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I have an EE background, but am new to metering hardware. Looking at metering equipment for high voltage measurements (up to 6.6 kV), it seems most only go up to 480 V, even when classified as industrial. Some are marked as having "Transformer input" or "resistive divider input" for voltage. Couldn't any meter have input come from a PT? Are there some models that are more or less accurate when measuring through PTs? Am I missing something obvious about how to measure high voltage signals?

Thanks

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  • \$\begingroup\$ What is "PT"? Power transformer? \$\endgroup\$ – Elliot Alderson Jul 25 '18 at 19:34
  • \$\begingroup\$ PT = Potential (Voltage) Transformer \$\endgroup\$ – Errorum Jul 25 '18 at 19:49
  • \$\begingroup\$ Normally HVAC is reduced with HV cap divider and HVDC with R divider with suitable design and probe insulation. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 25 '18 at 19:49
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Any AC meter can be used with a potential transformer. At some voltage level, you may find that it is not standard practice to use PTs, but 6.6 kV is probably within the range where they are commonly used. A search for PTs to use will tell you that. You can buy panel meters designed for specific PT ratios and voltage ratings. That type of meter will read the primary voltage directly without having to calculate. That is the kind of meter you should probably be looking for.

Note that potential transformers and current transformers are also called instrument transformers. Meters that display the primary voltage or current are often referred to as "PT rated" or "CT rated." Panel meters used to display power distribution level values are sometimes called "switchboard meters" or "switchboard instruments."

The better instrument manufacturers should have information about meter ratings, how to order etc.

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  • \$\begingroup\$ Thanks, are there keywords to search for this kind of meter? I assume any listed voltage ratings apply to direct or PT voltages. \$\endgroup\$ – Errorum Jul 25 '18 at 20:13
  • \$\begingroup\$ See revised answer. \$\endgroup\$ – Charles Cowie Jul 25 '18 at 20:38
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Meters would need to have really large coils, conductors and connectors if they were rated to continuously meter above 480V.

Many high voltage conductors are very difficult to bend, you would have a hard time creating a circuit in a reasonable about of space.

Most importantly, it would also make meters really expensive, for such a ubiquitous device. It’s cheaper to transform the signal and use meters rated for a smaller voltages and currents.

We step down the high voltage using a potential transformer (PT) and similarly using a current transformer (CT) to reduce the amplitude of a current signal. If they are ideal transformers the signal is completely preserved with the exception of its magnitude.

Yes, there is an input called “transformer input” which you connect the PT or CT to on the meter.

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