Inverse Time Characteristics - ABB REG650 Technical Manual

Generator protection

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1MRK 502 043-UUS B

Technical Manual

EQUATION1647 V1 EN

Pickupn is the set pickup current for step n

is set time multiplier for step n

is the measured current

The RD inverse curve gives a logarithmic delay, as used in the Combiflex protection

RXIDG. The curve enables a high degree of selectivity required for sensitive residual

ground-fault current protection, with ability to detect high-resistive ground faults. The

curve is described by equation 119:

EQUATION1648 V1 EN

Pickupn is the set pickup current for step n,

is set time multiplier for step n and

is the measured current

The timer will be reset directly when the current drops below the set pickup current

level minus the hysteresis.

Inverse time characteristics

When inverse time overcurrent characteristic is selected, the operate

time of the stage will be the sum of the inverse time delay and the set

definite time delay. Thus, if only the inverse time delay is required, it is

of utmost importance to set the definite time delay for that stage to zero.

Time inverse characteristics

(Equation 118)

(Equation 119)