ABB 615 series Technical Manual page 625

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1MAC059074-MB A

615 series ANSI

Technical Manual

The operation of 27 can be described using a module diagram. All the modules in the

diagram are explained in the next sections.

GUID-9D762D4C-404B-4F4B-93A9-B1F071DF12F2-ANSI V1 EN

Functional module diagram

Level detector

The fundamental frequency component of the measured three phase voltages are

compared phase-wise to the set Pickup value. If the measured value is lower than the set

value of the Pickup value setting, the level detector enables the phase selection logic

module. The Relative hysteresis setting can be used for preventing unnecessary

oscillations if the input signal slightly varies above or below the Pickup value setting.

After leaving the hysteresis area, the pickup condition has to be fulfilled again and it is not

sufficient for the signal to only return back to the hysteresis area.

The Voltage selection setting is used for selecting the phase-to-ground or phase-to-phase

voltages for protection.

For the voltage IDMT mode of operation, the used IDMT curve equations contain

discontinuity characteristics. The Curve Sat relative setting is used for preventing

unwanted operation.

For more detailed description on IDMT curves and usage of Curve Sat

Relative setting, see the

in this manual.

The level detector contains a low-level blocking functionality for cases where one of the

measured voltages is below the desired level. This feature is useful when unnecessary

pickups and trips are wanted to avoid during, for example, an autoreclose sequence. The

low-level blocking is activated by default (Enable block value is set to "True") and the

blocking level can be set with the Voltage block value setting.

Protection functions

IDMT curves for under voltage protection

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