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Electrical Protection Systems

Electrical power system operates at various voltage levels from 415 V to 400 kV or even more. Electrical apparatus used may be enclosed (e.g. motors) or placed in open (e.g. transmission lines). All such equipment undergo abnormalities in their life time due to various reasons.

Power System Protection Practices // ABB
Power System Protection Practices // ABB

For example, a worn out bearing may cause overloading of a motor. A tree falling or touching an overhead line may cause a fault.

A lightning strike (classified as an act of God!) can cause insulation failure. Pollution may result in degradation in performance of insulators which may lead to breakdown. Under frequency or over frequency of a generator may result in mechanical damage to it’s turbine requiring tripping of an alternator.

Even othervise, low frequency operation will reduce the life of a turbine and hence it should be avoided.

It is necessary to avoid these abnormal operating regions for safety of the equipment. Even more important is safety of the human personnel which may be endangered due to exposure to live parts under fault or abnormal operating conditions. Small current of the order of 50 mA is sufflcient to be fatal!

Whenever human security is sacrificed or there exists possibility of equipment damage, it is necessary to isolate and de-energize the equipment.

Designing electrical equipment from safety perspective is also a crucial design issue which will not be addressed here.

To conclude, every electrical equipment has to be monitored to protect it and provide human safety under abnormal operating conditions. This job is assigned to electrical protection systems. It encompasses apparatus protection and system protection.

Here, on this page you will find 10+ ABB’s power system protection practices that can be of great help to protection engineers and others. Guides are free to download.

Browse guides and papers

Note that not all documents in this section are free to download. Navigate through sub-pages to discover all documents.

Relay Coordination and Selective Protection

The selected protection principle affects the operating speed of the protection, which has a significant impact on the harm caused by short circuits. The faster the protection operates, the smaller… Read more

Feb 07, 2015

Distribution Automation Handbook – Power System Protection Practice // Relay Coordination and Selective Protection – by ABB

Electrical Safety

Metallic parts of electrical equipment that can be exposed to voltage due to insulation failures are usually connected to earth potential, that is, earthed. This is done to protect the… Read more

Feb 07, 2015

Distribution Automation Handbook – Power System Protection Practice // Electrical Safety – by ABB


  1. Azegbea Jonathan
    Feb 08, 2018

    This is a very standard and concise way. Thanks for the job.

    Oct 05, 2016

    It’s very important information for an engineer for details and depth in electrical engineering and mastering the note calculated for each part of the electrical installation Low Voltage and Medium Voltage.

  3. Rommel Diaz
    Jun 08, 2016

    this website is very helpful to electrical engineers. good work!

  4. mahendrakumar
    Feb 14, 2015

    this website very useful to know about practically what happening in electrical terms especially in power systems….would you help to download totally power system in single book.because i search lot of websites for some practical terms about power systems.
    thank you for your regular updates,,,

  5. pramod kumar yadav
    Feb 12, 2015

    What is different from kva &kvar

    • Anwar Pasha
      Feb 22, 2015

      I think your question is: “What is the difference between KVA and KVAr”

      KVA is the apparent Power
      and KVAr is the reactive power. In case of inductive circuit the current lags behind the voltage and in case of capacitive circuit current leads the voltage..

  6. ram
    Feb 11, 2015

    this site is so good and I am really addicted to this.

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