ABB RELION 620 Series Technical Manual page 835

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1MAC504801-IB E

620 series ANSI

Technical Manual

Current based inverse definite minimum time

characteristics

IDMT curves for overcurrent protection

In inverse-time modes, the trip time depends on the momentary value of the current: the

higher the current, the faster the trip time. The trip time calculation or integration starts

immediately when the current exceeds the set Pickup value and the PICKUP output is

The TRIP output of the component is activated when the cumulative sum of the integrator

calculating the overcurrent situation exceeds the value set by the inverse-time mode. The

set value depends on the selected curve type and the setting values used. The curve scaling

is determined with the Time multiplier setting.

There are two methods to level out the inverse-time characteristic.

The Minimum operate time setting defines the minimum operating time for the IDMT

curve, that is, the operation time is always at least the Minimum operate time setting.

Alternatively, the IDMT Sat point is used for giving the leveling-out point as a

multiple of the Start value setting. (Global setting: Configuration/System/IDMT

Sat point). The default parameter value is 50. This setting affects only the overcurrent

and earth-fault IDMT timers.

IDMT operation time at currents over 50 x In is not guaranteed.

General function block features

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