Field Ground Protection Power Supply

[mgtrp]

Typically protection devices are sourced from the station DC power source, but I note that a lot of older-style field ground monitors (e.g., ABB/Westinghouse 64F, Basler BE1-64F, GE 3S7932YA122) require a 120 or 240V AC power source. I've seen this addressed in two ways - either to use a supply from a UPS (e.g., an inverter from the station DC), or a supply from the PPT that provides power for the excitation system.

My questions are these:
1. Does anyone know the reason or history behind this?
2. Is there a preferred power source? Supply from the PPT would obviously only be available when the unit is running, which might be a motivating factor to either use or not use this supply.

Thanks,
mgtrp

 

[davidbeach]

Frankly, I can't imagine. Relays should always be powered from DC unless self powered. Full stop.

 

[mgtrp]

That matches my thoughts as well, however clearly three different reputable relay manufacturers all offer only the AC option. I'm hoping to get an answer from the application engineers at one of the companies, and will post any response here.