Group Members

• Kamran Mustafa 26• Mohsin Arif 19-A• Haq Nawaz Qasmi 19• Waqar Tayyub 39

Contents

• Introduction• Components• Protective Devices• Types of Protection• Coordination• Performance Measures

Introduction

• 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 faulted parts from the rest of the electrical network.

Components

Protection systems usually comprise five components:• Current and voltage transformers• Protective relays• Circuit breakers• Batteries• Fuses

Continue……• Current & Voltage Transformer: Current &

Voltage Transformer to step down the high voltages and currents of the electrical power system to convenient levels for the relay.

Current Transformer Voltage Transformer

Continue…..

• Protective Relays to sense the fault and initiate a trip, or disconnection.• Circuit Breakers to open/close the system based on

relay and auto reclose commands.

Digital Relay Circuit Breakers

Continue….

• Batteries to provide power in case of power disconnection in the system.

• Fuses for parts of a distribution system, fuses are capable of both sensing and disconnecting faults

Batteries Fuses

Protective Devices

Functionality:• Automatic operation, such as auto-re-closing or

system restart• Monitoring equipment which collects data on the

system for post event analysis.

Parts of Protective Devices

There are three parts of protective devices:• Instrument transformer• Relay• Circuit Breaker

Circuit Breaker Relay Inst Transformer

Advantages (Protective Devices)

Major advantages of protective devices are:

• Safety• Economy• Accuracy

Types of Protection

1. Primary protection2. Backup protection

Primary Protection 

The primary protection is the first line of defence and is responsible to protect all the power system elements from all the types of faults.

Primary Protection 

C.BC.BC.BC.B

Main bus

Line bus

Over current relay C.B Circuit breaker

Primary protection may fail due to the following reasons• Failure of DC supply to the tripping Circuit• Failure in relay operating current or voltage• Failure in circuit breaker tripping mechanism• Failure of main protective relay operation• Failure in the wiring of relaying system• Failure of CTs or PTs operation

back-up Protection

• The backup protection comes into play only when the primary protection fails.• when we disconnect primary protection for testing or

maintenance purpose, then secondary or back-up protection will act as primary protection.

Backup protection

C.BC.BC.BC.B

Main bus

Line bus

Over current relay C.B Circuit breaker

C.B

Types of Secondary or backup protection

• Relay Backup Protection• Breaker Backup Protection• Remote Backup Protection• Centrally Co-ordinate Backup Protection

Relay Backup Protection

• In this scheme, a single breaker is used by both primary as well as backup protection but the two protective systems are different.

 Breaker Backup Protection

• In this method, separate breakers are provided for primary and backup protection. Both the types of breakers are at the same station.

 Remote Backup Protection 

• In this method, separate breakers are provided for primary and backup protection. The two types of breakers are at the different stations and are completely isolated and independent of each other.

Centrally Co-ordinated Backup Protection • In this method, primary protection is at various

stations. There is a central control room and backup protection for all the stations is at central control room. Central control continuously inspects the load flow and frequency in the system. If any element of any part of the system fails, load flow gets affected which is sensed by the control room. The control source consists of a digital computers which decides the proper switching action. The method is also called centrally controlled backup protection

Coordination

• Protective device coordination is the process of determining the "best fit" timing of current interruption when abnormal electrical conditions occur. The goal is to minimize an outage to the greatest extent possible.

Performance Measures

We can measure a protection systems performance with following:• Reliability• Selectivity• Speed• Economy• Simplicity

Questions ?

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