DDG Heating Transformer Low Voltage High Current

The DDG is a dry-type transformer built for one job: delivering very high current at very low voltage. Where a distribution transformer steps voltage up and current down, the DDG does the opposite, taking a 220V or 380V supply and producing the tens or hundreds of volts at hundreds or thousands of amps that resistance heating, metal melting and temperature rise testing need. Everything about the construction follows from that. The core uses high-permeability silicon steel to carry the high flux density. The low-voltage winding is not wire at all but solid copper bar, thick copper plate, or several large copper tubes in parallel, because at these currents anything thinner would simply melt. And cooling is active: water-cooled tubes or forced air, because a unit of this kind generates serious heat by design. We build DDG units from 5kVA to 100kVA in Yueqing, and most of what we ship goes to test laboratories and switchgear manufacturers running temperature rise and protection characteristic tests.

Key Specifications

What You Get

• DDG heating transformer built to your voltage, current and duty requirement
• Heavy-section copper secondary – bar, plate or parallel tubes, not wire
• Water-cooled or forced-air cooling sized for continuous duty at your rating
• Reinforced high-temperature insulation system
• Heavy-duty terminal pads ready for busbar or cable lug connection
• Full test report including dielectric strength and temperature rise
• 12-month replacement-first warranty

Why Choose This Model

You cannot build a high-current low-voltage transformer the way you build an ordinary one, and the DDG is engineered around that difference. At a few thousand amps, the resistance of the winding itself becomes the dominant design problem – the secondary has to be heavy copper section with generous cross-section and short current paths, or the transformer heats itself rather than the load. The magnetic design is reinforced too, because high flux density in a standard core would drive it into saturation and the waveform would collapse. And the insulation has to survive not just voltage but sustained temperature, which is why we use a reinforced high-temperature system and cool the unit actively rather than relying on natural convection. The main application we ship into is electrical testing. Switchgear manufacturers run temperature rise tests on circuit breakers, contactors, thermal relays and switchgear assemblies, and those tests require holding a precise high current for hours while logging the temperature. A DDG is what supplies that current, because it can hold the load continuously and be adjusted across its range. The other applications are resistance heating and induction heating assist, and small-scale metal melting, where the same combination of low voltage and very high current does the work.

How to Size It

Start from the test or process current and the voltage needed to push it through the load resistance – that product is your kVA. Then decide the duty: a unit that holds full current continuously is a different machine from one that runs in short bursts, and if you specify continuous you need the cooling to match. Confirm the cooling water supply if you are going water-cooled: flow rate and inlet temperature both matter, and a low flow rate will trip the unit on thermal protection regardless of its kVA rating. Tell us the load resistance or the required test current, the duty cycle, and what cooling services you have available, and we will specify the unit.

How It Works

A heating transformer is a transformer optimised for the opposite of the usual job. A distribution transformer steps voltage up and current down so power can be carried a long distance over thin conductors. The DDG steps voltage down and current up, because the load is a short length of resistance – a heating element, a test busbar, a circuit breaker under test – that needs hundreds or thousands of amps at only a few volts. Everything in the construction follows from the current. Winding resistance becomes the dominant loss, so the secondary is heavy copper section: solid bar, thick plate, or several large copper tubes in parallel, chosen for cross-section and short current paths rather than for turn count. The core has to carry a high flux density without saturating, so it uses high-permeability steel with a reinforced magnetic design. And because the losses are concentrated in a small volume, cooling is a design input rather than an accessory: water-cooled tubes carry heat away directly from the winding, or forced air moves it out of the enclosure. Get any one of those three wrong and the transformer heats itself instead of the load.

Typical Applications

• Temperature rise testing of circuit breakers and switchgear
• Protection characteristic testing of thermal relays and contactors
• Continuous load testing and electrical parameter measurement
• Current transformer testing
• Industrial resistance heating processes
• Induction heating assist and small-scale metal melting
• Research and development test benches

Testing Before Shipment

Every DDG is tested before it ships, and on a high-current transformer the tests matter more than usual. We verify the turns ratio, measure the output voltage and current into a calibrated load bank, check insulation resistance, and carry out dielectric strength testing at the level appropriate to the rating. Critically, we run a temperature rise test: the unit is held at rated output until the winding and core temperatures stabilise, and we confirm they settle inside the design limit. On water-cooled units we confirm flow rate and inlet and outlet temperatures under that same load, because a unit that tests correctly in the workshop will still trip on thermal protection on site if the cooling water supply is marginal. The full report ships with the order. If your laboratory or your customer requires witnessed testing or specific documentation, agree it with us at quotation stage.

Ordering, Samples and Shipping

DDG units from 5kVA to 100kVA are built to order with a 10 pcs minimum and a 15-25 day lead time. To specify one we need the required output current, the load resistance or the output voltage you need, the duty cycle, and what cooling services you have – water flow rate and inlet temperature, or available forced air. The duty cycle changes the design more than anything else: a unit that holds full current for eight hours is a different machine from one that runs in thirty-second bursts, and specifying continuous duty when you need it is far cheaper than discovering the limitation after delivery. If you are building a test bench, tell us what you are testing and to which standard, and we will work back from the test requirement to the transformer. We can also supply the matching current shunt, busbar kit or load bank if you want the whole test set as one package. Samples are paid by T/T before production. Standard shipping is FOB Ningbo or Shanghai.

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