When used on plating lines operating under harsh environmental conditions, air-cooled rectifiers can face serious problems such as corrosion of electronic parts and power components and/or foreign particles entering the system.

The result can be short circuits and a malfunction of the power supply.

This is especially the case in production situations where clean cooling air is not available. It can cause an unnecessarily short lifespan of the rectifier in addition to the nuisance of production down time, while requiring a frequent maintenance schedule.

While a sealed enclosure would prevent these pitfalls, the design of an air-cooled system requires sufficient openings for proper ventilation, thus rendering the sealed enclosure impossible. .

Oil-cooled Rectifiers

An enclosed liquid-cooling system can eliminate the corrosion/contamination risk posed by the air-cooled method. This solution is not only technically advanced, but also addresses the financial concerns related to investment and maintenance costs. Similar to substation transformers, mineral oil is used as a liquid coolant to dissipate heat and squelch any sparks that might be generated. As a result, the internal corrosion problems seen with forced air-stream methods are overcome.

Oil or combined oil-water cooled rectifiers do not require openings in the enclosure for the cooling process. The main power components are submerged into a corrugated steel tank filled with commonly used insulation oil. The natural convection of the oil inside the tank cools the components. The rectifier is well protected from the aggressive surrounding and potentially damaging air-borne particles. While air-cooled rectifiers require installation in a separate room or apart from the plating tanks, the oil-cooled rectifiers can be installed in a much closer proximity to the tanks. The reduced installation expenses, coupled with the lower process voltage, are additional advantages provided by oil-cooling.

To reduce the size of the rectifier, corrugated tanks are used as an enclosure instead of a barrel design. For extremely compact designs, oil can be cooled by means of an oil/water heat exchanger using forced-oil circulation. The heat losses are then removed from the proximity without affecting the plating shop’s ambient temperature.

As with traditional air-cooled rectifiers, oil-cooled rectifiers can be controlled by SCR’s. Additionally, it is also possible to use a variable ratio transformer control. This control system offers a constant low DC ripple of only 5% from 0 – 100 % output power, unlike SCR systems with a variable ripple of 5%– 60% under normal operating conditions.

Oil cooled rectifiers are commercially useful alternatives for plating applications in the range from 1000 A up to almost 15000 A.