Transformers
Pad mounted transformers
Ground level, tamper resistant transformers with their connections in a lockable cabinet, used on North American style underground distribution networks.
At a glance
- Standard
- IEEE C57.12.34three phase, compartmental, self cooled
- Scope of that standard
- 10 MVA and smaller, 60 Hzhigh voltage up to 34.5 kV, low voltage up to 15 kV
- Feed
- loop or radialset by the network design
- Front
- commonly dead frontlive front on some older networks
- Placement
- outdoors on a pad
A pad mounted transformer sits on a concrete pad at ground level, with its high and low voltage connections behind locked doors in a compartmental cabinet. It is built to be installed in public places without a separate enclosure, which is why it is the standard arrangement for underground residential and commercial distribution on North American style networks.
The specification is set largely by the network the unit joins. Loop feed or radial feed, the high voltage connection system, the fusing and the switching arrangement all have to match what the utility or the site network already uses, so an existing unit's nameplate and the network operator's standard are the most useful documents to send.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Rating | Three phase, in kVA | The load, within the scope of the standard |
| Feed arrangement | Loop feed or radial feed | The network design |
| High voltage front | Dead front with separable connectors, or live front | The network's existing connection system |
| Switching | Internal load break switching where specified | How the network is operated |
| Fusing | Internal fuses, with current limiting fuses where specified | The protection philosophy of the network |
| Voltage | Primary and secondary to the network standard | The utility or site network |
| Insulating liquid | Mineral oil or ester | Environmental and fire requirements |
Typical options are the ones buyers most often specify. They are not a list of what is available, which is confirmed per enquiry.
Applicable standards
| Standard | What it covers |
|---|---|
| IEEE C57.12.34 | Pad mounted, compartmental type, self cooled, three phase distribution transformers, 10 MVA and smaller, at 60 Hz, with high voltage up to 34.5 kV and low voltage up to 15 kV |
| IEEE C57.12.00 | General requirements for liquid immersed distribution, power and regulating transformers |
North American destinations also apply their own minimum efficiency rules for distribution transformers. The applicable rule is confirmed for the destination in each quotation.
Documents normally requested
| Document | What it evidences | When it is normally provided |
|---|---|---|
| Technical datasheet | Rating, voltages, losses, impedance, dimensions and weight of the unit offered | With the quotation |
| Outline drawing | Footprint, lifting points and cable connection positions | With the quotation or at order |
| Routine test report | The individual unit's tests to its standard | With the delivered unit |
| Type test report | The design has passed the type tests of its standard | On request, where a type test exists for the design |
| Rating plate details | The declared values carried on the unit itself | With the delivered unit |
| Declaration of conformity | Conformity with the legislation of the destination market | Where the destination market requires one |
| Operating and maintenance manual | Installation, operation and maintenance instructions | With the delivered unit |
Which documents apply depends on the destination market, the standard and the manufacturer. Documents are confirmed in the quotation for the specific unit offered.
What we need to quote accurately
| 01 | Rated power in kVA, or the connected load and the largest motor if the rating is not fixed yet |
| 02 | Primary and secondary voltage, and the tapping range if the network operator sets one |
| 03 | Loop or radial feed, dead front or live front, and the connection system the network uses |
| 04 | Switching and fusing requirements |
| 05 | The nameplate or model of an existing unit, where this is a replacement |
| 06 | The standard and the loss requirement the destination market applies |
| 07 | Quantity, destination and the date the equipment has to be on site |
| 08 | Whether surplus or refurbished units are acceptable, or new only |
Delivery and logistics
Distribution equipment is heavy, and a delivery date is only real once the site is ready for it. The dimensions and weight of the unit offered decide the vehicle, the lifting equipment and the route to the foundation, and they come from the manufacturer's drawing rather than from the rating.
Liquid immersed transformers are usually shipped filled, which affects transport rules and the handling on arrival. Anything crossing a border also carries customs documentation, and where the destination applies its own conformity or energy efficiency rules the paperwork has to match that market rather than the country of manufacture.
Lead times vary widely with rating, specification and manufacturer loading. We state a delivery basis in each quotation for the specific unit offered and do not publish a general lead time we cannot hold.
Common questions
Can a pad mounted transformer be supplied to an IEC market?
Pad mounted units are designed around North American practice. On IEC networks the equivalent function is usually served by a compact substation. A requirement for either can be submitted, and we confirm which fits the destination.
Related
Request a quote for this equipment
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.