Transformers
Power transformers
MVA rated transformers for primary substations, generation connections and large industrial supplies, engineered to the project rather than chosen from a series.
At a glance
- Rating
- in MVAset by the connection and the load or generation
- Voltage regulation
- commonly an on load tap changerset by the network voltage range
- Cooling
- ONAN, ONAF or forced oil stagesset by the load profile
- Engineering
- designed per projectno standard catalogue value applies
- Standard
- IEC 60076 seriesIEEE C57.12.00 on North American specifications
Power transformers sit above the distribution range. They connect transmission and subtransmission networks to distribution, connect generation to the grid and supply the largest industrial loads. Each is engineered to its project, so the specification carries far more weight than for a distribution unit and the documents exchanged before an order are correspondingly longer.
Three matters decide feasibility early. Transport, because the weight and dimensions of the main tank decide the route and sometimes the site. Voltage regulation, because an on load tap changer adds cost and maintenance but lets the unit follow the network. And testing, because factory acceptance tests are normally witnessed and scheduled into the programme.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Rating | In MVA, with cooling stage ratings where applicable | The connection, the load or the generation |
| Voltage ratio | Transmission or subtransmission to distribution voltage | The networks on either side |
| Tap changer | On load or off circuit, with the tapping range | The voltage variation to be followed |
| Cooling | ONAN, ONAF, OFAF or equivalent stages | The load profile and ambient |
| Impedance | Specified per project | The fault level and the parallel operation |
| Transport limits | Maximum shipping weight and dimensions | The route to site |
| Testing | Routine, type and special tests, and witnessing | The specification and the owner's standard |
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 |
|---|---|
| IEC 60076-1 | Power transformers, general requirements |
| IEC 60076-7 | Loading guide for mineral oil immersed power transformers |
| Regulation (EU) No 548/2014, as amended | Above 3 150 kVA the regulation sets a minimum Peak Efficiency Index rather than absolute loss ceilings |
| IEEE C57.12.00 | General requirements for liquid immersed power transformers on North American specifications |
The standard that applies is set by the specification and the destination market. Editions change, so the edition cited in a specification is confirmed in the quotation.
Documents normally exchanged
| Document | What it evidences |
|---|---|
| Technical specification and data schedule | The owner's requirements and the manufacturer's guaranteed values |
| Outline and transport drawings | Dimensions, shipping weight and the arrangement on site |
| Test plan | Routine, type and special tests, and which are witnessed |
| Factory acceptance test report | Results of the tests carried out before dispatch |
| Transport and erection instructions | Handling, assembly and filling on site |
| Operating and maintenance manual | Operation, the tap changer and maintenance intervals |
What we need to quote accurately
| 01 | Rating in MVA and any cooling stage ratings |
| 02 | Voltage ratio, vector group and impedance requirement |
| 03 | Tap changer type and tapping range |
| 04 | The standard and the owner's technical specification |
| 05 | Site location and any known transport restriction |
| 06 | Testing and witnessing requirements |
| 07 | Required delivery date and acceptable condition |
Delivery and logistics
Power transformers normally travel as abnormal loads, often without their liquid and with fittings removed, and are assembled, filled and tested on site. The route survey is part of the project rather than an afterthought, and the shipping weight of the main tank is one of the first values to fix.
Delivery dates depend on manufacturer loading and are stated in each quotation for the specific unit offered. We do not publish a general lead time.
Related
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Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.