Info on relays and voltages.

[peetey]

I am an electrical meterman by trade but am interested in voltages related to relaying and metering. In somes substations there are 69v taps and 120v taps for metering and relays. If the 69 volt is a phase to neutral voltage am I to asssume that the 120v is a phase to phase voltage. Is it necessary for a relay to see 120v phase to phase for operation? From the standpoint of metering the 69v would be a wye connection and the 120v would be a delta connection? What voltages are normally provided at substations for the metering and relays? Any comments on this topic would be appreciated.

--peetey

 

[alehman]

If the PT primary voltage matches the line-to-line voltage and you connect it line-to-neutral, you will see 69V on a 120V secondary.

Some relays are configured for 120V line-to-line, which means 120V PT secondaries would need to be connected in delta or 69V PT secondaries could be used if connected in wye.

Basically 120V / sqrt(3) = 69V.