatic cylinder charging
circuit.
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Figure E-05-A-37 Pneumatic Mechanism
Alarms And
Indications
Alarms:
•
Low air pressure
Indications:
•
Semaphore
Applications
Pneumatic mechanism permits high speed closing, therefore it is used
on voltages from 33 kV to 500 kV.
Typical
Malfunctions
The Operator should be aware of the following when operating with a
pneumatic mechanism:
•
Improper maintenance restoration:
o Know the location of the DC switch.
•
Compressor problems:
o Proper compressor operation set points.
o Know the location of the compressor control switch.
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o Know what to do if a pressure alarm sounds.
o Lock out or tripping points.
o Know how to reset a tripped compressor.
o Look for any broken parts.
o Check compressor oil level if indicating devices are available.
o Know the location of the air receiver drain valve.
•
Air pressure problems
o Pressure gauges and what are their normal indications.
o What actions required for a loss of air pressure.
o Listen for air leaks.
o Look for any broken parts.
Motor Spring
Basic Construction The motor spring mechanism uses an electric motor, usually DC, to
compress one or more springs as illustrated in Figure E-05-A-38. The
And Operation
motor in the mechanism is energized and de-energized through auxiliary
contacts in the mechanism, called pallets or micro switches, and
through a DC knife switch. The compressed spring stores energy until a
closing signal is received.
When a close signal is received, the circuit breaker operates by
mechanically releasing the springs. The spring then expands and uses a
series of linkages to shut the circuit breaker’s main contacts. The
circuit breaker simultaneously charges or compresses a smaller coil
spring that is used to trip the circuit breaker. The motor spring
mechanism provides high speed closing and tripping.
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Figure E-05-A-38 Spring Motor, Shutting
Alarms And
Indications
Alarms:
•
None
Indications:
•
Semaphore
•
Spring charge
Applications
This mechanism is used on breakers operating in a voltage up to 115kV.
Typical
Malfunctions
The Operator should be aware of the following when operating with a
motor spring mechanism:
•
Maintenance restoration errors:
•Know the location of the DC knife switch
•Know the location of the motor control switch
•
Breaker operation problems:
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o Identify that the breaker failed to close
o What to do if the breaker fails to close
•
Compressor problems:
o Look for any loose parts on the floor of the mechanism cabinet
o What to do if the compressor tripped on thermal overload
o What to do if the compressor tripped
Hydraulic
Basic Construction A hydraulic mechanism, as seen Figure E-05-A-39, operates similar to a
pneumatic mechanism except that hydraulic fluid is used instead of
And Operation
compressed air. The two mechanisms use similar devices, except the
hydraulic system uses a pump, check valve, and a relief valve instead of
the compressor assembly of the air system in the pneumatic mechanism.
A motor governor switch, low-pressure alarm, and closing lockout
function the same way as they do on an air system.
Figure E-05-A-39 Hydraulic Operated Mechanism
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Hydraulic operating mechanisms use a liquid, not a gas to transport the
energy needed by the mechanism to operate the breaker. Because fluids
cannot be compressed, an additional device called an accumulator is
used. The accumulator is to the hydraulic system as the air receiver is
to the pneumatic system, a means of storing energy.
The hydraulic fluid is pressurized by the pumping system that has low
energy consumption requirements. The major difference between the
hydraulic and pneumatic system is the hydraulic system tends to be
pressurized to a higher pressure. Hydraulic operating mechanisms are
smaller in design and susceptible to operational failure if a leak occurs.
This form of operating mechanism can generate more closing force than
the other mechanisms presented. Unfortunately, the cost associated
with this system limits the use of hydraulic operated mechanisms to
systems that require high-energy output mechanisms.
To close the circuit breaker, an electrically operated valve is opened
between the accumulator and the closing piston. This allows the piston
to move against the mechanical linkage and close the circuit breaker
contacts. When the breaker has reached the closed position, the closing
valve is de-energized and the piston returns to its normal position.
OA3 Hydraulic
Operating
Mechanism
Figure E-05-A-40 illustrates an opened OA3 hydraulic operating
mechanism.
Figure E-05-A-41 illustrates a closed OA3 hydraulic operating
mechanism.
Figure E-05-A-42 illustrates an OA3 hydraulic operating mechanism’s
accumulator.
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Figure E-05-A-40 OA3 Hydraulic Operating System, Opened
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Figure E-05-A-41 OA3 Hydraulic Operating System, Closed
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Figure E-05-A-42 OA3 Hydraulic Operating System, Accumulator
ABB Breaker That
Is Spring, Motor,
And Hydraulic
Operated
A new mechanism (HMB) design was developed by ABB. The new
design uses a merging of a spring, motor and hydraulic design. This
new breaker mechanism is shown in Figure E-05-A -43. Hydraulics is
used to charge the spring, which stores a high quantity of potential
mechanical energy. The spring is used to open and shut the breaker and
the motor is used to charge the hydraulic system.
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Figure E-05-A -43 ABB Spring, Motor, Hydraulic Mechanism
Alarms And
Indications
Alarms:
Hydraulic fluid high-pressure alarm
Hydraulic fluid low-pressure alarm
Indications:
Semaphore
Spring charge (on new ABB Mechanism)
Applications
This mechanism is used on breakers operating 66kV and above.
Typical
Malfunctions
To identify potential problems with this mechanism, use the following
listed items.
Things to know:
•
Location of the DC knife switch
•
Location of the hydraulic pump motor control switch
On the pressure gauge know:
•
Normal pressure
•
Normal pump start pressure
•
Normal pump stop pressure
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•
High-pressure Alarm set point
•
Low-pressure Alarm set point
•
Lockout pressure
Inspection items:
•
Check for hydraulic oi1 leaks
•
Check for broken parts
Gas
Basic Construction Gas operating mechanisms use compressed high-pressure nitrogen to
apply closing forces directly to the mechanism. The gas (nitrogen)
And Operation
operating mechanisms use the same principles as the pneumatic
operating mechanisms. Refer to the pneumatic operating mechanism in
this section for more information.
Alarms And
Indications
Alarms:
•
Low pressure
Indications:
•
Semaphore
Applications
This mechanism permits high speed closing. It is used on voltages from
16kV to 500kV.
Typical
Malfunctions
The Operator should be able to perform the following when operating
with a nitrogen mechanism:
•
Know the location of the DC switch.
•
Know actions required for a loss of pressure.
•
Pressure gauges and what they indicate.
•
Listen for leaks.
•
Look for any broken parts.
•
Check compressor oil level if indicating devices are available.
•
Know the location of the air receiver drain valve.
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5. Circuit Switches
Circuit switches provide the system with additional switching
capabilities at a reduced cost, but circuit switches are not designed to
interrupt faults. Generally, they are used for connecting items such as a
capacitor bank to the system.
Common Suppliers
Common Suppliers Common suppliers of circuit switches to the typical system includes:
•
Soslyn
•
A.C.
•
Kyle
•
S&C
Construction
Oil
Oil circuit switches rely solely on the head of oil in its case and the
pressure of the gas that will be developed to control and extinguish the
arc. The oil circuit switches has an insulated cylinder attached to the
fixed contact with an aperture through which the moving contact draws
the arc on opening. The high-pressure gas that is generated within the
circuit switches sweeps the arc, and the ionizing gas, through the
aperture. Coupled with the oil’s ability to absorb heat, the arc is readily
extinguished by cooling.
Gas
Gas circuit switches use SF6 gas as their dielectric. Because SF6 is an
electronegative gas, it combines with the arc and produces a relative
immobile ion. The loss of available conducting electrons causes the arc
to be extinguished at current zero.
Vacuum
Vacuum circuit switches use a vacuum as their dielectric. A vacuum is
an excellent insulator. Electrical current cannot flow across a gap
between two conductors unless there is present, between the conductors,
some source of ions or electrons. Obviously, if the gap is in a perfect
vacuum, there are no ions or electrons to allow the arc to continue.
Therefore, the arc is quickly extinguished.
Operation
Motor
The motor mechanism uses a motor to open or shut the switches
contacts. When a close signal is received, the switches motor operates
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using a series of linkages to shut the switches contacts.
Motor-Spring
Motor charged spring operating mechanisms, uses a motor to compress
a coil spring. The compressed spring stores energy until a closing signal
is received. When a close signal is received, the switches operate by
mechanically releasing the springs. The spring then expands and uses a
series of linkages to shut the switches contacts. This mechanism
provides high-speed operation.
Solenoid
The solenoid mechanism incorporates a solenoid or coil that produces a
strong magnetic field when a DC current flows through it. An armature
or iron bar that is connected by mechanical linkages to the switches
contacts will be attracted into the solenoid by the magnetic field. By
energizing the solenoid, the switches contacts are opened or closed.
Alarms and Indications
Motor operated switches may provide a loss of AC alarm.
Application
Capacitors
Circuit switches are used to add or remove capacitor bank(s) as the
kVAR requirements of the system changes.
Lines
Circuit switches are used to sectionalize lines. They are used to make
or break parallels between lines.
Configurations
The switches are generally three-phase ganged switches.
Interlocks
There are no interlocks associated with circuit switches.
Malfunctions
Due to how they are used, switches typically operate without problems.
However, they do require routine maintenance to perform properly.
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