Package Substation Sizing and Configuration Guide

What a package substation actually contains

A package substation is a factory-assembled enclosure containing a transformer, the medium-voltage incoming section, the low-voltage outgoing section and the associated protection, metering and control, all tested together before it leaves the factory.

That structure is the whole point and also the whole constraint. The substation becomes a single item on the site programme, with a single delivery and a single commissioning sequence instead of a dozen separate items — but every dimension, weight and connection point is fixed before the site is surveyed.

The transformer rating decision

The rating is normally set by the connected load and the diversity factor, with a check on the starting currents of the largest motor on the busbar, because a large motor started across the busbar can pull the voltage down far enough to trip the incomer.

Where two transformers are used for redundancy, the arrangement matters as much as the rating: whether they operate in parallel, in standby, or as a duty/standby pair with an automatic transfer. That decision changes the switchgear inside the package.

The medium-voltage arrangement

The incoming arrangement can be a single cable termination, a ring main unit with two or three ways, or a switch-and-fuse combination. The choice is a network decision: if the package sits on a ringed distribution system, an RMU section inside the package is what allows the section to be isolated without cutting the load.

For a radial feed, a single incomer with a fuse or a breaker is sufficient and cheaper.

The low-voltage side

The low-voltage outgoing arrangement carries the outgoing feeders, the metering and the panel lighting and auxiliary supply. Where the package feeds a distribution board rather than final circuits, the LV section may be a single outgoing busbar coupling point rather than a full distribution assembly.

The panel arrangement, the outgoing configuration and the reserved space have to be confirmed against the site requirements at quotation stage, because adding them later means opening the package.

Site interface — the part that causes delay

The package is delivered as a finished unit, so the site has to be ready for it. The foundation, the access route for the transformer and the crane, the cable entry positions, the earthing arrangement and the enclosure clearance around the unit all have to be agreed before delivery.

We supply the foundation drawing and the general arrangement drawing with the equipment, and the envelope dimensions and weight of the finished package are given in the offer so that the access route can be checked against the actual site conditions rather than against a catalogue picture.

Environmental and protection requirements

The outdoor protection class, the canopy arrangement and the ventilation strategy follow from the site climate. In a high-temperature or high-dust environment the ventilation and filter arrangement matter as much as the protection class, because a sealed-to-specification unit can still overheat if the air path is restricted.

The earthing arrangement, the neutral treatment and the fence and access arrangement should be settled with the utility and the design institute before manufacture.