Explaining Watts and Volt Amps - or "What the hell is a KVA?"

Have you ever wondered why some powers are expressed in WATTS, some in AMPS, some in volts, and some in KVA? For many in the industry that hosts this can be a very confusing topic. Face it, industry professionals, the content is not likely to electrical engineers, electrical engineers, and most know nothing about the creation and distribution of content.

This article explains in simple terms the difference between the major powers, and describe when each should be used in planning network architecture.

According to APC, the main difference between watts and volt amps has the Watt balance determines the actual energy from a power source and the heat generated by the equipment. The VA rating is used for sizing equipment such as switches, cables, and UPS. The VA rating is normally equal to or greater than the power in watts, as it includes the "power factor" in its calculation.

Power factors

The power factor is a calculation used to explain the difference of power supplies used to convert alternating current into direct current for use in electrical equipment and computer equipment. There are two types of power - the input capacitor and the power factor corrected power supply.

Power factor corrected supplies are used in calculating the final and highest switching equipment, and have a relationship 1VA: 1W - allowing a simple calculation for the electrical and UPS scale. So, in theory, if your power factor is 1:1, and your UPS is an 80KVA UPS, then you would be able to charge the UPS at 100% of its rating.

Older electrical equipment, as well as the lower-end computer and video equipment by use of the input capacitors and the power supplies have a power factor anywhere from.55 to.75 times the VA.

Typically when scaling a UPS for use in a data center to use a load factor of 60% on UPS. If you overload a UPS it is almost certain to fail during a power outage, as the draw of the battery will exceed the capacity of the UPS. Most of the new UPS will automatically bypass the battery when an overload condition. 60% of the load factor accounts for the high probability that the most of the power drawing equipment through the UPS will be of a category that has a power factor of between.55 and.75.

Example 1

You have a UPS 10 kVA. Your data center has racks of low-end self-assembled computers with a total estimated rating of 9000 watts. The UPS will be how it works, as the power factor is probably around.70. You would need at least 12.85KVA for backup to adequately describe the data center.

Example 2

You have a UPS 10 kVA. Your data center has racks of low-end self-assembled computers with a total estimated rating of 6000 watts. The UPS will be able to handle the load, because the correct power factor assessment will require approximately 8.5KVA of UPS.

Some modern UPS able to notice the average power factor and real-time load capacity of the UPS.

Some useful conversion factors

or refrigeration

- 1 watt = 0.86 kcal / h

- 1 watt = 3.412 Btu / h

- 1 x 10-4 watts = 2,843 tons

- 1 tonne = 200 Btu / min

- 1 ton = 12,000 Btu / h

- 1 ton = 3,517.2 W

Conversions or kVA

Three-phase

kVA V = ï - ï ïEUR-A - ïEUR-√ 3 / ïEUR-1000

Single Phase

kVA V = ï - ïEUR-A / ïEUR-1000

Formulas

kVA = voltage x current (amperes)

Watts = VA x PF

BTU = Watts x 3.41 ......