Xray and Transformer Question

[Kidd]

Hi guys,

I'm working on a project with an Xray machine involved. I haven't really dealt with these before, but from what the sales guy says, the main panel for the x-ray room only accepts 480V, 3 phase, and has a 60amp breaker on it. the x-ray machine itself is rated at 65kW / 99kVA.

I'm assuming since the breaker is 60amps, that 99kva is the momentary rating since 50% of that is right under 60 amps.

The building only has 120/208V, 3 phase available, so the sales guys says we'd need a transformer to step up the voltage. Since the main panel for the x-ray room is only 60amps, should i size the transformer according to the 60 amps (about 50kva) or the 99kVA rating of the xray machine?

The only code I could find mentions the branch circuit and over current protection device, which technically shouldn't apply to me since we're only providing power to their panel. So the branch circuit and ocpd of the xray itself is not really in our scope.

Thanks for any input guys!

 

[thanoscar]

What is the running load on the x-ray machine? I would think that the panel may need to be upsized as well

 

[thanoscar]

I probably won't have the best answer but I feel like there are some details missing here, I would make sure it is going to handle the load of the x-ray machine, and also that the panel and conductors are properly capable of supplying the transformer you decide to use.

 

[jim dungar]

Size it based on your protection.
X-ray machines draw power in bursts, not unsimilar to motor starting.

 

[Kidd]

What is the running load on the x-ray machine? I would think that the panel may need to be upsized as well

I'm not sure, I asked if the rating they gave me was the momentary or the long time load, but never got an answer. I'm assuming it's the momentary, but the 60A panel that will feed the xray machine is being supplied by the xray designer/vendor. We're just bringing power to it. Which is why I'm leaning towards sizing the xfmr based on the 60 amps. So a 75kVA transformer to step up the voltage from 208V to 277/480V and a 150amp breaker on the primary side.

 

[Kidd]

Size it based on your protection.
X-ray machines draw power in bursts, not unsimilar to motor starting.

That's what I was thinking too and yea that's what I keep reading, but since I haven't dealt with these before I figured I'd ask the question to more seasoned pros.

Thanks!

 

[d0nut]

Is the X-ray for healthcare or is it for an industrial process? If it is healthcare, you may want to look into a power conditioner rather than a standard isolation transformer. The X-ray vendor should have recommendations for power conditioners that have been used with that particular machine. They might even bundle it with the x-ray and provide a package deal for your installation.

 

[Kidd]

Is the X-ray for healthcare or is it for an industrial process? If it is healthcare, you may want to look into a power conditioner rather than a standard isolation transformer. The X-ray vendor should have recommendations for power conditioners that have been used with that particular machine. They might even bundle it with the x-ray and provide a package deal for your installation.

It's for healthcare. The vendor hasn't been much help. He basically stated it's my job to figure out what size transformer, breaker and circuit I need on the primary side, not his. I appreciate the input though!

 

[zbang]

Then they complain that something isn't correct and you reply "We did ask."

 

[winnie]

Check the specs for minimum voltage or maximum impedance.

From the point of view of transformer heating, you will be fine sizing the transformer based on the breaker.

But for purposes of maintaining sufficient operating voltage you might need a larger transformer or a custom low impedance transformer.

Jon

 

[Kidd]

Then they complain that something isn't correct and you reply "We did ask."

Right!

Check the specs for minimum voltage or maximum impedance.

From the point of view of transformer heating, you will be fine sizing the transformer based on the breaker.

But for purposes of maintaining sufficient operating voltage you might need a larger transformer or a custom low impedance transformer.

Jon

The only specs they sent over don't show any info regarding impedance. It does mention +/- 10% voltage and a max line regulation of 6%.

 

[winnie]

I think that the max line regulation spec is the one which defines how much the voltage is permitted to change under load, but don't know enough to confirm this or calculate what it exactly means.

In particular, I don't know if that means 'voltage drop at the moment the xray is operating' or 'voltage drop at the breaker rating of the machine '

Jon