Operation Principle - ABB Relion 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, picks up

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

Operation principle

Mode of operation

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

If current in any phase exceeds the set pickup 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 (pickup value minus the hysteresis) and the

reset time has elapsed.

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

EQUATION1640 V1 EN

are constants defined for each curve type,

is the set pickup current for step n,

is set time multiplier for step n and

is the measured current.

1MRK 502 048-UUS A

(Equation 116)

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