Medium Voltage Field measurements 2

[tmahan]

After spending the afternoon doing some troubleshooting low voltage troubleshooting I started wondering about medium voltage troubleshooting. Measuring the input and output voltage was required for what we were doing (at 480V)

On a 4160V system how would a service tech take voltage measurements? Would PT's be installed and voltage measured indirectly? or is there some procedure/equipment that safely allows the measurement of voltage directly.

Please note this question is for general information only.

 

[busbar]

Good question. Fixed/drawout fused PTs are common, but not recommended on a temporary or portable basis. Use something like

http://www.rossengineeringcorp.com/hizdet.htm

"125KV TO 300KV BIL AC/DC TO 100KV Power Class" or

http://www.stbinc.com/products/volt/9_36kv.html

And, they must be used on 100kV/ft-rated hosticks. Do read the instructions.

Please Do NOT Attempt USE of a NON-POWER-CLASS "accessory probe." They are deadly and have no BIL rating necessary for most all 60Hz AC circuits. These are intended only for things like servicing bug zappers and boiler igniters.

 

[tmahan]

So the idea is use the stick to maintain a safe standoff distance between the service tech and actual voltage source?

Would a hotstick like this be suitable for waveform capture with an o-scope?

My lines of thinking regard medium voltage softstarters and VFD's. Cases where it would be desireable to have independent verification of frequency, voltage and waveform. Clearly, a 13.8 kV softstarter is not something that lends itself to casually measure the output voltage on without prep work.

 

[busbar]

Find instruments like those, for example, at:

http://www.rossengineeringcorp.com

Voltage dividers for connection to power systems need ANSI-defined Basic Impulse Levels expressed in kV.

(Ehh, generally one per phase)

 

[busbar]

If you find that you are severely brain-damaged and have some end-of-year money burning a hole in your pocket, see:

http://www.sensorlink.com/products/litewires/index_litewires.html

{tell duane hi, too.}

 

[BJC]

IF you have never done it ( measure voltage in switchgear ) hire someone that knows what they are doing and watch them a couple of times. If you don't have a test buggy for your gear, buy one.
So far no one here has mentioned a rubber blanket, protective clothing or gloves. This ain't like checking the 110 outlet in your house. Checking this kind of voltage by amatures has made more than one set of widows and orphans.

 

[jbartos]

Suggestion and addition to the previous posting. When it comes to medium and high voltages, the single failure criterion is often considered or mandatory. This for example means that an extra isolation transformer is applied, which somewhat increases the cost of testing. This is a regular price paid for the increased safety.