Phase Loss Protection
Phase Loss Protection
(OP)
Working on a new, low-rise, office building project. Since the building was completed the utility has lost a phase several times, probably due to construction in the local area. No problems with equipment, only partial lights out. Client wants to know why we didn't specify phase loss protection. Told him this was not a common practice especially since we have no large motors. (Roof top units are the only 3 phase motors.) On commercial buildings, are most of you guys specifying phase loss relays for motor starters or for main breakers? Or include this in RTU specs? Or are we worrying about something that is just not a problem?






RE: Phase Loss Protection
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.- http://www.flaminsystems.com
RE: Phase Loss Protection
You should have PL detection in 3 phase motors however. Cheap insurance.
RE: Phase Loss Protection
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
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Phase Loss Protection
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.- http://www.flaminsystems.com
RE: Phase Loss Protection
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.
RE: Phase Loss Protection
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
RE: Phase Loss Protection
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
http://www.lmphotonics.com
RE: Phase Loss Protection
RE: Phase Loss Protection
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Phase Loss Protection
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.