Figure 218: Functional module diagram
Level detector
The calculated negative-sequence voltage is compared to the set
Start value
setting.
If the value exceeds the set
Start value
, the level detector enables the timer.
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.
4.4.4.5 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
.
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
441
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