Protection Engineering Basics and Schemes Protection Engineering | Page 4

Contents
Chapter 1 Instrument Transformers: ......................................................................................................... 8
1.1 Current Transformer: .......................................................................................................................... 8
1.1.1 Operation ..................................................................................................................................... 9
1.1.2 Burden: ....................................................................................................................................... 11
1.1.3 Errors: ......................................................................................................................................... 13
1.1.4 Exitation or magnetization Current: .......................................................................................... 14
1.1.5 CT types as per applications:...................................................................................................... 16
1.1.6 Accuracy limit Factor: ................................................................................................................. 16
1.1.7 Knee point Voltage: .................................................................................................................... 17
1.1.8 Circuit Diagram of Excitation /Magnetization Test .................................................................... 19
1.1.7 Polarity of CT: ............................................................................................................................. 23
1.1.9 Ratio Test: .................................................................................................................................. 27
1.1.10 CT by location is divided in two types ...................................................................................... 29
1.1.11 CT by construction is divided in three types ............................................................................ 30
1.1.13 Nameplate Data: ...................................................................................................................... 36
1.1.14 Special Type of CT (Class X): ..................................................................................................... 38
1.2 Potential Transformer ....................................................................................................................... 41
1.2.1 Operation: ...................................................................................................................................... 41
1.2.2 Errors .......................................................................................................................................... 42
1.2.3 Voltage transformers for extra high voltage .............................................................................. 45
1.2.4 Capacitive Voltage Transformer: ............................................................................................... 47
1.2.5 Protection of Voltage Transformer: ........................................................................................... 49
1.2.6 Test need to be conduct on Voltage Transformer ..................................................................... 49
Chapter 2 Auxiliary Relays and Trip circuits ............................................................................................. 63
2.1 Auxiliary Relays ................................................................................................................................. 63
2.2 Types of Contacts .............................................................................................................................. 65
2.2.1 Make contact ............................................................................................................................. 65
2.2.2 Break contact ............................................................................................................................. 65
2.2.3 Change over Switch .................................................................................................................... 66
2.2.4 Delay Switches ........................................................................................................................... 66
2.3 Trip circuits: ....................................................................................................................................... 67
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