B Pickup Level - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

10.6 PROTECTION SCHEMES
b) PICKUP LEVEL
1. With the interval timer disabled, apply the current signal and increase its magnitude slowly until the trip
relay and all the selected auxiliary relays operate. If the element has a very inverse time characteristic, it is
easier and more accurate to increase the current far above the pickup level until the trip relay operates
then reduce the current to just above the operate level. Then, current can be slowly reduced below the
operate level and observed for a reset action on the trip relay. This reset level for the current should be
approximately 98% of the pickup level. Once the relay drops out, slowly increase the current until the trip
contact closes. The operate level should correspond to the pickup setting.
2. Check that the following message is displayed:
SS LATCHED (OPERATED) ∅A
SS W1 Phase Time OC
The message will indicate LATCHED or OPERATED, depending on the setting for the target.
c) OPERATING TIME
Using a table like the one shown below, select 3 or 4 values of current multiples at which the timing is to be
measured. Enter the expected operating times from the timing curve applied in the settings. Using the setup
shown in Figure 10–9: GENERAL TEST SETUP on page 10–21 and the Interval Timer enabled, set the current
level to the desired value and apply suddenly by closing the double-pole switch. Record the operating time and
compare it to the expected value. Repeat for all desired values of current.
CURRENT
MULTIPLE
1.5
3
5
d) RESET TIME
A precise measurement of the reset time requires a relay test set capable of dynamic operation, with three
sequenced stages, each with programmable current levels and time duration external contact, and flexible trig-
gering. To perform such a test, please contact GE Power Management for detailed test instructions.
A simple verification the selected reset mode can be obtained using Figure 10–9: GENERAL TEST SETUP on
page 10–21. The procedure consists of performing repetitive operating time measurements in quick succes-
sion. If the reset is selected for instantaneous, the operating time will always be equal to the nominal time
derived from the selected curve. If the reset is selected as linear, the operating time will vary as a function of
the time between successive application of the current signal. If performed at current multiples of 2 to 3 times
the pickup level, the variations in operating time will be easier to detect.
e) PHASE B AND C ELEMENTS
If the A-phase element performed correctly and met specifications, repeat the PICKUP LEVEL portion of the
above test for the B and C phases of Winding 1. For the B-phase, X = H2 and Y = G2. For the C-phase, X = H3
and Y = G3. The displayed message should change to indicate the correct phase, winding, and element that
operated.
10
10-22
NOMINAL MEASURED
TIME TIME
745 Transformer Management Relay
10 COMMISSIONING
GE Power Management