Menu
Search
Where and When Do We Use Arc Suppression Coil (Petersen Coil)?
Where and When Do We Use Arc Suppression Coil (Petersen Coil)? (on photo: 20 kV Arc Suppression Coil; credit: trenchgroup.com)

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.

Ideal situation from the system point of view would be a compensation degree of 100%, where the total capacitive earth fault current would be compensated.

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).

Principle of centralized (left) and distributed earth fault current compensation
Figure 1 – Principle of centralized (left) and distributed earth fault current compensation

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.

Construction of an ASC with air gap (reactance) adjustment
Figure 2 – Construction of an ASC with air gap (reactance) adjustment

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.

Installation of oil-immersed arc suppression coil with external air-cooled load resistor (on the left-hand side)
Figure 3 – Installation of oil-immersed arc suppression coil with external air-cooled load resistor (on the left-hand side)

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.

The purpose of the resistor is to increase the resistive earth fault current component to a level which the outgoing feeder protection relays can detect.

For insulation level reasons, the resistor connection to primary circuit is typically done through intermediate current transformer.

Principle of load resistor connection to ASC
Figure 4 – Principle of load resistor connection to ASC

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!

22kV Arc Suppression Coils
22kV Arc Suppression Coils (photo credit: Swedish Neutral)

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

Basic Sketch Of Arc Suppression Coil
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

References //

  1. Distribution Automation Handbook – Elements of power distribution systems by ABB
  2. Arc Supression Coils by Swedish Neutral AB

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

Leave a Comment

Tell us what you're thinking... we care about your opinion!

Time limit is exhausted. Please reload CAPTCHA.

Get PDF