How would you fix it?

[lapseofmind]

In a fruit packing warehouse, we installed 7 large MCC panels, placed in various locations depending on their proximity to the motors they control. Our PLC guy designed them and I built them. Currently, on one of the panels, they're having a lot of issues with transient voltage and harmonics, at least, that's what I'm told(I'm stuck in the shop sad to say).

A quick run down of the setup: 480v 3 phase power coming in. The panel controls everything from motors to solenoids, photoeye's to a few other things. It has a 12k btu air conditioner installed on one of the doors. I was told that the air conditioner only kicks on for a few seconds at a time and is really noisy.

The electrical contractor that is doing the majority of the electrical work(we install fruit sizers and the MCC's) wants to put a sine wave filter on it. These panels are full of MSP's and contactors and VFD's. He designed it with Load Reactors on all the VFD's though not all the motors are more than 100' feet away.

How would you go about smoothing it out? I was thinking of putting Line Reactors in or some combination of other, smaller filters that aren't as bulky as the one the EC wants to put in. Of course, that just leads to the question: Bad design?

 

[LEO2854]

In a fruit packing warehouse, we installed 7 large MCC panels, placed in various locations depending on their proximity to the motors they control. Our PLC guy designed them and I built them. Currently, on one of the panels, they're having a lot of issues with transient voltage and harmonics, at least, that's what I'm told(I'm stuck in the shop sad to say).

A quick run down of the setup: 480v 3 phase power coming in. The panel controls everything from motors to solenoids, photoeye's to a few other things. It has a 12k btu air conditioner installed on one of the doors. I was told that the air conditioner only kicks on for a few seconds at a time and is really noisy.

The electrical contractor that is doing the majority of the electrical work(we install fruit sizers and the MCC's) wants to put a sine wave filter on it. These panels are full of MSP's and contactors and VFD's. He designed it with Load Reactors on all the VFD's though not all the motors are more than 100' feet away.

How would you go about smoothing it out? I was thinking of putting Line Reactors in or some combination of other, smaller filters that aren't as bulky as the one the EC wants to put in. Of course, that just leads to the question: Bad design?

Yes it is a bad design.

 

[StarCat]

Control Cabinet Cooling

Control Cabinet Cooling

I will second on the design flaws, especially on the cooling arrangement which is incorrect.
Control cabinets need to be set up on what is known as " Return Air Control ".
Typically this is done with an air handler and definitely not a window AC.
IN essence your control cabinet should be set up ideally with supply air being ducted in the bottom of one end and out the top of the far end.
Your system control is located in the return air stream at the air handler and the unit is sized correctly for the heat load. As thus with a careful setting of the differential on the operating control you can arrive at keeping your cabinet at a fair constant within about a 2-4F swing range.

 

[petersonra]

Bad design?

Hard to say with the information you supplied.

How did someone come to the conclusion that there are issues with transients and harmonics? how did they come to this conclusion?

IME, blaming problems on transients and harmonics is about like blaming them on 'bad grounds". It just does not mean anything.

 

[petersonra]

I will second on the design flaws, especially on the cooling arrangement which is incorrect.
Control cabinets need to be set up on what is known as " Return Air Control ".
Typically this is done with an air handler and definitely not a window AC.
IN essence your control cabinet should be set up ideally with supply air being ducted in the bottom of one end and out the top of the far end.
Your system control is located in the return air stream at the air handler and the unit is sized correctly for the heat load. As thus with a careful setting of the differential on the operating control you can arrive at keeping your cabinet at a fair constant within about a 2-4F swing range.

why would any of this matter?

as long as the ambient temperature surrounding the equipment is kept within the equipment's operating range, what difference does it make.

Its seems to me like maybe the A/C is just oversized and that is why it only runs for short periods of time.

 

[brian john]

First I would install a line disturbance recorder and do a complete site survey to ascertain the problem. From what I read it is tough to know what may or may not be your problem.


Then I would come up with the fix.

 

[Jon456]

It has a 12k btu air conditioner installed on one of the doors. I was told that the air conditioner only kicks on for a few seconds at a time and is really noisy.

Its seems to me like maybe the A/C is just oversized and that is why it only runs for short periods of time.

It the cycle time is only a few seconds, then oversizing cannot explain the symptoms. I'm not saying that the AC isn't oversized, but even a massively oversized air conditioner will not cycle off that quickly. Something else is wrong.

 

[StarCat]

The points

The points

why would any of this matter?

as long as the ambient temperature surrounding the equipment is kept within the equipment's operating range, what difference does it make.

Its seems to me like maybe the A/C is just oversized and that is why it only runs for short periods of time.

It matters because you don't want any cooling unit short cycling and ideally you want the air distribution to be uniform. If you could baffle the tendency of a window AC to short circuit supply to return air it might be optimized, but its not ideal. Window ACs are made to blow out into open space and not be working against static pressure or in situations where the air flow will stratify or short corcuit.
Your points about the operating range are valid, but why not make it as good as possible for long life of all components....

 

[jim dungar]

If you could baffle the tendency of a window AC to short circuit supply to return air it might be optimized, but its not ideal. Window ACs are made to blow out into open space and not be working against static pressure or in situations where the air flow will stratify or short corcuit.

This is all true of a unit designed to mount in a window, but there are many AC units specifically designed to be mounted on the doors of electrical enclosures.
It would probably help if the OP provide more information.

For all intents, reactors installed on the output (load side) of the VFD's will not do anything that impacts the line side (incoming power).

 

[hurk27]

All our MCC panels that have plc controls in them also have a separate power source for the PLC supply's and or any other electronics, this supply comes from what we call a clean source usually a dual conversion UPS system or a heavily filtered surge protected panel or both, if you have control transformers and or power supplies fed off the same circuits that also supply the motors and or VFD's then this could be a problem.

 

[Jraef]

Hard to say with the information you supplied.

How did someone come to the conclusion that there are issues with transients and harmonics? how did they come to this conclusion?

IME, blaming problems on transients and harmonics is about like blaming them on 'bad grounds". It just does not mean anything.

I completely agree. Often when someone doesn't want to take the time to fully investigate an electrical puzzle, they will call it "harmonics" and dump it on someone else...

 

[Aleman]

We have built a good amount of controls at my job and have not had any problems. Some recommend line reactors on VFD's.
So far we have not needed to do that. We run AC units on our motor cabinets but they are made for the application and run off 480V.
Usually the control side 24VDC is a separate cabinet or on one side and the 480 on the other. I would look at your grounding. You
didn't say much as far as what problems you are having. More info = more help.