O&M of Protection System and Relay Coordinationsasidharan.webs.com/documents/4. Relay Type and...
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O&M of Protection System and Relay Coordination
Dr. Sasidharan Sreedharan www.sasidharan.webs.com
Relay Types and Applications
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Detailed Schedule
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SIMPLE RELAY
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Actuating Quantities
• Magnitude
• Rate of Change
• Phase Angle
• Direction
• Frequency
• Wave Shape
• Duration (Time)
• Ratio
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Construction
Solenoid
Attracted Armature
Electro dynamic
Moving Coil
Induction
Applications
Over V/I
Under V/I
Directional Relay
Differential Relay
Distance or Impedance Relay
Characteristics
Instant
Definite time
Inverse time
Inverse definite minimum time
RELAY Classification
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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.
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Advantages/Disadvantages • Electromagnetic Relays (EMRs)
– Simplicity
– Not expensive
– Mechanical Wear
• Solid-state Relays (SSRs)
– No Mechanical movements
– Faster than EMR
– No sparking between contacts
• 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
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
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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
o rF F F Fo is the operating force. Fr is the restraining force.
F is the net torque Relay operates when the net torque is positive
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Type of Relay units
• 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
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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.
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Attracted Armature Type
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Applications
• Over Current Protection
• Definite time lag over current and earth fault protection
• Differential Protection
• Auxiliary Relays
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Balanced Beam Relay
• Difficult to design over wide range of current
• Very fast and instantaneous
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Induction Disc Type
Shaded Pole Type
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Watt hour meter type
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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
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Induction Disk Relay
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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.
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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
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Permanent Magnet Moving Coil Relay • Relay responds to DC only • Uniform torque • Inverse time current Characteristics
Operating Torque
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• DC Operation only
• Characteristics varied by adjusting the control spring
• Operating Torque is proportional to current.
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Rectifier Relay Systems
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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
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Directional Relay
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Frequency Relays • Under Frequency Relays
• Over Frequency Relays
• Rate of Change of Frequency Relay
Applications
Load Shedding
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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
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Frequency Relay
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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
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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)
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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.
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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.
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Over Current Relay
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Over Voltage relay
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Numerical Relays
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Dr. Sasidharan Sreedharan
YBL Systems and Solutions
(Electrical Power System Research Consultants)
www.sasidharan.webs.com
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Regards,