Delta MCS-1800 Specifikace stáhnout pdf (Strana 61)

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POWER MONITORING & PROTECTION

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POWER EQUATIONS

FORMULAS TO DETERMINE AMPERES, hp, kW, and kVA

To Find

Direct Current

Alternating Current

Single-Phase Three-Phase

Amperes (I) when hp x 746 hp x 746 hp x 746

horsepower is known E x %eff E x %eff x pf 1.73 x E x %eff x pf

Amperes (I) when kW x 1000 kW x 1000 kW x 1000

kilowatts is known E E x pf 1.73 x E x pf

Amperes (I) when kVA x 1000 kVA x 1000

kVA is known E 1.73 x E

Kilowatts (kW) I x E I x E x pf I x E x 1.73 x pf

1000 1000 1000

kVA I x E I x E x 1.73

1000 1000

Horsepower (output) I x E x %eff I x E x %eff x pf I x E x 1.73 x %eff x pf

746 746 746

COMMON ELECTRICAL TERMS

Ampere (I) Unit of current or rate of flow of electricity

Volt (E) Unit of electromotive force

Ohm (R) Unit of resistance

Ohms Law: I = E

R (DC or 100% pf)

%eff Motor efficiency Note: If unknown assume %eff x pf = 0.7 for 25 hp or less

0.8 above 25 hp

Megohm 1,000,000 ohms

Volt amperes (VA) Unit of apparent power

E x I (single-phase)

E x I x 1.73 (three-phase)

Kilovolt Amperes (kVA) 1000 volt - amperes

Power Factor (pf) Ratio of true to apparent power

W or kW

VA kVA

Watt Hour (Wh) Unit of electrical work

One watt for one hour

3.413 Btu

Kilowatt Hour (kWh) 1000 watt hours

Horsepower (hp) Measure of time rate of doing work

Equivalent of raising 33,000 pounds 1 foot in 1 minute

746 watts

MOTOR APPLICATION FORMULAS

Torque (lb-ft) = hp x 5250

rpm

Shaft stress = hp x 321,000

(pounds per square inch) rpm x shaft dia

For pumps

Horsepower = gpm x head in feet x specific gravity* (*Water - 1.00, Ethylene glycol - 1.125)

3960 x mechanical efficiency of pump

Speed

Synchronous rpm = Hertz x 120

Poles

Percent slip = synchronous rpm - full load rpm x 100

synchronous rpm

= COSØ (Ø = angle current leads or lags voltage)

()

March 2014

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