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Home / Technical Articles / Maintenance and troubleshooting guidelines for a typical high voltage switchgear

The need for maintenance

Like any other major component of the high voltage electrical network, a switchgear also needs maintenance schedules for trouble-free operation during its life cycle. No one should work on the system itself or on any plant controlled by it, without obtaining authorisation and work permit from the responsible person.

Maintenance and troubleshooting guidelines for a typical high voltage switchgear
Maintenance and troubleshooting guidelines for a typical high voltage switchgear (on photo: Performing testing of earthing a 66kV circuit prior to the sheath test; credit: Andrew)

Once such work has started, then it should not be possible for someone to re-connect the supply accidentally to the associated system or plant. Reconnection of supply should be done only after the work permit has been taken back by the concerned authority.

In order to ensure that this safety precaution is implemented, inter-lock and padlocking features are provided on the switching devices.

Contents:

  1. Maintenance Requirements
  2. Inspection Schedule
  3. Preparation Before Maintenance
  4. Maintenance Procedure
  5. Switchgear Spares
  6. Lubrication of Operating Mechanisms
  7. Troubleshooting Guide For Older Switchgears
    1. Outdoor Porcelain-clad Vacuum Circuit Breaker
    2. Indoor Metal-clad Vacuum Switchgear
    3. Spring-Charged Mechanism

1. Maintenance Requirements

Maintenance covers a wide range of activities, all of which are required to keep the switchgear in ready condition at all times to enable it perform its functions satisfactorily. The parts subjected to normal wear and aging need to be serviced for ensuring full reliability of the operations.

These parts may be mechanical components or electrical components.

The major mechanical components comprise  the mechanism and pole unit where mechanical wear and aging are caused by frequent operations. The electrical components are worn out due to arc interruption and heating. If oil or SF6 is used as an arc-quenching medium, then these also need replacement after a certain number of operations.

The interval at which the maintenance should be carried out depends upon the following factors:

  1. The number of short-circuit interruptions
  2. The switching frequency
  3. The actual service time

The actual conditions of use in terms of the frequency of operations, environment and severity of switching duty vary so much that it is impossible for the manufacturer to give detailed guidelines to the user concerning the frequency of maintenance.

A distinction needs to be made between the basic switching device with its moving parts, and the rest of the equipment which performs the supporting role of connection.

The latter components are likely to need periodic inspection and servicing only, to ensure that the equipment is free from dirt, dampness and deterioration, such as corrosion of metal work and contamination of insulation.

The maintenance of the basic switching unit should be the first priority! For vacuum interrupters, however, no such maintenance is needed.

Applicable standards draw attention to the importance of the methods for determining when various maintenance procedures need to be carried out.

As an example, with vacuum circuit breakers the most likely criterion that needs to be monitored occasionally is contact wear, and the timing of the opening operation.

The O&M manual of the manufacturer normally describes how to perform these operations and the acceptable levels of performance before putting the switchgear back into service. It also gives special instructions for the design of switchgear from maintenance point of view, apart from general switchgear practices.

For example, the proper method to release any stored energy in the closing mechanism before beginning an examination is spelt out.

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2. Inspection Schedule

The following guidelines must be included while formulating inspection schedules for switchgear:


Guideline #1

Once a year, a general visual inspection should be carried out and insulators wiped clean. More frequent checks are necessary if the breakers are exposed to a dust-laden atmosphere.


Guideline #2

The operating mechanism should be lubricated after two years or on completion of 2,000 make-break operation at lubrication points for a typical mechanism. After a specified number of operations, the mechanism should be overhauled.

The number of operations may vary with the type of breaker. Hence instructions given in the O&M manual of the switchgear should be followed in this regard.

Guideline #3

Constructions of the interruption unit are different for oil, SF6 or vacuum switchgear. Under normal service conditions, vacuum interrupters need no maintenance but in the case of other arc-interrupting media, special care needs to be taken as per the manufacturer’s instructions.


Guideliene #4

Vacuum interrupters must be replaced after the stipulated number of mechanical operations or when the contact erosion has reached its limit, whichever is earlier.

An inspection should be carried out after an examination or overhaul to ensure that the overall condition of the equipment has been restored after completion of the work. An operation check, or preferably a series of operation checks, must be carried out to establish that the correct performance has been achieved and that the equipment may safely be restored to service.

In the case of fully sealed vacuum circuit breakers, manufacturers do not normally recommend examination or overhaul of the pole unit during the economic life of the installation. Moreover, the latest trend is to use gas insulated switchgear (GIS), which is sealed for life. In such designs, carrying out of any maintenance by the staff of the user is not recommended.

In the unlikely event of GIS needing an overhaul, this task should be entrusted to the manufacturer.

Maintenance MUST be carried out by trained staff and guidelines provided in the O&M manual should be followed. Earthing before maintenance is very important.

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3. Preparation Before Maintenance

Safety features need to be planned before switchgear units are ordered. The requirement of locking off parts of the system (for carrying out maintenance work on the associated plant) should be finalised. Proper interlocking arrangements should be provided for this purpose.

All metal-enclosed switchgears are designed so that all live conductors are placed behind either metal enclosures or locked/bolted doors.

In order to ensure safe operation of the plant, a written set of rules governing these operating safety principles MUST be available. It is the responsibility of the plant-in-charge to frame such rules. Further, the rules must be understood by all who work in the environment, which necessitates a positive training programme.

The use of switchgear to gain access to the system for earthing conductors, for testing cables and other equipment, along with maintaining the switchgear itself is covered below.

The general safety rules mentioned above must also be followed in maintenance of the switchgear. The person responsible for authorising the action must be identified so that all those concerned know the co-ordinator for each procedure.

For example, when the system needs to be earthed at a point, all possible supply routes to that point should be locked off. The earthing should not open inadvertently till work on the earthed equipment is being carried out.

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4. Maintenance Procedure

There are many standards on the subject pertaining to different voltage levels of switchgear, which normally defines four separate aspects of maintenance, with each new stage based on the preceding one,

  1. Inspection,
  2. Servicing,
  3. Examination and
  4. Overhaul.

These are dealt with in detail below:


4.1 Inspection

This is a maintenance action, which calls for a careful scrutiny of a switchgear component. The inspection is carried out without dismantling the component from its assembly.

The inspection should be carried out by using all the available diagnostic methods for detecting potential malfunction/failure. It may include an operational check.

4.2 Servicing

Servicing implies work that is carried out for ensuring that the equipment is kept in an acceptable condition. It does not involve any dismantling, and is typically limited to cleaning, lubrication and adjustments as specified in the operation and maintenance (O&M) instructions of the switchgear.


4.3 Examination

This is an inspection carried out with partial dismantling, as required, supplemented by means such as measurement and non-destructive tests in order to arrive at a reliable conclusion about the condition of a particular switchgear component.

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Edvard Csanyi - Author at EEP-Electrical Engineering Portal

Edvard Csanyi

Hi, I'm an electrical engineer, programmer and founder of EEP - Electrical Engineering Portal. I worked twelve years at Schneider Electric in the position of technical support for low- and medium-voltage projects and the design of busbar trunking systems.

I'm highly specialized in the design of LV/MV switchgear and low-voltage, high-power busbar trunking (<6300A) in substations, commercial buildings and industry facilities. I'm also a professional in AutoCAD programming.

Profile: Edvard Csanyi

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