EOL phase loss off

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chris kennedy

chris kennedy

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Miami Fla.
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60 yr old tool twisting electrician
Just hooked up a NEMA 0 starter for a 3Ø 5.5A 1960's Hobart mixer. This is on the load side of a static phase converter. Before I fired it up I turned off phase imbalance but when I fired it up it would run for a couple secs then trip the EOL. Turned off phase loss and all is well.

Why would phase loss on trip the OL relay???

Thanks
 
Many SSOLs detect a phase loss by looking at the current. Less than xx% of rated current in any phase for more than 2 or 3 seconds means phase loss. But if it's all three, as in an unloaded motor, that still satisfies the condition. They do this BECAUSE it can't be fooled by motor regen voltage (which looks the same as a Phase Converter). The problem is in that xx% value. Some use 20% of rated, Sq. D MotorLogics unit uses 30% of rated. A lot of pump systems will have very low current until a valve opens fully and allows flow, so if the value (or time frame) is not programmable, the only option is to disable it. That was a big problem for Sq. D, who had to issue a "special version" of their MotorLogics SSOL that allowed you to disable it (the initial version did not).

Generally the installation manual will explain this, but sometimes it's buried in the BS that we tend to ignore.
 
Does a static phase converter, unlike a rotary converter, provide identical voltages on all legs?
I can see that the unloaded motor current on a mixer will be far lower than it is after you have added ingredients.
Usually it is not practical to put all of the ingredients into the mixer before starting it.

mobile
 
chris kennedy said:
Just hooked up a NEMA 0 starter for a 3Ø 5.5A 1960's Hobart mixer. This is on the load side of a static phase converter. Before I fired it up I turned off phase imbalance but when I fired it up it would run for a couple secs then trip the EOL. Turned off phase loss and all is well.

Why would phase loss on trip the OL relay???

Thanks
Click to expand...

It's doing what it's supposed to. The phases on utility three phase service is three identical phase with 120 degree (5.555mS) of shift. Passive static converters do not provide correct phase relationship so the current in three legs are not in balance and phase loss relay is designed to trip under this condition.
 
chris kennedy said:
Siemens 48ATC3S00
Click to expand...

Ok, that's the newer version of the old Furnas ESP100 OL relay, now made in Germany and called the ESP200 for a while. I used to work for Siemens, I know it well. For sure then, it will trip in 3 seconds at any (or all) of the phases having less than 20% of the current SETTING. That one goes 3-12A, so if you have it set for 10A, the current must get to 2A within 3 seconds or it will trip (if Phase Loss is enabled).

It also has phase IMBALANCE protection that will trip after 3 seconds if the DIFFERENCE between any 2 phases is more than 20% (might be 30%, can't remember now). But if it works when you disable the Phase Loss, I think that's it and not the imbalance issue.
 
With a static converter just starting the motor & letting the motor single phase how does that play? Or am I missing something?
 
norcal said:
With a static converter just starting the motor & letting the motor single phase how does that play? Or am I missing something?
Click to expand...

You would have to be confident that the static converter itself would shut down if its output does not at least meet voltage specs, or you may need to provide an alternative way of recognizing actual phase loss.
 
norcal said:
With a static converter just starting the motor & letting the motor single phase how does that play? Or am I missing something?
Click to expand...
The motor has to be de-rated by 35-50% because it's running on single phase. NEMA design 230V 3HP and below (some say 5HP) or with a 1.25 SF you can get away with the 35% de-rate, above that and all IEC design motors you must use a 50% de-rate. Rotary phase converters and solid state versions are different, static phase converters are cheaper for single small motors.

So that's another factor in this application. If rated at 5.5A, that's likely a 2HP 230V motor the no load current should be something around 1.2A. If the OL relay is set for 5.5A* that no load current might be too low to avoid tripping the OLR on phase loss.

*The thing is, that motor should not be USED on a static phase converter at more than about 3.5A anyway, so I would turn the OL setting down to there and I doubt the relay will trip any more in Phase Loss. Now if the mixer is being used at the full 5.5A, the motor will burn out eventually by being run on that SPC, unless perhaps the duty cycle is really short and it's a long time between batches. OEMs often play numbers games like that knowing how a machine will be used.
 
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