Phase Loss Affecting Some Single phase machines

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StarCat

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
During a loss of one phase incident this week I noticed a 230V single phase refrigeration machine trying to self destruct.
I opened the line disconnect and found 120V potential [not ghost voltage] and the main contactor coil seeing that power with the typical results.

Some background on this type of effect by my experience.
What I have seen and dealt with in similar situations sometimes involves a neutral downstream that the 230v circuit interacts with which can cause this kind of thing to happen. An example would be on a 230V single phase refrigeration condenser with 120V Fan bank. Its common and typical to feed the Liquid Line Solenoid at the Fancoil unit from the N.C. contact [4] on the condensing unit defrost timer. Often times the solenoid coil is 115v because the fancoil unit is also 115v and they are set up that way. I have had to wire more complex control schemes such as nonrecycling pumpdown which require extra 230V coil relays in the condensing unit cabinet which do not like to interact with a 115V LLSV. Do away with the neutral and change the LLSV to 230V coil and the problem goes away. You will no longer get strange feedbacks that give you a partial voltage to a relay coil that could burn it.
This is just one example.

SO I am getting through the power phase loss and next day I have another piece of gear with a smoked contactor coil which I did not catch during the outage. Its a 3phase ice machine remote condenser, so the main contactor control coil is 230V.

ON a per equipment basis it could come of as time consuming to sort out.
I have maybe 3 units remaining that I will have to address that are single phase which could be a problem.

I am interested in any other experience and solutions for this type of scenario.

Warren
 
Since all of the 1ph !oads have a common neutral and each line is fed from (3) coils with a common core transformer I would be suspect that the deenergized line is being back fed by the other lines fed by the energized lines through the cvore of the transformer. As such I would conclude that the voltage present on the phase that has been lost would be strange.
 
You need undervoltage monitoring in the control circuit(s). If you lost one phase on service or a feeder - any phase to phase loads (single or three phase) still connected to that line are going to have some backfeed voltage on them, how much depends on conditions and will vary depending on what loads are currently connected. Even though you had 230 volt control coils in some of these items, they may not have pulled the armature of the coil in, but still had high enough voltage applied to draw significant enough current to cause them to overheat and burn out the coil.
 
Advised measures

Advised measures

Kwired, I am using ICM-408 devices on the 3 phase gear and they are working well.
What type of device may I use on the single phase loads to achieve this end?
Or would one monitor the 3 phase service close to the load in question and port the control circuit through that protection device?
Please advise and thanks for the response.
 
If you have a delta or wye source, and you lose (open) one hot conductor, the opposite line to line phase will still be hot.
In a delta that leaves the two other windings as a voltage divider in parallel to that phase. This puts half the phase voltage present on the open supply lead.
Even with a wye source any connected delta non-motor loads will have the same voltage divider effect.
Three phase motors running at the time the line opened will put an unpredictable voltage on the open line.
 
THanks

THanks

GoldDigger said:
If you have a delta or wye source, and you lose (open) one hot conductor, the opposite line to line phase will still be hot.
In a delta that leaves the two other windings as a voltage divider in parallel to that phase. This puts half the phase voltage present on the open supply lead.
Even with a wye source any connected delta non-motor loads will have the same voltage divider effect.
Three phase motors running at the time the line opened will put an unpredictable voltage on the open line.
Click to expand...

I appreciate these responses. The Power Company Engineer did not have any good answers for me so I am going to forward these responses to them. I don' think they have many other people in this area that are being proactive or even care about such issues.
 
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