Compensation with Arc Suppression Coil
The arc suppression coil (ASC), also known as Petersen coil, is used to compensate the capacitive earth fault currents supplied by outgoing feeders at a substation. The compensation can be either centralized or distributed. With the centralized design, one ASC unit will handle the compensation of all of the outgoing feeders.
The distributed compensation is designed to compensate one feeder with one unit, thus locating on the consumption side of the medium voltage feeder circuit breaker in question.
With distributed ASCs, the compensation degree for the particular feeder is though kept well below 100% in order to avoid overcompensation under all of the system-switching conditions affecting the feeder length. That is, the distributed compensation sort of reduces the feeder’s electrical length from supplied earth fault current point of view.
The current use of distributed ASCs is very limited and the clear trend is towards a centralized arc suppression coil (ASC).
The centralized ASC must compensate the capacitive earth fault current supplied by a number of outgoing feeders. On the other hand, it is also noted that a compensation degree close to 100% would be preferred. To be able to fulfill these two conditions, it is clear that the ASC’s inductive reactance has to be adjustable to match the different system-switching situations (feeder’s total length).
Remote Adjustable Air Gap
One implementation method is to provide remote adjustable air gap in the ASC core.
The adjustment of the air gap will affect the coil’s inductance. The adjustment can be performed manually using a crank, or it can be motorized. The motorized adjustment enables the use of a control device performing the adjustment automatically.
The centralized ASC is connected between the system neutral point and earth, typically between the neutral of a star-connected main power transformer and earth. If the power transformer is delta-connected, the earlier introduced earthing transformer can be used to create the connection point.
External loading resistor
As shown in the figure above, ASC is often installed with external loading resistor. The resistor is installed in parallel to ASC, and the control (switching on/off) of the resistor can be carried remotely by a dedicated controller.
For insulation level reasons, the resistor connection to primary circuit is typically done through intermediate current transformer.
Resonance Grounding In Scandinavia
Resonance grounding by Petersen coils (Arc Suppression Coils) has been used in Scandinavia and other European countries for last 80 years. The excellent properties of this grounding concept are mirrored by very low outages rates.
Resonance grounding is mainly used in overhead networks where most of the faults are single phase‐to‐ground and often of transient nature. The Petersen coil chokes the fault current below the level of self‐extinction (< 35 A) by compensating for the capacitive fault current of the network.
By this action all transient faults can be cleared without feeder tripping!
However sustained faults on overhead lines and cable faults cannot be cleared by any Arc Suppression Coil since no coil can compensate for the active part of the fault current. Due to this remaining fault current it is necessary to trip the feeder to minimize the risk for fire and personal hazards in the network!
Basic Sketch Of Arc Suppression Coil
Solution with Ground Fault Neutralizer
The Ground Fault Neutralizer (GFN) is connected to the neutral of the supplying power transformer (Y-winding) or a separate grounding transformer (Z-winding).
A complete ground fault neutralizer system is composed of an arc suppression coil, a cabinet for power electronics and the GFN control cabinet.
Beside the controls for the residual current compensation the GFN also provides automatic retuning for the arc suppression coil and a new twin scheme fault locating with superior detection capabilities. Distance-to-fault information can easily be obtained by feeder looping.
Tree Fire Explosion
A loose power line shocking the ground
- Distribution Automation Handbook – Elements of power distribution systems by ABB
- Arc Supression Coils by Swedish Neutral AB