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¿Watts and Volt Amps – What’s a KVA and How is it Calculated?

WHAT DOES KVA MEAN?

There are many technical terms related to generators and they can be confusing if you are not familiar with them. One term you will frequently see in power generator specifications is kVA. Essentially, it is an indication of output power. Below we explain it in more detail and give you advice on what kVA power rating you might need.

Have you ever wondered why some power ratings are expressed in WATTS, some in AMPERE or AMPS, some in VOLTS and some in KVA? This page will explain in simple terms the difference between power ratings and describe when each should be used in planning your data center and network architecture.

A KVA is simply 1000 volt-amps. A volt is electrical pressure. An ampere is electrical current. A term called apparent power (the absolute value of complex power, S) is equal to the product of volts and amps.

On the other hand, a watt (W) is a measure of real power. Real power is the amount of actual power that can be drawn from a circuit. When the voltage and current in a circuit match, the real power equals the apparent power. However, as the current and voltage waves match less, less real power is transferred, although the circuit still carries current. Differences between real and apparent power, and therefore between watts and volt-amperes, arise because of inefficiencies in electrical transmission.

The resulting inefficiency of electrical transmission can be measured and expressed as a ratio called the power factor. The power factor is a ratio (a number from 0 to 1) between real power and apparent power. In the case of a power factor of 1.0, the real power equals the apparent power. In the case of a power factor of 0.5, the real power is about half the apparent power.

Implementing systems that have higher power factors results in lower electrical loss and can help improve power usage effectiveness (PUE). Most uninterruptible power supply (UPS) units will indicate the average power factor and the real-time load capacity of the UPS in addition to the KVA.

THE FORMULAS FROM KVA TO KW / KW TO KVA

• kVA to kW Apparent power (kVA) x power factor (pf) = real power (kW) p. e.g. 100 kVA x 0.8 = 80 kW

• kW to kVA Real power (kW) / power factor (pf) = apparent power (kVA) p. e.g. 80 kW / 0.8 = 100 kVA

Example: You have a 500 KVA (apparent power) UPS unit with a power factor of 0.9. The resulting real power is 450 kilowatts.Some Useful Conversion Factors and Formulas

• VA = Voltage x Amps

• Watts = Voltage (root-mean-squared) x Amps (root-mean-squared) x Power Factor (PF) (a three-phase circuit would multiply the voltage by the square root of 3 or approximately 1.732)

• 1 BTU (British thermal unit) = Watts x 3.413

• 1 BTU = 1,055.053 joules (J)

• 1 watt = 3.413 BTU/hour

• 1 ton = 200 BTU/minute

• 1 ton = 12,000 BTU/hour

• 1 ton = 3.517 kilowatts

Data Center Power

Data center power includes the infrastructure, systems, and processes that provide and manage power. This includes backup systems, power supply distribution, and management tools.