Skip Headers

Oracle® SL8500 StorageTek Modular Library System Systems Assurance Guide E24254-08 |
| Library | Contents | Index

Previous | Next |

# D Electrical Conversions

This appendix describes how to calculate and convert common electrical values.

## Units

The units used in most basic electrical conversions are in the following table.

Table D-1 Basic Electrical Units

A =Amperes (Amps) | PF =Power Factor
Btu =British Thermal Unit | V =Volts
kVA =Kilovolt-amperes | VA =Volt-amperes
kW =Kilowatts | W =Watts

## Volts, Watts, and Amperes

Equation: Watts [W] =Amperes [A] x Volts [V]

Example

Given the following values you can use any two values to calculate a third: Watts =2400 (2.4 kW), Volts =120, Amps =20.

2.4 kW ÷ 20 A =120 V

120 V x 20 A =2,400 W (or 2.4 kW)

2,400 W ÷ 120 V =20 A

## Volt-Amperes (VA)

Equation: Volts [VAC] x Amps [A-rms] =Volt-amperes [VA]

Example: A small server is plugged into a 120 VAC 60 Hz power source and is rated at 2.5 amps.

120 VAC x 2.5 amps =300 VA

## Kilovolt-Amperes (kVA)

Equation: Volts [VAC] x Amps [A-rms] ÷ 1000 =kilo-volt-amperes [kVA]

Three Phase Equation: kVA (phase 1) +kVA (phase 2) +kVA (phase 3) =kVA (total)

Examples:

- Single Phase:

  120 VAC x 2.5 amps ÷ 1000 =0.3 kVA

- Three Phase:

  Phase 1: 120 VAC x 2.5 amps ÷ 1000 =0.3 kVA

  Phase 2: 120 VAC x 2.5 amps ÷ 1000 =0.3 kVA

  Phase 3: 120 VAC x 2.5 amps ÷ 1000 =0.3 kVA

  Total kVA: 0.3 kVA +0.3 kVA +0.3 kVA =0.9 kVA

## Kilowatts

The formula requires a value for the "power factor." The power factor (PF) is not a precise value (unless specifically known for the equipment). This factor can vary from 60–95% and is rarely published on the equipment.

Equation: Volts [V] x Amps [A] x Power Factor [PF] ÷ 1000 =Kilowatts [kW]

Examples: For these calculations a power factor of 0.85 is used.

- Single Phase:

  A medium-sized server is plugged into a 120 VAC 60 Hz power source and is rated at 6.0 amps.

  120 VAC x 6 amps x 0.85 (PF) =612 ÷ 1,000 is 0.612 kW

- 208–240 Two Phase:

  A server using a 220 VAC power source is rated at 4.7 amps.

  220 VAC x 4.7 amps x 2 (phases) x 0.85 (PF) =1757.8 ÷ 1,000 =1.76 kW

- Three Phase:

  For 3-Phase power configurations you also need to multiply by 1.73.

  A large disk subsystem has 192 physical volumes, a power source of 208 VAC, and is rated at 22 amps.

  208 VAC x 22 amps x 1.73 x 0.85 (PF) ÷ 1000 =6.729 kW

## Convert kW and kVA

The power factor is used to convert between kW and kVA. The power factor is an approximation (unless known for the equipment).

Equation: Kilowatts [kW] x Power Factor [PF] =kilo-volt-amperes [kVA]

## British Thermal Units

Equation: 1 kW =3,413 Btu

Thus: 3.41214 x Watts [W] =Btu/hr

Many manufacturers publish kW, kVA and Btu in their equipment specifications. Often, dividing the Btu value by 3413 does not equal the published kW value.

- Use the value provided by the manufacturer, otherwise use the formula.