An electrical relay is a device that uses an electromagnet to operate switch contacts to open or close a circuit. It senses conditions in one circuit to automatically trigger changes in another circuit. There are several types of relays based on their characteristics, logic, actuating parameters, and operating mechanisms. The key requirements for protection relays are reliability, sensitivity, speed, and selectivity to ensure they isolate faults while avoiding unnecessary tripping of healthy portions of the system. Relays can be electromagnetic, static, or mechanical and are used in various power system protection applications and schemes.

1. RELAY
PRESENTED BY
* M NAEEM 2K15 ELE 70
* M MASHAB 2K15 ELE 66
* M WAQAS ASHRAF 2K15 ELE 54
* RUKAN ABDULLAH 2K15 ELE 59
* M.DAUD 2515 ELE 56

2. An electrical device, typically incorporating an electromagnet, which is
activated by a current or signal in one circuit to open or close another
circuit.
 What is relay ?
A relay is automatic device which senses an abnormal condition of
electrical circuit and closes its contacts. These contacts in turns close and
complete the circuit breaker trip coil circuit hence make the circuit breaker
tripped for disconnecting the faulty portion of the electrical circuit from rest
of the healthy circuit.
or

3. SELECTIVITY
The relay must be operated in only those conditions for which relays are
commissioned in the electrical power system. There may be some typical
condition during fault for which some relays should not be operated or
operated after some definite time delay hence protection relay must be
sufficiently capable to select appropriate condition for which it would be
operated.
FUNCTIONAL REQUIREMENTS OF PROTECTION RELAY
RELIABILITY
The most important requisite of protective relay is reliability. They
remain inoperative for a long time before a fault occurs; but if a fault
occurs, the relays must respond instantly and correctly.

4. Sensitivity
The relaying equipment must be sufficiently sensitive so that it can be
operated reliably when level of fault condition just crosses the predefined
limit.
 Speed
The protective relays must operate at the required speed. There must be a
correct coordination provided in various power system protection relays in
such a way that for fault at one portion of the system should not disturb other
healthy portion. Fault current may flow through a part of healthy portion since
they are electrically connected but relays associated with that healthy portion
should not be operated faster than the relays of faulty portion otherwise
undesired interruption of healthy system may occur. Again if relay associated
with faulty portion is not operated in proper time due to any defect in it or
other reason, then only the next relay associated with the healthy portion of
the system must be operated to isolate the fault. Hence it should neither be
too slow which may result in damage to the equipment nor should it be too
fast which may result in undesired operation.

5. When a power is supplied to the coil, it generates a magnetic force that
actuates the switch mechanism. The magnetic force is, in effect, relaying the
action from one circuit to another. The first circuit is called the control circuit;
the second is called the load circuit.
 Basic working principle
All relays contain a sensing unit, the electric coil, which is powered by AC or
DC current. When the applied current or voltage exceeds a threshold value,
the coil activates the armature, which operates either to close the open
contacts or to open the closed contacts. When a power is supplied to the coil,
it generates a magnetic force that actuates the switch mechanism. The
magnetic force is, in effect, relaying the action from one circuit to another.
The first circuit is called the control circuit; the second is called the load
circuit.

8. Definite time relays
Inverse time relays with definite minimum time(IDMT)
Instantaneous relays.
IDMT with inst.
Stepped characteristic.
Programmed switches.
Voltage restraint over current relay.
 Types of Relays
Types of protection relays are mainly based on their characteristic, logic,
on actuating parameter and operation mechanism. Based on operation
mechanism protection relay can be categorized as electromagnetic relay,
static relay and mechanical relay

9. Distance schemes.
Bus bar protection.
Reverse power relays.
Loss of excitation.
Negative phase sequence relays etc.
 Based on of logic the protection relay can be categorized
as-
Differential.
Unbalance.
Neutral displacement.
Directional.
Restricted earth fault.
Over fluxing

10. Based on application the protection relay can be categorized
as-
Primary relay.
Backup relay.
 Based on actuating parameter the protection relay can be
categorized as-
Current relays.
Voltage relays.
Frequency relays.
Power relays etc.

11. Pressure switches.
Mechanical interlocks.
Pole discrepancy relay.
 Thermal
OT trip (Oil Temperature Trip) (b) WT trip (Winding Temperature Trip) (C)
Bearing temp trip etc.
 Float type
(a) Buchholz (b) OSR (c) PRV (d) Water level Controls etc.

12. Electromagnetic Relay Working
Practically all the relaying device are based on either one or more of the
following types of electromagnetic relays.
Magnitude measurement,
Comparison,
Ratio measurement.
 Some Relays working
Electromagnetic Relay
Electromagnetic relays are those relays which are operated by
electromagnetic action. Modern electrical protection relays are mainly micro
processor based, but still electromagnetic relay holds its place. It will take
much longer time to be replaced the all electromagnetic relays by micro
processor based static relays. So before going through detail of protection
relay system we should review the various types of electromagnetic relays.

13. Attraction Armature Type Relay
Attraction armature type relay is the most simple in construction as well as its
working principle. These types of electromagnetic relays can be utilized as
either magnitude relay or ratio relay. These relays are employed as auxiliary
relay, control relay, over current, under current, over voltage, under voltage
and impedance measuring relays.
Principle of electromagnetic relay working is on some basic principles.
Depending upon working principle the these can be divided into following
types of electromagnetic relays.
Attracted Armature type relay,
Induction Disc type relay,
Induction Cup type relay,
Balanced Beam type relay,
Moving coil type relay,
Polarized Moving Iron type relay.

15. Working
The working principle of a Balance Beam Relay is quite simple. Here one
beam is supported by one hinge. The hinge supports the beam from some
where in the middle of the beam. There are two forces acts on two ends of the
beams, respectively. The direction of both of the forces are same. Not only
direction, in normal working condition the torque produced by the forces in
respect of the hinge, are also same. Due to these two same directional
torques, the beam is held in horizontal position in normal working condition.
 Balanced Beam Relay
Balanced beam type relay can be said a variant of attraction armature
type relay, but still these are treated as different types of relay as they
are employed in different field of application.
Balanced beam type relays were used in differential and distance
protection schemes. The use of these relay becomes absolute as
sophisticated induction disc type relay and induction cup type relays
supersede them.

16. As this torque is increased, the balance of the beam is being disturbed. Due
to this unbalanced torque condition, the beam end associated with operating
torque, moves downward, to close No contacts of the relay.
One of these torques is restraining torque and other is operating torque.The
restraining torque can be provided either by restraining coil or by restraining
spring.
This is a kind of attracted armature type relay. But balance beam relay is
treated separately from their application point of view. When any fault
occurred, the current through the operating coil, crosses its pick up value, and
hence the mmf of operating coil increases and crosses its pick-up value. Due
to this increased mmf, the coil attracts more strongly the beam end and
hence, torque on respective end of the beam increases.

19. Static relays are superior to electro-magnetic relays in the following aspects:
The moving parts and the contacts are largely eliminated. The only moving
element in a static relay is the final tripping contact.
C.T.s and P.T.s employed are of lesser VA rating as static relays require a
very little volt-ampere for their operation.
More precise and high speed operation
 Static Relay
The conventional relay type of electromagnet relays can be replaced by static
relays which essentially consist of electronic circuitry to develop all those
characteristics which are achieved by moving parts in an electro-magnetic
relay.
For example, in an induction type relay, the operating time can be adjusted by
adjusting the distance travelled by the disc whereas in a static relay it can be
achieved by adjusting the value of the resistance in the R-C time delay circuit.
In other words static relays are capable of performing the same functions with
the use of electronic circuit control as an electro-magnetic relay performs with
the use of moving parts or elements.

20. The rectified output is supplied to a measuring unit comprising of
comparators, level detectors, filters, logic circuits.
The output is actuated when the dynamic input (i.e., the relaying quantity)
attains the threshold value. This output of the measuring unit is amplified by
amplifier and fed to the output unit device, which is usually an
electromagnetic one
 Operation of Relay
The essential components of static relays are shown in figure below. The
output of CT and PT are not suitable for static components so they are
brought down to suitable level by auxiliary CT and PT. Then auxiliary CT
output is given to rectifier
Rectifier rectifies the relaying quantity i.e., the output from a CT or PT or a
Transducer

22. THANK YOU ALL