3.11
Date Code 20170601
Instruction Manual
SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Differential Element
Restrained Element Operating Current Pickup (O87P)
Set the operating current pickup at a minimum for increased sensitivity but
high enough to avoid operation because of steady-state CT error and
transformer excitation current.
Restraint Slope Percentage (SLP1, SLP2)
Range: SLP1: 5–100%, in 1% steps; SLP2: OFF, 25–200%
Use restraint slope percentage settings to discriminate between internal and
external faults. Set SLP1 or SLP2 to accommodate current differences from
power transformer tap-changer, CT saturation, CT errors, and relay error.
Restraint Current Slope 1 Limit (IRS1)
A two-slope, or variable-percentage differential application, improves
sensitivity in the region where CT error is less and increases security in the
high-current region where CT error is greater. We must define both slopes, as
well as the slope 1 limit or point IRS1, where SLP1 and SLP2 intersect.
Unrestrained Element Current Pickup (U87P)
Range: 1.0–20.0, in 0.1 steps • TAP
The purpose of the instantaneous unrestrained current element is to react
quickly to very heavy current levels that clearly indicate an internal fault. Set
the pickup level (U87P) to about 10 times tap. The unrestrained differential
element only responds to the fundamental frequency component of the
differential operating current. It is unaffected by the SLP1, SLP2, IRS1,
PCT2, PCT5, or IHBL settings. Thus, you must set the element pickup level
high enough so as not to react to large inrush currents.
Second-Harmonic Blocking Percentage of Fundamental (PCT2)
Range: OFF, 5–100%, in 1% steps
Energization of a transformer causes a temporary large flow of magnetizing
inrush current into one terminal of a transformer, without other terminals
seeing this current. Thus, it appears as a differential current that could cause
improper relay operation. Magnetizing inrush currents contain greater
amounts of second-harmonic current than do fault currents. This even-
harmonic current can be used to identify the inrush phenomenon and to
prevent relay misoperation. The SEL-387 measures the amount of second-
harmonic current flowing in the transformer. You can set the relay to block the
percentage restrained differential element if the ratio of second-harmonic
current to fundamental current (IF2/IF1) is greater than the PCT2 setting.
Range: 0.1–1.0 • TAP
Note:
1 A: TAP
MIN
• O87P
0.1 • I
n
5 A: TAP
MIN
• O87P
0.1 • I
n
Range: 1.0–20.0, in 0.1 steps • TAP
Note:
1 A: TAP
MAX
•IRS1
31.0
5 A: TAP
MAX
• IRS1
155.0
Содержание SEL-387-0
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