Mobile transformers and mobile substations

Emergency and temporary use

The most common reason to need a mobile unit is an in-service failure. A permanent replacement may be years away through a new order, so a mobile unit carries load in the meantime. Other uses include:

• Storm, fire or physical damage to a substation.
• Planned maintenance or replacement of an existing transformer.
• Temporary service for construction, commissioning or a short-term load.
• Restoring a critical facility, such as a military installation or hospital feed, while a permanent fix is arranged.

See what to do when a large transformer fails for the wider picture.

Ratings and practical limits

Mobile units are designed to fit within road weight and size limits, so they are generally smaller in rating than the largest permanent transformers. They are often built with multiple voltage taps so one unit can serve several substations. In exchange, they may run hotter, use forced cooling such as ONAF or ODAF to reach their rating, and have a shorter intended service life than a permanent unit.

For a large transmission transformer, a mobile unit may only carry part of the load. Utilities sometimes combine a mobile unit with load transfers to nearby substations.

What to check

• High-voltage and low-voltage ratings, and the available taps.
• MVA rating at each cooling stage, and how long it can be carried.
• Impedance and vector group, so it can operate with your system and protection settings.
• Trailer condition, axle configuration and road permits for the route to your site.
• Site access, pad or ground preparation, and connection points.
• Test records and recent DGA results, as for any transformer.
• Whether the unit is offered for sale, lease or short-term rental.

How we find them

The supply of mobile units is small and spread out. Some are owned by utilities as shared spares, some by rental and service companies, and some by manufacturers. Units sometimes become available when an owner retires or replaces part of a fleet.

We run the same search process on a compressed schedule: build a list of likely owners, contact them in parallel, and check documentation on every possible match. At the same time we look for a permanent replacement, either a surplus unit or a new order, so the temporary fix has a planned end.

Planning ahead

Utilities that review their most exposed substations before a failure are in a much better position. Knowing which mobile units would work, where they are, and how they would reach the site can cut days from a response. We can help with that review as part of a spares planning engagement. You can start a search whether the need is urgent or not.