ABB UNITROL 1020 - Limiters and Monitor Functions

 Chapter 3 - Device Overview
UNITROL 1020 User Manual 3BHS335648 E82 55
If there is neither left nor right side breaker, the corresponding digital input (Secondary
Net1 / 2) must be forced to logical 1.
Each AVR is collecting all status information of the ring tie breakers over the RS485 bus
in order to select the correct load sharing group. In case of a separated segment the load
sharing takes place on the remaining ones and separately on the isolated segment.
3.4.4 Limiters and Monitor Functions
3.4.4.1 Limiters
V/Hz Limiter
- V/Hz knee point frequency
- Slope
(diff between fknee and
0Hz)
fknee [Hz]
Slope [%/fk]
fknee
[%]
[Hz]
100
Machine voltage
In case of a short circuit at the machine terminals, the frequency is calculated out of the
machine current. This guarantees a correct functioning of the V/Hz limiter in any
condition.
During soft start the V/Hz limiter minimum output is limited to 5%
Sudden AUTO SP drop
at frequency drop
- Freq. drop threshold
- Freq. drop time span
V/Hz Fdrop [Hz]
V/Hz MeasDe [ms]
Time [s]
[Hz]
50
Machine Frequency
V/Hz drop
V/Hz MeasDealy
- AUTO SP drop
- SP hold time
- SP recovery time
V/Hz Udrop [%]
V/Hz Hold [sec]
V/Hz Recov. [sec]
Time [s]
[%]
100
AUTO SP
V/Hz Hold
V/Hz Udrop
V/Hz Recovery
The function is blocked:
 During Soft Start
 When PQ Limiter is active
 When Voltage Relay is active
 When Generator state is “no load” or “Parallel with grid”