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3-50
Differential, Restricted Earth Fault,
Date Code 20020129
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
Overcurrent Element External Torque-Control
The SEL-387E Relay allows you to either enable or block selected overcurrent elements using a
SEL
OGIC
control equation. You may wish, for example, to control an overcurrent element using
an external contact from a toggle switch, control switch, external directional relay, or recloser.
Or, you may wish to use some combination of relay elements to enable or block the overcurrent
element. These choices are easily accomplished by creating a SEL
OGIC
control equation that
describes what is needed, and storing the equation as the setting for the specific overcurrent unit’s
torque-control variable. For example, to torque control the inverse-time phase overcurrent unit
for Winding 1, an equation is needed for the setting 51PTC. A few simple possibilities might
include:
To enable the unit with an external contact input IN104, set 51PTC = IN104.
To block the unit with this same input, set 51PTC = !IN104 (i.e., NOT IN104).
To enable the unit with IN104, but only if Breaker 3 is open, set 51PTC = IN104*!IN106
(i.e., IN104 AND NOT IN106, where IN106 was previously defined as representing the
52a-3 contact input)
To enable the unit continuously (default setting), set 51PTC = 1.
Overcurrent Settings for Example Application
The differential settings for the example transformer application (see Figure 2.15 in
Section 2:
Installation
) were defined earlier. Overcurrent settings were chosen to complete the protection
settings package. These settings are listed at the end of this section of the instruction manual.
Before setting of any overcurrent elements can occur, these must be enabled by the configuration
settings EOC1 through EOC3. EOC1, EOC2, and EOC3 are set to Y.
For the 230 kV primary winding (Winding 1), three elements are set for overcurrent tripping of
230 kV Breaker 1. The phase definite-time element, 50P11, is set for 20 A secondary, with a
five-cycle trip delay time. The phase and negative-sequence inverse-time elements, 51P1 and
51Q1, are set to pick up at 4 A and 6 A, respectively, both using the U2 or U.S. Inverse curve, on
Time-Dial 3, with electromechanical reset characteristics. One of the phase instantaneous
elements, 50P13, is set very low at 0.5 A, along with 50P23 and 50P33 on the other two
windings. These elements are employed in a supervisory mode for the Unlatch Trip function,
effectively defining when the breaker has opened by the dropping of phase current below the
element setting. The 50P14 phase instantaneous element has been set at 4 A, and is used in an
internal supervision function (LED targeting).
For the 138 kV secondary winding (Winding 2), tripping is set for the phase and negative-
sequence inverse-time elements, 51P2 and 51Q2. These are set at lower pickup values of 3.5 and
5.25 A secondary, using the same curves as Winding 1, but at a higher Time Dial of 3.5.
Tripping is done for the 138 kV Breaker 2. Phase instantaneous elements 50P23 and 50P24 are
used for supervision, as with Winding 1, set at 0.5 A and 3.5 A, respectively.
For the 13.8 kV tertiary, Winding 3, tripping is by the definite-time element, 50P31, set as an
instantaneous element at 7 A and zero time delay, and by the phase inverse time element 51P3.
51P3 is set for 4 A, at Time Dial 1.3 of the U2 inverse curve, with electromechanical reset.
Tripping is for the 13.8 kV Breaker 3. The 50P33 and 50P34 phase instantaneous elements are
used for supervision, set at 0.5 A and 4 A.
Содержание SEL-387E
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