O&M of Protection System and Relay Coordination

Dr. Sasidharan Sreedharan www.sasidharan.webs.com

Relay Types and Applications

2

Detailed Schedule

SIMPLE RELAY

Actuating Quantities

• Magnitude

• Rate of Change

• Phase Angle

• Direction

• Frequency

• Wave Shape

• Duration (Time)

• Ratio

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

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

• 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

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

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

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

Dr. Sasidharan Sreedharan

YBL Systems and Solutions

(Electrical Power System Research Consultants)

www.sasidharan.webs.com

35

Regards,