Industrial applications of large current rectifiers:

• Factory general DC supplies
• DC supplies to industrial Machines & processes
• Electro-plating
• Aluminum smelting
• Caustic Soda plant
• Graphite furnace.

Ratings

Rectifier equipment can be supplied from the smallest size upwards with any combination of output current and voltage. They are available for light or heavy industrial service with overloads in accordance with IEC 146-1973

Typical overload class II – 150% for 60secs once in 24 hours.

Equipment can be designed to suit any special duty cycles or over loads upon request.

Cooling

Transformer

Oil Natural (ON)
Oil Natural Air Forced (ONAF)
Oil Forced Air Forced (OFAF)
Oil Forced Water Forced (OFWF)

Rectifier

Natural
Forced Air
Forced air with air to water heat exchanger
DM water forced with AM water to raw water heat exchanger

Basic Connection

The choice of connections depends partly upon the DC voltage required, however it is determined by a combination of efficiency and cost considerations.

3 Phase bridge (6 pulse) the double way connection gives a 6 phase rectification with a 120 degree conduction angle. This is most commonly used for industrial power supplies.

Double Star (6 pulse) with this connection the 6 phase secondary windings are separated in two opposed star groups, the neutral points of which are connected through an inter-phase transformer. The voltage equalizing effect of the IPT enables the two star group to share the current & 120 degree conduction occurs

12 Pulse circuits : For 12 pulse working two 6 pulse rectifier circuits, two equipment or two groups of equipment to be phase by 30 degree from each other. This is usually achieved by having star-delta primaries. On very large installations, pulse numbers greater than 12 can be obtained by suitable phase shifted a no. of 6 or 12 pulse rectifier.

Protection

The rectifier and transformer are protected against over current surge voltage and excess temperatures, etc. and are designed so that internal component failure cannot cause damage. Additional protective circuitry can be provided when specified.

For Rectifier

Cooling Failure
Air /Water temperature
Supply failure
Over Current/Short circuit
Over Voltage
Diode failure

For Transformer

Buchholz gas and surge
Over Current
Oil temperature high & excess
Winding temperature high & excess