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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.

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The standard IEC 61439 practice workbook

This workbook contains general information and proposals for designing, planning and building low voltage switchgear and controlgear ASSEMBLIES in compliance with the applicable laws, directives and provisions. Basic knowledge in… Read more

Jun 24, 2019

The standard IEC 61439 workbook (LV switchgear and controlgear assembly in practice)

Elements of power distribution systems

A primary distribution substation is the connection point of a distribution system to a transmission or a sub-transmission network. Outgoing feeders from a primary distribution substation are typically feeding secondary… Read more

Nov 30, 2016

Elements of power distribution systems

Impedance Based Fault Location

As utilities today concentrate on continuity and reliability of their distribution networks, fault location has become an important supplementary function in modern IEDs. These fault location algorithms typically rely on… Read more

Feb 07, 2015

Automatic Reclosing

Most overhead line faults are transient in nature, such as an insulator or a spark gap flashover or a temporary contact with foreign objects or animals. The majority of these… Read more

Feb 07, 2015

Backup protection

According to the International Electrotechnical Vocabulary [8.13.5], backup protection is intended to operate when a power system fault is not cleared or an abnormal condition is not detected in the… Read more

Feb 07, 2015

Protection of Synchronous Generators

Most power systems tolerate the disconnection of one generating unit, one power transformer, one power line or one busbar section without running into serious problems. A fault on adjacent power… Read more

Feb 07, 2015

Motor Protection

Electric motors are exposed to many kinds of disturbances and stress. Part of the disturbances is due to imposed external conditions such as overvoltage and undervoltage, overfrequency and underfrequency, harmonics,… Read more

Feb 07, 2015

Protection of Shunt Capacitor Banks

Shunt capacitor banks (SCBs) are widely used in transmission and distribution networks to produce reactive power support. Located in relevant places such as in the vicinity of load centers the… Read more

Feb 07, 2015

Protection of Meshed Networks

The structure of modern distribution and sub-transmission networks is developing toward meshed and looped configurations. At the same time, the demand for maintaining high reliability and safety in operation is… Read more

Feb 07, 2015

Protection of HV Transformers

The transformer substations are important parts of a power system. Many utilities design their power systems so that they withstand the loss of a single transformer. In case of an… Read more

Feb 07, 2015

MV Feeder Earth-fault Protection

This chapter contains a description of the earth-fault protection of MV feeders. A feeder may consist of: An overhead line with bare conductors, An overhead line with covered conductors, An… Read more

Feb 07, 2015

MV Feeder Short-circuit Protection

A short circuit is a serious incident that affects power system components. It is therefore very important that the protection system detects short circuits and trips the associated switching equipment…. Read more

Feb 07, 2015


  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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