Types of Protective Relays and its Function
There are very different functions of protection relays, every one of those relays are ready to touch upon sure type of faults. Every equipment wants different types of protection relays. As example, Distance relays are suitable for transmission lines, and differential relays for power transformers and bus bars. Before undergo protection relays, will see the list different types of protection relays by it’s operate and ANSI code as shown in table below:
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ANSI Code and Relay Function
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|
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ANSI Number
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DESCRIPTION
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|
2
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Time-delay
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|
21
|
Distance
|
|
25
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Synchronism-check
|
|
27
|
Under voltage
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|
30
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Annunciator
|
|
32
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Directional power
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|
37
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Undercurrent or under power
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|
38
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Bearing
|
|
40
|
Field
|
|
46
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Reverse-phase
|
|
47
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Phase-sequence voltage
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|
49
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Thermal
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|
50
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Instantaneous over current
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|
51
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AC time over current
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|
59
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Over voltage
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|
60
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Voltage balance
|
|
63
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Pressure
|
|
64
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Apparatus ground
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|
67
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AC directional over current
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|
68
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Blocking
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|
69
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Permissive
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|
74
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Alarm
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|
76
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DC over current
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|
78
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Out-of-step
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|
79
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AC re-closing
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|
81
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Frequency
|
|
85
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Carrier or pilot-wire
|
|
86
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Lock out
|
|
87
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Differential
|
|
94
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Tripping
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