Description - GE 750 Instruction Manual
Feeder management
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- Instruction manual (450 pages) ,
- Manual (102 pages) ,
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13 S6 MONITORING
13.3 FAULT LOCATOR
The relay calculates the distance to fault with fault resistance compensation. For the fault location feature, a
fault is defined as an event that has caused a current level greater than the pickup threshold of an overcurrent
protection feature programmed to Trip or Trip & AR (760 Only), which has remained for sufficient time to cause
the relay to produce a Trip command. After this has happened, the apparent distance to the fault is calculated
in a background mode, maintaining all other features in operation. The distance calculation is based on the
assumptions that:
(a) the feeder positive and zero sequence impedances are a constant per unit distance, and
(b) 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 loca-
tion 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
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 setpoint
SYSTEM SETUP \ BUS VT SENSING \ VT CONNECTION TYPE
NOTE
culations 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.
GE Power Management
Courtesy of NationalSwitchgear.com
ACTUAL VALUES \ A1 STATUS \ FAULT LOCATIONS
, to allow the fault locator to perform the cal-
750/760 Feeder Management Relay
13.3 FAULT LOCATOR
13.3.1 DESCRIPTION
.
S2
13-
7
13
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