ABB RET670 Product Manual page 19

ABB
Transformer protection RET670
Pre-configured
Product version: 1.1
The general function suits applications with
underimpedance and voltage controlled
overcurrent solutions. The general function
can also be utilized for generator transformer
protection applications where positive,
negative or zero sequence components of
current and voltage quantities are typically
required.
Secondary system supervision
Current circuit supervision CCSRDIF
Open or short circuited current transformer
cores can cause unwanted operation of many
protection functions such as differential,
earth-fault current and negative-sequence
current functions.
It must be remembered that a blocking of
protection functions at an occurrence of open
CT circuit will mean that the situation will
remain and extremely high voltages will
stress the secondary circuit.
Current circuit supervision (CCSRDIF)
compares the residual current from a three
phase set of current transformer cores with
the neutral point current on a separate input
taken from another set of cores on the
current transformer.
A detection of a difference indicates a fault in
the circuit and is used as alarm or to block
protection functions expected to give
unwanted tripping.
Fuse failure supervision (RFUF)
Failures in the secondary circuits of the
voltage transformer can cause unwanted
operation of distance protection,
undervoltage protection, neutral point voltage
protection, energizing function (synchronism
check) etc. The fuse failure supervision
function prevents such unwanted operations.
There are three methods to detect fuse failures.
The method based on detection of zero
sequence voltage without any zero sequence
current. This is a useful principle in a directly
earthed system and can detect one or two
phase fuse failures.
1MRK 504 091-BEN B
The method based on detection of negative
sequence voltage without any negative
sequence current. This is a useful principle in
a non-directly earthed system and can detect
one or two phase fuse failures.
The method based on detection of du/dt-di/
dt where a change of the voltage is compared
to a change in the current. Only voltage
changes means a voltage transformer fault.
This principle can detect one, two or three
phase fuse failures.
Control
Synchronizing, synchrocheck and
energizing check SESRSYN
The Synchronizing function allows closing of
asynchronous networks at the correct
moment including the breaker closing time.
The systems can thus be reconnected after an
autoreclose or manual closing, which
improves the network stability.
Synchrocheck, energizing check (SESRSYN)
function checks that the voltages on both
sides of the circuit breaker are in
synchronism, or with at least one side dead
to ensure that closing can be done safely.
SESRSYN function includes a built-in voltage
selection scheme for double bus and 1½
breaker or ring busbar arrangements.
Manual closing as well as automatic reclosing
can be checked by the function and can have
different settings.
For systems which are running asynchronous
a synchronizing function is provided. The
main purpose of the synchronizing function
is to provide controlled closing of circuit
breakers when two asynchronous systems are
going to be connected. It is used for slip
frequencies that are larger than those for
synchrocheck and lower than a set maximum
level for the synchronizing function.
Apparatus control APC
The apparatus control is a function for
control and supervision of circuit breakers,
disconnectors and earthing switches within a
bay. Permission to operate is given after
Issued: June 2010
19