GE 745 Instruction Manual page 268

PROTECTION SCHEMES
7.5.7.4 Operating Time
7.5.7.5 Reset Time
7.5.7.6 Winding 2 or 3 Elements
7–30
 Reduce the current until the element resets.
The reset level should be 97% of the operate level. When the element
resets, the Trip and Message LEDs should remain on if the
NEUTRAL TIME OC TARGET
the Trip LED remains on.
 Reset indicators and clear messages.
 Using a table like the one shown below, select three (3) or four (4)
values of current multiples at which timing is to be measured.
 Enter the expected operating times from the timing curve applied in the
settings.
 Using the setup in FIGURE 7–9: General test setup on page 7–25 and
the interval timer enabled, set the current level to the desired value and
apply suddenly by closing the double-pole switch.
 Record the operate time and compare to the expected value.
 Repeat for all desired values of current.
Current multiple Nominal time
1.5
3
5
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, and flexible external contact triggering. To perform such a test, contact GE
Multilin for detailed test instructions.
A simple verification of the reset mode selected by
NTRL TIME OC W1 NEUTRAL TIME OC RESET

FIGURE 7–9: General test setup on page 7–25. The test consists of repetitive operating time
measurements in quick succession. If the reset is set for "Instantaneous", the operating
time is always equal to the nominal time derived from the selected curve. If the reset is set
as "Linear", the operating time varies as a function of the time between successive
applications of current. The variations in operating time are easier to detect if this test is
performed at current multiples of 2 to 3 times the pickup level.
Since the winding 2 and 3 elements can be set with completely different parameters than
the winding 1 elements, it is necessary to repeat the full set of tests described above for
each winding.
 To test winding 2 elements, disable all protection elements except for
W2 NEUTRAL TIME OVERCURRENT
CHAPTER 7: COMMISSIONING
was selected as Latched. Otherwise only
Measured time
S4 ELEMENTS
is obtained using the setup shown in
.
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
W1
NEUTRAL OC W1
 