Silicon Controlled Rectifiers (SCRs)
Most precipitator electrical controls manufactured from the 70’s on use silicon controlled rectifiers (SCRs) as the electronic switch that ultimately controls the power to the primary of the TR and in turn to the precipitator.
The two most often used types of SCRs are the stud mount and the hockey puck. Both of these types take a significant amount of time to replace if they fail, and both are becoming more expensive to replace.
Today’s SCR assemblies contain “brick” type SCRs. The stud and hockey puck SCRs are individual devices (two required), the brick is a molded device that contains both SCRs in one package.
Stud and hockey puck SCRs are mounted directly to a heat sink or heat sinks that are electrically hot and need to mount to the control cabinet with the use of insulating material. The insulating material is a point of failure, and the electrically hot heart sink is a safety concern.
The brick SCRs however, are isolated from ground and therefore is mounted directly to a heat sink that does not become electrical hot, can be mounted directly to the control cabinet, and does not present a safety concern. And, since the brick is replaced from the front of the heat sink the replacement time is minimal (usually ½ hour or less).
Brick type SCR assemblies are available in sizes ranging from 240 amps to 600 amps, with a voltage rating of 1,600 volts. The assemblies fit within the space allotted for the stud and hockey puck assemblies so upgrading to the brick is easy.