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The most devastating fault type

An arc fault in medium voltage or low voltage switchgear is one of the most devastating fault types in power systems. Term ‘arc flash explosion’ is a good characterization of the fault type. It causes a serious burn hazard to personnel along with several other safety hazards. An arc fault may also lead to significant economic losses directly, by damaging the equipment and indirectly, through power supply outages and production process interruptions.

IEC 61850 based GOOSE messaging in arc protection of LV/MV switchgear
IEC 61850 based GOOSE messaging in arc protection of LV/MV switchgear

Several methods have been introduced to prevent arc faults and mitigate their impacts. In this research a comprehensive overview of the methods has been given, starting from the design of equipment until the extinction of the fault arc.

Development directions for arc protection have been investigated and suggested. Part of arc faults develop gradually and it is possible to construct systems for detecting such faults. In this research, mechanism and phenomena related to developing faults have been investigated.

Moreover, an online monitoring system enabling preemptive protection has been outlined, and suitable sensors have been tested in a laboratory.

The importance of communication technology in power systems increases along with the progress of smart grids. This also applies to arc protection systems that require extremely short operation time. This research has investigated the feasibility of IEC 61850 based GOOSE messaging in arc protection systems, verified the functionality of a developed implementation and evaluated benefits of the technology.

The dissertation suggests standardization of already existing, effective and proven protection methods, especially protection based on optical detection. In minimizing the arc duration, efforts should be directed towards development of circuit breaker technology. In most critical sites, short-circuit devices can be applied.


Design, education and maintenance

Design of switchgear is a key issue in arc prevention, and it is supported by IEC and IEEE standardization. In fact IEC 62271-200 states that if switchgear is designed and manufactured satisfying the requirements of the standard, internal arc faults should, in principle, be prevented.

However, internal arc faults still occur for a number of reasons.

An example of arc resistant technology with an exhaust plenum
Figure 1 – An example of arc resistant technology with an exhaust plenum

IEC 62271-200 presents a list of locations where internal arc faults are most likely to occur in metal-enclosed switchgear and controlgear:

  1. Connection compartments
  2. Disconnectors, switches, grounding switches
  3. Bolted connections and contacts
  4. Instrument transformers
  5. Circuit breakers

According to experience, another typical location of arc faults is cable termination. By focusing special design attention on the locations listed above, the probability of arc faults can be decreased.

Insulation of buses provides means to reduce the probability of arc faults caused by e.g. falling objects or vermin. Insulation can also prevent single-phase faults from escalating to high-power multi-phase faults. Another advantage of an insulated bus is that the insulation may help extinguish the arc.

This observation is not necessarily true in all cases since bus insulation can slow down the movement of the arc. If the arc becomes stationary at an insulation barrier, higher incident energy can be produced.

High-resistance grounding (HRG) is another design related technology aiming at reducing the probability of an arc fault. HRG system has a resistance sufficiently high enough connected between the earth and point of connection on the system that there is a minimal current that flows during an earth fault. However, HRG system for arc fault mitigation is only effective in earth faults.

The human factor is often the direct cause of an arc fault, especially in cases with casualties. Systematic education of personnel, delivering information on the equipment and related safety hazards, is an efficient way to increase safety and reduce the number of accidents.

The same kind of systematic approach also applies to maintenance practices that ensure adequate condition of the equipment and help in identification of possible risks. Preventive maintenance, e.g. visual inspection, thermal imaging, partial discharge (PD) testing, and time-based testing of protection devices are examples of common preventive maintenance actions.

Example of simple protection by a stand-alone device
Figure 2 – Example of simple protection by a stand-alone device

Protection systems based on the detection of light

The detection of light is the fastest arc detection method, applied by a number of manufacturers and by an increasing number of end-users. This is why the following is written from the light-based arc detection point of view, assuming that detection of light is at least one of the operation conditions of the arc protection relay.

Development of on-line monitoring of switchgear is one of the areas of contribution in this thesis, and an example of a more developed maintenance strategy, condition based maintenance.

Special attention should be paid to maintenance of circuit breakers. If a CB fails, the performance of other components of the protection system is insignificant, with the exception of the important breaker failure protection.


Stand-alone devices

In limited applications where no selectivity is required, simple stand-alone devices can be utilized. The operation criteria may be “light only” or a combination of light and overcurrent or pressure. Stand-alone protection can be applied in e.g. wind power and small switchgear applications.

Figure 2 presents an example of a switchgear application with “light only” condition. The dashed lines depict the division of the switchgear into several compartments, each one equipped with a light sensor.

Example of selective protection using common numerical relays equipped with arc protection option
Figure 3 – Example of selective protection using common numerical relays equipped with arc protection option

The protection system consists of light sensors with associated cabling (grey lines), stand-alone arc protection relay, and the circuit breaker. The protection relay consists of a power module, light sensor input channels, microprocessor, and the I/O module including the trip relay.


Arc protection integrated into protection relays

Numerical protection relays can be equipped with an arc protection option, including sensor inputs to light sensors and a high-speed overcurrent protection option. Communication between the relays is needed for selective protection, i.e. tripping of appropriate circuit breakers.

Figure 3 presents a scheme of an MV application enabling selective tripping of outgoing feeders, in case an arc fault occurs in outgoing cable compartment.

Example of a dedicated arc protection system (Vamp Oy).
Example of a dedicated arc protection system (Vamp Oy).

Dedicated arc protection systems

For complex systems, dedicated arc protection equipment can be applied. While numerical relays are multi-function relays, dedicated arc protection relays are committed to arc protection, and they are the key components of the arc protection system.

A typical system consists of sensors, light and current I/O units collecting data from light sensors and current transformers, communication cabling, and a dedicated arc protection relay as the central unit. There may be several central units for final collection of all the data, and tripping the correct circuit breakers if both light and overcurrent are detected.

Figure 4 presents a simplified example of a dedicated arc protection system of MV switchgear.

The system is composed of one central unit, one current I/O unit, and four light I/O units. Current is measured by the CTs of the incoming feeders, connected to the central unit and the current I/O unit. Three light I/O units collect information from point type light sensors (two units, VAM 12LD, for outgoing feeders on the left side, and VAM 12L for the incoming feeder on the right), enabling selective protection in case of faults in cable terminations.

Fibre type light sensors are connected to one of the light I/O units (VAM 3L). The system is divided into a number of protection zones, and it includes circuit breaker failure protection, tripping the upper voltage level CB in case of CB failure.

Title:IEC 61850 based GOOSE messaging in arc protection of LV/MV switchgear – Doctoral thesis by Lauri Kumpulainen at University of Vaasa, Faculty of Technology, Department of Electrical Engineering and Energy Technology
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IEC 61850 based GOOSE messaging in arc protection of LV/MV switchgear
IEC 61850 based GOOSE messaging in arc protection of LV/MV switchgear

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8 Comments


  1. Hanuman
    Jun 14, 2020

    Some corrections needed:
    1. IEC 62271-200 is applicable for switchgear rated above 1kV and up to and including 52kV. This standard is not applicable for LV swg.
    2. IEC/TR 61641 is applicable for LV switchgear classification.
    However, not that straightforward when it comes to certification. Many ‘flavors’.
    Personal Protection Criteria:
    – Doors and covers do not open
    – Neither fragmentation of the enclosure nor projection of small parts will occur
    arcg does not cause holes in the accessible sides of the enclosure
    Indicators do not ignite (usually cotton pieces)
    – the protective circuit for the accessible parts of the enclosure is still effective

    Assembly protection criteria:
    -no propagation of the arc outside of tested compartment.
    – Continued operation of the assembly.
    ——————————————
    IEC61641/TR does not cover for the effect of gases.
    —————————————

    2. Also, IEC 62271-200 does indeed state, as mentioned in the article, that “metal-enclosed switchgear and controlgear that satisfy the requirements of this standard is designed and manufactured, in principle, to prevent occurrence of internal arc faults.” However, if you read the standard, this is not encompassed anywhere. Standard talks about lowering risk of occurrence and switchgear classification to contain the arc.
    IAC classification is important here. AFL, AFLR…


  2. andrew wilcox
    Jun 14, 2020

    Excellent read. Have you considered performing a review of arc quench devices? These are used in conjunction with the dedicated relays mentioned above and light+current sensors. They operate before the upstream over current protection, assuring fast response even with older, slower breakers.


    • Hanuman
      Jun 14, 2020

      We have. It will not protect your incoming breaker side.


  3. Mokhtar
    Jun 13, 2020

    Great article!
    Recently we had a terrible accident in a LV switchgear (28kA arc flash).
    I was wondering if light sensor can be applied to Siemens siprotech 4?


  4. Piet Bosch
    Mar 21, 2020

    Helpful thank you


  5. muzaffar khan
    Mar 19, 2020

    indeed very very helpful clearing basic plus with help of diagrams …EXCELLENT!!!!

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