O&M of Protection System and Relay
Coordination
Relay Types and Applications
Dr. Sasidharan Sreedharan
www.sasidharan.webs.com
Detailed Schedule
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SIMPLE RELAY
Actuating Quantities
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•
•
•
•
•
•
•
Magnitude
Rate of Change
Phase Angle
Direction
Frequency
Wave Shape
Duration (Time)
Ratio
RELAY Classification
Construction
Applications
Characteristics
Solenoid
Over V/I
Instant
Under V/I
Definite time
Directional Relay
Inverse time
Differential Relay
Inverse definite
minimum time
Attracted Armature
Electro dynamic
Moving Coil
Induction
Distance or Impedance
Relay
Relay Types
• Electromagnetic Relays (EMRs)
– EMRs consist of an input coil that's wound to accept a
particular voltage signal, plus a set of one or more contacts
that rely on an armature (or lever) activated by the
energized coil to open or close an electrical circuit.
• Solid-state Relays (SSRs)
– SSRs use semiconductor output instead of mechanical
contacts to switch the circuit.
– The output device is optically-coupled to an LED light
source inside the relay.
– The relay is turned on by energizing this LED, usually with
low-voltage DC power.
• Microprocessor Based Relays
– Use microprocessor for switching mechanism.
– Commonly used in power system monitoring and
protection.
Advantages/Disadvantages
• Electromagnetic Relays (EMRs)
– Simplicity
– Not expensive
– Mechanical Wear
• Solid-state Relays (SSRs)
– No Mechanical movements
– Faster than EMR
– No sparking between contacts
Sold State relays are having
more
advantages
than
electromagnetic relays such as
small CT burden, less space,
fast operation, more accuracy,
long life and less maintenance
• Microprocessor-based Relay
– Much higher precision and more reliable and durable.
– Improve the reliability and power quality of electrical power
systems before, during and after faults occur.
– Capable of both digital and analog I/O.
– Higher cost
Electro Magnetic Relay
• In an electromagnetic relay, the operating
torque is produced by the electromagnetic
attraction/electromagnetic induction/thermal
effects of electric current.
• The restraining torque is produced by the
springs
F  Fo  Fr
F is the net torque
Relay operates when the net
torque is positive
Fo is the operating force.
Fr is the restraining force.
Type of Relay units
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•
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Attracted armature type relay (Electromagnetic)
Balanced Beam relay(Electromagnetic)
Induction disc relay (Electromagnetic)
Induction Cup relay(Electromagnetic)
Moving
coil
and
moving
iron
relay
(Electromagnetic)
• Gas operated Relay
• Rectifier relay units
• Static relay
Principle
• Simplest type of relays
• The relays have coil or electromagnet energized by the
coil
• Coil may be energized by the actuating quantity which
is proportional to circuit current and voltage.
• A plunger or vane is subjected to the action of the
magnetic field produced by the operating quantity.
• Respond to both AC and DC
• Very fast in action
• Don’t have directional feature
• Affected by transients
• Modern attraction armature type relays are compact,
robust and reliable.
Attracted Armature Type
Applications
• Over Current Protection
• Definite time lag over current and earth fault
protection
• Differential Protection
• Auxiliary Relays
Balanced Beam Relay
• Difficult to design over wide
range of current
• Very fast and instantaneous
Induction Disc Type
Shaded Pole Type
Watt hour meter type
Principle of Operation
• Electro- magnetic induction relays operate
on the principle of induction motor.
• An induction relay consists of a pivoted
Aluminium disc placed in two alternating
magnetic fields of the same frequency but
displaced in time and space.
• The torque is produced in the disc by the
interaction of one of the magnetic fields
with the current induced in the disc by the
other
Induction Disk Relay
Plug Setting and Time Setting
• In these relays there is facility of selecting the
plug setting and time setting such that the
same relay can be used for wide range of
current time and characteristics.
Induction Cup Relay
• Modern induction cup relays have 4 or more poles
• The relays can be responsive to voltage and current
• The double actuating quantity relay can be responsive to both voltage and
current
• The operating time characteristics depends on the type of structure
• Modern Induction cup relay may have an operating time of 0.010 second
Permanent Magnet Moving Coil Relay
• Relay responds to DC only
• Uniform torque
• Inverse time current Characteristics
Operating Torque
• DC Operation only
• Characteristics varied
by
adjusting
the
control spring
• Operating Torque is
proportional
to
current.
Rectifier Relay Systems
Thermal Relays
• Use bimetallic strips to open/close relay contacts
when temperature exceeds/drops to certain level.
• Require certain reaction time
• Inverse time/current relationship
Directional Relay
Frequency Relays
• Under Frequency Relays
• Over Frequency Relays
• Rate of Change of Frequency Relay
Applications
Load Shedding
Frequency Relays
• Either electromagnetic or
static
• Relay can operate on
under
frequency/over
frequency
• Under voltage relay is
normally
provided
in
conjunction with under
frequency relay
Frequency Relay
Under Voltage Relays
• Provided for AC circuits, bus bars, motors,
rectifiers, transformers etc.
• Necessary for voltage and reactive power control.
• Instantaneous or inverse characteristics
• Construction similar to usual induction relay or
attached armature relay
DC relays
• Induction relays are not suitable for DC
• MI and PMMC are suitabe for DC
• PMMC high accuracy and low consumption
Applications:
• Controlling direct current either rise in current or fall in
current or reverse current.
• DC voltage relays are generally suitable for control of DC
voltage (rise or fall)
All or Nothing Relays
• Pick up value not critical
• Does not perform precise measurement but it
does not operate but change its state (open
contacts , close contacts)
• Such relays assist in measuring relays and they
take over various duties such as time lag, tripping
indication etc.
• Works in coordination with protective relays such
that the protection relays can be designed for less
burden and more sensitivity.
Negative Phase Sequence Relay
• A negative phase sequence (or phase unbalance) relay is
essentially provided for the protection of generators and
motors against unbalanced loading that may arise due to
phase-to-phase faults.
• Such relay has a filter circuit, which is responsive only to the
negative sequence components.
Over Current Relay
Over Voltage relay
Numerical Relays
Regards,
Dr. Sasidharan Sreedharan
YBL Systems and Solutions
(Electrical Power System Research Consultants)
www.sasidharan.webs.com
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