Protection relays have very different functions and each of these relays can respond to specific types of faults. Each device requires different types of protection relays. For example, distance relays are suitable for transmission lines and differential relays are suitable for power transformers and busbars. Before we delve into protection relays, let's see the list of different types of protection relays by function and ANSI code as shown in the table below:
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ANSI code and relay function
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|
|
ANSI number
|
DESCRIPTION
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|
two
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Time delay
|
|
21
|
distance
|
|
25
|
Sync check
|
|
27
|
under tension
|
|
30
|
detector
|
|
32
|
Directional force
|
|
37
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Undercurrent or undervoltage
|
|
38
|
camping
|
|
40
|
Field
|
|
46
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Reversal phase
|
|
47
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Rotating Field Voltage
|
|
49
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Thermal
|
|
50
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Instantaneous overcurrent
|
|
51
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AC time over electricity
|
|
59
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Overload
|
|
60
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Voltage balance
|
|
63
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Pressure
|
|
64
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Equipment grounding
|
|
67
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AC directional overcurrent
|
|
68
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blocking
|
|
69
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Permissive
|
|
74
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alarm
|
|
76
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DC overcurrent
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|
78
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Out of step
|
|
79
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air conditioning Reseal
|
|
81
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frequency
|
|
85
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Carrier or pilot wire
|
|
86
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Block
|
|
87
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differential
|
|
94
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Stumble
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