800 amp breaker noise when 200 hp motor starts ?

[Davebones]

We have installed a 200 hp ( 480 V ) shop air compressor for the plant . We have a 400 amp feed to a disconnect at the compressor . ( fused at 350 amps ) The panel that feeds the air compressor is a 800 amp panel ( not much load on panel ) which is fed from one of our 4000 amp services . Total distance is about 400 ft from air compressor back to the main 4000 amp service . On start-up you can hear a ZZZP ( as our carpenter calls it ) in the instant it starts at the main 4000 amp panel . All connections have been checked so we figure it's just the start-up current . Should we have any other concerns about this ?

 

[kwired]

Is this across the line started?

Effect will likely be worst with across line starting - you have much higher current for a short time during starting then you have during normal running. The current produces magnetic fields around the conductors and they push and pull against one another as well as against ferrous raceways or other closures. Those fields are stronger at startup when current levels are higher.

Can even be components inside a breaker that are effected by magnetic fields in similar ways.

 

[Davebones]

Yes , this is across the line started .

 

[dmsv10]

We have installed a 200 hp ( 480 V ) shop air compressor for the plant . We have a 400 amp feed to a disconnect at the compressor . ( fused at 350 amps ) The panel that feeds the air compressor is a 800 amp panel ( not much load on panel ) which is fed from one of our 4000 amp services . Total distance is about 400 ft from air compressor back to the main 4000 amp service . On start-up you can hear a ZZZP ( as our carpenter calls it ) in the instant it starts at the main 4000 amp panel . All connections have been checked so we figure it's just the start-up current . Should we have any other concerns about this ?

I would check the inrush current and associated voltage drops, make sure there within manufactures specs. I've heard similar when other large chillers started as already answered. The only other thing that I would plan for, is futute loads being added to the 4000A and budget for interstart delays if applicable for new equipment!

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[Ingenieur]

imo normal
you are talking about 1500 A to start
does it start unloaded?
does it start smoothly within a few seconds?

 

[electrofelon]

800 amp breaker noise when 200 hp motor starts ?

I'll bet you would make some noise if you were trying to start a 200hp motor :lol:

 

[retirede]

I would not consider this uncommon when starting 200 HP across the line.

 

[Davebones]

Having worked in large industrial plants ( 9000 hp , 6900 volt largest I saw & heard ) I thought this was normal sound due to the inrush . Some of the shop maintenance guys were concerned due to the noise at the main 4000 amp panel . It does start across the line unloaded .

 

[Jraef]

I'll bet you would make some noise if you were trying to start a 200hp motor :lol:

And just think of how noisy 200 horses would be were it not for electricity!

Seriously though, is the sound definitely coming from the breaker itself, or could it just be that the cables are vibrating in the conduit and the sound is coming up into the switchboard? The breaker itself rattling could possibly be a warning sign of a loose mounting or connection. It's worth taking a look if it is the actual breaker. I'd hit it with an IR scanner too.

 

[petersonra]

And just think of how noisy 200 horses would be were it not for electricity!

Seriously though, is the sound definitely coming from the breaker itself, or could it just be that the cables are vibrating in the conduit and the sound is coming up into the switchboard? The breaker itself rattling could possibly be a warning sign of a loose mounting or connection. It's worth taking a look if it is the actual breaker. I'd hit it with an IR scanner too.

My first guess would be cable vibration.

You ever hear a #14 wire that has a dead short on it? Pretty impressive noise until the breaker trips.

 

[Besoeker]

imo normal
you are talking about 1500 A to start
does it start unloaded?
does it start smoothly within a few seconds?

Pretty much agree with that. Not unusual to quote Tom Jones.
In my experience, it is normal for compressors to be started up off load although it is probably not a major concern.

 

[retirede]

Pretty much agree with that. Not unusual to quote Tom Jones.
In my experience, it is normal for compressors to be started up off load although it is probably not a major concern.

Most positive displacement compressors (recip or rotary screw) cannot be started under load by a standard NEMA design B motor.

 

[Ingenieur]

Most positive displacement compressors (recip or rotary screw) cannot be started under load by a standard NEMA design B motor.

my point, not made clearly, was to make sure the unloader is working properly

 

[retirede]

my point, not made clearly, was to make sure the unloader is working properly

Absolutely. I was replying to Besoeker's comment:
"In my experience, it is normal for compressors to be started up off load although it is probably not a major concern"

 

[Ingenieur]

Absolutely. I was replying to Besoeker's comment:
"In my experience, it is normal for compressors to be started up off load although it is probably not a major concern"

imo on a recip a bent rod is a major concern
:happyyes:

 

[Besoeker]

Absolutely. I was replying to Besoeker's comment:
"In my experience, it is normal for compressors to be started up off load although it is probably not a major concern"

In relation to the noise.
From standstill the motor will take around 6-8 times FLC whether loaded or not. The last compressor we did was for a LNG plant. It was 6,630kW at 11kV. The LRC was a bit under the six times. We did an ATX starter because of supply capacity limitations.

 

[retirede]

In relation to the noise.
From standstill the motor will take around 6-8 times FLC whether loaded or not. The last compressor we did was for a LNG plant. It was 6,630kW at 11kV. The LRC was a bit under the six times. We did an ATX starter because of supply capacity limitations.

I've never worked with anything that size. The machines we produced were 600HP or less. Usually equipped with a NEMA design B induction motor with a typical locked rotor current of 6 X FLA. You're right, the starting current at T=0 is the same, loaded or not. Of course, the greater the load at startup, the longer the OP's noise is going to persist.

A 200 HP plant air compressor is not going to budge if under full load (full pressure) at startup.

 

[Besoeker]

I've never worked with anything that size. The machines we produced were 600HP or less. Usually equipped with a NEMA design B induction motor with a typical locked rotor current of 6 X FLA. You're right, the starting current at T=0 is the same, loaded or not. Of course, the greater the load at startup, the longer the OP's noise is going to persist.

A 200 HP plant air compressor is not going to budge if under full load (full pressure) at startup.

I'm sure you are correct. I didn't deal with much positive displacement. I'm reluctant to say never - in half a century you come across some odd stuff - and people.........

 

[dmsv10]

Nothing like a hard start on the big 5H Compressors, if you're sensitive to or in tune with your electrical system, most bigger chillers will create some type of a momentary vdrop, 1/4 cyle! Some buzz in the conduit!

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[zog]

What type of breaker is it? Older LVPCB's with oil dashpots will make that noise under those types of conditions.