4922c Instruction Manual Publication 189 SCR March 1995 Silicon Controlled Rectifier Hubbell Industrial Controls,Inc. a subsidiary of Hubbell Inc. 4301 Cheyenne Drive Archdale, NC 27282 (336) 434-2800 Fax (336) 434-2803 JPS-395-0M © 1995 Printed in U.S.A.
Silicon Controlled Rectifiers – SCRs Silicon Controlled Rectifiers The primary SCR bridge is an SCR/Heat Sink assembly with the power SCRs connected in inverse parallel. The function of the SCR bridge is to control the amount of voltage applied to the motor. The SCR, silicon controlled rectifier, is similar to standard rectifiers in that it will allow current to flow in one direction while blocking current in the reverse direction. However, SCRs will conduct current only when turned ON.
Silicon Controlled Rectifiers – SCRs Major Components Thyristor Power Module Protection Thyristor power modules (TPM’s) are SCR/SCR, full wave assemblies available in several horsepower ratings from 10–500 hp in ambients up to 140°F (60°C). Each assembly is configured as an inverse parallel bridge with snubbing circuit and voltage transient protection as shown in the illustration. The TPM’s are the units that control the applied motor voltage on primary thyristor controls.
Silicon Controlled Rectifiers – SCRs Troubleshooting Inverse parallel SCR bridges control AC power by providing a method of adjusting applied voltage as in the case of Primary Motor Control. The AC Power is handled on a half cycle basis by one of two SCR’s. Refer to the Primary SCR Bridge figure provided. SCR1 can conduct power on the first half of the cycle and SCR2 can conduct during the remaining half of the cycle thereby providing balanced currents.
