Schweitzer Engineering Laboratories SEL-387E, Инструкция по эксплуатации

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3-44 Differential, Restricted Earth Fault, Date Code 20020129
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
For CTR1>CTR2, the relay performs the following operation on the secondary quantities it
receives from the CTs:
( ) ( )
1 CTR
2 CTR
• 2 ICW 2 IBW 2 IAW 1 ICW 1 IBW 1 IAW
+ + + + +
Note: XXXX defines a vector quantity.
The following example illustrates the equivalent operation on the primary quantities entering the
CTs:
Assume
CTR1 = 1000/5 = 200
CTR2 = 500/5 = 100
Pickup = 400 A (primary)
Primary Currents
IAW1 = 3000
µ
5
•
A IAW2 = 1545
µ
3
•
A
IBW1 = 3010
µ
–123
•
A IBW2 = 1480
µ
–118
•
A
ICW1 = 2950
µ
115
•
A ICW2 = 1505
µ
124
•
A
Secondary Currents
IAW1 = 15
µ
5
•
A IAW2 = 15.45
µ
3
•
A
IBW1 = 15.05
µ
–123
•
A IBW2 = 14.80
µ
–118
•
A
ICW1 = 14.75
µ
115
•
A ICW2 = 15.05
µ
124
•
A
Then,
( )
( )
200
100
• A 124 05 . 15 A 118 80 . 14 A 3 45 . 15
A 115 75 . 14 A 123 05 . 15 A 5 15
• µ + • - µ + • µ
+ • µ + • - µ + • µ
A 76 230 . 2 A 73 11370 . 0 A 76 1164 . 2
• µ = • µ + • µ =
Note: Because CTR1>CTR2, the relay uses CTR1 as the common base.
A 2
200
A 400
P 1 NC 51
= =
secondary
The combined secondary current value is greater than the 51NC1P setting, so 51NC1 asserts and
the time overcurrent curve begins timing.
As with the phase current element, four settings define the curve: 51NC1P is the pickup setting,
51NC1C defines the curve equation, 51NC1TD defines the time dial, and 51NC1RS determines
how the curve resets.
Curve time-out causes the Relay Word bit 51NC1T to assert. When the current drops below
pickup, 51NC1 deasserts and the element resets according to the setting 51NC1RS. At the
completion of the reset, Relay Word bit 51NC1R asserts. This bit normally will be at logic state