Some kind of Phase Lost Monitor

[regs09]

good day!
Recently, we found out that one of our motor compressor for wall type chiller was burned..this is due to the welded contact point of its magnetic contactor resulting in single phasing when the contactor released...is it possible to install a phase lost monitor, or is there a kinfd of phase lost monitor that could be installed on the line side of the contactor..??....or any suggestions to protect our compressors and other motors from this unpredected scenario.??..please help me..thanks!!!!

 

[waross]

Google is your friend. There are any number of monitors specifically designed for refrigeration compressors.
They will monitor and trip on a number of things such as;
Undervoltage.
Phase loss.
Voltage unbalance.
They often have restart timers.
Digital displays of voltages.
Alarm logs.
Some have contactor monitoring which will detect an open pole on the contactor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Look here:

http://www.rsd.net/search/prod.php?prod_id=764&prod_no=Phase+Monitors&cat=Electrical Components

Or here:

http://phaselossprotection.com/

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Also, many of the newer Solid State Over Load Relays on the market now include phase current loss protection, which is better on a motor than something that monitors voltage only. This is because if a phase is lost while a motor is spinning, the motor generates the missing phase voltage which can "fool" the relay. But it cannot balance its own current, so a current based phase loss / imbalance detection system works best.

If you have a motor starter from one of the major players, check to see if they offer a new style SSOL to retrofit it. If not, consider using a stand-alone version. I like the Siemens ESP200, but I'm slightly biased because I used to work for them and got a deep look at how it's made. Truth be told though, most of the majors offer a pretty good product, just don't take it for granted on the phase loss / imbalance feature though.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[waross]

And depending on where in the system one phase went open and the nature of the other loads on the system, the current may increase as the motor becomes an injection generator and tries to power common loads on the missing phase. This may happen, for example, in a plant that has mainly nonregenerative loads such as lighting and electric heating, but one or several large motors. If this plant losses power on one phase, possibly from one primary fuse opening on a three phase transformer bank, the current on the other phases will rise also, and as well as phase loss, there may be reversed current in one phase, voltage unbalance, current unbalance and/or over current.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[busbar]

If it is a critical motor, negative-sequence overvoltage protection [voltage imbalance] should be applied to inhibit starting, and negative-sequence overcurrent protection [current imbalance] should be applied to initiate stopping.