1.2.2 Single Line To Neutral Fault Page 1 of 4

1.2 Unbalanced Faults

2.4 Single Line to Neutral Fault

Assume that the fault occurs on phase A and the fault impedance to the neutral is 0. The phase currents are.

= If Ib = O t = 0

The symmetrical components of the phase currents are:

_ + In ho 3 3

+I.! +12 .r, T.; r = b al

rt +i2, 1; g. = Ir 3

ra0 = !al = r.2 =

The phase A to neutral voltage at the fault is 0:

= 0 tart +t +Lai = 0

To find the current at the fault, we must know the sequence impedances for all network equipment. In our case, it is only the line between the generator and the fault that will be in the path of the fault current. The positive impedance of the line is the impedance calculated from the data for the line conductors and spacing. The negative sequence impedance is equal to the positive sequence impedance for transmission lines. The zero sequence impedance can be approximated by

2o a 21 + 32n . The calculation of the actual value is more complex because all mutual inductances between phase wires and ground must be included.

3 3

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1.2.2 Single Line To Neutral Fault Page 2 of 4

The sequence networks than are:

Positive sequence network

Negative sequence network

Ia2 Z2 F2 M

E 2

N2

Zero sequence network

Imo! Fo >

No

From the networks,

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N,

ZI

F ,

Eat

Earn

N2

'JD ZO FD

1.2.2 Single Line To Neutral Fault Page 3 of 4

Eau = 2 1Ta1 + tail

t2 f +fat, o=gotto +Ewa

Combining of all these equations will give the symmetrical components of the fault current and the total fault current:

fal = 112 = 110 = E . 3E.

. .IF =Ial +I.2 11.0 ZrEZ2 +Zo Z 1 + 2 + 0

Model for Line to Neutral Fault is a circuit that satisfies the equations for the symmetrical components of the fault current and of the voltages at the fault. For line to neutral fault these equations are.

= ra0

Emil + E arn Ego =

These equation describe a series connection of the three sequence networks.

ND

2004

Continue to

1.2.3 Line To Line Fault 1.2.4 Double Line To Neutral Fault

1.2.5 Zero Sequence Networks For Three Phase Transformers

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1.2.2 Single Line To Neutral Fault Page 4 of 4

Return to

1.2 Unbalanced Faults

itTELE7E606

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