12500KVA Transformer

Baoding Zhongyi Electric Corporation is one of the leading manufacturers and suppliers of 12500kva transformer in China, featured by quality products and good price. Please rest assured to buy advanced 12500kva transformer for sale here from our factory.

A 12500 kVA transformer - the same machine most project specifications list as 12.5 MVA - is the 33/11 kV step-down unit that feeds a whole plant or a group of substations, not a single building. We build it to order at our factory in Baoding, China, as an oil-immersed, three-phase transformer with ONAN/ONAF/ODAF cooling and the protection set that this rating class needs. This page sets out how the unit is designed, what protects it, how it is tested before it leaves the works, and what you receive with it.

Where a 12.5 MVA unit is normally used:
At 33/11 kV this rating class usually sits at the interface between a utility's 33 kV network and an 11 kV distribution system. Typical positions are industrial substations for steel, cement, mining and chemical plants; captive power plants and cogeneration sites; large industrial parks and logistics hubs; and railway or metro traction substations. Two practical points come up again and again at this size: the unit often has to run in parallel with transformers already on site, which fixes its impedance and vector group, and it usually has to fit an existing bay, so the footprint and cable or busbar positions matter as much as the rating.

Three ratings on one nameplate: ONAN, ONAF and ODAF
This transformer carries three capacity stages rather than one, and that is usually what makes it economical:

- ONAN - oil natural, air natural. The base rating. Radiators work by convection, no fans or pumps running.
- ONAF - the same tank with fans on the radiator bank. Continuous output rises, typically by a quarter to a third.
- ODAF - oil pumps plus forced air, for the highest stage, normally reserved for peak load or a failed parallel unit.
Stage control comes from winding temperature and load current through the cooling control cabinet, so the unit never moves up a stage before it needs to. The exact figures for each stage are fixed in your rated-power schedule and printed on the nameplate.

Core technical data
The values below are the design envelope for this rating. Impedance, losses, dimensions, oil quantity and weight are calculated for your system and confirmed on the guaranteed technical particulars and general arrangement drawing issued with the quotation.

Rated power: 12500 kVA (12.5 MVA), three-phase
Primary voltage: 33 kV (36 kV class insulation)
Secondary voltage: 11 kV (12 kV class insulation)
Frequency: 50 / 60 Hz
Cooling: ONAN / ONAF / ODAF
Vector group: to specification (commonly Dyn11, or YNd11 when the earthing and parallel-operation scheme requires it)
Impedance: set to your system study - typically 10 to 12% for this rating class, and matched to any unit it will run in parallel with
Taps: off-circuit ±2 x 2.5% as standard; on-load tap changer available where voltage regulation is needed
Insulation levels: standard IEC values for the 36 kV and 12 kV classes (HV 170 kVp impulse / 70 kV AC; LV 75 kVp / 28 kV AC)
Temperature rise: designed inside the IEC 60076-2 limits at every cooling stage, verified in the temperature-rise type test
Standards: IEC 60076, ISO 9001, CE
Efficiency: above 99% at the design load point, per the loss budget agreed at order

Drawings and documents you receive:
Approval drawings come first: general arrangement with footprint, oil quantity, transport weight and cable or busbar terminal positions, so your civil and erection planning can start before the tank is fabricated. On completion you receive the routine test report, guaranteed technical particulars, nameplate data per IEC 60076-1, the operation and maintenance manual, an accessory list and the export packing list. Where your contract requires it, third-party inspection certificates are issued with the same set.
 

Testing before dispatch:
Every 12500 kVA transformer is routine tested to IEC 60076-1 and 60076-3 in our works. The routine set covers winding resistance, voltage ratio and vector group, short-circuit impedance and load loss, no-load loss and current, insulation resistance, and the applied and induced AC dielectric tests. Insulating oil is tested for dielectric strength and moisture content, and the tank is pressure tested and checked for oil tightness before filling. Type tests - full lightning impulse and temperature rise - are carried out on the design, and the reports can be supplied with the unit. On a project of this size most buyers witness the routine tests themselves, and we welcome that: tell us at order stage if you want your engineer or a nominated inspector such as SGS, BV or Intertek present, and we will plan it into the test schedule. Noise measurement and special tests such as harmonics or zero-sequence impedance are quoted separately when the specification calls for them

Product Certification:
Our 12500KVA Transformers are certified to meet industry standards, including IEC, ANSI, and NEMA specifications. We offer a range of certifications and approvals, including ISO 9001, CE, and UL, to provide our customers with the assurance of quality and safety.

Transport, site readiness and lead time:
For sea freight a unit of this size is normally shipped oil-filled with an impact recorder fitted, or nitrogen-filled with oil supplied separately, depending on the route and the time it will spend in transit. Accessories travel in separate crates with their own packing list, and transport brackets or tie rods hold the active part against the loads of shipping rather than the loads of service. On site the transformer should go into covered or well-ventilated storage with the silica gel breather active; if the unit arrives oil-filled we normally advise a settling period and oil dielectric test before energisation, and we provide commissioning guidance so your electrical contractor knows the sequence. Lead time depends on whether the tap changer is off-circuit or on-load and on the inspection requirements, so we quote a date against your actual specification rather than a generic figure.

Frequently asked questions

Q: Is 12500 kVA the same as 12.5 MVA?
A: Yes. One MVA is 1000 kVA, so 12500 kVA and 12.5 MVA describe the same rating. Specifications and load studies tend to use MVA while nameplates, test reports and customs documents often use kVA - expect to see both on your paperwork, and make sure they agree with the guaranteed technical particulars.

Q: How much more power can the transformer deliver with fans or pumps running?
A: Each cooling stage adds continuous capacity rather than a short-term overload. ONAF typically lifts the rating by around a quarter to a third, with ODAF higher again. The governing figures are the stage ratings in your rated-power schedule, and the cooling control cabinet switches stages from winding temperature so the unit does not run on forced cooling unnecessarily.

Q: Which vector group and impedance should a 33/11 kV unit have?
A: Dyn11 is the common choice for 33/11 kV distribution, with YNd11 where your earthing arrangement and protection scheme call for it. Impedance is not a free choice: it has to match any transformer the unit will operate in parallel with, and it affects fault levels, so we set it from your system study and state it on the guaranteed technical particulars.

Q: Do I need an on-load tap changer?
A: If the 33 kV supply wanders beyond the range an off-circuit tap can cover, or if you need to regulate the 11 kV bus while the transformer is energised, choose an OLTC. For sites with a stable supply, off-circuit ±2 x 2.5% taps changed at commissioning are the simpler and cheaper answer. We supply both - see the on-load tap changer distribution transformer for that configuration.

Q: What tests and documents come with the unit?
A: Routine tests to IEC 60076 on every unit - ratio and vector group, winding resistance, impedance and load loss, no-load loss and current, insulation resistance, applied and induced dielectric tests, plus oil dielectric strength and moisture and a tank pressure test. Type test reports for impulse and temperature rise are available for the design. With the transformer you receive the test report, approval and final drawings, nameplate data, O&M manual and packing list; third-party certificates if your contract requires them.

Q: Can the same unit be built for a 60 Hz network?
A: Yes. Core flux and winding design are adjusted for 60 Hz, and the tap range is set to the voltages of your network. If you also need a different secondary voltage - 11 kV, 10.5 kV or 6.6 kV - tell us at enquiry stage; we will quote the closest standard design or a purpose-built one, and where a nearby rating suits your load better we will say so rather than oversizing you. For a comparable MV application at a slightly smaller rating, see the 10 MVA 33/11 kV transformer.

If you are specifying a 12500 kVA transformer, send us the primary and secondary voltages, the impedance requirement or parallel units already on site, the cooling stages you need and the site conditions. You will get the general arrangement drawing, the guaranteed technical particulars and a realistic lead time you can plan procurement around.

Hot Tags: 12500kva transformer, China, suppliers, manufacturers, factory, buy, price, for sale, transformer pcb mounting, 2500kva transformer, 1000 kva transformer, 2500 kva transformer, 10 mva 33 11kv transformer, transformer 500 kva