GE Multilin 565 Instruction Manual page 93

Auto-Reclosure Application for 575
1. Introduction
Utility statistics indicate that a large percentage of feeder
faults are of a transient nature, for example, phase conduc-
tors blown together by the wind, branches falling across
phase conductors, or animals shorting to a grounded struc-
ture. In most cases, after the fault arc is initiated, the
shorting media is burned off and the feeder is cleared.
A variety of overcurrent protective devices are used on
feeders, starting with a feeder circuit breaker at the distribu-
tion station and fused sectionalizers as well as various
reclosers downstream. All these devices are in series with
each other. Should the transient fault current magnitude be
larger than the melting current of the fuses, sections of the
feeder will be incapacitated until line crews are sent out to
locate the open device, replace the fuses and place the
feeder back in service. Many customers will then be incon-
venienced unnecessarily. It is for this reason that reclosure is
necessary.
Ideally, when a fault is sensed on a feeder, the relaying
scheme at the distribution station will cause the appropriate
circuit breaker to trip, thus clearing the fault regardless of its
location along the feeder. At the same time a reclosure
scheme will be initiated causing only a very short distur-
bance to the system if the fault is transient.
Essentially, a reclosure scheme is a pre-programmed se-
quence of commands to reclose a circuit breaker a pre-
determined number of times (or shots) after pre-determined
time delays (dead times), after the feeder circuit breaker is
tripped initially by the feeder protection scheme. When the
maximum number of reclosures has been reached the breaker
will be locked out since the fault has not been cleared and
thus is likely not of a transient nature.
Sequentially, the events leading to a lockout situation in a
four shot reclosure scheme are as follows:
1. First trip.
2. Wait until dead time #1 has expired.
3. Reclose breaker.
4. Second trip.
5. Wait until dead time #2 has expired.
6. Reclose breaker.
7. Third trip.
8. Wait until dead time #3 has expired.
9. Reclose breaker.
10. Fourth trip.
11. Wait until dead time #4 has expired.
12. Reclose breaker.
13. Fifth trip.
14. Breaker is locked out.
After this sequence of events the reclosure & relay must be
manually reset at the relay or through remote supervisory.
Certain trip features may also be blocked (disabled) after the
SETPOINTS MODE - AUTORECLOSURE
nth reclosure attempt. For example, Phase Lowset Instanta-
neous trips may be blocked after the nth reclosure to allow
whatever is causing the fault to burn off at a higher fault
current level than that allowed by the Phase Lowset setting.
Phase Lowset trips would then be re-enabled after the
scheme is reset.
The scheme can be "reset" to its initial condition if, after any
of the reclosures, a reclaim or reset timer expires without a
new trip being initiated.
2. Multilin 575 Reclosure Scheme
The Multilin 575 reclosure scheme is based on a scheme
developed by some major North American utilities. The
scheme follows the overview shown in Figure 3.5 with some
additional features unique to the Multilin 575, but allows
some flexibility through user setpoint programming. Note
that Figure 3.5 is a conceptual drawing to develop the 575
software and is not intended to be implemented in hardware.
Two modes of 575 operation are provided: LOCAL and
REMOTE. LOCAL mode indicates that control is provided by
the 575 keypad. REMOTE mode indicates that control is
provided by dry contacts external to the 575.
Reclosure Enable/Disable can be executed in either LOCAL
or REMOTE mode. A LOCAL/REMOTE switch (device #43)
must be wired to the 575 to select the mode.
A hardware latching relay is used in the 575 to enable or
disable the reclosure scheme. This is implemented in hard-
ware to provide another level of security. If the reclosure
scheme is disabled the breaker cannot be reclosed by incor-
rect operation of the reclosure algorithm.
The reclosure routine will not perform any function until the
reclosure scheme is enabled (either locally or remotely) and
one of the following conditions occurs:
1. Low set instantaneous trip (any two phases or ground).
2. High set instantaneous trip (any phase or ground).
3. Timed overcurrent trip (phase or ground).
4. External Initiate of Reclosing.
To improve co-ordination with OCR line reclosures the 575
can be programmed to change the time overcurrent curve
shapes during reclosure. The curve shapes are custom,
extremely inverse, very inverse, normal inverse and moder-
ately inverse.
As soon as the scheme is initiated the BLOCK TAP CHANGER
output relay activates to block operation of a transformer tap
changer. This relay resets when lockout condition is reached
or the reset time causes the scheme to reset. Thus, this
output relay is also an indication of "auto-reclosure in
progress".
The PHASE INST HISET and/or GROUND INST HISET trip
feature can be blocked (disabled) after any reclosure if
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