ABB RELION REX640, Техническое руководство, Страница: 1145 / 1960

Timer 1
Once activated, the timer activates the alarm timer. The timer characteristic is
according to DT. When the alarm timer has reached the value set by
Alarm delay
time, the
ALARM
output is activated.
If the fault disappears before the alarm activates, the alarm timer is reset
immediately.
Timer 2
Once activated, the timer activates the operation timer. The timer 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 fault disappears before the operate activates, the operation timer is reset
immediately.
If the input
RESO_IN
becomes active, the
OPERATE
output is activated immediately.
If the resonance protection at a higher-order filter branch has already operated,
the function in lower-order filter branches can be tripped immediately using this
feature.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the
BLOCK
input and the global setting 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 IED
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. In the “Block all”
mode, the whole function is blocked and the timers are reset. In the “Block
OPERATE output” mode, SRCPTOC operates normally but the
OPERATE
output is
not activated.
4.12.4.6 Application
Switched shunt capacitor banks are widely used by utilities and customers in
industrial distribution systems to provide voltage support and to improve the
power factor of a load. Capacitor steps may be switched in and out of circuits
routinely as the demand for capacitive VAR compensation of a load fluctuates.
Normally, automatic power factor controllers are employed which automatically
switch on or off the capacitors of the capacitor bank, depending upon the prevalent
reactive power requirement in the system.
One potential problem for the application of automatic power factor controllers is
that it may cause harmonic resonance under certain system conditions. Capacitor
switching changes the parameters of the system, which may cause the resonance
frequency of the circuit to be equal to one of the frequencies of the harmonic
sources prevalent in the system. Harmonic resonance, when it occurs, may result
in severe voltage and current distortions, which increases losses and causes
overheating of other equipment in the circuit.
A traditional way of solving the problem is to conduct a detailed system study for
each individual installation and use the results to properly size the capacitors and
determine the right operating range of capacitors to avoid harmonic resonance
1MRS759142 F Protection functions
REX640
Technical Manual
1145