ABB Relion REC615

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Blocking logic

There are three operation modes in the blocking function. The operation modes

are controlled by the BLOCK input and the global setting in Configuration>

System> Blocking mode which selects the blocking mode. The BLOCK input can

be controlled by a binary input, a horizontal communication input or an internal

signal of the protection relay's program. The influence of the BLOCK signal activation

is preselected with the global setting

Blocking mode

The

Blocking mode

setting has three blocking methods. In the "Freeze timers"

mode, the operation timer is frozen to the prevailing value, but the OPERATE output

is not deactivated when blocking is activated. In the "Block all" mode, the whole

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.

4.3.2.5 Application

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

and I

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

equation.

Iratio

(Equation 43)

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

1MRS758755 C

Protection functions

REC615 & RER615

Technical Manual

417

ABB Relion REC615 - Page 417