Definition of MVA - Mega Volt Ampere

[jreed]

Mike's First DVD in Basic Electrical Theory uses a term: MVA. I believe this means Mega Volt Ampere. Mega = million. Volt is simple and amp. But how does the term MVA apply exactly? A million volts AND amps combined?

 

[Smart $]

Mike's First DVD in Basic Electrical Theory uses a term: MVA. I believe this means Mega Volt Ampere. Mega = million. Volt is simple and amp. But how does the term MVA apply exactly? A million volts AND amps combined?

One megawatt at a power factor of 1.

 

[LarryFine]

Mike's First DVD in Basic Electrical Theory uses a term: MVA. I believe this means Mega Volt Ampere. Mega = million. Volt is simple and amp. But how does the term MVA apply exactly? A million volts AND amps combined?

First you must understand that volts and amps "combined" to make volt-amps means they are multiplied together. For example, your typical 200a home service is capable of (240v x 200a) 48Kva, or 48Kw if the power factor is 1, as S$ points out.

Watts and volt-amps are equal when there is no significant reactive (capacitive and/or inductive (unless the two are equal)) impedance. Otherwise, volt-amps will be greater than watts; the ratio is the power factor, and will be less than one.

 

[George Stolz]

VA are volts times amps.

2400 VA is the same whether the voltage is 120V or 480V.

The amps will vary, depending on the voltage, for a given VA.

So, 2 MVA is 2,000,000 VA.

If the voltage is 120V, that is 16,666 amps.

If the voltage is 4160V, that is 480 amps.

 

[templdl]

1,000va =1kva
or
1,000,000va=1mva
or
1,000kva=1mva

 

[Smart $]

But how does the term MVA apply exactly? A million volts AND amps combined?

After reading your profile I see you are an apprentice inside wireman. You are more likely to run into the term KVA much more often in this field.

1 MVA = 1,000 KVA = 1,000,000 VA​

VA is nothing more than the numerical product of voltage and current (i.e. E ? I). As you will learn, perhaps, this is a measure of apparent power. Watts, on the other hand, is a measure of true power. The ratio of watts to volt-amperes is known as the power factor (PF or pf).

VA = E ? I
W = E ? I ? pf = VA ? pf​

The difference results from an AC circuit where the voltage and current are not exactly in-phase. This occurs in loads that have reactance: capacitive and/or inductive. A purely resistive load has a power factor of 1.

 

[charlie b]

Just in case this isn?t confusing enough, let me pile on (no I mean let me add) one more level of complexity.

The fundamental units that make up one ?volt? are ?joules per coulomb.? What this means is that voltage is a measure of the amount of energy (in units of ?joules?) it takes to move an amount of charge (in units of ?coulombs?) from one point to another. It is in this sense, the sense of ?from one point to another,? that gives us the voltage ?across? two points.

The fundamental units that make up one ?amp? are ?coulombs per second.? What this means is that current is a measure of the movement of charge (in units of ?coulombs?) in a given amount of time (in units of ?seconds?).

If you multiply these two terms, you get ?(joules times coulombs) divided by (coulombs times seconds).? Since ?coulombs? shows up in both the top half and the bottom half of this fraction, it cancels out. What is left is that the fundamental units that make one ?VA? are ?joules per second.? That is what should be expected, since power, be it given in watts or VA or VAR, is defined as the rate of use of energy, and the units of ?rate of use of energy? is ?joules per second.?

 

[LarryFine]

Just in case this isn?t confusing enough, let me pile on (no I mean let me add) one more level of complexity.

On the other hand, if this is confusing enough for you, and you're wondering how it applies to you, think about the instantaneous value of power consumption in kilowatts, and the rate of such consumption, in kilowatt-hours; the latter of which you pay for.

 

[charlie b]

. . . think about the instantaneous value of power consumption in kilowatts, and the rate of such consumption, in kilowatt-hours. . . .

Actually, it is fairly easy to use the various terms related to power in imprecise ways that may or may not confuse the listener. I would try to avoid the use of the word ?rate,? in the context of ?kilowatt-hours.? Nothing is a ?rate,? unless it has the sense of something happening during a period of time. It is not obvious from the name, but the term ?watts? (or kilowatts or megawatts) does have the sense of ?during a period of time.? It is the amount of energy that is consumed (or generated by the utility) over a period of time. A ?watt? is defined as ?one joule of energy in one second of time.? We just see the word ?watt,? and we don?t see the ?in one second of time,? but it is certainly there.

You can think of the rate your car burns gasoline in a period of one hour. Depending on many conditions (the size of your car?s engine, the roads, the weather, your driving speed, etc.), you can be burning ?many gallons per hour? or ?very few gallons per hour.? That is a rate. At the end of the trip, you refill the tank, and you are measuring that task in terms of gallons alone. In this instance, we do not have a single word that carries the meaning of ?gallons per hour,? so the nature of that phrase (i.e., being a ?rate of consumption?) is fairly obvious. Not so with the word ?watt.? In a single word, we have the notion of energy, and the notion of time, and their relationship (i.e., amount of energy being used in a period of time).

More confusing, perhaps???

 

[LarryFine]

At the end of the trip, you refill the tank, and you are measuring that task in terms of gallons alone. In this instance, we do not have a single word that carries the meaning of ?gallons per hour,? so the nature of that phrase (i.e., being a ?rate of consumption?) is fairly obvious.

Actually, when filling up, and adding the miles traveled into the mix, I end up with miles per gallon.