Transformer Problem, Pls help

[nimeshasilva]

Hi all,
I got a little problem recently. :-(

An HID MH lamp in a UV curing machine (a.k.a platemaker or printing down frame) used in printing industry, is using a Transformer to step up 230V to 800V to supply the necessary voltage for the lamp. the transformer primary is working as an Autotransformer and providing this voltage. and the secondary is just a 11V-0-11V design. I attached the rough sketch of the wiring diagram.



The problem is when the machine is powered up, and after the lamp has ignited, the transformer's 230V winding is drawing ~65A (measured by my clamp Ammeter at point P2) current which is totally unacceptable (the machine is rated to 30A with including lamp, several motors, and all other stuff, but this time, I turned off all other stuff except the lamp) and the main service breaker is tripped due to exceed of the maximum current. but in the lamp circuit it only draws the ~19A (Measured at point P1) which (I think) is the normal current for the lamp. And when I disconnect the lamp and turn the machine on, the transformer primary alone is drawing ~15A and I think its unacceptable too. and the (such a big) transformer is getting hot quickly in the time period which the lamp has turned on and the main service breaker is tripped. which is less than 2 seconds.

It is a big transformer with about 20Kg of weight.

Can anyone help me to solve this problem?

 

[FvM]

There are two points:
- the measured lamp current of 19A matches almost perfectly the input current 65 A according to 19 * 800 = 66 * 230
- the other question is, if the lamp power is actually as high as 15 kW? And is the transformer rated for this power? This could be only answered by referring to the lamp and transformer specification.

In my ears, both the 800 V operation voltage and the 15 kW power are sounding rather high, but not impossible, depending on the lamp size.

In addition, a 15 A no load current won't be a problem, if 65 A is actually the rated current, referring to a cos phi as high as 0.97.

 

[mtwieg]

20Kg doesn't sound heavy enough to be a 15KW transformer, even if it's just an autotransformer... I'd make sure it's rated for the primary current.

 

[nimeshasilva]

Thanx FvM for very very quick answer.
The Machine is "Theimer Montakop 95" and its a Platemaker. (you might have heard of it). The whole machine is rated to 30A not 65A. Unfortunately the lamp and transformer specification are unavailable. the voltages are indicated in the label above the transformer's connector terminal. and my multimeter is reading the exact voltage values which are on the label. but, the lamp can't be 15KW. it should be less than 8KW. coz Theimer never built 15KW HID MH lamps according to info in their web site. so is the lamp making all problems? do you have any suggestions to fix that problem?

---------- Post added at 19:53 ---------- Previous post was at 19:51 ----------

Thanx mtwieg. but the whole machine is rated to 30A according to label on the back of the machine

 

[mtwieg]

Thanx FvM for very very quick answer.
The Machine is "Theimer Montakop 95" and its a Platemaker. (you might have heard of it). The whole machine is rated to 30A not 65A. Unfortunately the lamp and transformer specification are unavailable. the voltages are indicated in the label above the transformer's connector terminal. and my multimeter is reading the exact voltage values which are on the label. but, the lamp can't be 15KW. it should be less than 8KW. coz Theimer never built 15KW HID MH lamps according to info in their web site.

Well according to your own measurements, you were delivering 15.2KW to the lamp. So either your measurements are wrong or the specs on the lamp are not what you think. Or it's defective somehow.

Thanx mtwieg. but the whole machine is rated to 30A according to label on the back of the machine

So the transformer is included in that 30A number? If so then there's definitely something up on the load side.

 

[FvM]

20Kg doesn't sound heavy enough to be a 15KW transformer, even if it's just an autotransformer... I'd make sure it's rated for the primary current.

Good point. A 230 to 800 V autotransformer only has 40% higher rated power than an isolation transformer of same size. So the the said 20 kg aren't good for more than 3 or 4 kW rated power, possibly somewhat more, if it's designed for low duty cycle.

 

[nimeshasilva]

Well according to your own measurements, you were delivering 15.2KW to the lamp. So either your measurements are wrong or the specs on the lamp are not what you think. Or it's defective somehow.
So the transformer is included in that 30A number? If so then there's definitely something up on the load side.

I suspected that too. but the lamp's light seems normal and with my experience, I cannot see any anomalies in the lamp. But now I can understand the 19A is pretty much higher for the lamp. So maybe the ballast is defective.,

But how do I check the ballast without knowing the specs or lamp wattage correctly (the lamp manufacturer didn't print a single letter on the lamp :-( ?? ). coz all the documentation are unavailable for the machine and I had to totally depend on the multimeter readings. :-(

---------- Post added at 20:38 ---------- Previous post was at 20:17 ----------

maybe my weight measurement is wrong. may be more than 20 Kg. I didn't measure it using a scale, just a rough value. anyway, I ll post a photo of that transformer soon. then you'll be able to think of.

 

[FvM]

You should be able to get the required information, either from Printer Supplies (PVT) Ltd. Sri Lanka or Theimer Germany. A defective ballast could explain a too high lamp current, but the reported no load current of the transformer suggests a different problem, e.g. a wrong machine wiring. I'm somewhat surprized to hear about 230 V transformer primary voltage, because the standard machine supply seems to be three phase 400 V. At power levels above 2 or 3 kW, one would preferably use a phase-phase 400V input voltage to the transformer. It's only a guess. But if I'm right, the correct transformer circuit could be something like 400V : 560 V. An interesting point would be to determine the lamp voltage in operation.

 

[nimeshasilva]

Thanx for the valuable information FvM.
But as I can remember, the labels on the machine says its 230V 30A and 60Hz (we use 50Hz here in Sri Lanka though.). it is very dangerous to measure lamp voltage in operation. isn't it?? coz, if the ignitor doesn't cut off properly, it would be several KV's coming to the lamp isn't it. anyway, I'll try to measure it.

However., I'll contact printer supplies (PVT). Ltd and ask for the details. and if I fail on that, I'll contact Thiemer.

Thank you for spending your valuable time helping me. If I fail both of above steps, I'll be expecting your help again. And if I succeeded, I'll let you know.

 

[FvM]

In this case, I would believe the machine type plate. Operating a 60 Hz ballast at 50 hz involves an unwanted 20% current increase, but much less than the factor you're looking for.