Application - ABB RELION Series Technical Manual

Section 4
Protection functions
4.4.5.5
432
input signal slightly varies from the Start value setting. After leaving the hysteresis
area, the start condition has to be fulfilled again and it is not sufficient for the signal
to only return to the hysteresis area.
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 undervoltage condition persists. If the
positive-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.

Application

PSPTUV can be applied for protecting a power station used for embedded generation
when network faults like short circuits or phase-to-earth faults in a transmission or a
distribution line cause a potentially dangerous situations for the power station. A
network fault can be dangerous for the power station for various reasons. The
operation of the protection can cause an islanding condition, also called a loss-of-
mains condition, in which a part of the network, that is, an island fed by the power
station, is isolated from the rest of the network. There is then a risk of an autoreclosure
taking place when the voltages of different parts of the network do not synchronize,
which is a straining incident for the power station. Another risk is that the generator
can lose synchronism during the network fault. A sufficiently fast trip of the utility
circuit breaker of the power station can avoid these risks.
The lower the three-phase symmetrical voltage of the network is, the higher is the
probability that the generator loses the synchronism. The positive-sequence voltage is
also available during asymmetrical faults. It is a more appropriate criterion for
1MRS758755 A
REC615 and RER615
Technical Manual