GE 745 Instruction Manual page 279

CHAPTER 7: COMMISSIONING
7.5.15.4 Operating Time
7.5.15.5 Reset time
7.5.15.6 Winding 2 and 3 Elements
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
LATCHED a: W1 Neg Seq Time OC or OPERATED a: W1 Neg Seq
Time OC
 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
TIME OC TARGET
LED remains on.
 Reset indicators and clear messages.
 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 in FIGURE 7–9: General test setup on page 7–25 with
the interval timer enabled, set the current level to the desired value
(taking into account the relationship mentioned above) 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 simple verification of which reset mode, selected with the
W1 NEG SEQ TIME OC
 
the simple test setup in FIGURE 7–9: General test setup on page 7–25. The procedure
consists of repetitive operating time measurements in quick succession. If the reset is
selected for "Instantaneous", the operating time is always equal to the nominal time
derived from the selected curve. If the reset is selected as Linear, the operating time varies
as a function of the time between successive applications of the current signal. If this test
is performed at current multiples of 2 to 3 times the pickup level, the variations in operating
time are easier to detect.
Because the negative-sequence time overcurrent elements on windings 2 and/or 3 can be
set with completely different parameters than those for the first element, it is necessary to
repeat the full set of tests described in this section for each winding.
was selected as Latched. Otherwise only the Trip
Measured time
W1 NEG SEQ TIME OC RESET
PROTECTION SCHEMES
W1 NEG SEQ
S4 ELEMENTS NEG SEQ OC

setpoint, can be obtained using
7–41