ABB RELION REX640, Техническое руководство, Страница: 877 / 1960

Timer
Once activated, the timer activates the
START
output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Operate
delay time, the
OPERATE
output is activated if the overvoltage condition persists.
If the negative-sequence voltage normalizes before the module operates, the reset
timer is activated. If the reset timer reaches the value set by
Reset delay time, the
operate timer resets and the
START
output is deactivated.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is
available in the monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the
BLOCK
input and the global setting in Configuration >
System > Blocking mode which selects the blocking mode. The
BLOCK
input can
be controlled by a binary input, a horizontal communication input or an internal
signal of the protection relay's program. The influence of the
BLOCK
signal activation
is preselected with the global setting
Blocking mode.
The
Blocking mode setting has three blocking methods. In the "Freeze timers"
mode, the operation timer is frozen to the prevailing value, but the
OPERATE
output
is not deactivated when blocking is activated. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the
OPERATE
output is not activated.
4.5.5.6 Application
A continuous or temporary voltage unbalance can appear in the network for
various reasons. The voltage unbalance mainly occurs due to broken conductors or
asymmetrical loads and is characterized by the appearance of a negative-sequence
component of the voltage. In rotating machines, the voltage unbalance results in a
current unbalance, which heats the rotors of the machines. The rotating machines,
therefore, do not tolerate a continuous negative-sequence voltage higher than
typically 1-2 percent x U
n
.
The negative-sequence component current I
2
, drawn by an asynchronous or a
synchronous machine, is linearly proportional to the negative-sequence component
voltage U
2
. When U
2
is P% of U
n
, I
2
is typically about 5 x P% x I
n
.
The negative-sequence overcurrent NSPTOC blocks are used to accomplish a
selective protection against the voltage and current unbalance for each machine
separately. Alternatively, the protection can be implemented with the NSPTOV
function, monitoring the voltage unbalance of the busbar.
If the machines have an unbalance protection of their own, the NSPTOV operation
can be applied as a backup protection or it can be used as an alarm. The latter can
be applied when it is not required to trip loads tolerating voltage unbalance better
than the rotating machines.
If there is a considerable degree of voltage unbalance in the network, the rotating
machines should not be connected to the network at all. This logic can be
implemented by inhibiting the closure of the circuit breaker if the NSPTOV operation
has started. This scheme also prevents connecting the machine to the network if
the phase sequence of the network is not correct.
1MRS759142 F Protection functions
REX640
Technical Manual
877