Transformer-Rectifiers

Jemelec is able to design and manufacture a wide range of single and three phase uncontrolled rectifiers or transformer-rectifiers. Current ratings up to 10 kA and voltage ratings up to 1.5 kV are possible, within a maximum rating of 1000 kW load power for transformer fed units. Line fed units are limited only by the ratings of the rectifier. Choke and capacitor input filters can be added to the output of all rectifiers to provide smoother d.c. Filtering is almost always required on single phase rectifiers and can provide a smoother output on three phase units where necessary.

Controlled rectifiers come in two broad categories. Open Loop and Closed Loop. Both types will generally employ thyristors (SCRs) in the rectifier bridge. Jemelec offers a full manufacturing service for both open and closed loop systems.

Open Loop Controlled Rectifiers.

Open loop control is the simplest form of control which can be employed. This is similar to the way in which a lamp dimmer switch works. As you adjust the control, the amount of power fed into the load is adjusted and, in the case of a lamp dimmer, the lamp either gets brighter or dimmer. If the supply voltage varies then so will the voltage fed to the load. Equally, varying the load will cause similar, though usually lesser, effects. For many applications, such as varying the power to heaters, this simple form of control is adequate. Often, it will be combined with other forms of control, such as thermostatic, where the thermostat will control the actual temperature to be maintained and the controlled rectifier will govern the heating rate.

Closed Loop Controlled Rectifiers.

Closed loop control systems monitor the output voltage (or current) of the system and automatically adjust for any variation in the monitored parameter. Regulation can be, and usually is, tightly controlled, thus ensuring that the supply to critical systems is maintained at the correct level at all times, regardless of any supply and load variations within the capabilities of the system.

Closed loop control is much more sophisticated than open loop and will frequently incorporate many enhancements, such as microprocessor control, comprehensive instrumentation and other such refinements.