Neutral Displacement Current Limiting Reactor
Neutral Displacement Current Limiting Reactor
(OP)
The dataplate of a 3 phase Neutral Displacement Current Limiting Reactor shows:
- Limited earth fault current = 7.22 A
- Throughput kVA = 7.22 A
- System volts = 11000 V
- System amps = 131 A
The 3 phase Neutral Displacement Current Limiting Reactor ( NDCLR ) is intended to reduce earthfault current on a solidly earthed system as shown in attached file.
The NDCLR is intended to be used because voltage drop across an isolating transformer would be unacceptably high.
However the NDCLR would also have a reactance !
What would typical z1, z2 and z0 and x1/r1, x2/r2, xo/ro be ?
Can anyone explain how a NDCLR has negligible positive sequence ( and negative sequence ? ) impedance while having a high zero sequence impedance ?
Assuming z1 = z2 = 0, then Ik1 = ( 3/zo )*Ibase
zo = 3 * Ibase / Ik1 = 54.4321 pu on 2500 kVA base
Zn = ( 54.4321 / 3 )* ( 11000^2 / 2500000 ) = 878.1717 Ohm
Ik1 = ( 11000 / sqrt(3) ) / 878.1717 = 7.231 A
- Limited earth fault current = 7.22 A
- Throughput kVA = 7.22 A
- System volts = 11000 V
- System amps = 131 A
The 3 phase Neutral Displacement Current Limiting Reactor ( NDCLR ) is intended to reduce earthfault current on a solidly earthed system as shown in attached file.
The NDCLR is intended to be used because voltage drop across an isolating transformer would be unacceptably high.
However the NDCLR would also have a reactance !
What would typical z1, z2 and z0 and x1/r1, x2/r2, xo/ro be ?
Can anyone explain how a NDCLR has negligible positive sequence ( and negative sequence ? ) impedance while having a high zero sequence impedance ?
Assuming z1 = z2 = 0, then Ik1 = ( 3/zo )*Ibase
zo = 3 * Ibase / Ik1 = 54.4321 pu on 2500 kVA base
Zn = ( 54.4321 / 3 )* ( 11000^2 / 2500000 ) = 878.1717 Ohm
Ik1 = ( 11000 / sqrt(3) ) / 878.1717 = 7.231 A






RE: Neutral Displacement Current Limiting Reactor
RE: Neutral Displacement Current Limiting Reactor
EddyWirbelstrom, could you please help us to understand better what this is with respect to typical reactor classifications shown below?
RE: Neutral Displacement Current Limiting Reactor
The three individual phase windings are on one core.
Under balanced three phase operation, the vector sum of positive sequence flux is zero.
The only positive and negative sequence impedance would be due to leakage flux, say 1.0%.
Under single phase to earth fault, the zero sequence flux flows around the air gapped core.
The variable gap is adjusted to vary the reluctance of the zero sequence flux path to limit earth fault current to the desired value.
If the CLNDR limited earth fault current to a known value, then the zero sequence impedance could be calculated as follows :
Ik1 = 3 / ( z1 + z2 + zo )
Assume z1 = z2
zo = 3 / Ik1