Operation Principle; Mode Of Operation - ABB REG650 Technical Manual

Generator protection

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Time inverse characteristics

If there is a risk of intermittent faults. If the current relay, close to the faults, starts

and resets there is a risk of unselective trip from other protections in the system.

Delayed resetting could give accelerated fault clearance in case of automatic

reclosing to a permanent fault.

Overcurrent protection functions are sometimes used as release criterion for other

protection functions. It can often be valuable to have a reset delay to assure the

release function.

Operation principle

The function can operate in a definite time-lag mode or in a current definite inverse

time mode. For the inverse time characteristic both ANSI and IEC based standard

curves are available.

If current in any phase exceeds the set start current value , a timer, according to the

selected operating mode, is started. The component always uses the maximum of the

three phase current values as the current level used in timing calculations.

In case of definite time-lag mode the timer will run constantly until the time is reached

or until the current drops below the reset value (start value minus the hysteresis) and

the reset time has elapsed.

The general expression for inverse time curves is according to equation 116.

EQUATION1189 V1 EN

For inverse time characteristics a time will be initiated when the current reaches the set

start level. From the general expression of the characteristic the following can be seen:

are constants defined for each curve type,

is the set start current for step n,

is set time multiplier for step n and

is the measured current.

1MRK 502 048-UEN A

(Equation 116)

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