Introduction
7SV512
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C53000---G1176---C91
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Introduction
1.1
Application
The numerical circuit breaker failure protection relay
7SV512 provides rapid back-up fault clearance in-
struction to the associated circuit breakers in case
the circuit breaker nearest to the fault fails to re-
spond.
It is suitable for power systems of all voltage ranges.
The initiation signal can be derived from any protec-
tion or supervision equipment or, in case of manual
opening, from the discrepancy control switch of the
breaker. Information from the circuit breaker auxilia-
ry contact(s) is required for the breaker failure pro-
tection to function during faults which produce little
or no current flow (e.g. Buchholz protection).
The breaker failure protection can operate single-
stage or two-stage. When used as single-stage pro-
tection, the bus trip command is given to the adja-
cent circuit breakers if the protected feeder breaker
fails. When used as two-stage protection, the first
stage can be used to repeat the trip command to the
relevant breaker, normally on different trip coils, if the
initial trip command from the feeder protection is not
executed. The second stage will result in a bus trip to
the adjacent breakers, if the command of the first
stage is not successful.
The bus trip command from the breaker failure pro-
tection can be routed to all circuit breakers linked to
the same bus-bar (section) as the breaker that
failed. It can also be transmitted to the remote end
by means of a suitable communication link (e.g.
PLC, radio wave, or optical fibre). The distribution
logic which is necessary in case of multiple bus-bar
sections is not part of 7SV512 relay.
The current level is monitored in each of the three
phases against a set threshold. In addition, the re-
sidual earth current is monitored or --- if this is not
available --- the negative sequence component of
the phase currents derived by symmetrical compo-
nent analysis. This ensures high security against
malfunction by use of a 2-out-of-4 check of the cur-
rent detectors.
Phase segregated current monitoring enables reli-
able breaker failure detection even during single-
pole auto-reclose cycles provided the phase segre-
gated trip signals of the feeder protection are con-
nected to 7SV512. If two-stage breaker failure pro-
tection is used in conjunction with single-pole trip-
ping by the feeder protection, the first stage trip may
be performed single-pole or three-pole, as selected
by the user. Different delay times can be set for
single-phase faults and multi-phase faults.
If the protected circuit breaker is not operative (e.g.
air pressure failure), instantaneous bus trip of the
adjacent circuit breakers can be achieved following
a feeder protection trip provided the relay is in-
formed by an external breaker monitor.
An end fault protection function is integrated in the
7SV512 relay. An end fault is a short-circuit located
between the circuit breaker and the current trans-
former set of the feeder. For this fault current flow is
detected although the auxiliary contacts of the
breaker indicate open breaker pole(s). A command
signal is generated which can be transmitted to the
remote end breaker.
A circuit breaker pole discrepancy supervision is in-
tegrated in the 7SV512. It prevents that only one or
two poles of the breaker are open continuously. A
three-pole trip is initiated when pole discrepancy is
detected for a set time.
Special measures are taken to prevent malfunction
of the relay. Besides the mentioned 2-out-of-4 check
of the current detection elements the trip signals of
the feeder protection must be connected in redun-
dant manner so that they can be checked for plausi-
bility. An additional hard-ware monitor ensures mul-
ti-channel control of the trip relays. Continuous mon-
itoring of the measured values permits rapid annun-
ciation of any fault in the measuring transformer cir-
cuits. Continuous plausibility monitoring of the inter-
nal measured value processing circuits and moni-
toring of the auxiliary voltages to ensure that they re-
main within tolerance are obviously inherent fea-
tures.
Throughout a fault in the network the magnitudes of
the instantaneous values are stored for a period of
max. 3 seconds (0.66 seconds at 50 Hz for trans-
mission to a central computer station) and are avail-
able for subsequent fault analysis.
Serial interfaces allow comprehensive communica-
tion with other digital control and storage devices.
For data transmission a standardized protocol in ac-
cordance with DIN 19244 is used. The device can
therefore be incorporated in Localized Substation
Automation networks (LSA).
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