5.3.2.2 Functionality
The phase discontinuity protection PDNSPTOC is used for detecting unbalance
situations caused by broken conductors.
The function starts and operates when the unbalance current I
2
/I
1
exceeds the set limit.
To prevent faulty operation at least one phase current needs to be above the minimum
level. PDNSPTOC operates with DT characteristic.
The function contains a blocking functionality. It is possible to block the function
output, timer or the function itself, if desired.
5.3.2.3 Application
In three-phase distribution and subtransmission network applications the phase
discontinuity in one phase can cause 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 positive and negative sequence
currents. This gives better sensitivity and stability compared to plain negative
sequence current protection since the calculated ratio of positive and negative
sequence currents is relatively constant during load variations.
When the three phase currents are measured, the positive-sequence current is
calculated using Equation 1
I I aI a Ia b c1
1
3
2
= + +
( )
A070700 V1 EN (Equation 1)
The negative sequence current is calculated using Equation 2
I I a I aIa b c2
1
3
2
= + +
( )
A070701 V1 EN (Equation 2)
I
a
, I
b
, I
c
phase current vectors
ɑ phase rotation operator (defined to rotate a phasor component forward by 120 degrees)
The unbalance of the network is detected by monitoring the negative and positive
sequence current ratio, where the negative-phase sequence current value is I
2
and I
1
is the positive-phase sequence current value. The unbalance is calculated using
Equation 3
Section 5 1MRS756378 D
Protection functions
160 REF615
Application Manual
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