GE Multilin 745 Instruction Manual page 223

Protection Schemes
NOTE
GE Multilin
c) Pickup Level
1. With the interval timer disabled, apply the current signal and slowly increase its
magnitude until the trip relay and all selected auxiliary relays operate. If the
relay 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, slowly reduce the cur-
rent below the operate level and observe 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
W1 NEG SEQ TIME OC
!"
With current applied to a single phase, the negative sequence current
component is calculated from:
Hence, the phase current will be three times the pickup setting.
2. Check that, when the element operates, the Trip and Pickup LEDs are on and
one of the following messages is displayed:
LATCHED a: W1 Neg Seq Time OC or OPERATED a: W1 Neg Seq Time OC
3. 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
W1 NEG SEQ TIME OC TARGET
Otherwise only the Trip LED remains on.
Reset indicators and clear messages.
d) 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 in FIGURE 7–9: General Test
Setup on page 7–18 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 NOMINAL
MULTIPLE TIME
1.5
3
5
e) Reset Time
A simple verification of which reset mode, selected with the
OC W1 NEG SEQ TIME OC
! !"
using the simple test setup in FIGURE 7–9: General Test Setup on page 7–18. 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.
f) Winding 2 and 3 Elements
Because the Negative Sequence TOC 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.
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Transformer Management Relay
setting.
W1 NEG SEQ TIME OC PICKUP
1
I --- × I
=
neg seq phase
3
MEASURED
TIME
W1 NEG SEQ TIME OC RESET
745
S4 ELEMENTS !" NEG SEQ OC
(EQ 7.16)
was selected as "Latched".
S4 ELEMENTS !" NEG SEQ
setpoint, can be obtained
7–29
!