Schweitzer Engineering SEL-387-0, Instruction Manual

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1.3
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Introduction and Specifications
Relay Functions
harmonic) provide security against inrush currents during transformer
energization, complemented by the dc element which measures the dc offset.
The even-harmonic element offers the choice between harmonic blocking and
harmonic restraint. In the blocking mode, the user selects either blocking on
an individual phase basis or on a common basis, as per application and
philosophy. The second-, fourth-, and fifth-harmonic thresholds are set
independently, and the dc blocking and harmonic restraint features are enabled
independently.
Restricted Earth Fault
Protection
The SEL-387 provides sensitive detection of internal ground faults via the
Restricted Earth Fault (REF) protection element. The Winding 4 inputs are
used for introduction of neutral CT polarizing current. Operating current is
derived from the residual current calculated for the protected winding. A
directional element determines whether the fault is internal or external.
Tripping is supervised by zero-sequence current thresholds and a positive-
sequence current restraint setting. The REF function is applicable to a single
grounded wye winding or an autotransformer with one breaker and set of CTs
at one terminal and either one or two breakers and sets of CTs at the other
terminal. Since the Winding 4 inputs are used for the neutral CT, only three of
the winding inputs may be used for normal differential or overcurrent
protection purposes.
Thermal Protection
(SEL-387-6 Relay)
The SEL-387-6 provides a thermal element based on advanced transformer
models. This thermal element calculates the operating temperature and
insulation aging of mineral-oil-immersed power transformers being protected
by the SEL-387-6. The element calculates operating temperature based on
load currents, type of cooling system, and/or actual temperature inputs
(ambient and top oil). It then uses operating temperature as a basis for
calculating the insulation aging acceleration factor (FAA) and loss-of-life
quantities. The thermal element asserts Relay Word bits to indicate alarm
conditions when the following quantities exceed settable limits:
➤
Top-oil temperature
➤
Winding hot-spot temperature
➤
Insulation aging acceleration factor (FAA)
➤
Daily loss of life
➤
Total loss of life
Overcurrent
Protection
The SEL-387 provides nondirectional overcurrent elements for each winding/
terminal:
➤
Phase Overcurrent: Three level instantaneous; definite time;
inverse time
➤
Residual Overcurrent: Instantaneous; definite time; inverse
time
➤
Negative-Sequence Overcurrent: Instantaneous; definite time;
inverse time
In addition, the SEL-387 has a special overcurrent function:
➤
Combined overcurrent (inverse time, phase and ground), for
summed currents from Windings 1 and 2 and Windings 3 and 4
Overcurrent element pickup settings and operating characteristics are
independent of the differential element settings. Most elements can be torque
controlled.