ABB RELION 620 Series Technical Manual page 435

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1MAC504801-IB E

620 series ANSI

Technical Manual

the different waveform and the different rate of change of the normal inrush current and

the inrush current containing the fault current. The algorithm does not eliminate the

blocking at inrush currents, unless there is a fault in the protected area.

The feature can be enabled and disabled through the Harmonic deblock 2.H setting.

Fifth harmonic blocking

The inhibition of the protection relay operation in situations of overexcitation is based on

the ratio of the fifth harmonic to the fundamental component of the differential current

(Id5f / Id1f). The ratio is calculated separately for each phase without weighting factors.

If the ratio exceeds the set value of Pickup value 5.H and blocking is enabled through the

Restraint mode setting, the operation of the biased stage of the protection relay in the

concerned phase is blocked.

At dangerous levels of overvoltage which may cause damage to the transformer, the

blocking can be automatically eliminated. The blocking is removed if the ratio of the fifth

harmonic to the fundamental component of the differential current exceeds the set value

of the Stop value 5.H setting, and the blocking removal is enabled. The enabling and

disabling of deblocking feature is done through the Harmonic deblock 5.H setting.

Stop value 5 . H

Pickup value 5 . H

5 th harmonic block

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The fifth harmonic blocking limits and the operation when both blocking

and deblocking features are enabled through the Harmonic deblock 5.H

Fifth harmonic blocking has a hysteresis to avoid rapid fluctuation between TRUE and

FALSE. The required consecutive fulfillments of the condition can be counted using the

blocking counter. When the condition is not fulfilled, the counter is decreased (if >0).

Also fifth harmonic deblocking (based on the higher limit, Stop value 5.H, if enabled with

Harmonic deblock 5.H) has a hysteresis and a counter which counts the required

Protection functions

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