Selecting an industrial rectifier

What this guide covers

A rectifier is defined by the process it serves. The DC output, the way it is controlled and the conditions around it decide the design, and they are what distinguish a rectifier enquiry from a general power-supply enquiry. This guide sets out those decisions so the first engineering conversation can start from the process rather than from a catalogue rating.

Define the DC duty

State the DC voltage and current the process needs. Give both the maximum and the normal operating point, because a rectifier that spends most of its life well below its rating behaves differently from one that runs near it. Invitrona's silicon, industrial and AC-to-DC rectifiers are typically built for 50–5,000 A DC with process-defined output voltages, typically 6–220 V DC, under constant-current or constant-voltage control.

Describe the duty cycle. Surface treatment and other batch processes often run in cycles, with high current for a period followed by idle time. Continuous processes run at a steady output for long periods. The duty cycle affects thermal design, cooling and the size of the semiconductor stack, so an estimate is better than none.

Choose the control mode

Most processes are controlled in one of three ways:

• Constant current, where the rectifier holds the set current and the voltage follows the load
• Constant voltage, where the rectifier holds the set voltage and the current follows the load
• A programmed sequence, such as a ramp up to set point or timed stages

State which the process needs, the adjustment range, and how precisely the set point must be held. If the process records or controls its own parameters, say whether the rectifier must accept a set point or report its output to another system.

Output quality

Some processes are sensitive to ripple, the AC component left on the DC output. If the process or its chemistry supplier specifies a ripple limit or a pulse requirement, include it. Without filtering, ripple from a six-pulse rectifier is typically 3–5% RMS; filtering or a twelve-pulse arrangement lowers it. If no limit is given, the review states the basis it has assumed.

Incoming supply

Rectifiers are typically fed from a 415 V AC three-phase, 50 Hz supply. State the available capacity and the fault level at the point of connection where known. Large rectifiers draw harmonic currents from the supply; if the site has limits on harmonics or power factor, list them so the design can address them.

Cooling and environment

Cooling is chosen against rating, duty and room conditions: natural air, forced air or oil cooling. Many process areas carry corrosive fumes, moisture or dust. Describe the area where the rectifier will stand, the ambient temperature, and whether it can be placed in a separate room away from the process.

Distance to the load

At high current, the DC connection between rectifier and process becomes part of the design. Long busbars or cables drop voltage and dissipate heat. State the expected route and length so that the output voltage at the process, not only at the rectifier terminals, can be considered.

Control, protection and maintenance

Rectifiers are typically supplied with a local control panel. State whether remote control or indication is needed, which alarms the operators expect, and how the unit will be isolated for maintenance. Protections included are listed in the specification and quotation for the agreed configuration.

Next step

Use the rectifier enquiry checklist to collect the information and send it through the enquiry form. Where the process is new or the duty is uncertain, the review states its assumptions and the measurements that would confirm them.