For the station interlock function conditions to be interrogated, there needs to be a communication link with the substation control level. If the P632 detects a communication error or if there is no communication interface available, there will be an automatic switch to bay interlock without the station interlock function.

If there is to be a check on the bay interlock and the station interlock function, the bay interlock will be checked first. If bay interlocking issues a switching enable, a switching request will be sent to the substation control level. At substation control level, there will then be a check – taking into account the station interlock functions – as to whether switching is permitted or not. If the substation control level also issues an enabling command, the switching operation is carried out provided that the enable from the bay interlock is still present. Optionally, the “Open” or “Close” switching operation can be carried out without checking the station interlock function conditions. In this case, the bay interlock conditions defined for operation without station interlock functions will be considered.