Delta-Delta Transformer bank, Phase loss and Ground fault

[John5445]

I have a Delta-Delta transformer bank, 13,200-480. I would like to monitor both phase loss(ie. loss of a primary fuse) and ground fault on the secondary.
I would like to send a signal to trip a shunt trip molded case circuit breaker during a phase loss to prevent single phasing loads and alarm for a ground fault.

Any ideas. I know I can use the Ground Detection Lights for the ground fault, but is there a relay that can handle both.

Whats the best way?

 

[alehman]

These are really two separate functions. I dont know of any single device that does both. You mention ground detection lights so I assume your secondary is ungrounded.

See

http://www.schneider-electric.ca/

http://www/en/products/ground/html/general.htm

For loss of phase detection, see

http://basler.com/downloads/practical.pdf

 

[busbar]

As implied in the original post, there are two conditions that should be handled in different manners. The problem with low-voltage ungrounded-system transient overvoltage and consequent insulation damage {often in motors} has been acknowledged in power-systems publications for 50 years. Adaptation/retrofit to high-resistance grounding and associated indication/annunciation is well recognized in various electrical publications.

Phase “loss” or imbalance is a bit trickier. Voltage-imbalance detection is adequate to inhibit starting of a group of motors, but has significant limitations in protecting motors once they are running. Unfortunately, once motors have accelerated and settle to namplate current, voltage-imbalance sensing has serious limitations, and in many cases is quite useless. Current-imbalance protection is far more effective, but cannot reliably be applied to groups of motors.

There are a number of “ice-cube” type devices that promise to protect against electrical ills and look good in advertisements, but in terms of reliably protecting against equipment damage and production loss leave a lot to be desired.

A search in electrical topics at Eng-Tips under ‘ungrounded’/’high-resistance grounding’ and ‘phase loss’/‘phase imbalance’ will yield discussion on the matter.

 

[jbartos]

Suggestion to John5445 (Electrical) Jan 23, 2004 marked ///\\I have a Delta-Delta transformer bank, 13,200-480. I would like to monitor both phase loss(ie. loss of a primary fuse)
///Some disconnect switch manufacturers offer the blown fuse monitor with their product as an option. E.g. see

http://www.pringle-elec.com/bolted.html

\\\
and ground fault on the secondary.
///Modern electronic circuit breakers do have this feature available via the electronic trip unit, e.g. Square D Micrologic.\\I would like to send a signal to trip a shunt trip molded case circuit breaker during a phase loss to prevent single phasing loads and alarm for a ground fault.
///See the Pringle Blown Fuse Detector. It can open the switch.\\Any ideas. I know I can use the Ground Detection Lights for the ground fault, but is there a relay that can handle both.
///See above comments\\

 

[PWR]

I'm also not aware of any single device that would do both. I have had excellent results applying the Taylor Electronics phase unbalance relay. It's a small company that is located in Florida. For many years they were the standard choice furnished with Square D switchboards when you ordered the phase loss/unbalance option.

For ground detection, I recommend you use the wye connected resistors approach rather than PTs. The latter can develop ferroresonance effects under certain conditions and the resistors work just fine in a 480V application. I'm away from the office and can't think of a brand name but there are companies who offer them in a NEMA 12 or other enclosure with audible and visual alarms and dry contacts for remote indication or tripping.