Transformer Substation Maintenance: What, How Often and Who Is Qualified to Perform It

A transformer substation is a piece of equipment that rewards routine.
When it is maintained regularly, it can operate for decades without drama and without attracting attention. When it is neglected, it makes its presence known at the worst possible moment, through an outage that brings the entire facility to a standstill.

Ownership of a transformer substation therefore does not end when construction is completed. That is when the responsibility actually begins.

The owner of an electrical power installation is required to keep it in a safe and operational condition. In practice, this means carrying out periodic inspections and testing in accordance with applicable regulations and equipment manufacturers’ instructions, maintaining proper records and correcting any identified deficiencies.
This is not merely an administrative formality. Inspection and testing records are among the first documents requested after any incident, both by insurance companies and by regulatory authorities.
A regular maintenance programme covers several areas.

Visual inspections should be carried out at shorter intervals and should include the condition of the room, signs of moisture, unusual noise or smells, and instrument readings.

Thermal imaging under load can identify loose connections and overheating before they develop into failures.
For oil-immersed transformers, the condition of the oil should be monitored because the oil can reveal the entire operating history of the transformer.

Protection relays should be tested and trip functions verified, because a protection system that has never been tested is one whose operation is merely assumed.

Grounding resistance must also be measured.

Cleaning, tightening of electrical connections and servicing of circuit-breaker mechanisms should be carried out at longer intervals, in accordance with the manufacturer’s recommendations.
Work on medium-voltage installations is not a task for a general maintenance worker, regardless of how capable or resourceful that person may be.

Inspections and testing must be performed by properly trained and authorised personnel, using the prescribed equipment and following procedures applicable to work on electrical power installations.
For most companies, this effectively means entering into a maintenance agreement with a specialised service provider. The agreement should clearly define the scope of work, inspection intervals and response times for emergency interventions.

The cost of such an agreement is generally lower than the cost of a single hour of production downtime.
Failure statistics for transformer substations are remarkably consistent. A large proportion of outages are caused by issues that regular inspections would have detected: a loose connection, deteriorated insulation or protection settings that have been incorrect since commissioning.

Annual preventive maintenance typically costs only a fraction of the value of the equipment it protects, while transformer failure can result in weeks or even months of waiting for a replacement.

There are few areas in industry where the relationship between the amount invested and the value protected is so clear, and yet so frequently ignored.

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One Large Transformer or Two Smaller Ones

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Connecting a facility to the medium-voltage grid is a procedure with clearly defined steps, but there are also enough points where a project can lose several months if those steps are carried out in the wrong order.

Dry-Type or Oil-Immersed Transformer

When selecting a power transformer, one question arises in almost every project: dry-type or oil-immersed?

Your Own Transformer Substation or a Connection Through a Third-Party Substation

Many companies operate for years connected to the low-voltage network through a distribution transformer substation. They only begin considering their own substation when the distribution system operator informs them that no additional capacity is available for a planned expansion.