Thyristor based Control Panel for 75VDC/300A Rectifier

The control panel featured here is designed to generate a variable DC supply of 0 to 75VDC at max. 300A current. Libratherm model POW-3-DCR-400A, a three-phase AC to DC rectifier made using 6 SCRs in full-wave full control configuration has been incorporated. The application of this control panel is to meet the requirement of an Electroplating plant requiring variable DC voltage at the constant current for the electrolysis process.

Three-phase input to the DCR is derived from an external 3 phase 25KVA step down transformer having a primary of 415VAC and a Secondary of 120VAC. DCR generates the DC voltage proportional to the control signal received either from the Libratherm model DVC-966 in Auto control or from the front panel potentiometer in Manual control. DVC 966 is the high-speed PID controller specially designed for rectifier control to maintain a constant voltage and constant current across the variable load.

The DC voltage and DC current output of the DCR is fed to the DVC-966 through the signal conditioner/isolator. DVC-966 indicates both DC voltage and DC current and also has the facility to set the desired voltage across the load. The constant current control across the load is achieved by the CT feedback to the DCR. The ripple in the DC voltage output is filtered using suitable electrolytic capacitors. The programmer version of DVC-966 also facilitates the user to program the voltage versus time profile for the gradual increase, soaking, and gradual decrease of the desired DC voltage across the load.

The front of the panel also has separate digital voltage and current meters to online monitor voltage appearing across the load and current flowing through the electrochemical in the plating process. The presence of an incoming 3 phase supply is indicated by the RYB lamp. The incoming supply is turned ON or OFF using the 100A MCCB accessible to the user from the front side of the panel.

The POW-3-DCR-400A, MCCB, DVC-966, a DC Voltmeter, a Currentmeter along-with the other required accessories are housed in the MS fabricated control panel which is duly Siemens grey color powder coated. Terminals and busbars are provided for connecting the transformer primary, DC output, and incomer 3 phase supply. The panel is mounted on a stand for onsite wiring and cabling.

This rectifier control panel has been installed and working satisfactorily at the customer end since January 2019.