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Home / Technical Articles / Learn how to troubleshoot the operation of distribution substations (problematic breakdowns)

Troubleshooting techniques

The distribution substation is one of the most important yet arguably the most troublesome section of the power system. Prolonged operation and frequent switching make distribution substations more prone to breakdowns and failures. While the part of preventive maintenance is essential to avoid these breakdowns, once they occur, the operators and engineers are under immense pressure to rectify the underlying issue and resume the power supply as soon as possible.

Troubleshooting operation of distribution substation
Troubleshooting operation of distribution substation (on photo: Insulation test of VCB terminals)

In this article, we will primarily focus on the most common and the most problematic breakdowns in a typical power distribution substation and measures to troubleshoot them.

Preventive maintenance is an equally important aspect that helps to minimize the possibility of breakdowns or troubles.

In this article, we keep our focus on the troubleshooting and rectifying techniques of distribution substations that are essential for prompt power resumption after abrupt interruption or fault. In reality, each component within the substation play their part for interrupted power supply and problem in any of them can easily turn catastrophic.

The article will be as extensive as possible in that regard.

Table of Contents:

  1. The principle of troubleshooting
  2. Troubleshooting the disturbances in circuit breakers
    1. Probable troubles in LV CBs and respective remedy
      1. Problem with closing and false tripping
      2. Problems with circuit breaking/opening
    2. Probable troubles in VCB and other MV equipment
        1. Brief procedure for general troubleshooting the VCBs for closing malfunction
      1. Brief procedure for general troubleshooting the VCBs for tripping malfunction
    3. Special mentions:
      1. Electrical treeing
      2. Problems in control or wiring diagrams
  3. Conclusion: Problems with troubleshooting and getting past them

1. The principle of troubleshooting

Simply put, troubleshooting is 80% diagnosis and 20% remedy. It is a process that includes a rigorous search for any abnormality that caused the disruption and remedial measures to make them normal or reinstate in the operating state. The electrical system works in a well-planned hierarchy of voltage and insulation levels.

Most of the problems in the electrical system are caused because of the compromised insulation level.

Apart from that, there are other various internal and external factors recorded over the years as the most common faults/ source for the power supply disturbance. Yet, some succeed to occur completely out of the blue and surprise everyone, including the trained technicians who sweat themselves heavily to diagnosis the fault.

Breakdown troubleshooting requires swift identifying and fixing of the issue that broke the equipment, most possibly interrupting the power supply. This requires a series of inspections and tests which shall be described further in this article.

On contrary, preventive troubleshooting is more about finding the actual cause of the occasional malfunctions, niggles, or abnormalities in the system in compliance with the manuals and schematics. This is practiced when the equipment is not broke completely but it might be problematic in near future with some occasional malfunctioning without a specific reason.

Figure 1 – Preventive troubleshooting of an LV panel

Preventive troubleshooting of an LV panel
Figure 1 – Preventive troubleshooting of an LV panel

Go back to the Contents Table ↑


2. Troubleshooting the disturbances in circuit breakers

Circuit breakers are arguably the most important part of the protection system in any distribution substation. While the VCBs are in abundance in the category of MV/LV, ACBs sit firmly at the top of the protection system of the LV power distribution substation.

Tripping/closing coils, trip circuit supervisions, vacuum interrupters, spring charging mechanisms, secondary contacts, master trip relay, protection relays, etc. are major components of circuit breakers in the MV/LV distribution substation.

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Bishal Lamichhane

Electrical Engineer (B.E Electrical, M. Sc Engineering) with specialization in energy systems planning. Actively involved in design and supervision of LV/MV substations, power supply augmentations and electrification for utilities and bulk consumers like airports and commercial entities. An enthusiast and scholar of power systems analysis.

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