3.35
Date Code 20050919
Instruction Manual
SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Restricted Earth Fault Element
Setting Descriptions
REF Directional Element Enable (E32I)
Range: SEL
OGIC®
control equation
The setting E32I is a SEL
OGIC
control equation setting that uses Relay Word
bits to define the conditions under which the relay will enable REF. A logical
state of 1 for this control equation enables the other REF settings and satisfies
one of the conditions the REF element needs to activate. A logical state of 0
for this control equation disables the other REF settings; the relay hides these
settings, and they are unavailable for use.
Operating Quantity from W1, W2, W3 (32IOP)
Range: 1, 2, 3, 12, 123
The setting 32IOP tells the relay which winding or combination of windings it
should use in calculating residual current, which acts as the Operate quantity
for the directional element.
Positive-Sequence Current Restraint Factor, I0/I1 (a0)
Range: 0.02–0.50, in 0.01 steps
For the relay to enable REF, the zero-sequence current at Winding
n
must be
greater than a0 times the positive-sequence current at that input, or |I0W
n
| >
a0•|I1W
n
|. This supervision provides security against “false I0” that can occur
because of CT saturation during heavy three-phase faults.
Residual Current Sensitivity Threshold (50GP)
Range: 1 A: 0.05-3 A, in 0.01 A steps
5 A: 0.25–15.00 A, in 0.01 A steps
You can set the residual current sensitivity threshold to as low as 0.05 times
nominal current (0.25 A for 5 A nominal CT current), the minimum residual
current sensitivity of the relay. However, the minimum acceptable value of
50GP must meet two criteria:
➤
50GP must be greater than any natural 3I0 imbalance caused by
load conditions.
➤
50GP must be greater than a minimum value determined by the
relationship of the CTR
n
values used in the REF function.
You must set the threshold setting, 50GP, at the greater of the two criteria
values. Determine criterion 1 for load imbalance. The second criterion relates
to the relative sensitivity of the winding CTs compared to the neutral CT.
Setting Calculation
Operating Quantity
depicts how to determine the Operate quantity, 32IOP, setting.
Summary of Contents for SEL-387-0
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