transformer output

[chris54]

Hello and thanks for the time to read and reply. I have a transformer that I believe to be the problem. It is a multi output transformer. Looking at the specs the HV secondary should be 1750 volts ac with the transfomer in the unit and operating I read 1500 volts a/c. A difference of 250 volts looks low to me.

What is your opinion

 

[Diver300]

The output of a transformer varies with the load, it called regulation. There is more variation with smaller transformers.

1750 V ac is a lot for a transformer, so I would expect it to be quite high power, but you don't say what power it is. 1500 V is 15% low which could be OK but more information is needed.

 

[chris54]

The reason I asked is because if I replace it the spec on the replacement wuld be either of two depending on wahr I want. One would be 0-1750 or 0-1950. The driect replacment is 0-17050. so I assume it would be 1750 no load This is why I was asking about the difference between what I am reading and waht is designed

 

[Diver300]

Transformers usually quote the output at full load, with a resistive load. With no load, the voltage will be higher.

You haven't said what the application is, or what power it is. 1750 V is very high for a transformer. What transformers are you considering?

 

[chris54]

It is an rf linierpower amp it supplys the voltage for 3 3cx400at triodes.

 

[Diver300]

I can't find any reference to those triodes. What is the power rating of the amplifier?

 

[ericgibbs]

I can't find any reference to those triodes. What is the power rating of the amplifier?

hi diver,
The closest I can find is this pdf.

 

[Diver300]

This is getting way outside what I am familiar with.

I guess that you are looking at a transformer around 1000 W to 2000 W, in which case I would expect the voltage to change by less than 10% under load.

However, I have no experience with such high voltage transformers, and the voltage measured depends on the load type. I guess you are rectifying, and that will only load the peaks of the output waveform, so the loaded voltage will be far from sinusoidal, and the voltage you measure depends on how your voltmeter interprets odd waveforms.

 

[Nigel Goodwin]

I can't find any reference to those triodes. What is the power rating of the amplifier?

They are bleeding great big things

Three of those is a BIG amplifier.

However, I wouldn't expect the transformer to be faulty, to give low output would require shorted turns, and a transformer that large (and VERY expensive) would be pouring smoke out if it had shorted turns.

 

[JimB]

At the risk of stating the obvious:

Are you sure of the voltmeter calibration?

What is the input voltage? if the input is low, the output will be low.

JimB

 

[marcbarker]

Would 250 V make much difference?

For 250 V to have been 'lost' somewhere along the line to me would mean shorted turns (plus a room filling with transformer-smoke) or if not, that the turns-ratio changed itself!