Command Outputs During Link Failure - ABB ETL600 Instruction Manual

ETL600
unblocking signal is only released if both levels are below the threshold
and the other conditions mentioned above are fulfilled too).
3.6.8.9.

Command Outputs During Link Failure

By means of the HMI600, the user can program how the command
outputs respond to a channel failure, i. e. to SNR alarm or Rx level
alarm in the corresponding channel of the TPE. The following
alternatives are available:
a) All command outputs assume states in accordance with current
input signal processing, i.e. they disregard the TPE link alarm
(default setting).
b) All command outputs are set to their quiescent states (i.e. no trip).
c) The outputs configured for direct tripping are set to guard state and
the outputs configured for permissive tripping or blocking are set to
command state.
d) Received commands are immediately "frozen" at the command
outputs in case of an interrupted or disturbed link.
These settings apply to all signals in the case of units equipped for
several commands.
The corresponding HMI600 settings are given in section 5.3.3.
Alternative a) is the default setting when the units are supplied from
the works. With this setting the NSD600 responds normally to changes
in the statuses of the input signals. This is permissible in spite of the
alarm condition, due to the high security of tripping signal evaluation.
Sometimes setting b) is preferred to setting a), for example, when
redundant sets of communications equipment are installed.
Setting c) is only used in seldom cases with overreaching or blocking
protection schemes having special logics and in certain instances for
blocking auto-reclosure relays.
Setting d) "freezing of commands" is used when commands of long
duration are transferred and they should not be interrupted at the
command outputs –when the link is lost or disturbed by noise bursts.
The responses of the command outputs according to b) and c)
become effective after an internal alarm processing time (e.g. less
than 1 second for low level alarm) from the instant the alarm condition
arises and remain so throughout the alarm condition and for a further
processing time of the same quantity after it disappears.
The alarm condition pick-up time and the hold time for the command
outputs according to b) and c) can be further delayed by 0 to 15
seconds (default pick up: 10 s; default hold: 0 s). This might be
necessary if, for example, clamping of the command outputs should be
avoided in case of recurrent noise bursts on the power line, produced
by switching operations involving slow speed isolators. The
interference so generated is characterized by high amplitude and
relatively long duration of up to 8 seconds.
Structure and Function
1KHW001489-EN
November 2005
ABB Switzerland Ltd
3-81