Controls:

• Variac Controlled (Stepless) :-
  The working of the rectifier can be controlled using a stepless variac and the output can be controlled from zero to the rated value.
  
• Static Variac Contolled :-
  The working of rectifier can be controlled smoothly using back-to-back thyristor at input side. By controlling the firing angle of thyristor, output of rectifier can be controlled.
  
• Thyristor Controlled :-
  The rectifier out-put can be controlled using thyristor at secondary of the transformer. The thyristor rectifier can be provided with 6, 12, or 24 pulse configuration.

The cooling system is designed to ensure highly reliability and optimum performance of the rectifier. In high atmospheric temperature and in highly corrosive conditions, “Natural oil cooled” (ONAN) is recommended. In this system vital components like transformer; choke, diodes etc are immersed in an oil tank for cooling. If the rectifiers are placed in a room with proper ventilation, then “Natural Air Cooled” scheme can be deployed. For rectifiers of high rating “Forced Air Cooling” is preferred. Under this system, the internal components are cooled using a blower fan.

Transformer :

The transformer used in the units are rugged and of robust construction. They are used to step up or step down the input supply. They are available in both oil cooled as well as air cooled/forced cooled type. In hexa phase rectifier units, an interphase transformer is used. It is connected between two star points of the secondaries of main transformer.

Protection :

Following protection schemes are generally deployed :

• Electric DC over voltage / over current
• Semiconductor fuses for rectifiers
• MCB / MCCB at Input or Output.
• Snubber circuits for devices.
• Temperature control for devices and transformer.
• Phase sequence and phase loss protection