Are there any universal standards for what is considered low, medium, and high voltage as it pertains to transmission and distribution?

I've tried to find the answer, but am getting numbers all over the place with MV starting at 1, 4, or 7kV and HV starting at 36, 45, or 69kV. Are these just arbitrary designations within different POCOs?

Also, does anyone know anything about EHV and SHV as they pertain to transmission lines? Are those terms even used much?

Thanks a lot.

-John

A universal standard? Now you are an optimist!

The easiest is the LV->MV: In the metric world, the threshold is usually 1000V. In North America and areas under its influence, it seems that 600V is the limit. This is reflected in the electric codes, the voltage ratings of cables and tools.

The transisition from MV to HV is more uncertain. It seems it is usually somewhere between 35 and 70kV but even the 33kV systems are sometimes considered to be HV.

As to the limits of EHV and so on I don't know.

“Official” boilerplate for the North American continent is: ANSI Std C84.1-1995 Electric Power Systems and Equipment—Voltage Ratings (60 Hertz)

  2.1.3 System voltage classes

2.1.3.1 low voltage: A class of nominal system voltages 1000 volts or less.

2.1.3.2 medium voltage: A class of nominal system voltages greater than 1000 volts and less than 100,000 volts.

2.1.3.3 high voltage: A class of nominal system voltages equal to or greater than 100,000 volts and equal to or less than 230,000 volts.

[ANSI Std C92.2 considers EHV above 230kV and up to 800kV. Above 800kV is UHV.]




[This message has been edited by Bjarney (edited 03-10-2004).]

It seems like 1000V is a universal limit then. Sometimes it's nice to be wrong

C-H, you raise a valid point. 600 or 1kV may be a breakpoint by many—with the range between being a sort of “no man’s land,” except for 690V IEC and 830V ANSI {oil fields}.

Also, some consider above 35kV (above distribution voltage) or possibly 60kV as lower end of “high” voltage. I do not know for certain if IEC standards reflect the same numbers as ANSI.

830V? Is that 500/830V? Used for what? Oil fields hint motors.

Isn't there a rare 577/1000V system in the ANSI world too?

Side note: Both 690V disconnects and motors that can operate on 690V are fairly common in Sweden. Presumably the difference in cost vs. 400V is very small. Thus you can get the disconnect and the motor, but try getting a 690V supply

I once saw a 690V 3-phase disconnect used as a light switch. The electrician must have been out of ordinary switches and not minded the extra cost. I looked around the room for a switch several times, before I realised that the grey box with a lever was the way to enlightenment.

The British IEE now follows the "harmonized" European designations as mentioned above, but prior to the early 1980s the classes were LV up to 250V, MV for 250 to 650V, and HV for 650V and above.

These were applied as the maximum voltage either between conductors, or from any conductor to ground, so a single-phase 240V service was classed as LV, but a 3-phase 240/415V system was MV.

Aaak! Sorry for the delayed response, C-H. 830Y/480V has special application in oilfields given long circuit lenghts—some for downhole pumps. Given added insualtion, 480V delta-connected motors {and transfomers} reconfigured for wye accommodate the higher voltage. There is also 1040Y/600V used in mining, which likewise are 600v motor and transfomer coils reconnected for wye.

Like going to any higher voltage, there is decreased voltage drop but greater stress on ground and phase insulation. Also, don’t forget the switching and protection aspects—starters and fuses/circuit breakers have to be designed for the application.

Paul,
that was a rather different take on it! What did they call the 400kV lines? Ultra Super Extra High Voltage?

Bjarney,
I better brush up on my math: 830/sqrt(3) isn't 500... Interesting part about the delta-wye rewind. 1040/600V makes sense if you use rewound 600V motors.

The cables shouldn't be a problem, most metric underground cables are designed for 600/1000V but
Meaning they will charge you an arm and a leg for every single component. Only octopuses need bother ordering entire installations

Aside to C-H and other offshore readers — At least one major US motor manufacturer has sort of ‘copied’ the rest-of-the-world trend for motor-voltage ratings. [In the US, as opposed to wye-delta configured motors, the series/parallel stator-coil arrangement is more common in low-voltage models.]

In higher voltages, [>2kV] stock motors {~200-1000hp} are offered with 2300/4000V nameplates for use on 2400(∆) or 4160V(Y) distribution. It seems like we may have learned a little for other countries’ standard practices. www.baldor.com/pdf/MedVolt.pdf




[This message has been edited by Bjarney (edited 03-15-2004).]

LOL!

I'm not sure how far back those IEE definitions of LV and MV go, but I think it was probably many decades.

By the way, they did define extra-low voltage as well: Less than 50V between conductors, and less than 30V AC or 50V DC from any conductor to ground.

For the NEC in the US, it used to be that ’50 volts’ was the magic number for generally non-hazardous voltage. A few code editions back, the levels changed to ‘no greater than 30 volts rms, 42 volts peak or dc.

Later, a proposal was accepted from the telecomm industry to keep 30 VAC, 42V peak, but cahnge to 60VDC with very little supporting information other than telecoms had historically done it. [As far as why not a 50VDC limit, nominally 48VDC central-office battery floats at about 53.5V, and batteries are sometimes equalized at about 56 volts.]

In the preprint it sounded as though, with little substantiation, it may have been ‘railroaded’ through the acceptance process.


[This message has been edited by Bjarney (edited 03-17-2004).]

I can see why telecoms would have supported such a limit. If stricter rules were to be implemented for a 42V DC limit, it would have meant many expensive changes to the distribution systems in the average telephone exchange.

U.K. telecom power is nominally 50V rather than 48V, but even though a high battery voltage would just exceed the 50V ELV limit, the classifications were based on nominal levels rather than the highest which could actually be attained. (Similarly, the upper permissible limit for our nominally 240V supplies works out as 254.4V, but still classed as LV despite being 4.4V over the boundary.)