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Join Date: Aug 2012
Posts: 1

### Class of Power Analyzers

08/14/2012 4:47 AM

Hi all,

I have a doubt regarding the class of power analyzer with its respective CT.

From my understanding, if we have a power meter with class0.5 for V&I and class1.0 for kW & kWh, in order to obtain class1.0 for kW & kWh, we must use a class 0.5 CT. kindly correct me.

However, i do see that there is power meter that comes with class 0.5 for V&I and class 0.5 for kW & kWh. If we use the same class0.5 CT , how do we get a class0.5 kW & kWh? Is it so that we need to use a class 0.2 CT in order to get a class 0.5 kW & kWh?

I have an enquiry saying that if we are using a direct meter(without CT) then class 1.0 for kW & kWh is acceptable. However, if we are using an indirect meter(with CT) then the minimum class must be 0.5 for kW & kWh. the reason behind this is that with direct meter there will be less error compared to those with CT. Is there such thing?

Pardon me for my ignorance as I have not much background in electrical engineering.

Thank you.

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Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 2371
#1

### Re: Class of Power Analyzers

08/15/2012 3:02 AM

The performance of a system is only as good as its worst component.

The classifications are acceptable error indicators. There would be a high end and low end to the error range.

If you have two identically classified components and it just so happens that their error margins both err in the same direction and to the full extent of the class boundary then the result may be outside the class boundaries.

By having a tighter class delivering to a looser class then the looser classed boundaries will not be violated even if the error was maxed on each.

I think your anecdote does ring credibly.

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