the parallel resistor of the coil, with security margin. For example, if the resistive
current of the parallel resistor is 10 A, then a value of 0.7×10 A = 7 A could be used.
The same setting is also applicable in case the coil is disconnected and the network
becomes unearthed. Generally, a smaller value should be used and it must never
exceed the value of the parallel resistor in order to allow operation of the faulted
feeder.
Fault indication logic
Depending on the set
Operation mode, INTRPTEF has two independent modes for
detecting earth faults. The "Transient EF" mode is intended to detect all kinds of
earth faults. The "Intermittent EF" mode is dedicated for detecting intermittent
earth faults in cable networks.
To satisfy the sensitivity requirements, basic earth-fault protection
(based on fundamental frequency phasors) should always be used in
parallel with the INTRPTEF function.
The Fault indication logic module determines the direction of the fault. The
fault direction determination is secured by multi-frequency neutral admittance
measurement and special filtering techniques. This enables fault direction
determination which is not sensitive to disturbances in measured Io and Uo signals,
for example, switching transients.
When
Directional mode setting "Forward" is used, the protection operates when
the fault is in the protected feeder. When
Directional mode setting "Reverse"
is used, the protection operates when the fault is outside the protected feeder
(in the background network). If the direction has no importance, the value "Non-
directional" can be selected. The detected fault direction (FAULT_DIR) is available in
the monitored data view.
In the "Transient EF" mode, when the start transient of the fault is detected and
the Uo level exceeds the set
"Voltage start value", Timer 1 is activated. Timer 1 is
kept activated until the Uo level exceeds the set value or in case of a drop-off, the
drop-off duration is shorter than the set
Reset delay time.
In the "Intermittent EF" mode, when the start transient of the fault is detected and
the Uo level exceeds the set
Voltage start value, the Timer 1 is activated. When a
required number of intermittent earth-fault transients set with the
Peak counter
limit setting are detected without the function being reset (depends on the drop-
off time set with the
Reset delay time setting), the
START
output is activated. The
Timer 1 is kept activated as long as transients are occurring during the drop-off
time defined by setting
Reset delay time.
Timer 1
The time characteristic is according to DT.
In the "Transient EF" mode, the
OPERATE
output is activated after
Operate delay
time if the residual voltage exceeds the set "Voltage start value". The Reset delay
time starts to elapse when residual voltage falls below Voltage start value. If there is
no
OPERATE
activation, for example, the fault disappears momentarily,
START
stays
activated until the the
Reset delay time elapses. After
OPERATE
activation,
START
and
OPERATE
signals are reset as soon as Uo falls below
Voltage start value.
Protection functions
1MRS757644 H
422
620 series
Technical Manual
