Replacement of synchro verifier relays and relocation of LV fuses

Purpose of modification 709-EE-L was replacement of worn synchronization verification relays. These relays serve purpose during ''Fast Transfer'' procedure, when power supply is switched from regular T1 and T2 transformers to auxiliary transformer T3. T1 and T2 are supplied from plants generator, while T3 gets power from network, hence the possibility that there is phase shift between two voltages, which could cause damage to running equipment during supply switch.

Such relays with one contact in control scheme of transformer’s circuit breakers prevent closing of breaker in case of non-synchronization. Existing relays did operate, but they experienced strong contact chatter, that caused problem when performing ''Fast Transfer'' procedure. With this modification, eight existing relays were replaced with new versions; these required power supply that was not originally needed.


Picture 1: "Synchro Verifier" relays

In scope of this modification, LV fuses from voltage indication circuits were relocated from HV compartment to LV compartment. This was done to ensure greater safety for maintenance personnel, who were exposed to possibility of arc flash due to close proximity of high voltage. Therefore fuses were relocated to low voltage compartment, where there is no high voltage danger. This modification required new cabling in voltage indication circuits.  

Project manager: Matjaž Stanko, B.Sc.E.E.