# How do linemen measure voltage and current in medium voltage systems?



## Black Dog

José_Fuentes said:


> For low voltage we can use a multimeter, but for medium and high voltage, I understand that in the substations there are current transformers and potential transformers that output a small fraction of the current and voltage (one for each relevant circuit for each phase), so that it can be measured by more conventinal means (again a multimeter, a electricity meter, etcetera). However, how do linemen measure these parameters in the field, for instance, to tell from which lateral MV feeder an overload comes from?. and how do they measure voltage?. Do they carry current transformers and potential transformers?. In addition, how do linemen know whether a line is live (I assume they can just measure the voltage and see if it's nonzero, but maybe there's a more practical way)?. Regards and thanks.


They use big Hot sticks to see if it is hot, but they have an extensive safety system that they follow.


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## José_Fuentes

Black Dog said:


> They use big Hot sticks to see if it is hot, but they have an extensive safety system that they follow.


I see, but what about measuring voltage and current in the field (I don't mean the permanent measurement instruments at the substations)?.


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## Zog

Phasing sticks, just voltmeters on the ends of really long hot sticks.


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## Meadow

^^^^ what Zog said


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## MXer774

I use an amprobe tic tracer to see if a circuit is energized, however tic's are useless on shielded cable unless you are certain where the terminations are, granted the terminations are exposed terminals such as a cutout or open terms on equipment. To check what voltage a cable or overhead is I can tell by how the pole is built or type of terminations and cable. When unsure I have my Salisbury non contact voltage meter. To check amperage I also have a Salisbury amprobe, however your standard digital amp clamp will be able to check amps. Not recommended but does work as long as the circuit amperage does not exceed your amp clamp rating.


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## José_Fuentes

Thanks everybody for the answers.


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## Bipeflier

They use these: http://www.hubbellpowersystems.com/lineman/meters/phasing-testers.asp


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## JW Splicer

You can use phasing sticks like Zog mentioned, basically a voltmeter designed for higher voltages. Some live line testing tools have a PT or CT built in. You can use an tic tracer as mxer suggested, works just like an inductance tester, hot or not. Many switchgear now come with voltage or current indicators built in. Underground cable is a different story. We have a few different methods, one is a chance meter, it measures current difference between the shield and the semicon. Another method is a statiscope, basically a neon lamp that required the tool to be in contact with the insulation. Obviously both methods require the cable to be opened to a certain degree. We use them only for testing zero volts after the cable has been deenergized and grounded.


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## micromind

For simple voltage readings, we have a capacitive analog meter attached to an 8' hot stick. 

While it's not all that accurate, it'll certainly tell you if the line is energized or not, along with a rough voltage measurement.


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## backstay

http://www.vitrek.com/4700-precision-high-voltage-meter/


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## BaritoneGary

A simple way to determine if a cable is hot (or not), is to use a Glo-Tube attached to the end of your hot stick. Cheap and effective. Watch the ranges when you order one. There are different voltage classes (5kV, 15kV, 25kV, 35kV). Just be careful! The voltage may have dropped below the proper voltage, and there may still be residual energy in the line. The brighter it glows, the higher the voltage. It's just a good way to determine which leg is faulted, and which are not.


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## degupita

Do they prefer to use Analog meters?


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## Big John

In EHV substations I often have to use my analog Simpson because the electric field is so high I can read dozens of volts on a digital meter when not connected to anything.


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## BaritoneGary

AB Chance make a whole line of test equipment and kine materials. Check out this tester page: http://www.hubbellpowersystems.com/lineman/meters/


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## slingnit

Sensorlink primary volt and amp meter. Can use a no load transformer to get secondary voltage and multiply by the transformer's ratio. Regulator stations and capacitor stations with primary ct's. Many different ways, all depends at what point of a cct you need the info.


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