Measuring High Voltage AC

Thanks for the response to my question. It is stated 30kV. 100V. Does that mean full deflection is actually 100 volts?

I am a physicist and have been designing and building Tesla Coils for over 30 years, so I am very familiar with both high voltage and high current. But this is the first time that I actually need to measure the ac output of a HV transformer and have never used a hv ac meter before.

Yes, the scale is 50kV = 100 volts. A potential transformer (PT) would be normally used, at that voltage, a capacitively coupled PT would be less, but less accuracy. You may find a 30kV rated probe for a meter, ie Fluke, for lab work, will be easier. If you know the internal resistance of the meter, you can use a voltage divider, ratio 30kV to 100V with high accuracy. Those resistors are mounted on ceramic insulators, 30kV creep distance is something you will want to look up.

I forgot you just need 12kV, lots easier & cheaper to buy a standard 14400V to 150V transformer and replace the meter with a standard 150 volt scale meter, 0-150Vac. You will be far ahead of where you are now. These transformers come with HV current limiting fuses mounted on the top, so all you need is clearance.

Hi,

The ac voltage I want to measure is from a distribution transformer that I have rebuilt.

The actual meter is 30kV and not 50kV as in the image I uploaded. I think that the information you have supplied me will suffice. Thanks!

Here is a video of a real high voltage termination:

https://youtu.be/sQrHTU8Mtow

A simple line diagram of voltage distribution.

https://youtu.be/gpbBhZcLrWs

As others have said, the panel meter you show requires some form of a calibrated (resistive and/or transformer) network to accurately reduce the voltage at the panel meter. Redesigning another network for a different voltage ratio requires additional knowledge of the panel meter, voltage source and all leakage paths to provide accuracy. I suspect you need accuracy in your measurement. You probably should instead use a HV probe like this.

You can even get a calibration certificate if you need it.

Would they feed 30KV to a panel meter?

You normally would use a transformer. It is likely the meter is a 120Vac full scale, so your potential transformer would be 12kV to 120Vac. The transformer is designed for high turns ratio accuracy.

Perhaps you have the meter movement for a 30KV instrument without the rest of the parts. Please show us a picture so that we can determine it. Is it in a wood box? Are there input terminals? If so what DC resistance is measured on them?

Thanks for the response to my question. It is stated 30kV. 100V. Does that mean full deflection is actually 100 volts?

I am a physicist and have been designing and building Tesla Coils for over 30 years, so I am very familiar with both high voltage and high current. But this is the first time that I actually need to measure the ac output of a HV transformer and have never used a hv ac meter before.

All I see is a meter movement, you didn't answer any questions. You probably need a transformer as stated in post 3 but with 100V output @ 30KV input. Full scale on the meter shown is 50KV, not 30KV. Does it have any resistors or capacitors on the back?

Be certain you know what you are doing,otherwise,you will be a copper splattered shadow on the enclosure wall.

30Kv does not play,and rarely gives second chances.I know one person that survived a 13,200 volt short,because it blew him backwards away from the bus bars,but it flash blinded him for several weeks and peppered his body with molten copper.

Asking your question makes me question your qualifications.Have you ever seen a high voltage fault?Imagine a stick of dynamite exploding and it will be close to the result.

I have seen a complete substation tower fed by 13,200v melt down to the ground,with large I beams turned into molten metal puddles.A chain link fence surrounding the substation had a bulge of a worker running away.

You could really see the outline in the fence wire.

There are plenty of old electricians,and plenty of bold electricians,but there are no old,bold electricians.Be very careful.

Thanks for the response to my question. It is stated 30kV. 100V. Does that mean full deflection is actually 100 volts?

I am a physicist and have been designing and building Tesla Coils for over 30 years, so I am very familiar with both high voltage and high current. But this is the first time that I actually need to measure the ac output of a HV transformer and have never used a hv ac meter before.

I've never seen or heard of a 30kV panel meter. It is probably a panel meter that accepts a much smaller voltage (say 100V or even 10V)and the panel face is just scaled to read 30kV maximum.

I suggest you test the meter with smaller voltages first to find its maximum deflection voltage. Then choose a step down transformer for 30kV to 100V (or whatever the max deflection volt) and connect it to the meter. A 30kV stepdown transformer, however, isn't small and wouldn't be installed in the monitoring panel.

30kV is much too high for someone who is inexperienced (as I assume you are). Better to give the job to someone who knows what he's doing.

regards,

Vulcan

I am presuming you are measuring a low power high voltage source, such as the 25kv on old analog televisions, not a high current source like on the electrical grid.

If so this changes the recommended measurement methods.

The Fluke probe above is a good method for such voltage, If the voltage source is a low amp capacity short circuit type, like a spark plug ,etc.

These voltages will hurt, but not vaporize you upon contact like a utility type HV transformer. You did not specify the source of high voltage, so I took the safe presumption for safety.

The ac source is from a distribution transformer that I have rebuilt.

Hello all, I'm wincing at this thread. Asking an anon forum about 30kV metering, providing a picture of an obviously LV panel meter and then comment about having rebuilt a transmission network transformer.

I'm wondering about the insulation tests on the transformer, the connection quality (not the resistance, but the actual shape of the joint), and a heap of other concerns.

To the OP, PLEASE (yes in caps) engage a suitably qualified professional in this field and even pay them some extra to involve you as they do the necessary verification of the work. Having them independently verify your work and provide feedback will assist you to move forward in this field.

I support your enthusiasm and with time, you may become one of those suitably qualified professionals.

I worked on HV for use in underground, gassy coal mines.

Here is a high voltage explosion and a mere 480v explosion arc.

https://www.youtube.com/watch?v=k41zThvzqc0

https://www.youtube.com/watch?v=2Xoyb9M5-EA

I repeat,BE VERY CAREFUL.

All analog meters work on milliamps,internally,so internal resistance of meter must be known to calculate proper v/a applied to meter.Applying 30kv to a meter is very silly and dangerous.

Is your life insurance paid up?