ABB RELION REX640 Technical Manual page 835

Protection and control

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1MRS759142 F

function is blocked and the timers are reset. In the "Block OPERATE output" mode,

the function operates normally but the OPERATE output is not activated.

In three-phase distribution and subtransmission network applications the phase

discontinuity in one phase can cause an increase of zero-sequence voltage and

short overvoltage peaks and also oscillation in the corresponding phase.

PDNSPTOC is a three-phase protection with DT characteristic, designed for

detecting broken conductors in distribution and subtransmission networks. The

function is applicable for both overhead lines and underground cables.

The operation of PDNSPTOC is based on the ratio of the positive-sequence

and negative-sequence currents. This gives a better sensitivity and stability

compared to plain negative-sequence current protection since the calculated ratio

of positive-sequence and negative-sequence currents is relatively constant during

load variations.

The unbalance of the network is detected by monitoring the negative-sequence and

positive-sequence current ratio, where the negative-sequence current value is I

Broken conductor fault situation can occur in phase A in a feeder.

Figure 472: Broken conductor fault situation in phase A in a distribution or

subtransmission feeder

Technical Manual

is the positive-sequence current value. The unbalance is calculated with the

Protection functions

(Equation 236)