ABB RELION 620 Series Technical Manual page 804

Section 4
Protection functions
4.12.3.5
798
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.
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
1MRS757644 F
620 series
Technical Manual