ABB RELION REX640 Technical Manual page 688

Protection and control

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Protection functions

5.H parameter, the blocking removal is enabled. The enabling and disabling of

deblocking feature is also done through the

Figure 390: The limits and operation of the fifth harmonic blocking when both

blocking and deblocking features are enabled using the Harmonic deblock 5.H

control parameter.

The fifth harmonic blocking has a hysteresis to avoid rapid fluctuation between

"TRUE" and "FALSE". The blocking also has a counter, which counts the required

consecutive fulfillments of the condition. When the condition is not fulfilled, the

counter is decreased (if >0).

Also the fifth harmonic deblocking has a hysteresis and a counter which counts

the required consecutive fulfillments of the condition. When the condition is not

fulfilled, the counter is decreased (if >0).

Waveform blocking

The biased low stage can always be blocked with waveform blocking. The stage can

not be disabled with the

The first part is intended for external faults while the second is intended for inrush

situations. The algorithm has criteria for a low current period during inrush where

also the differential current (not derivative) is checked.

Biased low stage

The current differential protection needs to be biased because the possible

appearance of a differential current can be due to something else than an actual

fault in the transformer (or generator).

In the case of transformer protection, a false differential current can be caused by:

• Varying tap changer positions (if not automatically compensated)

• Transformer no-load current

• Transformer inrush currents

• Transformer overexcitation in overvoltage

• Underfrequency situations

• CT saturation at high currents passing through the transformer

Harmonic deblock 5.H parameter.

Restraint mode parameter. This algorithm has two parts.

1MRS759142 F

Technical Manual