GE Power Management DGP Digital Generator Protection System 2-
37
2 CALCULATION OF SETTINGS 2.3 PROTECTION FUNCTION SETTINGS
2
An appropriate combination of functions 81, 32, 64G2, 27TN, and VTFF should be blocked during start-up
(generator off-line) as required. For example, to prevent nuisance operation, Setting 2501:
SELBKDI1
may be
set as follows:
• BLK #6 to block 81, 32, and VTFF for cross compound machine.
• BLK #8 to block 81 if generator field is applied at a speed lower than the speed corresponding to lowest
81U setpoint.
• BLK #9 to block all four functions for a gas turbine generator with static start.
Settings 2502:
DI3 TRIP
, 2503:
DI3 ALARM
, 2504/5:
DI4 TRIP
, and 2505/6:
DI4 ALARM
can be used to oper-
ate any or all of the Trip (94G to 94G3) or Alarm (74A to 74D) relays. If the settings are selected, energizing the
corresponding digital input will cause the appropriate Trip and Alarm relay to operate after time delay, if appli-
cable.
Setting 2508:
DI6 FUNC
can be set to 0 (EXTVTFF) or 1 (DISPROT) to configure the DI6 input. If set to 0
(EXTVTFF), the DI6 is configured to receive an external VTFF signal. If set to 1 (DISPROT), the DI6 is config-
ured to disable all protection functions as long as the input signal is present. It should be set to 0 (EXTVTFF) if
the input DI6 is not used.
2.3.18 VOLTAGE TRANSFORMER FUSE FAILURE VTFF
Setting 2601:
VTFF
can be set to either 0 (DISABLE) or 1 (ENABLE) as desired. It is recommended to set
VTFF
= 1 (ENABLE) if the external VTFF input (DI6) is not used. If the external VTFF input is used, the
VTFF
setting will depend on user preference.
2.3.19 ACCIDENTAL ENERGIZATION AE
Setting 2703:
AE ARM
can be set to 0 (AND) or 1 (OR) as desired. If set to 0 (AND), the logic will be armed
when the positive sequence voltage V1 < 30 volts
and
the generator is off-line. If it is set to 1 (OR), the logic will
be armed when the voltage V1 < 30 volts
or
the generator is off-line. The setting of 0 (AND) is recommended.
However, if
both
of the following conditions apply, it must be set to 1 (OR) for effective arming of the logic.
• The generator system includes a generator disconnect device (breaker or switch),
and
• The VTs are connected on the power system side of the disconnect device.
Since the pickup flag of function 51V is used for instantaneous overcurrent signal in the Accidental Energiza-
tion logic (Figure 1–3: SIMPLE LOGIC DIAGRAM – 87G, 32, 27, 59, AND AE on page 1–12), the following
additional criteria should be used in setting the 51V PICKUP.
The 51V PICKUP (Setting 1003:
PICKUP
) should be set with a safe margin above
I
LMAX
, where
I
LMAX
is an
expected maximum load current of the machine. If Setting 2703:
AE ARM
is set to 1 (OR) and simultaneous
loss of all three phase voltages is likely, then
PICKUP
should be set with a safe margin above 3.33
×
I
LMAX
.
Note that function AE will be effectively disabled if function 51V is disabled by setting both its
TRIP
and
ALARM
codes (Settings 1001 and 1002) to 0000. This is in addition to the normal way of disabling function AE
by setting its
TRIP
and
ALARM
codes (Settings 2701 and 2702) to 0000.
For the sample generator system,
set
AE ARM
= 0 (AND)
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