ABB REG670 Technical Manual page 322

Section 7
Impedance protection
316
• Generator voltage < set value and generator circuit breaker open: Reference
impedance 1
• Generator voltage > set value and generator circuit breaker open: Reference
impedance 2
• Generator voltage > set value and generator circuit breaker closed: Reference
impedance 3
The monitoring, enabled in ICT, will give indication if several reference impedance
values are needed.
From the measured impedance the stator earth fault resistance can be estimated since
the reference impedance is known. An alarm level (Ω) is set at a higher value and the
ALARM signal is activated after a set alarm delay time. A trip level (Ω) is also set at
a lower value. When the trip level is reached a TRIP signal is activated as shown in
figure 142.
1MRK502052-UEN B
Technical manual