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Electrical Unit Conversions
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Transcript of Electrical Unit Conversions
5/13/2018 Electrical Unit Conversions - slidepdf.com
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11/26/11 Electrical Unit Conversions
GENERATORJOE
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ELECTRICAL UNIT CONVERSIONS
This information page provides formulas and documentation to take certain electrical values and convert them into
other electrical values. The formulas below are known and used universally in the Generator Industry but you can
use them for computer, network, telecom and powered equipment
VALUE 1-PHASE 3-PHASE
WATTS (W) IXEXPF IXEX 1.73XPF
KILOWATTS (kW)E._X_b_XPF E X IX 1.73 X PF
1000 1000
AMPERES (I)kWX 1000 kWX 1000
EXPF EX1.73XPF
KILOVOLT AMPERES lX_E LX_E_X 1.73
(kVA) 1000 1000
FREQUENCY (Hertz or f)Rotor Poles X RPM Rotor Poles X RPM
120 120
RPM (n)Hertz X 120 Hertz X 120
Rotor Poles Rotor Poles
NUMBER OF ROTOR Hertz X 120 Hertz X 120
POLES (P) RPM RPM
POWER FACTOR (PF)Actual Watts Actual Watts
IXE IX 1.73X E
HORSEPOWER (HP) IvE X PF lX_E_X 1.73 X PF746 X EFF 746 X EFF
AMPERES (when kW is kWX 1000 kWX 1000
known) EXPF EX1.73XPF
AMPERES (when kVA is kVAX 1000 kVAX 1000
known) E EX 1.73
I I
I = current in amperes
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E = voltage in volts
W = watts
kW = power in ki lowatts
kVA = apparent power in kilo-volt-amperes
HP = output power in horsepower
RPM (n) = motor speed in revolutions per minute (RPM)
ns = synchronous speed in revolutions per minute (RPM)
Rotor Poles (P) = number of poles
Hertz (f) = frequency in cycles per second (CPS)
T = torque in pound-feet
EFF = efficiency as a decimal
PF = power factor as a decimal
HP = horsepower
For a detailed explanation of each formula, Click on the links below to go right to it.
To Find Watts
To Find Volt-Amperes
To Find Kilovolt-Amperes
To Find Kilowatts
To Convert Between kWand kVA
To Find kBTUs from Electrical Values
Background
It is often necessary to tum \Ultage, amperage and electrical "nameplate" values from computer, network and
telecom equipment into kW, KVA and BTU information that can be used to calculate overall power and HVAC
loads for IT spaces. The following describes how to take basic electrical values and convert them into other types
of electrical values .
• NOTE #1:
The informational nameplates on most pieces of equipment usually display electrical values. These values
can be expressed in volts. amperes, kilovolt-amperes, watts or some combination of the foregoing.
• NOTE #2:
If you are using equipment nameplate information to develop a power profile for use in selecting a generator
the total power values will exceed the actual output of the equipment. Reason: the nameplate value is
designed to ensure that the equipment will energize and run safely. Manufacturers build in a "safety factor
when developing their nameplate data. Some nameplates display information that is higher than the
equipment will ever need - often up to 20% higher. The result is that, in total, your profile will "over
engineer" the power requirements of the equipment. This is not generally bad, you should just be aware of
it.
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• NOTE #3:
We advise: Dewlop the power profile using the nameplate information and the formulas below and use the
resultant documentation as your baseline. Why? Because it's the best information available without doing
extenslve electrical tests on each piece of equipment. If you must lower your estimates, make sure you
haw a good reason. In years to come you will want ewry watt you can get. Better to be "oversized" then
"undersized".
The Formulas
To Find Watts
1. When Volts and Amperes are Known
POWER (WATTS) = VOLTS x AMPERES
• We haw a appliance with a nameplate shows 2.5 amps. Giwn a normal 120 Volt, 60 hz power source an
the ampere reading from equipment, make the following calculation:
POWER (WATTS) = 120 * 2.5 ANSWER: 300 WATTS
To Find Volt-Amperes (VA)
1. Same as above. VOLT-AMPERES (VA) = VOLTS x AMPERES ANS: 300 VA
To Find kilovolt-Amperes (kVA)
1. SINGLE PHASE
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES
1000
Using the previous example: 120 * 2.5 = 300 VA 300 VA 11000 = .300 kVA
2. TWO-PHASE
• Giwn: We haw a Sun server with an amp rating of 4.7 and requiring a 208-240 power source. We'll use
220 volts for our calculations.
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES x 2
1000
220 x 4.7 x 2 = 2068 2068/1000 = 2.068 kVA
3. THREE-PHASE
• Giwn: We haw a large appliance with nameplate data of 50-amp 208 VAC receptacle. For this
calculation, we will use 21 amps. Do not calculate the value of the plug or receptacle. Use the value on
nameplate.
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES x 1.73
1000
208 x 20.5 x 1.73 = 7,376.72 7,376.72/1000 = 7.377 kVA
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To Find Kilowatts
Electrical Unit Conversions
• Finding Kilowatts is a bit more complicated in that the formula includes a value for the "power factor". T
power factor is a nebulous but required value that is different for each electrical device. It in\{)lws the
efficiency in the use of the electricity supplied to the system. This factor can vary widely from 60% to 95%
and is never published on the equipment nameplate and further, is not often supplied with product
information. For purposes of these calculations, we use a power factor of .85. Most generators haw a
power factor of .80. Whatewr the number, it places a slight inaccuracy into the numbers. Its OK and it
gets us wry close for the work you need to do.
1. SINGLE PHASE
Giwn: We haw a medium-sized appliance that draws 6.0 amps.
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES x POWER FACTOR
1000
120 * 6.0 = 720 VA 720 VA * .85 = 612 612/1000 = .612 kW
2. TWO-PHASE
• Giwn: We haw a larger appliance with a running amp rating of 4.7 and requiring a 208-240 power source.
We'll use 220 volts for our calculations.
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES x POWER FACTOR x 2
1000
220 x 4.7 x 2 = 2068 2068 x .85 = 1757.8 1757.8/1000 = 1.76 kW
3. THREE-PHASE
• Giwn: We haw a wry large appliance that shows a requirement for a 50-amp 208 VAC receptacle. For
this calculation, we will use 21 amps. Do not calculate the value of the plug or receptacle. Use the value o
nameplate.
KILOVOLT-AMPERES (kVA) = VOLTS x AMPERES x POWER FACTOR x 1.73
1000
208x20.5x1.73 = 7,376.72 7,376.72 * .85 = 6,720.21 6,720.21/1000=6.27 kW
To Convert Between kWand kVA
• The only difference between kW and kVA is the power factor. Once again, the power factor, unless known
is an approximation. For purposes of our calculations, we use a power factor of .80 which most generatoruse. The kVA value is always higher than the value for kW.
kW To kVA
kVA To kW
kW 1 .80 = SAME VALUE EXPRESSED INkVA
kVA * .80 = SAME VALUE EXPRESSED IN kW
To Find BTUs From Electrical Values
• Known and Giwn: 1 kW = 3413 BTUs (or 3.413 kBTUs)
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11/26/11 Electrical Unit Conversions
• The above is a generally known value for conwrting electrical values to BTUs. Many manufacturers publis
kW, kVA and BTU in their equipment specifications. Often, di\liding the BTU value by 3413 does not equa
their published kW value. So much for knowns and giwns. Where the information is pro\lided by the
manufacturer, use it. Where it is not, use the above formula.
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