Transformer Rectifier and Circuit Breaker Locks

It is apparent when considering the design of an electrostatic precipitator interlock system that the point of energization must be addressed. From one standpoint, access must be allowed to the high voltage sections of the precipitator only when the Transformer-Rectifier has been placed in a ground position. From another standpoint, however, it is also necessary that no power is available to the transformer-rectifier or its associated controls when maintenance is performed on the precipitator, such as when maintenance is required on the controls or transformer-rectifier.

Dead bolt type locks are generally used to secure transformer-rectifier ground switches or circuit breakers in the proper position. The locks used for this purpose are generally the end-mounted or side mounted variety with the equipment design dictating the mounting type used. Further, depending upon the design of the actual switch mechanism, a single- or multi-tumbler lock might be utilized. 

A multi-position ground switch on a transformer-rectifier, for example, may require only the use of multiple single tumbler locks. The design of the switch allows or prevents the extension of the lock bolt and the extension or non-extension of the lock bolt allows or prevents key release. For example, placing a transformer-rectifier ground switch in the ground position might allow the bolt of one lock to be extended to release the ground key whose presence is necessary in a transfer block to release access door keys. The same switch position would disallow the extension of the bolt on a lock containing the circuit breaker key, thus preventing the energization of the transformer-rectifier. Moving the ground switch to another position would reverse the sequence described.

Circuit breaker locks work similarly to those used on transformer-rectifiers. The lock is usually either a single one-tumbler lock or a single two-tumbler lock. At least one tumbler will be keyed the same as a lock on the corresponding transformer-rectifier ground switch. This key would be released from the circuit breaker only when the lock bolt was extended; thus assuring that power was turned off. The transformer-rectifier ground switch could then be "unlocked" and moved to the appropriate ground position. The two-tumbler lock is used when a panel switch lock is used on the transformer-rectifier control panel. The extra key is released when the lock bolt is retracted, the key released is used in the control panel switch lock which when turned to the proper position allows the controls to be switched on.

The position of the dead bolt determines when the key in each tumbler can be released. In either the single or double tumbler arrangement, the lock is mounted so that the breaker is locked in the OFF position when the bolt is extended.