Presentation on

Substation Protection Devices

Presented by: Rahul KumarRoll no. 125069Regd. No. 1201211280Department of Electrical EngineeringOrissa engineering college

Guided by:ER.DEBASHISH MISHRAASST. PROFESSORDEPARTMENT 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.

Switchgear And 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.

Current Transformer contd…

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 Panel

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 Protection

CTs

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 Ram TMH publication.

Fundamentals of Power system protection by Yeshwant G. Paithankar, S.R. Bhide.

Electrical Power system by A Wright. Wikipidia

Questions…

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