Autoreclosing in transmission and distribution systems
Autoreclosing in transmission and distribution systems (on photo: A disconnect switch for a power line that’s maybe 200kV. The moveable members are the horizontal poles that are hinged atop the left set of insulators. – by Xylographile)


Two main functions of Utility Electric System Operations department are Control and Protection.

Control function deals with all operational aspects involved in efficient and optimal dispatching of available real power (with reactive power support) from the Generating units (and reactive sources) to geographically distributed consumers through available system of Transmission and distribution (T&D) network (s).

Control function thus performs all operations line connection and disconnection of circuits, equipment, changing levels of voltage (e.g. Power Transformer tap changes, changing power flow directions, load shedding, synchronizing, decreasing/increasing generation etc).

Some of these functions are performed automatically and some manually by system operators. Various monitoring and alarming systems help perform these control functions.

Protection function deals with automatic detection of faults or abnormal/unsafe system operation conditions and automatically disconnects involved circuits or equipment. Thus protective system helps in minimizing the damage to circuit components and equipment. Circuit components and equipment are thus available for reuse in most cases.

Automatic Reconnection

Once a circuit component or equipment is automatically disconnected by protective functions, its reconnection is mostly a control function. Reconnection of a circuit component or equipment (after its trip due to protective device action) is performed either manually or automatically.

It is often essential to make sure that reconnecting it will not thermally degrade the life of major equipment or damage it beyond acceptable level or results in major financial burden.

Protection action for equipment like Generators, Transformers, Reactors, Capacitor banks, Filter banks, Power cables etc. are always results in ‘Locked out’ (meaning are blocked from closing both manually or automatically). This is because it is always a permanent fault needing some kind of maintenance/repair.

Well, only time I feel requires no maintenance after a protection trip is when it is known for sure that it is a ‘protection mal-operation’ or it is a sympathetic protection operation due to some other fault/abnormal condition in the system. In any case, reconnecting without any test is a SCARY business and involves a bit of personal risk!!!!
TriMod™ 600R Vacuum Recloser w/ Single or Three-Phase Operation
TriMod™ 600R Vacuum Recloser w/ Single or Three-Phase Operation

Every utility will have well decided operation policy in regard to reconnection of equipment or circuit component after a protection trip. Before reconnecting a major equipment considerable testing and maintenance procedures are followed (requires some equipment down time).

Overhead (OH) Transmission and distribution circuits are the only circuits which are often reconnected automatically without any testing or maintenance performed after its trip due to protection action. This is because most often the protection action is due to a fault which is transient in nature and the fault vanishes once it is de-energized.

Depending on the magnitude of fault current and strength of electric potential (voltage level), some ionization occurs in the surrounding dielectric media (air) which neutralizes with time and regains required dielectric strength making it available for successful reconnection. Thus Automatic reconnection called Auto-reclosing, can be performed for OH Transmission and Distribution circuits.

From Auto-reclosing perspective, it becomes very important therefore to understand types of faults which can occur in OH T&D circuits and amount of risk involved in auto-reclosing and its advantages.

Finally, a quick question to readers… Whether Auto-reclosing is a Control function or a Protection function?

I guessed your answer… if you are a Protection Engineer, you will surely say it is a Control function and… he he, if you are a Control system Engineer (operation person) you will surely say it is a Protection function!!!!

Because it is performing a closing operation not a trip action, a Protection Engineer says it is a control function. Control Engineer says otherwise because it is performed by a protective relay or device following a definitive and sequential action decided (major part of sequence and conditions for reclosing action) by Protection Engineers.

Psst… I strongly believe most common real reason behind the views of Control and Protection Engineers is the risk involved with unsuccessful re-closing and failing to initiate it in the first place…analyzing the events, making reports etc… LOL … guys accountability is a major issue in competitive power companies (excepting some utilities in corrupt systems)… anyway, we will go back to Auto-reclosing folks!

Resource: Autoreclosing in Transmission and Distribution Systems by mr. S.R. Javed Ahmed

About Author //


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


  1. […] primary feeder main is usually sectionalized by reclosing devices positioned at various locations along the feeder. This arrangement minimizes the extent of primary […]

  2. Shashwat Gawshinde
    Jul 19, 2016

    Are autoreclosers being used at DTR level in any part of the world??

  3. […] fault isolation functionality has been achieved with the correct coordination of protection and auto-reclosing scheme settings. Red color marks for a closed switch and green color marks for an open switch. Furthermore, a solid […]

  4. Claudette D. Pusing
    Nov 16, 2014

    Sir, good day! Will you please / kindly extend some help / clever advises on how to deal with a distribution utility company environment, who has a corrupt managements with its board of directors…..for 35 years of existence they never hired licensed / professional engineers! For now, I am the only licensed electrical engineer employed….How will I influence them to welcome new technologies for our distribution lines (we have a dilapidated lines already) where in fact they were busy in their “corruption activities”…. Just an advises sir ! Thank you!

  5. […] when applied with a signalling channel.In this form it is eminently suitable for application with high-speed auto- reclosing, for the protection of critical transmission lines. Principles of Distance RelaysSince the […]

  6. […] generation to consumers. The electricity delivery network functions via two primary networks: the transmission system and the distribution system. The transmission systems deliver electricity from power plants to […]

  7. […] 12.47 kV, which has a line-to-ground voltage of 7.2 kV.The dividing line between distribution and subtransmission is often gray. Some lines act as both subtransmission and distribution circuits. A […]

  8. omeralnahi
    Aug 02, 2012

    thank u

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