feedback problem

this is not a plc problem but i know that there are many intelligent people on this site who can help me. i have made a phase monitor for a lift station which lets a person on trouble call know if he has a power company problem or an electrician problem. the system is a 240v delta with a stinger leg. i used a 240v ice cube relay and a 110v indicating light. "a" phase to one side of relay coil "b" phase to other side of relay coil (stinger leg) and "c" phase to light so when any phase is out the light will go out. my problem is when the stinger leg goes out due to lightning/storm/fallen tree ect. there is enough feedback voltage to hold the ice cube relay coil in. the power company is using a 2 transformer bank. can i use a resistor to the relay coil in the stinger side or is there a better way to do this. the power company says there will be a feedback no matter if it is a 2 or 3 transformer bank. i am worried that if i use a resistor that it might cause a problem when the "true" power is there. thanks for any help!!

roddbodd,

Pick up a Time-Mark 258BM.

Link http://www.time-mark.com/dox/pdf/114-258.pdf

i know i can use a phase monitor, i was just wondering if the resistors would work. there are 10 of these stations and it would be much less expensive if the resistors would work.

If these are lifts used for moving people, then they are required to have real phase monators. The monator's primary function is to protect aganst reverse phase, not just phase loss. Also consider time is money. Anything your likely to save in materials will likely be lost 3 fold on re-inventing the wheel. Also consider the liabily involved in the event of a catostrophic event where the insuing investigation reveals that YOU installed an inadaquate homebrew protection device.

these are sewage pumping stations and as i stated in my original post this is just something for a person on trouble call to be able to tell if he needs to call an electrician or call the power company. trouble call personell change in and out every week. they may be from the gas dept., water dept., ect. some have no clue about electricity. this is just a way to save time and the expense of an electrician on overtime if he is not needed.

Rodd,

I cant count how many of these things I've installed and serviced. (dual chain drive, right?).

For about $200.00 you can get a power monator that will indicate phase loss, phase reversal, low voltage, and high voltage. All of these faults would be clearly indicated by LED indicators. Anybody who can see and read could report exacty what they see to the proper higher-ups.

Go here for a simple circuit. Figure 3 is a complete unit.

Rodd,

As I would say to my buddy, "Just buy the dang thing" as Mike has suggested.

OK, i installed a phase monitor on one of the stations today. i had the power company take each jack (fuse) out 1 at a time. phase "a" my indicating light went out. phase "b" light out. phase "c" (stinger leg) light went out for about a second then came back on. as i have said there is a feed back on a delta power system. i still have aprox. 120 volts on the stinger leg even though the jack is out. the instant the jack is pulled the monitor works but then it sees the feedback voltage and thinks the power is back on. is there some other type of monitor that will work. i used a sq d which we had in the shop.

This looks like the model you might need:

http://www.time-mark.com/dox/pdf/106-2500_2501.pdf

I would suggest calling Timemark for application assistance.

the system is a 240v delta with a stinger leg....
the power company is using a 2 transformer bank...
still have aprox. 120 volts on the stinger leg even though the jack is out.

Click to expand...

I think the name of your type power is an "open delta" system, one that I avoid like the plague! An Open Delta system has two single-phase transformers with one side of each secondary coil connected. It is often said that one phase of an Open Delta system has a "phantom" transfomer. The Open-Delta system is by nature unbalanced, ungrounded, and an overall travesty. The only thing that can be said for it is that it is cheap --it saves the power utility the cost of one single-phase transformer.

the power company says there will be a feedback no matter if it is a 2 or 3 transformer bank....

Click to expand...

That is true for an ungrounded delta system, whether it be the open-delta or standard delta with 3 transformers. On the other hand, for the preferred Delta primary -grounded Wye secondary system, then everything is balanced and there should be no feedback.