Phase Loss Protection 2

Phase loss probably kills more refrigeration compressors than all other causes. They die in seconds. Personally I would never install any 3ph compressors without $100 phase loss detectors. Or at the very least recommend them and allow the customer to "blow it". Compressors cost thousands of dollars and a "burn-out" can effectively ruin an entire system by contaminating everything with acids that wreak havoc.

So to answer your question: Yes single phasing is always a potential problem. Just a pole fuse can blow outside your installation single phasing you.

Keith Cress
Flamin Systems, Inc.-

Aside from motor controls however, Phase Loss protection is not typically specified for buildings. As you have already noticed, when you lost a phase you lost some lights. If there were PCs plugged into that phase you would have lost them too, but others plugged in to other phases would have been OK. So to deliberately drop out an entire building because 1/3 of the circuits have been lost would not be a good thing for the 2/3 that were still OK.

You should have PL detection in 3 phase motors however. Cheap insurance.

Doesn't the standard thermal protection work?

Phase loss relays were used when drives didn't have that built-in. All modern drives have that today. For DOL, the current goes up enough for the thermal protection to do its job.

I do not specify equipment for buildings, but I see a lot of installations. Phase loss relays are not very common in my part of the world.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

Hello Gunnar. You'd think they would but all I can say is NO! They are the second biggest reason for burned out compressors all by themselves. One goes and doesn't trip the rest... Custom, local machine based, single phasing!

Definition:
Overloads :noun, A refrigeration service company's best friend!

I'll say Phase Loss Detectors aren't very common around here. Where you see them is in all the refrigeration sites, (including A/C), where the owners just got a $2-10K repair bill for a burn-out. The first $100 is for a phase loss detector.

It is really funny.. after all the business owner is paying fire insurance, indemnity insurance, theft, and huge liability, insurance policies endlessly and annually for stuff that may never happen but ya think they'd pay $100 one time to protect their hardest worker? Naw..

Keith Cress
Flamin Systems, Inc.-

In commercial facility designs in the US, phase loss protection is not normally provided, in my experience. Everything is designed to NEC minimum requirements, and if something is specified that is not required by Code, the contractor will "value engineer" that right out during construction.

The bi-metallic thermal overload typically used in the US do not reliably protect against motor damage due to phase loss. They don't reproduce the negative sequence "double frequency" heating that is going on inside the motor.

I've seen a saw mill that lost virtually every motor in the place when they were single-phased.

There are some nice refrigeration protection units on the market.
Most provide the following protection;
Voltage unbalance, adjustable.
Phase loss.
Delayed restart.
Undervoltage protection.
Overvoltage protection.
Digital display of all three phase voltages.
Fault description.
Memory recall of the last 25 faults.
The best ones add the following protection;
Monitor line and load side of the contactor and protect against high resistance or failed open contacts.
These are about 3" x 6" by about 1" thick. They are suitable for mounting inside many A/C or refrigeration control panels.
Re overloads. I see a lot of hermetic and semi hermetic units that take advantage of the returning refrigerant to cool the windings and run without overload protection.
Re the original post, I'd suggest, spec a reasonably featured monitor/protector for each 3 phase refrigeration compressor. Evaluate the other 3 phase motors on a motor by motor basis. Some IEC type overloads have a current unbalance feature that will trip on less than full load current in the event of a serious current unbalance condition.
Many overload relays don't include unbalance protection.
As I said, evaluate the individual motors.
respectfully

It is common these days for thermal overloads to include differential bar phase loss protection. This acts to increase the sensitivity of the relay as the current imbalance increases.
While I am not a fan of thermal overload relays, they will provide better protection than none at all provided that they are installed and set up correctly.
I would recommend that thermal overloads must have differential bar protection as a minimum spec. This should catch loaded motors under phase loss conditions.

Best regards,

Mark Empson

Anytime I specify fuses, I always specify phase loss protection. Whether it be on a service, feeder or branch circuit to a motor.

RonShap; THAT! Is good planning.

Keith Cress
Flamin Systems, Inc.-

Kamin Dave,
Hi i am relay Engineer. I have not seen critical load so my point of view bi-mettalic over load relays (SIEMENS MAKE or Merlin Gerin make etc.) are quite good to trip on single phasing. It is cost saving solution because compressor motor is not reqd. to trip immediately during single phasing. Areva & ABB make Thermal overload protection relays are also very good but, it is reqd. when your load is critical or semicritical. It's expensive solution than bi-metallic O/L relays.