The document discusses relays and protection in power systems. It provides an introduction to distance protection relays, explaining that they monitor voltage and current to trip circuit breakers during faults. The document then covers the principles, working, construction, types, advantages, disadvantages and applications of relays. It also discusses distance relay theory, the purpose of relays in distance protection, and different types of protection used in power systems.

1. RELAYS &
PROTECTION
VEERENDRA
CASE STUDY – I PRESENTATION

2. Agenda
 Introduction
 Principle
 Working
 Construction
 Types of relays
 Advantages & Disadvantages
 Applications
 Distance Relay Theory
 Purpose of relay in distance protection
 Types of protection
 Conclusion
6/22/2023 PRESENTATION TITLE 2

3. Introduction
• Distance Protection Relay. A distance protection relay is an essential device for tripping a circuit
breaker in case of an overload or a fault. However, in low-rating power circuits, a distance
protection relay carries the capacity to trip on its own without seeking any help from the circuit
breaker.
• The distance relay is also referred to as the impedance relay or distance protection element or
voltage-controlled device. It's working mainly depends on the distance between the impedances
of the points where the fault occurs and where the relay is installed (feeding point).
• A protective relay is an electrical device that monitors the voltage and current using CTs and
PTs. Thus, the main function of the protective relay is to trip the breaker under abnormal
operating conditions.
CASE STUDY – II RELAYS & PROTECTION 3

4. PRINCIPLE
• The protection relay compares the measured electrical quantities with the
set point. If the measured quantity is more than the set point, the relay
issues a trip command to the breaker.
• It also generates the pre-alarm before issuing the trip command. The trip
command of the relay goes to the tripping coil of the breaker. And thus,
the breaker isolates the faulty section.
• We use an over current relay for fault detection in the electrical network.
The sensing element for the over current relay is the protection class
current transformer. The df/dt relay monitors the frequency of the
electrical network.
• Therefore, the protection relay is the backbone of the electrical network. In
any case, the protection relay must trip the breaker under fault conditions.

5. WORKING
CASE STUDY - II RELAYS & PROTECTION 5
• When the fault occurs at point F, a huge current flow in the electrical
network. The current transformer (CT) senses that current and feeds into
the protective relay. The relay coil of the protective relay issues a command
to the circuit breaker which isolates the faulty section.
• Relay works on the principle of electromagnetic induction.
• When a voltage is provided to the electromagnetic coil, it magnetizes the
iron core and forms a magnetic field, which attracts the armature towards it.
I ordinarily closed, this causes the contact to close (closing the load circuit)
or open in case it is normally closed relay (depends upon the construction).
When the power is turned off, the spring pushes the contacts apart, to be
broken.

6. 6/22/2023 PRESENTATION TITLE 6
Electromagnetic coil An electromechanical relay’s most critical component is
the electromagnetic coil. It is made up of a magnetic core and a collection of
copper windings. The flow of current through the coil produces a magnetic field,
as you may know. When voltage is given to the coil, it transforms into an
electromagnet, attracting the armature.
Armature An armature is a movable piece of metal, balanced using a pivot.
Core The core is the metallic part over which the coil is wound.
Movable contacts and fixed contacts The contacts inside the relay are the
conducting elements that open or close when voltage is delivered to the coil. A
movable contact is one that is attracted by an electromagnet, while a fixed
contact is one that is immovable and attached to the terminals.
Spring arrangement They also have spring arrangements, such as those that
return the armature and contacts to their original positions after the coil is de-
energized.
CONSTRUCTION

7. CASE STUDY - II RELAYS & PROTECTION 7
TYPES OF RELAY
•Electromagnetic Relays
•Electronic Relays
•High-Voltage Relays
•Small Signal Relays
•Time Delay Relays
•Thermal Relays
•Differential Relays
•Distance Relays
•Automotive Relays
•Frequency Relays
•Polarized Relays
•Rotary Relays
•Sequence Relays
•Moving Coil Relays
•Buchholz Relays
•Ground Fault Relays

8. ADVANTAGES
CASE STUDY - II RELAYS & PROTECTION 8
Let’s start with the advantages of a
relay.
It allows us to control a remote
device. It is not necessary to be near
the device to make it work.
Change contacts easily.
Isolates the activating part of the
actuating part.
It works well at high temperatures.
It is activated with low current;
however, it can activate large machines
of great power.
With a single signal, you can control
several contacts at once.
It can switch direct current or
alternating current.
DISADVANTAGES
Contacts are damaged over time and
continuous use (wear, oxidation, etc.)
They generate a lot of noise with the
activation and deactivation of the contacts.
Switching time is high.

9. APPLICATIONS
Used for ON/OFF applications.
Capable of switching multiple circuits
Coil relays are used for the protection of
circuits.
Controls high power circuit with a low
power signal
For home appliances such as refrigerators,
washing machines.
For molding equipment, packing machinery,
vending machines
They are used in Motor & lighting control.
Used in Aerospace, Defense, and
automotive industries.
Used in the traffic signal controllers,
temperature controllers, heaters.

10. DISTANCE RELAY THEORY
• The distance relay is a distance protection device that is used to determine the location of a
defective point. The impedance value determines how well this relay works. When the
impedance of the defective point is less than the impedance of the relay, it trips the circuit
breaker and shuts the connections. The relay continually monitors the voltage and current
passing through the PT and CT, and it only operates when the ratio of voltage and current
(impedance value) is less than the relay’s specified impedance value.
• Impedance Relay: The relay estimates impedance up to the point of fault and provides a
tripping command if this impedance is less than the relay setting Z. The circular
characteristic of the impedance relay is centered at the origin of the R-X diagram. It is
mostly utilized as a defect detector and is non directional.

11. • Admittance Relay: The most common distance relay is the admittance relay. In pilot
schemes, it serves as the tripping relay, while in step distance schemes, it serves as the
backup relay. Its characteristic is directional since it goes through the R-X diagram’s
origin. It is round in the electromechanical design and can be curved to conform to the
transmission line impedance in the solid-state design.
Reactance Relay: A reactance relay is appropriate for the protection of a short
transmission line because its operation is independent of arc resistance. The relay which is
designated for a long transmission line should be slightly affected due to power swings.

12. ADVANTAGES OF DISTANCE RELAY
It takes the place of over current
transmission line protection.
Protects promptly.
It’s easy to coordinate and apply.
There is no need to alter the settings
because they are permanent.
The fault current magnitude is reduced
because of a generation of fault levels.
Allows for the high-load lining.
DISADVANTAGES OF DISTANCE RELAY
It is non-directional since it operates on
both sides of a line’s fault.
It is unable to distinguish between
interior and exterior line faults.
The distance relay’s function is
influenced by the resistance of a fault line’s
arc. When a defect occurs at any point, an
arc is created.
Because the region covered by the circle
on the sides of the R-X plane is vast, power
swings have an impact on distance relay
performance.
Fault resistance measuring capability is
restricted.

13. PURPOSE OF RELAY IN DISTANCE
PROTECTION
CASE STUDY – II RELAYS & PROTECTION 13
Protective relays are one of the critical components of the electrical power grid that
serve to detect defective equipment or other dangerous or intolerable conditions and
can either initiate or permit switching or simply provide an alarm to provide a safer,
more reliable delivery system.
Relays are the switches that aim at closing and opening the circuits electronically as
well as electromechanically. It controls the opening and closing of the circuit contacts
of an electronic circuit.

14. TYPES OF PROTECTION
Distance protection/ Impedence (Long distance Protection)
Differential protection(Short distance Protection)
Differential protection(For ICT & Reactor)
Restricted Earth Fault Relay(For ICT & Reactor)
Backup Protection
Over Voltage Protection
Over Current Protection
STUB Protection
SOTF(Switch On To the Fault)
CASE STUDY - II RELAYS & PROTECTION 14

15. CONCLUSION
A relay is an electrically operated switch. It
consists of a set of input terminals for a
single or multiple control signals, and a set of
operating contact terminals. The switch may
have any number of contacts in multiple
contact forms, such as make contacts, break
contacts, or combinations thereof.