Substation protection devices

Presentation on
Substation Protection Devices
Presented by:
Rahul Kumar
Roll no. 125069
Regd. No. 1201211280
Department of Electrical Engineering
Orissa engineering college
Guided by:
ER.DEBASHISH MISHRA
ASST. PROFESSOR
DEPARTMENT OF
ELECTRICAL Engineering

Contents
 Introduction
 Protection devices
 Protection requirement
 Current transformer(CT)
 Potential transformer(PT)
 Relay
 Circuit breaker
 Lightning arrester
 Isolators
 Conclusion

Introduction
Substation Protection system
 Power System-Protection is a branch of electrical power
engineering that deals with the protection of electrical
power systems from faults through the isolation of faulty
parts.
A typical substation

Why Do We Need Protection
 The objective of a protection scheme is to keep the
power system stable by isolating only the components
that are under fault, whilst leaving as much of the
network as possible still in operation.
 Under abnormal working condition protection is
necessary for safety of electrical equipments and safety
of human being.

SwitchgearAnd Protection Devices
 What are the Protection devices?
 The apparatus or equipments and their associated
auxiliaries employed for controlling, regulating and
switching on or off the electrical circuits in the electrical
power system is known as “Protection devices” or
“switchgear”.
 Protection devices protect the transmission lines,
generators, transformers and other electrical
equipments from various “faults”.

Faults
 Types of “faults”
 Short-circuit faults
 Open-circuit faults
 Faults are detected by relays(automatically) and faulty
section is isolated by circuit breakers.
 The combination of relays and circuit breakers is known
as “Protective system”.

Content of Automatic switchgear
 Current and voltage transformer
 Relays
 Circuit breakers
 Lightning arresters(or “Surge diverter”)
 Isolators(or “Disconnecting switch”)
 Fuse

Main Protection Requirements
 Reliability
 Selectivity
 Speed
 Sensitivity

Current Transformer(CT)
 A current transformer (CT) is used for
measurement of alternating electric current.
 When current in a circuit is too high to apply
directly to measuring instruments, a current
transformer produces a reduced current
accurately proportional to the current in the
circuit, which can be conveniently connected to
measuring and recording instruments.
 Current transformers are commonly used in
metering and protective relays in the electrical
power industry.

Potential Transformer(PT)
 Potential transformers (PT) (also called
voltage transformers (VT)) are a parallel
connected type of instrument transformer.
 They are designed to present negligible load
to the supply being measured and have an
accurate voltage ratio and phase relationship
to enable accurate secondary connected
metering.

Potential Transformer contd…
 It gives the reference voltage to the Relay for
Over-voltage or Under-voltage Protection.

Introduction To Relay
 A Relay is a logical elements which process the
inputs(mostly voltage and currents) from the system and
issue a trip decision if a fault within its jurisdiction is
detected.
 Inputs to the Relays are
 Current from current transformer(CT)
 Voltage from voltage transformer(VT)

Relay contd…
A typical protective Relay

How Do Relays Detect Faults?
 When a fault takes place, the current, voltage, frequency,
and other electrical variables behave in a peculiar way. For
example:
 Current suddenly increases
 Voltage suddenly decreases
 Relays can measure the currents and the voltages and
detect that there is an over-current or an under-voltage
or a combination of both.
 Many other detection principles determine the design of
protective relays.

Basic Elements of Relay
Sensing
Element
Comparison
Element
Control
Element
Relay
To trip or signal
circuit(CB)

Three-Phase Diagram of the
ProtectionCTs
VTs
Relay
CB
Control
Protected
Equipment

Advantages of Relay
 Maximum flexibility
 Provide multiple functionality
 Self checking and communication facility
 It can be made adaptive for any system

Circuit Breaker(CB)
 Circuit breakers are an automatically
operated electrical devices, design to close or
open contact members, thus closing and
opening an electrical circuit under normal or
abnormal conditions.
 It operates on relays command.
 It handles the large voltage and current.

Operating Principle of a
Circuit Breaker
 A circuit breaker consists of two contacts
namely “fixed” and “moving contacts” which
touches each other under normal condition
i.e. when circuit breaker is closed.
 Whenever a fault occurs(detected by relay),
the trip coil get energized, the moving
contacts get pulled by some mechanism and
therefore, the circuit breaker is opened and
circuit is broken.

Various Types of Circuit
Breaker
 CBs are categorized based on the intrrupting
medium used.
1. Air-Break Circuit Breakers (ACB)
2. Oil Circuit Breakers (OCB)
3. Vacuum Circuit Breakers (VCBs)
4. Air-Blast Circuit Breakers (ABCB)
5. SF6 Circuit Breakers

Circuit breaker contd…
An Oil Circuit Breaker SF6 Circuit Breaker

Lightning arrester(Surge
Diverter)
 The device or equipment used for the protection of the
power system against voltage surge is called “surge
diverter” or “lightning arrester”.

Isolators
 Isolators are used to isolate the high voltage from flow
through line into the bus. It allows only needed voltage
and rest is earth by itself if required.
Isolator

Conclusion
 The objective of the protection
devices(system) is to keep the power system
stable by isolating only the components that
are under fault, while leaving as much of the
network as possible.
 Now a days the Substation Protection System
is fully automatic.

References
 Power system protection and switchgear by
Badri RamTMH publication.
 Fundamentals of Power system protection by
Yeshwant G. Paithankar, S.R. Bhide.
 Electrical Power system by AWright.
 Wikipidia

Substation protection devices

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