GE 745 Instruction Manual page 270

PROTECTION SCHEMES
7.5.8.4 Operating Time
7.5.8.5 Winding 2 and 3 elements
Note
NOTE
Note
NOTE
7.5.9 Neutral Instantaneous Overcurrent 2
7.5.10 Ground Time Overcurrent
7.5.10.1 Description
7–32
 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 INST OC 1 TARGET
the Trip LED should stay on.
 Reset indicators and clear messages.
 With the setup shown in FIGURE 7–9: General test setup on page 7–25
and the interval timer enabled, set the current level to 1.5 times the
operate level of the element and apply suddenly by closing the double-
pole switch.
 Record the operate time and compare to the
OC

Because 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 in this
section for each winding.
Only two neutral instantaneous overcurrent 1 elements can be in service
simultaneously.
The blocking from logic input, if enabled, can be tested as described in earlier tests for
other elements.
The neutral instantaneous overcurrent 2 elements are identical to the neutral
instantaneous overcurrent 1 elements. Consequently, the same test procedure can be
used to verify their correct operation. Disable all protection features except neutral
instantaneous overcurrent 2 and follow the steps in the previous section, making the
appropriate changes for the LEDs and output relays operated by the neutral instantaneous
overcurrent 2 elements.
This procedure verifies that the ground time overcurrent performance matches the in-
service settings. Since these elements can be assigned a multitude of timing curves, a
table of expected operating times versus applied current should be prepared prior to
testing. The ground element measures the current signal connected to the ground current
input CT, H10 and G10 or F12 and E12. Refer to Time Overcurrent Curves on page 5–59 for
information on timing curves. There can only be one or two ground time overcurrent
was selected as "Latched". Otherwise only
W1 NTRL INST OC 1 W1 NEUTRAL INST OC 1 DELAY

745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
W1
S4 ELEMENTS NEUTRAL

value.