Measurement of electrical values on HV.side

I have seen the instruments for measurement Volt, Amp, Power factor at HV.line. I wonder what the benefits of measurement at HV.line. I think that we can measure this parameters at LV.line and calculate to know value of HV.line with much cheaper instruments.

 

[busbar]

Simply, PTs and CTs aren't always in the ideal location.

 

[busbar]

Also, CTs and PTs may have limited frequency response, BUT you must only apply fully system-BIL-rated components directly to anyplace on a MV/HV system. To do otherwise may lower the world average life expectancy; however a slight degree.

 

[scottf]

There can be many advantages to measureing power from the "high" side. I assume we are talking about revenue metering here. A few points are as follows and vary with the type of installation/situation/voltage levels you have:

1) In generation station metering where the transmission utility does not own the generation station, metering on the high side (normally in the switchyard) can eliminate the need for the utility to "own" anything in the generation station.

2) Metering on the "high" side generally negates the need to estimate transformer losses, as is commonly needed if metering on the "low" side.

3) Obviously the cost of CTs and VTs goes up with voltage class, so the "up-front" cost of high-side metering ma be more expensive. Depending on the station lay-out, it may be cheaper to meter on the high-side, as few sets of IT's may be needed.