GE 750 Instruction Manual page 174

750/760
Feeder Management Relay
NOTE
5–78
1. The feeder positive and zero sequence impedances are a constant per unit dis-
tance, and
2. Mutual compensation is not required.
If the feeder utilizes conductors of different sizes, or more than one physical
arrangement of conductors, or shares poles or towers with a parallel feeder, these
assumptions are incorrect and errors are introduced.
The algorithm uses prefault system data to reduce the error caused by variable fault
resistance, so inaccuracy is introduced for a fault which occurs when no load current
was present. Also, error is introduced if the feeder has sources at locations other
than the location of the relay, due to infeed effects.
The algorithm contains three sets of equations that are used to perform the
calculations for a specific fault type: phase-to-ground, phase-to-phase-to-ground,
phase-to-phase, and three-phase. Each of the sets (other than three-phase)
consists of a subset which covers all combinations of phases. The algorithm
therefore uses a fault identification procedure to select the appropriate equations to
be used for calculation. This procedure uses both prefault and fault current phasors
from memory to identify the type of fault. The prefault data is taken from a sample
collected three power frequency cycles before the pickup of the overcurrent element
to ensure the sample contains only load current. The after fault data is taken from
samples collected 1.5 power frequency cycles after overcurrent pickup to ensure the
current had existed for at least one complete sampling interval.
As well as the apparent distance to the fault, the locator records the feeder apparent
reactance (with fault resistance removed if prefault current was available.) This
parameter can be very useful in estimating the location of a fault on a feeder tap,
where the apparent distance can be calculated as beyond the feeder end. The date,
time, type of fault, and phases involved are also stored for the event. Non-volatile
memory is provided for the past ten events, in a FIFO queue, available under
STATUS FAULT LOCATIONS
If the feeder has a source with a grounded neutral, and is therefore capable of
providing ground fault current, the bus VTs must be both connected and selected as
"Wye" in
S2 SYSTEM SETUP
locator to perform the calculations properly. If the fault classification results in a
phase to ground fault, the program checks that the setpoint noted above is set to
'Wye' before the calculation is permitted.
• LENGTH OF FEEDER: Enter the total length of the feeder, in kilometers or
miles as selected by the
• UNITS OF LENGTH: Enter the units of measurement, in kilometers or miles.
• Zpos (RESISTIVE/INDUCTIVE) OF FEEDER: Enter the total real/imaginary
component of the feeder positive sequence impedance, in actual ohms.
• Zzero (RESISTIVE/INDUCTIVE) OF FEEDER: Enter the total real/imaginary
component of the feeder zero sequence impedance, in actual ohms.
• FAULT TYPE OUTPUT TO RELAYS 4-7: Selects whether fault type indication
on output relays 4 to 7 is enabled. When enabled, relays 4 to 7 will operate to
indicate the most recent fault type (i.e. Fault Location 0 Fault Type). The
auxiliary relays are reset to their non-operated state after the relay is reset. Any
combination of relays 4 to 7 may be operated, with outputs as shown below:
Phase A faults operate the 4 Auxiliary relay.
Phase B faults operate the 5 Auxiliary relay.
Phase C faults operate the 6 Auxiliary relay.
Neutral faults operate the 7 Auxiliary relay.
• FAULT LOCATION AFTER TRIP: Users utilizing the Fault Distance feature may
define a fault distance message to display along with other active conditions.
When set to "Enabled", a fault distance message will be displayed when a trip
has occurred. The fault distance message will be removed when the active
conditions are reset. This message only appears after the first Trip condition;
any subsequent Trips will only update the fault distance value (if required).
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.
BUS VT SENSING VT CONNECTION TYPE
setpoint.
UNITS OF LENGTH
S6 Monitoring
A1
to allow the fault
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