Auxiliary Protection and Monitoring Functions
745
Transformer Management Relay
Commission
ing
http://www.GEindustrial.com/multilin
7–39
GE Multilin
b) Operating Time
To measure the basic operating time of this element, preset a fundamental and DC
component composite current signal to cause the element to operate. Using the
setup of Figure 10-1, apply the current suddenly, at the same time as you trigger
the timer. The measured operating time should correspond to the time delay setting
for the element.
c) Minimum Operating Current
The THD elements will only operate if the amplitude of the fundamental component
is above the threshold setting. To verify this threshold, initially set the fundamental
component above the threshold, with a harmonic content high enough to cause the
element to operate. Now reduce the fundamental component only. This will have for
effect to increase the THD level. When the fundamental component reaches a value
below the set threshold, the element will reset.
If an RMS-responding meter is used to measure the current signal, the
reading is the
total value
of current. To determine the fundamental
component only, use the relay values in
A2 METERING
!
CURRENT
!
W1 CURRENT
.
These values represent the fundamental component only.
d) Other THD Elements
A THD element can be programmed for each winding of the transformer. Use the
above procedures to verify the element(s) on the other winding(s).
Harmonic Derating
Function
a) Testing Note
Testing of the Harmonic Derating function requires that accurate transformer
parameters such as Load Losses at Rated Load and Winding Resistance be entered.
This feature makes use of the Harmonic Derating Factor (HDF) computed by the
relay, using the harmonic content of the current signals and the transformer data
(refer to IEEE C57.110-1986 for the computation method). Once the derating factor
falls below a set value, the 745 can trip and/or alarm.
b) Operating Level
1. To verify the correct operation of this element, a current signal containing har-
monics must be introduced into one phase of the relay. Use FIGURE 7–1: Test
Setup on page 7–3 to accomplish this. Set the fundamental component at rated
CT secondary into Winding 1 Phase A. Gradually increase the second harmonic
component (and the rest of the even harmonics) while displaying the
A2 METER-
ING
!"
HARMONIC CONTENT
!"
HARMONIC DERATING
!"
W1(3) HARMONIC DERATING
FACTOR
value. The element should operate when the displayed HDF equals the
element setting.
2. Check that the Trip, Pickup (and Alarm if selected) LEDs are on, and one of the
following is displayed:
LATCHED: W1 Harm Derating
or
OPERATED: W1 Harm Derating
3. Lower the DC component until the element resets. The reset value should be
approximately 2% larger than the operate value. Verify that the Pickup and
Alarm LEDs reset if the target function is set to “Self-resetting”. The Trip LED
should remain latched.
c) Operating Time
To measure the basic operating time of this element, preset a fundamental and DC
component composite current signal to cause the element to operate. Using the
setup of FIGURE 7–1: Test Setup on page 7–3, apply the current suddenly, at the
same time the timer is triggered. The measured operating time should correspond
to the time delay setting for the element.
CAUTION
Summary of Contents for Multilin 745
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