Pad Mounted Transformer Substation

As a large manufacturer of electrical devices, Cotenele has provided and exported lots of Pad Mounted Transformer Substation for customers both domestically and internationally. The pad-mounted transformer, whose full name is American-style box-type substation, is a distribution device that integrates the transformer body, medium-voltage load break switch, fuses, and associated auxiliary equipment into a single unit. Its main component is essentially the transformer rather than a substation, it is not a simple combination of a transformer with separate medium-and low-voltage switchgear, but rather an integrated electrical device developed on the basis of a transformer. Since its introduction, after years of promotion, it has been widely used in various settings such as urban power grids, residential communities, commercial centres, and industrial and mining enterprises.

Model and Meanings

Technical Parameters

Operating Conditions

Working Principle

The operating principle is based on Faraday's law of electromagnetic induction: the transformer steps down a medium voltage (e.g., 10 kV) to a low voltage (e.g., 0.4 kV) for end-user consumption.

The functional sequence is as follows:

1. Medium-voltage side: Power enters via medium-voltage cables terminated with elbow connectors (plug‑in type). The load‑break switch controls the on/off status, while a dual-fuse system (an insertion fuse + a backup current-limiting fuse) provides overcurrent and short-circuit protection.

2. Transformer tank: The step-down voltage conversion (e.g., 10 kV → 0.4 kV) takes place inside the oil-filled tank. The transformer oil serves both as electrical insulation and as a cooling medium.

3. Low-voltage side: The stepped‑down low-voltage power is distributed through the low-voltage circuit breaker to various outgoing feeder circuits for end-users.

The American-style pad-mount transformer can be used in either loop (ring) network systems (dual supply) or terminal (radial) systems (single supply), with easy changeover between the two modes.

Internal Construction

The unit is divided into front and rear sections:

Front section - HV/LV operation compartment

- HV and LV terminals

- Load‑break switch

- Off‑circuit tap-changer

- Insertion fuse (bayonet type, dual-element-sensitive to both temperature and current)

- Pressure relief valve, oil thermometer, oil level gauge

- Oil filling port and drain valve

Rear section - Sealed oil tank and cooling fins

- Transformer windings and core

- HV load‑break switch and ring‑network switch

- Protective fuses

- Transformer oil (insulation and cooling medium)

The American-style design eliminates the conventional oil conservator (expansion tank); the tank and cooling radiators are directly exposed to the air. All live parts are enclosed within the tank — there are no exposed energized components.

Based on operation method, the unit can be classified as with a walk-in aisle (operators work inside the enclosure) or without a walk‑in aisle (operators work outside the enclosure).

Application Scenarios

American-style pad-mounted transformers are widely used in:

1. Residential communities: urban housing estates

2. Commercial centres: shopping malls, office buildings

3. Industrial parks: factories and enterprises

4. Urban infrastructure: street lighting, road control systems

5. Transportation facilities: airports, light rail stations, harbours, railways

6. Public facilities: hospitals, schools

7. Renewable energy: step-up transformers for wind farms and solar PV plants

8. Temporary power: construction sites

9. High-rise buildings: internal distribution

Installation Diagram

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