NPU, SW Version 1.8, ©ComAp, September 2003
NPU-1.8r2.PDF 9
4. Function
Protection types
Overvoltage protection
The protection responds to raising the voltage above set threshold (A11, A12, A13) with it’s own delay
(A14). Limits can be set for any phase extra. By setting zero value the protection is switched off.
Undervoltage protection
The protection responds to voltage drop under set threshold (A15, A16, A17) with it’s own delay (A18).
Limits can be set for any phase extra. By setting zero value the protection is switched off.
Overfrequency protection
The protection responds to raising frequency above set threshold (A7) with it’s own delay (A8). Limit is
common for all three phases. By setting zero value the protection is switched off.
Underfrequency protection
The protection responds to fall frequency under set threshold (A9) with it’s own delay (A10). Limit is
common for all three phases. By setting zero value the protection is switched off.
Voltage assymetry protection
The protection responds to raising of the voltage difference between any two phases above set threshold
(A19) with it’s own delay (A20). By setting zero value the protection is switched off.
Vector shift supervision
The protection (A21) responds to voltage vector shift (e.g. this can be caused by jump loading generator).
No delay it is possible to adjust. By setting zero value the protection is switched off. The vector shift
supervision delay (A22) can be set from 0 s to 99.98 s (skip factor 20 ms) only at power supply switch on. It
could be used when connecting of asynchronous generators to the mains.
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