An electrochemical plant converts DC current into a chemical reaction, and the rectifier transformer is what supplies that current. When it stops, the process stops, and on a chlor-alkali or electrolysis line that is measured in lost production rather than lost convenience.
What the process asks of the transformer
Electrochemical cells operate at low voltage and very high current. The current does the work directly, so the transformer secondary has to deliver it continuously, at or near full load, for as long as the plant is running.
Three characteristics follow from that: a high current secondary with the conductor and busbar design to match, cooling sized for continuous duty, and harmonic losses calculated against the actual rectifier spectrum rather than a sinusoidal approximation.
Harmonics in electrochemical service
Rectifier loads draw non-sinusoidal current, and the harmonic content grows with the delay angle on thyristor-controlled units. Those harmonic components produce additional eddy losses in the windings and in structural steel, so a transformer sized on RMS current alone will run hotter than predicted.
Multi-pulse configurations reduce the harmonic content reaching the supply, and the transformer is where that is implemented. Twelve-pulse arrangements, using star and delta secondaries feeding two bridges, cancel the fifth and seventh harmonics and are common in this sector. Where the supply connection imposes tighter limits, twenty-four pulse arrangements are used.
Continuous duty and what it means for cooling
Unlike a furnace transformer, an electrochemical rectifier transformer usually runs at a steady high load rather than a cyclic one. That makes cooling easier to size, but it removes the recovery periods that a cyclic duty provides, so any cooling shortfall accumulates instead of averaging out.
Forced oil circulation with forced air over the coolers covers most medium and large units. Forced oil with water cooling is used where the heat load exceeds what air can remove, and most electrochemical plants already have a cooling water system that makes this straightforward.
Cooler redundancy is worth specifying. Two coolers each rated for the full losses let the plant continue at full load with one cooler or pump out of service, and on a continuously running line the cost of an unplanned stop is far greater than the redundant equipment.
Corrosion
In chlor-alkali service the transformer sits in an atmosphere containing chlorine and alkaline mist. Coolers, radiators, fins and tube materials need heavy-duty coating and corrosion-resistant materials, and this applies to the air side of a forced-air cooler and to the water side of a heat exchanger alike.
Temperature rise limits
In continuous electrochemical duty it is common to specify winding hotspot and top-oil temperature rise limits below those of a general-purpose transformer. A margin of a few kelvin slows insulation ageing materially, and on a unit that runs at full load continuously, insulation ageing is what ends its life.
What to confirm at enquiry stage
- DC output required, and the rectifier topology.
- Expected harmonic spectrum and the delay angle range if thyristor controlled.
- Secondary voltage and current range.
- Cooling medium actually available on site, with flow and temperature for water.
- Whether cooler redundancy is required by the plant standard.
- Ambient conditions, and the corrosive atmosphere the unit will sit in.
- Applicable standard and any testing or inspection requirement.
Send the process data and the electrical ratings, and we can come back on the configuration. See the rectifier transformer range, or contact us.
Related Products
Related Applications
- Transformers for Electrochemical Industry
- Transformers for Aluminum Industry
- Transformers for Industrial Equipment
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Related equipment
If you are specifying this as part of a larger distribution scheme, the surrounding scope is covered on the industrial power distribution, MV switchgear and switchgear control and protection pages.
Frequently Asked Questions
How do I approach specifying a rectifier transformer for a plant?
Start from the load and the environment, then let the equipment follow. Working from a catalogue rating backwards is how projects end up with either a marginal unit or one that costs money sitting under-loaded.
What pulse number should I specify?
It comes from the harmonic limits your supply authority imposes and from the cost of the filters you would otherwise need. A six-pulse arrangement is simplest and produces the most harmonic current; twelve and twenty-four pulse arrangements reduce it at the cost of a more complex transformer.
How do harmonics affect the transformer design?
Harmonic currents raise winding losses and local heating beyond what the fundamental current suggests. The winding configuration, conductor selection and, where the content is high, a K-factor rated design are chosen for the actual current waveform rather than a pure sine wave.
Which standard applies, and is it certified?
The applicable standard and clause set are agreed against your project specification before production starts. Where a project names IEC 60076 for the transformer, we work to those clauses and the routine test report ships with the unit.
What do you need from us to quote?
The single-line diagram or a description of the application, the voltages, the load with its duty, the site conditions, and any standard the project specifies. Send what you have – if something is missing, it can be worked out together rather than delaying the enquiry.