GE L30 Instruction Manual page 452

CONTROL ELEMENTS
Before a permanent cable fault occurs, there are usually signs of degrading insulation manifesting itself as a short, mostly
half-cycle spikes asserting at the phase voltage peak. Due to shortness of such spikes, they are not usually detected by the
instantaneous protection of the feeder, which operates on the RMS or fundamental component of the phase current with a
relatively high pickup.
The number of detected incipient faults in each phase is counted and available in the
menus. The counters can be reset with the
INCIPIENT FAULT
command.
COUNTERS
Changes to any of the incipient cable fault detector settings resets of the number of the incipient faults detected to
zero.
To provide a clear timing indication when the incipient fault occurred, the incipient fault event is time-stamped with
the time the fault actually occurred. However, the FlexLogic operand is asserted four cycles later, when the incipient
fault pattern is confirmed and therefore detected.
The figure illustrates a recorded field case of an incipient phase B fault. The top portion of the figure shows the raw A, B,
and C currents. The bottom portion shows the neutral current (blue) and reveals the fault period from under the load and
the superimposed phase B current (red). The superimposed current shows two fault current blips as the data slides through
the two-cycle memory window. During the actual fault, the neutral current and the superimposed phase B currents closely
correspond, confirming the incipient fault hypothesis and identifying the affected phase.
5
The following settings are available for each incipient cable fault detector.
INCIPIENT FAULT 1 FUNCTION
INCIPNT FLT 1 BLOCK
assigned to this setting blocks operation.
INCIPIENT FAULT 1 SOURCE
assigned a valid CT bank.
INCIPIENT FAULT 1 PICKUP
current.
5-274
Figure 5-145: Illustration of the incipient fault detector algorithm
— This setting enables and disables operation of the incipient fault detection element.
— Blocks operation of the incipient cable fault detector element. Assertion of the FlexLogic operand
— Selects a current source for the incipient cable fault detector element. This source must be
— Specifies the pickup level of the overcurrent detector in per-unit values of the CT nominal
ACTUAL VALUES  STATUS 
COMMANDS  CLEAR RECORDS  CLEAR INCIPENT FAULT
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS