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Monthly Archives: October 2014

  • Oil Circuit Breaker Contacts

  • The Importance of Switchgear Maintenance

    Oil circuit breakers have been in use since the turn of the 20th century.  Although new types of circuit breakers have been developed, due to cost and other factors there are still tens of thousands operation today with many being in services for 50 years or more!

    Oil circuit breakers work by extinguishing the arc created, interrupting the fault current by drawing oil between the gap created by the male contact as it moves away from the fixed female contact. The process of the oil rushing through the circuit breaker turbulator extinguishes the arc. This is done typically within 50 to 120 ms but still results in degrading the oil by breaking it down and the burning of the contact material. Without fault monitoring equipment the circuit breaker will require urgent after fault/ post fault maintenance after around four operations.

    Regular switchgear maintenance is extremely important.  Over time insulating oil will deteriorate. When first filled you would have a breakdown voltage compliant with BS148 but after time this will fall and eventually fail if not replaced. This is mainly due to the oil being contaminated with the carbon created with the extinguishing of each fault.

    The main components for interrupting an arc are the fixed female / moving male contacts and a turbulator.  Once a fault current is interrupted the oil circuit breaker contacts are submitted to extreme temperatures.  This will melt and damage the contacts making them inefficient or even useless at interrupting a fault current.  Once the contact is damaged it will be less able to carry load current let alone interrupting fault current. This can cause catastrophic damage to the switchgear and surrounding area putting human life in danger also.

    Within the UK, Ofgem has put pricing control in place which begins on 1st of April 2015 until 31st March 2023.  Fourteen Distribution Network Operators are part of the RIIO-ED1 (Revenue=Incentives + Innovation + Outputs) price control model.

    So what importance does this have over the switchgear maintenance?  Well suppliers now have price controls in place which means tightening the purse strings!  This gives operators three basic choices when it comes to maintenance.

    • Overhaul and refurbish existing equipment
    • Retrofit and upgrade equipment
    • Replace with new equipment

    Due to the sheer number of oil circuit breakers in operation it would not be cost effective to replace them all.  So a strict policy of maintenance is adhered to.  This involves changing the oil and cleaning or replacing of the oil circuit breaker contacts.  Replacing the oil circuit breaker contacts is more time and cost effective.  As the retrofitting or replacement of switchgear is a huge logistical task meaning costs can be extremely high before taking in to account the cost of the switchgear itself.

    Alcomet offers next day deliveries on many stock items kept in our central warehouse in the West Midlands. The large range of original manufacturers fixed female and moving male contacts covers an extensive range of switchgear manufacturers.  For specials we can even reverse engineer parts to original customer requirements in a short time frame, as we understand how super critical these contacts are.

    In need of oil circuit breaker contacts – then contact Alcomet.

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