EEE 420 HIGH VOLTAGE
TECHNIQUES
Dr. K. Çağatay Bayındır
Course Content
1)Introduction
Definition of High Voltage and Standard Voltage Ranges
Transmission of Electric Energy (AC and DC)
Standards and Regulations
2)High Voltage Power System Components and Technology
Isolators, Disconnectors, Circuit Breakers
Instrument Transformers, Surge Arresters, Transformers
3)HV Substations and Design Principles
Circuit Configurations For High Voltage Substations
Substation systems and arrangements
Feeder components and configurations
Design Approach and Calculations
Course Content
4) Electrostatic Fields
Field Analysis Methods
Experimental and Numerical Methods
5) Electrical Breakdown in Gases
Ionization Process
Electronegative Gases
Streamer-Kanal mechanism,
Breakdown in non-uniform fields
Partial Breakdown and Corona Discharges
6) Electrical Breakdown of Liquids
Breakdown theories for liquids
Liquid insulating materials
7) Electrical Breakdown of Solids
Breakdown theories for solids
Solid insulating materials
Course Content
8) Generation and Measurement of High Voltages
AC, DC Voltages
Electrostatic Generators
Testing Systems
9)Protective Measures for Persons and Installations
Protection against contact in installations above 1000V
Earthing
Lightning Protection
EMC
10) A Review of Local Regulations
Elektrik İletim Sistemi Arz Güvenilirliği ve Kalitesi Yönetmeliği
Elektrik Kuvvetli Akım Tesisleri Yönetmeliği
Elektrik Piyasası Şebeke Yönetmeliği
References
High Voltage Engineering: Fundamentals by E. Kuffel , Newnes
2000
High Voltage Engineering Fundamentals by E. Kuffel , W. S.
Zaengl, Pergamon Press 1984
Yüksek Gerilim Tekniğinin Temelleri by Prof. Dr. Sefa Akpınar,
1997
Yüksek Gerilim Tekniği by Prof. Dr. Muzaffer Özkaya, 1996
Various Industrial Booklets
Introduction
The potential benefits of electrical energy supplied to a number of consumers from
a common generating system were recognized shortly after the development of the
“dynamo” commonly known as the generator.
Power transfer for large systems, whether in the context of interconnection of large
systems or bulk transfers, led engineers invariably to think in terms of high
voltages.
The rapidly increasing transmission voltage level in recent decades is a result of the
growing demand for electrical energy, coupled with the development of large
hydroelectric power stations at sites far remote from centres of industrial activity and
the need to transmit the energy over long distances to the centres.
Introduction
In order to meet the growing demand, more and more power stations, substations
and transmission lines are being built and the transmission voltages are being raised
for efficient transmission.
Increase in transmission voltage by 20 times results in 400 times reduction in
transmission losses. This illustrates the main reason for the need of “High Voltage”.
It is desirable to increase the transmission voltage to obtain higher efficiency, but “the
insulation of high voltage system “ limits this desire. The insulation of all parts of high
voltage power system (generators, transformers, cables, insulators, circuit breakers,
etc.) should be preserved in order to provide an “uninterruptable energy supply”or
continuous energy flow.
Gas, liquid and solid insulating materials are utilized for the insulation of high voltage
systems. The loss of insulation is technically called “breakdown”. Mechanisms of
electrical breakdown of insulation is one of the subjects of this course.
Introduction
In High Voltage Installations Regulation (Elektrik Kuvvetli Akım Tesisleri Yönetmeliği)
published by Turkey Ministry of Energy and Natural Sources ;
Low Voltage is the phase-phase voltage with rms value of 1000 Volts and less than
1000 Volts
High Voltage is the phase-phase voltage with rms value of greater than 1000 Volts
These voltage ranges are also valid for IEC (International Electrotechnical Commission)
Definition of some important standardized rated insulation levels for high voltage
equipment according to IEC 62271-1 is given above
Introduction
Rated voltage: Upper limit of the highest voltage of the network for which a switching
device is rated.
Rated short duration power frequency withstand voltage : rms value of the sinusoidal
a.c voltage at operating frequency that the insulation of a device must withstand
under the specified test conditions for 1 minute.
Rated lightning impulse withstand voltage: peak value of the standard voltage surge
1.2/50us that the insulation of a device must withstand
Rated switching impulse withstand voltage: peak value of the unipolar standard
voltage surge 250/2500us which the insulation of a device with a rated voltage of 300
kV and above must withstand.
Introduction
Table of 154 kV and 380 kV insulation levels and table of electrical parameters used for
design of power distribution substations as stated in “Elektrik İletim Sistemi Arz
Güvenilirliği ve Kalitesi Yönetmeliği” is given below .
1.Anma Değerleri
a) Normal işletme gerilimi kV rms
380
154
33
10.5
b) Max. sistem gerilimi kV rms
420
170
36
12
c) Anma frekansı Hz
50
50
50
50
d)Sistem topraklaması
Direkt
Direkt
Direkt veya
direnç üzerinden
Direkt veya
direnç üzerinden
e) Max. radio interference level µV (RIV)
(1.1 Sistem geriliminde ve 1 MHz'de)
2500
2500
-
-
-Tüm primer teçhizat baralar ve bağlantılar
50
31.5
25
25
-Kısa devre süresi
1
1
1
1
2.5x(Ith)
2.5x(Ith)
2.5x(Ith)
2.5x(Ith)
35
20
15
15
f) 3 Faz simetrik kısa devre termik akımı kA
(Ith)
(sn)
-Dinamik kısa devre akımı
g) Tek faz-toprak kısa devre akımı (kA)
2.İzolasyon Değerleri
(Güç Trafosu Hariç)
380
154
33
10.5
1550
1550(+300)
750
860
170
75
1175
(900+430)
-
-
-
620
760
325
375
70
28
-Yıldırım darbe dayanım gerilimi
kV-tepe(faz-toprak)
1425
650
170
95 (YG nötrü)
-Açma-kapama darbe dayanım
gerilimi kV-tepe
1050
-
-
-
-1dk. Güç frekansında dayanım
gerilimi (yaşta) kV-rms
630
275
70
38 (YG nötrü)
a) Yıldırım darbe dayanım
gerilimi kV-tepe
- Toprağa Karşı
- Açık Uçlar Arası
b) Açma-kapama darbe dayanım
gerilimi kV-tepe
- Toprağa Karşı
- Açık Uçlar Arası
c) 1 dakika Güç frekansında
dayanım gerilimi (yaşta)
kV-rms
-Toprağa Karşı
- Açık Uçlar Arası
3.İzolasyon Değerleri
(Güç Trafosu için)
4.Yardımcı Servis Besleme Gerilimi :
-3faz-N AC sistem
-1faz-N AC sistem
- DC sistem
380 V + % 10 - % 15, 50 Hz
220 V + % 10 - % 15, 50 Hz
110 V (veya 220 V) + % 10 - % 15
Transmission of Electric Energy
Although the bulk of world’s electric transmission is carried on ac systems, recent
progress in high-voltage direct current (HVDC) technology has enabled the
development of large scale dc transmission by overhead lines and submarine cables
which have become economically attractive in long distance transmission of large bulk
power. HVDC permits a higher power density on a given right-of-way than a.c.
Transmission and thus helps the electric utilities in meeting the environmental
requirements imposed on the transmission of electric power.
HVDC transmission can transmit more power per line and is much more efficient and
cost effective over large distances. In addition the losses are quite low.
Transmission of Electric Energy
Today’s HVDC transmission schemes can carry up to 3000 MW of power over distances
between 1000 – 1500 km. Atypical scheme consists of two stations that convert AC to
DC and vice versa. It uses overhead lines or cables with only two conductors.
Transmission of Electric Energy
Increasing demands and strict environmental regulations mean that more and more
remote hydro power plants are being considered. There is an almost unlimited source
of solar power. If it could be harnessed properly and combined with hydro, wind and
pump storage a totally renewable electrical system is possible.
Transmission of Electric Energy
Transmission of Electric Energy
Standards and Regulations
Standardization work for the field of electrical engineering is conducted almost
entirely on an international level.
In Europe IEC (International Electrotechnical Commission), in USA ANSI (American
National Standards Institute) are valid. There are other Canada, Russian and Japan
standards.
In Turkey TSE standards are valid. They are mostly Turkish versions of IEC standards.
Some of IEC standards related with hih voltage systems is listed below.
Standards and Regulations
• IEC 60038 Standard Voltages
• IEC 60265-1 High Voltage Switches - Switches for Rated
Voltages above 1 KV and less than 52 KV
• IEC 60265-2 High Voltage Switches for Rated Voltages of 52
KV and above
• IEC 60282-1 High Voltage Fuses – Current Limiting Fuse
• IEC 62271-1 Common specifications for high voltage
switchgear and controlgear standards
• IEC 62271-100 High voltage switchgear and controlgear high voltage alternating current circuit breakers
• IEC 62271-102 High voltage switchgear and controlgear alternating current disconnectors and earthing switches
Standards and Regulations
Besides standards there are also local regulations for
transmission, distribution of electric energy and energy market.
In Turkey EPDK is the regulating agency. Below are some
important local regulations for energy market.
• Elektrik İletim Sistemi Arz Güvenilirliği ve Kalitesi Yönetmeliği
• Elektrik Kuvvetli Akım Tesisleri Yönetmeliği
• Elektrik Piyasası Şebeke Yönetmeliği
High Voltage Power System
Components and Technology
Main components used in high voltage power systems are as follows:
• Synchronous generators
• Power transformers
• Disconnectors
• Circuit breakers
• Overhead lines and conductors
• Towers
• Insulators
• Cables
• Bus bars
High Voltage Power System
Components and Technology
Measuring and protection components used in high voltage power systems
are as follows:
• Voltage and current transformers
• Relays
• Surge arresters
• Control circuits
• Voltage dividers
• Earthing switches
Voltage regulating components used in high voltage power systems are as
follows:
• Series and shunt reactors
• Series and shunt capacitors
Insulators
to insulate means "to separate or cover with a nonconducting material in order to
prevent the passage or leakage of electricity, heat, or sound." Communication and
electric line wires in service must be kept as dry as possible in order to function
efficiently, and to cut down on loss of current. The wires are kept off of the ground by
being strung between poles. But something was needed to keep the wires and
(sometimes wet) poles apart. This "something" had to meet three basic needs:
• it must be made of a fast-drying nonconducting material
• it must be able to hold the line wire in place
• it must stay on the pole
This "something" is the insulator. It was developed and improved upon over the years
to meet those basic requirements is most commonly made of glass or porcelain
Insulators
There are a lot of insulator types used for various purposes:
•
•
•
•
•
•
•
•
Post insulators
Pin type insulators
String insulators
Transformer bushing insulators
Lightning arrester insulators
Wall bushing insulators
Capacitive voltage transformer bushings
Special type insulators.
Insulators
Insulators
Insulators
Insulators
Insulators
Disconnectors
Disconnectors are used for galvanic isolation of networks or sections of
switchgear installations. As an independent air insulated-device, they form a
visible isolating distance in their open position.
More than 10 different designs are in use around the world. The most
important are:
• knife -contact disconnectors
• rotary disconnectors
• two column vertical break disconnectors
• single-column disconnectors.
Disconnectors
Knife-contact disconnectors
The classic design of the disconnector is the knife-contact disconnector. Their
moving contacts have the knife shape. There are indoor and outdoor types.
They can be actuated manually and in remotely operated installations by
motor or compressed air drives.
Indoor knife-contact disconnectors
Indoor types are used in switchgears in buildings. Control arm is brought out
to a safe distance .
They are used in 10,15,30,45 KV systems with current ratings of 400, 630 and
1250 Amps. They have a simple and standard structure. The parts are:
chassis, post insulator, fixed and moving contacts and armed moving
mechanism.
Outdoor knife-contact
disconnectors
Outdoor types are used out of the buildings and are subject to environmental
conditions like rain, dust, wind etc.
Disconnectors with fuse
These connector include a pair of fuse for protection against short circuits.
There are indoor and outdoor knife-types.
They are used at the feeders of consumers with low power demand, at
measuring voltage transformer feeders, and at auxiliary transformer feeders
for substations.
Two column rotary disconnectors
This disconnector type is used for rated voltages of 72.5 to 420 kV preferably
in smaller installations and also in larger switchgear installtions as incoming
feeder or sectionalizing disconnector. An earthing switch can be installed on
both sides.
Two rotating bases are mounted on a sectional steel frame and connected by
a braced tie-rod. Post insulators are fixed to the rotating bases and carry the
swivel heads with the arms and the high-voltage contacts. Both arms swivel
90 degrees with their insulators during the switching movement.
Two column rotary disconnectors in their open position form a horizontal
isolating distance. The rotary bases should be weather protected and should
have maintenance-free ball bearings.
Two column rotary disconnectors
Two column rotary disconnectors
Three column rotary disconnectors
These disconnector types are used with a side-by-side configuration of the three poles
of a group. In comparison to two column rotary disconnectors, they allow smaller pole
spacings and higher mechanical terminal loads.
The two outer insulators are fixed to the base frame and carry the contact system. The
middle insulator is fastened to a rotating base and carries the one-piece arm, which
rotates approximately 60 degrees during a switching operation and engages the
contact systems on the outer insulators.
Single column (pantograph)
disconnectors
In installations for higher voltages (> 170 kV) and multiple busbars , the single column
disconnector (also referred to as pantograph or vertical-reach disconnector) requires
less space than other disconnector designs. For this reason and because of the clear
station layout , it is used in many switchgear installations. The switch status is clearly
visible with the vertical isolating distance.
The base of the disconnector is the frame, which holds the post insulator carrying the
head piece with the pantograph and the gearbox. The actuating force is transferred
through the rotating insulator to the gearbox. The suspended contact is mounted on
the busbar situated above the disconnector. On closing, it is gripped between the
pantograph arms.
During the closing movement, the pantograph arms swivel through a wide range and
are therefore capable of carrying the fixed contact even under extreme position
changes caused by weather conditions. The feeder line is connected to the highvoltage terminal of the gearbox. In general, the single column disconnector allows
higher mechanical terminal loads than the two column rotary disconnector.
Single column (pantograph)
disconnectors
Single column (pantograph)
disconnectors
Single column (pantograph)
disconnectors
Two column vertical-break
disconnectors
This type of disconnector is preferred for higher voltages (>170 KV) as a
feeder or branch disconnector. It differs from two-column rotary
disconnectors by smaller space savings (with side-by-side configuration) and
higher mechanical terminal loads. In its open state there is a horizontal
isolating distance with the contact arm open upwards.
The two post insulators are mounted on a frame. The gearbox with contact
arm and high-voltage terminal and the fixed contact with high-voltage
terminal are mounted on them. The rotating insulator fastened to the rotary
bearing transfers the actuating force to the gearbox, which transmits the
force into a torque for opening the contact arm.
For rated voltages up to 245 KV one mechanism per three-phase disconnector
is sufficient, at higher nominal voltages one mechanism per pole is generally
used.
Two column vertical-break
disconnectors
Circuit Breakers
High voltage circuit breakers are mechanical switching devices capable of
making, carrying continuously and breaking electrical currents both under
normal circuit conditions and for a limited period, abnormal circuit conditions
such as in the event of a short circuit. Circuit breakers are used for switching
overhead lines, cable feeders, transformers, reactor coils and capacitors. They
are also used in bus ties in installations with multiple busbars to allow power
to be transmitted from one busbar to another.
The following points are important when selecting circuit breakers.
• Maximum operating voltage on location
• Maximum load current occurring on location
• Maximum short circuit current occurring on location
• Network frequency
• Duration of short circuit current
• Switching cycle
• Special operational and climatic conditions
Circuit Breakers
Important standards are
IEC
62271-1 General and definitions
62271-100 Classification, Design and construction, Type and routine testing,
Selection of circuit breakers for service, Informationin enquiries, tenders and
orders
ANSI (American National Standards Institute)
C37 04 – 1979 Rating structure
C37 06 – 1979 Preferred ratings
C37 09 – 1979 Test procedure
C37 10 – 1979 Application guide
C37 11 – 1979 Application guide for transient recovery voltage
C37 12 – 1979 Capacitance current switching
Electrical Characteristics
Rated value: Value of a characateristic quantity used to define the operating
conditions for which a switching device is designed and built and which must
be verified by the manufacturer.
Rated normal current: The current that the main circuit of a switching device
can continuously carry under specified conditions.
Rated short-time withstand current: Current that a switching device in closed
position can carry during a specified short-time under prescribed conditions.
Standardized rated normal currents: 200, 250, 400, 500, 630, 800, 1000,
1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300A.
Standardized rated short-time currents: 6.3, 8, 10, 12.5,16, 20, 25, 31.5, 40,
50, 63, 80, 100 kA.
Electrical Characteristics
Rated voltage: upper limit of the highest voltage of the network for which a
switching device is rated.
Standardized rated voltages: 3.6, 7.2, 12, 17.5, 24, 36, 52, 72.5, 100, 123,
145, 170, 245, 300, 362, 420, 550, 800 kV.
Peak making current: peak value of the first major loop of the current in one
pole of a switching device during the transient period following the initiation
of current during a making operation.
Breaking current: current in one pole of a switching device at the instant of
initiation of an arc during a breaking process.
Electrical Characteristics
Applied voltage: voltage between the terminals of a circuit breaker pole
immediately before making the current.
Recovery voltage: voltage occurring between the terminals of a circuit
breaker pole after interrruption of the current
Opening time: interval of time between application of auxiliary power to the
copening release of a switching device and the seperation of contacts in all
three poles.
Closing time: interval of time between application of auxiliary power to the
closing circuit of a switching device and the contact touch in all poles.
Electrical Characteristics
Break time: interval of time between the beginning of opening time of a
switching device and the end of the arcing time
Make time: interval of time between application of the auxiliary power to
the closing circuit of a switching device and the instant in which the current
begins to flow.
Rated insulation level: standardized combination of the rated values for the
lightning impulse voltage, the switching impulse withstand voltage and the
short time power frequency withstand voltage assigned to a rated voltage.
Electrical Characteristics
Rated short duration power frequency withstand voltage : rms value of the
sinusoidal a.c voltage at operating frequency that the insulation of a device
must withstand under the specified test conditions for 1 minute.
Rated lightning impulse withstand voltage: peak value of the standard
voltage surge 1.2/50us that the insulation of a device must withstand
Rated switching impulse withstand voltage: peak value of the unipolar
standard voltage surge 250/2500us which the insulation of a device with a
rated voltage of 300 kV and above must withstand.
Electrical Characteristics
1. Transient recovery voltage
2. Recovery voltage
3. Breaking time
e(t) system voltage
ea(t) arcing voltage
ik short circuit current
Circuit breaker types
There are still a number of “small-oil-volume” circuit breakers in use for rated
voltages up to 52 kV in systems, but for new installations only vacuum or SF6
circuit breakers are used.
Circuit breakers can be stationary mounted or integrated into the panel in
withdrawable unit design ith appropriate interlocking mechanism.
Circuit breakers must be capable of making and breaking all-short circuit and
service currents occurring at the operational site.
Vacuum circuit breakers
Vacuum circuit breakers are available for short circuit breaking currents up to
63 KA with rated currents from 400 to 4000 A with rated voltages 12, 17.5, 24
and 36/40.5 KV.
Vacuum circuit breakers
Vacuum circuit breakers
The components of the main current path (upper breaker terminal, vacuum
interrupter, lower terminal etc.) are embedded in cast resin and thus
completely enclosed by insulating material.
The contacts are
copper/chromium composite material, a copper base containing evenly
distributed fine-grained chromium particles, which has a good extinguishing
and arc-resistant response when switching short-circuit currents.
Vacuum circuit breaker contains no arc extinguishing and quenching media.
Vacuum circuit breakers
Actuating systems
The travel of the moving contact between the open and closed positions in
the vacuum circuit breaker is between 8 and 14 mm depending on the rated
voltage. At the end of closing stroke , the energy for tensioning the contact
pressure spring is required. The relatively low total energy requirement for
vacuum circuit breaker is generally provided by mechanical spring stored
energy operating mechanisms. Tripping is initiated by magnetic releases or
manually.
SF6 circuit breakers
Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and
arc extinguishing properties. The dielectric strength of the gas increases with
pressure and is more than of dielectric strength of oil at 3 kg/cm2.
The puffer type arc quenching principle provides an effective arc-quenching
gas flow by a mechanically driven piston.
SF6 circuit breakers
During the arcing period SF6 gas is blown axially along the arc. The gas
removes the heat from the arc by axial convection and radial dissipation. As a
result, the arc diameter reduces during the decreasing mode of the current
wave. The diameter becomes small during the current zero and the arc is
extinguished. Due to its electronegativity, and low arc time constant, the SF6
gas regains its dielectric strength rapidly after the current zero, the rate of rise of
dielectric strength is very high and the time constant is very small.
SF6 circuit breakers
SF6 circuit breakers
Switchgear
There are two types of switchgear commonly applied today for switching and
protection of high voltage power distribution systems. One is metal-clad
switchgear using draw-out circuit breakers and relays for protection. The
other is metal enclosed switchgear using interrupter switches for load
switching and power fuses for fault protection. Metal-clad switchgear
contains drawout circuit breakers which are removed for required scheduled
maintenance and removal of a breaker interrupts its load. Metal-clad
switchgear also contains insulated bus which, when tested periodically,
requires a shutdown of the gear.
Metalenclosed switchgear is available with interrupter switches and fuses
that require no scheduled maintenance, and the air-insulated bus does not
require periodic dielectric testing. Annual maintenance normally
consists of little more than a visual inspection through the windows of the
gear. This switchgear should be seriously considered if only infrequent
Interruptions can be tolerated by plant operations.
Switchgear
Switchgears are designed to comply with fixed minimum clearances of live
components from one another, from earth potential and from protecting
barriers.
When setting up these installations in electrical equipment rooms with
restricted accessibility, protection against accidental contact with live
components is sufficient.
Metal enclosed switchgear are generally assembled from type-tested panels.
The metallic and earthed enclosure protects personnel against approach to
live components and against contact with moving parts. It also protects the
installation against the penetration of foreign bodies.
Switchgear of this type has the largest market share worldwide.
Switchgear
Switchgear
Switchgear
Switchgear
Switchgear
Switchgear
A third type of switchgear is the gas insulated switchgear (GIS). The term “gasinsulated” refers to the fact that atmospheric air is not used as the gaseous
insulating material inside the panels, i.e. The enclosure of the installation
must be gas-tight against the environment.
The advantage of gas-insulated switchgear compared to an air insulated
installation is its independence from environmental influences such as
moisture, salt fog and pollution. This results in less maintenance, increase
operational safety and high availability. The samller dimensions due to
compact design and increased dielectric resistance of the gaseous insulating
material are also advantages.
Switchgear
Control systems for Switchgear
A wide range of devices for protection, control and monitoring tasks is
available for conventional secondary technology in medium voltage
switchgear installations. The planning engineer selects the required units and
combines them into one installation. The outputs are predominantly
standardized to 1 A for current and 100 V for voltage.
Circuit breakers > 52 KV
Basic design of HV outdoor circuit breakers with the following components is
shown in the next figure: operating mechanism, insulators, interrupting
chamber .
Higher voltages and higher capacities are dealt with by increasing the number
of interrupting chambers. Single chamber breakars are used for voltages up to
300 KV and breaking currents of 50 KA. Multiple chamber breakers are used
for higher currents up to 80 KA in this voltage range. Multiple chamber
breakers are used for voltages >300 KV.
In the lower voltage range and for three-phase autoreclosure, it is best to
mount the three poles on a common base frame.
Single pole mounting and a seperate mechanism for each pole are standard
for voltages above 245KV.
The same interrupting chambers and mechanisms as indoor circuit breakers
are also used with the integrated circuit breakers of gas insulated switchgear
installations.
Circuit breakers > 52 KV
Circuit breakers > 52 KV
Circuit breakers > 52 KV
Circuit breakers > 52 KV
Circuit breakers > 52 KV
Circuit breakers > 52 KV
Some requirements for electrical
control
of
circuit
breakers
SF6 Gas monitoring : The breaking capacity of a circuit breaker is dependent
on the gas density in the breaker chamber. This is measured by a
temeperature-compensated pressure gauge. If the gas pressure falls to
aspecified value, an alarm is triggered.
Local/remore control: To allow work on the breaker, it can generally be
controlled from the local control cubicle; control can be switched from
remote local by a selector switch.
Autoreclosing: A single or three-pole autoreclosing is selected on the type of
system earthing, the degree of the interconnection, the length of the lines
and the amount of infeed from large power plants.
Instrument transformers for
switchgear
installations
Instrument transformers are transformers used to feed measuring
instruments, electricity meters, protection relays and similar equipment.
Their function is to transform high voltages and currents to values that can
be unified or measured safely with low internal losses. With current
transformers , the primary winding
carries the load current, while with
voltage transformers, the primary winding is connected to the service voltage.
The choice of a current transformer is based on the values of the primary and
secondary rated current, the rated output of the transformer cores at a given
accuracy class rating and the overcurrent limit factor or accuracy limit factor.
Selection of the values for the primary and secondary rated currents should
be based on standard levels. Secondary rated currents of 1A, 2A or 5A are
available. Modern protection devices and measuring instruments have a
relatively low burden, and so 1A is becoming the most frequently used
secondary current.
Instrument transformers for
switchgear
installations
Measuring instruments or meters, for instance KW,KVAR or KWH measure
under normal load conditions. These devices require high accuracy, a low
burden and low saturation. They normally function in the range of 5-120% of
the rated current in accordance with accuracy classes 0.2 to 0.5.
Burden is the load which may be imposed on a transformer secondary by
cables and connected devices without causing an error greater than the
stated accuracy classification.
For protection relays and disturbance recorders, the information about the
fault on the primary side has to be transmitted to the secondary side.
Measurement under fault conditions in the overcurrent range requires lower
accuracy, but the ability to transmit high fault currents which enable the
protection relay to measure and selectively shut down the fault. Typical
classes are 5P, 10P or TP.
Several measuring and protection cores can be combined in each transformer.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear
installations
Depending on the design of primary winding , current transformers are
divided into various types. This basically depends on the application (high or
low voltage).High voltage transformers are as a rule designed with oil-paper
or SF6 insulation.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear
installations
Voltage transformers can fundamentally be divided into two groups:
inductive and capacitive voltage transformers. Inductive voltage transformers
are the most economical solution for voltages up to 145 KV and above that
level capacitive transformers have advantages.
High voltage transformers are generally designed as oil-paper insulated
transformers.
Apart from inductive voltage transformers, capacitive voltage transformers
ara available for higher system voltages up to 765 KV. They fundamentally
consist of a capacitive divider and an inductive voltage transformer.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Optical current transformers use the Faraday effect in crystalline structures
for passive measurement of currents. Monochromatic light is sent polarized
into a solid body of glass, which surrounds the current carrying conductor.
Reflection from the bewelled corners of the glass container directs the light
beam around the conducting line before it exits again on one side.
The magnetic field around the conductor rotates the polarization plane of the
light, whose phase difference is proportional to the magnetic field intensity H.
The phase difference at the end of the path in the glass body is directly
proportional to the current.
Instrument transformers for
switchgear installations
Surge arresters
Surge arresters are used for protection of important equipment, particularly
transformers, from atmospheric overvoltages and switching overvoltages.
Arresters are primarily selected on the basis of two basic requirements:
-the arrester must be designed for stable continuous operation
-it must provide sufficient protection for the protected equipment.
Today surge arresters are based on metal oxide (MO) resistors, which have an
extremely nonlinear U/I characteristic and a high energy absorption capability.
They are known as metal oxide surge arresters.
The metal oxide arrester is characterized electrically by a current/voltage
curve. The current range is specified from the continuous operating range
(range A of the curve, order of magnitude 10-3 A) to a minimum of the double
value of the rated discharge current (order of magnitude 103 A). The MO
arrester corresponding to the characteristic is transferred from the high
resistance to the low resistance range at rising voltage without delay. When
the voltage returns to the continuous operating voltage or below, the arrester
becomes high ohmic.
Surge arresters
Surge arresters
Surge arresters are preferably installed parallel to the object to be protected
between phase and earth.Because of the limited protection distance with
steep lightning voltages, the arresters must be installed adjacent to the
equipment that is to be protected as much as possible.
Monitoring systems (surge counters) may be used to monitor surge arresters.
They are installed in the ground conductor of the arrester.
Surge arresters
Surge arresters
Transformers
Transformers
Oil Immersed Type Distribution Transformers
Hermetic
Iınside view
With conservator
Dry Type Distribution Transformers
With tap changer
Inside view
In metal encase
1.Core limbs
2.LV winding
3.HV winding
4.Tapping winding
5.Conductors
6.LV bushings
7.HV bushings
8.Pressing equipment
9. On-Load tap changer
10.Motor-drive mechanism
11.Oil conservator
12.Radiators
Stacking of core laminations
Lifting up of the core with special apparatus.Three
limbed transformer
A transformer core with five limbs
Step-lapped core
The difference between Transformers and Reactors ; Reactors have only primary winding and their
core has air-gaps as shown below.(But their periodical test and maintenance are the same as
transformers except turn ratio and magnetizing current measurings)
Single
phase
reactor
core
Winding apparatus for layer winding
Winding apparatus for disc winding
Winding apparatus for layer winding
Vertical winding apparatus
Pressing equipment for layer winding
INTRODUCTION
Upper clamping ring
Active part of a transformer
Bottom plate for the windings
INTRODUCTION
Active part with on-load tap changer
Due to the voltage variations in
the networks or in the substations,
transformers are normally equiped
with tapping windings having
necessary taps to accomplish the
requested voltage level. The
connections of these taps are
either made with no-load tap
changer(off-load tap changer)
when the transformer is
deenergized or with on-load tap
changer when the transformer is
under operating conditions.
The motor drive mechanism is
used for the, control of on-load tap
changer.This control can either be
made locally on the transformer or
remotely from the control
room.The operation of off-load tap
changers can either be made on
the cover or on the sidewall of the
transformer by manual drive
mechanism.Upon request, motor
drive mechanism can be provided
to operate the off-load tap
changers.
Active part with off-load tap changer
INTRODUCTION
Protection and control equipment
Bucholz relay
It is mounted on the pipe
connection from transformer tank
to conservator.The gasses which
occur in transformer for any
reason are collected here and
depending on the volume of gas it
gives an alarm or tripping signal.
Pressure relief device
It is mounted on the transformer
cover.It replies to the sudden
pressure increase that may occur
by an arc in the oil in the
transformer and gives tripping
signal by the contacts on itself.
Oil level indicator
It is mounted onto the sidewall
of the conservator. Depending
on the oil temperature
variations, it indicates the oil
level in conservator and gives
too low or too high indications
by the contacts on itself.
INTRODUCTION
Dehydrating breather
It is mounted onto the
conservator.It takes the moisture
and dust in the air that enters the
conservator and increases service
security of the transformer, the
amount of silicagel particles in it
varies with the amount of the oil in
the transformer.
Oil thermometer
It controls the temperature of the oil in the
transformer tank and gives alarm and trip signal
at the adjusted temperature limits.It gives start
and stop signal for the fans used at forced
cooling.If remote control is required,Pt 100
resistance or 4-20 mA output is added to it.
Winding thermometer
It controls the temperature of the windings
with its monitoring circuit and gives alarm
and trip signal at the adjusted temperature
limits.Like the oil temperature,it is used for
the controls of fans and pumps and if reqired
Pt 100 resistance or 4-20 mA output is
added to it.
Oil flow indicator
It controls the oil flow at forced oil cooled
transformers.It is mounted on the pipe
connection in which the oil flows
through.It gives alarm signal if the oil
does not flow for any reason.
CF101 air
cell alarm
relay
CL064 oil level OLTC
CL060oil level
CF 050
BUCHHOZ
CP096 pressure relief valve for OLTC
AT005 OLTC breathing
AT001 aircell
breathing
Main Tank
OLTC bucholz relayCF 061
CP081 pressure relief valve for main tank
HV Bushing
turret
CT033 winding temp. indicator
CT031 oil temp. indicator
BQ011Thermometer pocket for wind. Temp.
BQ010 Thermometer pocket
RADIATOR
Air Cell
SECTION .2 - CONSTRUCTION
RADIATORS
•
Butterfly
valve
Air ejecting plug (vent screw)
•O-ring
•Lifting eye
Transformer
Tank
•Radiators (cooling elements)
•Oil Drain plug
Radiators are important part of the cooling of the transformers.Radiators have two ducts for connection to transformers.
On upper and bottom connection pipes ,there are butterfly valves.
On upper side there is a ventilation plug.
On bottom side there is a draining plug.
On top of it, there is a lifting eye.
SECTION .2 - CONSTRUCTION
Ø The Fans and their Connections
RADIATOR
CONTROL
CUBICLE
FAN
FAN
TANK
Transformer Power Efficiency can be increased by adding fans. They are built under radiators to blow air upwards
for cooling the oil inside the radiators. They are operated automatically / manually when the oil temperature rise.
The basically cooling operations;
ONAN (Oil Natural Air Natural) (without fan or pumps)
ONAF (Oil Natural Air Forced) (air forced with fan)
OFAF (Oil Forced Air Forced) (air forced with fan or oil forced with pumps)
OLTC - MR Type
SECTION .2 - CONSTRUCTION
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
Transformers
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
HV Substations and Design Principles
Generation of High Voltages