400hz Generator - Tripping during startup

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natejonz80

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I am stumped -

We installed (2) 400hz generators in a aviator manufacturing facility. Only (1) genset runs at a time and manual changed through a control cabinet. At start up the breaker trips, however after 2/3 attempts it holds and runs fine with no issues. We are feeding the genset with a 200A breaker and the settings have been dialed to the highest setting. We have checked inrush and it seems within the perimeters at 864 amps. I had the generator manufacturer out to take a look and in the link below is their suggestion. I have suggestion a VFD to the engineer but he seems to disagree beings that the inrush is within the perimeters.

I have put in the link below the one line diagram, the genset tech's response. Below the link is the engineers response to the tech's.

https://drive.google.com/drive/folders/1n8_IcyCCqHj2nCdOHPySvb9438od9Dzf?usp=sharing

Some thoughts on manufacturer’s recommendations:

Per the NEC the 400 Hz system has to be grounded. This is accomplished by grounding the 400 Hz system neutral. This should have been done inside each 400 Hz generator with a bond jumper from the 400 Hz output neutral to the M-G set frame. Our drawings required that a #1/0 aluminum grounding electrode conductor run from the 400 Hz output neutral and frame to building steel. This is required by the NEC. Also, there is an equipment ground from the 60 Hz building system that runs to the 60 Hz motor frame (required by the NEC) that grounds the motor frame to the 60 Hz ground system.

• It is not clear to me how to isolate the 400 Hz system from the building’s 60 Hz system which is also bonded to the building steel.

• Is the M-G set frame constructed in a manner where the 60 Hz motor frame is already isolated from the 400 Hz generator frame or can it be isolated?

• If isolation of the 60 Hz and 400 Hz systems is achieved, what ground system should the sheet metal shielding be connected to?

• How can the sheet metal be installed to provide effective shielding? Maybe flexible metal conduit on all of the feeders the entire path to the contactors. I believe effective shielding will be difficult to achieve without rebuilding the entire control cabinet.

Thanks for any and all feedback!
 
I changed one out at an Air Force Base, they went from an inefficient motor/generator set to electronic, and that was quite a long time ago. Is this an old set? And did it just start giving issues? They used it to test plane electronics. They would start it in the morning, and let it run all day, only using it a couple of times during that period.
 
You are basically feeding a huge motor load. What is the nameplate input current or horsepower rating of that motor driving the 400Hz generator? With the wire size you have, it seems like you'd need a larger breaker (not sure what dialed up to the max means -- is that 200A or more than that??). I would expect there to be overloads somewhere for that motor, and a branch circuit breaker about 200% larger than the circuit rating (so a 400A breaker if the motor is a 200A motor). Is the breaker that's tripping the branch circuit one, or one in the control center?

I also don't see how grounding has anything to do with this or whether the 400Hz generator is bonded or not.
 
suemarkp said:
You are basically feeding a huge motor load. What is the nameplate input current or horsepower rating of that motor driving the 400Hz generator? With the wire size you have, it seems like you'd need a larger breaker (not sure what dialed up to the max means -- is that 200A or more than that??). I would expect there to be overloads somewhere for that motor, and a branch circuit breaker about 200% larger than the circuit rating (so a 400A breaker if the motor is a 200A motor). Is the breaker that's tripping the branch circuit one, or one in the control center?

I also don't see how grounding has anything to do with this or whether the 400Hz generator is bonded or not.
Click to expand...
nameplate input - 480 VAC, 60Hz, 115 F.L. Amps

The 200A breaker's trip setting is set to capacity. (feeding the control/load center)

The breaker that is tripping is the 200A feeding the load center.
 
hillbilly1 said:
I changed one out at an Air Force Base, they went from an inefficient motor/generator set to electronic, and that was quite a long time ago. Is this an old set? And did it just start giving issues? They used it to test plane electronics. They would start it in the morning, and let it run all day, only using it a couple of times during that period.
Click to expand...
These were new generators. This has been ongoing since the install. Once the breaker holds it runs fine and is never shut off except to switch over the other generator.
 
What is the breaker tripping on? It, overload, gf????

I agree with the poster that suggested looking at the nameplate on the device.

I don't think this has anything to do with grounding.
 
zbang said:
Is the 400Hz side loaded or unloaded when starting the M-G? If you're trying to start into a load with it's own inrush, that could explain the 2-3 starts before it holds.

I also think it has nothing to do with grounding, and most times that somebody suggests that because they can't think of anything else.
Click to expand...
The 400Hz side is unloaded.
 
petersonra said:
What is the breaker tripping on? It, overload, gf????

I agree with the poster that suggested looking at the nameplate on the device.

I don't think this has anything to do with grounding.
Click to expand...
The breaker is tripping in my opinion due to overload inrush, but again seems to be in the perimeters of inrush on a 200A breaker at 847A.
 
The grounding issue put forth by the technical people you post in that doc indicate to me that they are clueless. If this is a standard induction motor as the prime mover and based on your indication that the input current is 115 amps @480 that would seem to indicate about a hundred HP motor. I would be inclined to think that your 200 amp input breaker is way to small even if started unloaded.
 
texie said:
The grounding issue put forth by the technical people you post in that doc indicate to me that they are clueless. If this is a standard induction motor as the prime mover and based on your indication that the input current is 115 amps @480 that would seem to indicate about a hundred HP motor. I would be inclined to think that your 200 amp input breaker is way to small even if started unloaded.
Click to expand...
I don't think I would call it way too small, but it does seem a little underrated to me. I probably would have specified a 250 amp rated breaker. I'm not a big fan of skimping on the size of breakers to try and save a few bucks. It always seems to get you in the long run.
 
Treating this as a motor, your conductors need to be rated at 125% the FLA, so about 150A. You've got that and more. The overcurrent device can be up to 250% of the FLA, so a 250A or even a 300A breaker could be used. If it still fails to reliably start, you can go larger. It sounds like you're on the edge of the trip limit for the 200A breaker. Going to a 250A would probably fix it.
 
220701-0030 EDT

natejonz80:

You lack background knowledge relative to motors and breakers. You need to study the characteristics of each.

A motor by itself with no mechanical load will take time to get up to speed. During this time there is a starting current that for induction motors is generally well above full rate running current when the motor is at full speed at full rated load. For a typical induction motor this no mechanical load starting time will be a number of AC cycles. With an attached mechanical load this duration may be extended considerably.

Most breakers of a thermal type have, for a specific model, a trip time curve that starts out possible 6 times breaker rating dropping to something above rating after a fairly long time.

The breaker trip time curve has to be above the motor starting curve to avoid startup tripping.

Make some measurements on your devices, and/or look at data sheets.

.
 
My thoughts are similar to Gars' above....

What is the starting time (ie. how long from first applying power to the motor until it reaches full rated speed)? Is it the same for both motors?
 
are your breakers listed & tested for a 400hz system, along with the wire sizing. it has been a number of years since i quoted a 400 hz
job but what i remember was the breakers were different along with the wire sizing.
 
tesi1 said:
are your breakers listed & tested for a 400hz system, along with the wire sizing. it has been a number of years since i quoted a 400 hz
job but what i remember was the breakers were different along with the wire sizing.
Click to expand...
I am pretty sure the breaker he is referring to is on the 60 hz side.
 
natejonz80 said:
I have put in the link below the one line diagram, the genset tech's response. Below the link is the engineers response to the tech's.

https://drive.google.com/drive/folders/1n8_IcyCCqHj2nCdOHPySvb9438od9Dzf?usp=sharing
Click to expand...
Adding them as an attachment here for easy viewing of others
natejonz80 said:
Some thoughts on manufacturer’s recommendations:

Per the NEC the 400 Hz system has to be grounded. This is accomplished by grounding the 400 Hz system neutral. This should have been done inside each 400 Hz generator with a bond jumper from the 400 Hz output neutral to the M-G set frame. Our drawings required that a #1/0 aluminum grounding electrode conductor run from the 400 Hz output neutral and frame to building steel. This is required by the NEC. Also, there is an equipment ground from the 60 Hz building system that runs to the 60 Hz motor frame (required by the NEC) that grounds the motor frame to the 60 Hz ground system.
Click to expand...
So did you guys not ground the 400hz side?
 

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gar said:
220701-0030 EDT

natejonz80:

You lack background knowledge relative to motors and breakers. You need to study the characteristics of each.

A motor by itself with no mechanical load will take time to get up to speed. During this time there is a starting current that for induction motors is generally well above full rate running current when the motor is at full speed at full rated load. For a typical induction motor this no mechanical load starting time will be a number of AC cycles. With an attached mechanical load this duration may be extended considerably.

Most breakers of a thermal type have, for a specific model, a trip time curve that starts out possible 6 times breaker rating dropping to something above rating after a fairly long time.

The breaker trip time curve has to be above the motor starting curve to avoid startup tripping.

Make some measurements on your devices, and/or look at data sheets.

.
Click to expand...
I know what I lack Gars, that's why I am asking the question but appreciate you pointing that out.
 
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