WAZIPOINT Engineering Science & Technology: ESSENTIAL FORMULAS FOR MOTOR ENGINEERING

## Essential Formulas for Motor Engineering

Motor Engineering is a vital part of the Engineering sector. There is no industry where a motor is not used; from utility to machinery keeping it running is mandatory.

Due to the use of huge motors, a large portion of everyday work time also consumed this fellow; and need to face new and critical problems every time.

Yes, friends, to solve problems sometimes a quick and short-cut formula is very effective. That is the main reason today's presentation is on a very easy and basic formula related to motors which we call an Essential Formula for Motor engineering.

We know, You who are engaged with motor engineering know these formulas very well, but sometimes memory is lost. Hope this will help like a friend.

### Ohm's Law in Ectricity

Ohm's Law is the very basic formula for electrical engineering. Everybody knows this formula, here all of this formula is in a circle for easy understanding.

#### Three Phase Values

Just memories the value 1.732 which comes from the square root of 3; multiply with this value to get three values from a single phase. Follow the following table for some common values.

 For 208 volts x 1.732 use 360 For 230 volts x 1.732 use 398 For 240 volts x 1.732 use 416 For 415 volts x 1.732 use 719 For 440 volts x 1.732 use 762 For 460 volts x 1.732 use 797 For 480 volts x 1.732 use 831

### AC/DC Formulas

Horse Power, Kilowatts, KVA related some formula for AC-Alternating Current and DC- Direct Current when one term is known and other terms need to fiend out.

 To Find Direct Current AC 1 phase AC 3 phase Amps when Horsepower is Known HP x 746 E x Eff HP x 746 E x Eff x PF HP x 746 1.73 x E x Eff x PF Amps when Kilowatts is known kW x 1000 E kW x 1000 E x PF kW x 1000 1.73 x E x PF Amps when kVA is known kVA x 1000 E kVA x 1000 1.73 x E Kilowatts I x E 1000 I x E x PF 1000 I x E x 1.73 x PF 1000 Kilovolt-Amps I x E 1000 I x E x 1.73 1000 Horsepower (output) I x E x Eff 746 I x E x Eff x PF 746 I x E x Eff x 1.73 x PF 746

#### AC Efficiency and Power Factor Formulas

We need some formula to fiend out Motor Efficiency and Power factor for single phase or three phase motors. Follow the following table formula.

 To Find Single Phase Three Phase Efficiency 746 x HP E x I x PF 746 x HP E x I x PF x 1.732 Power Factor Input Watts V x A Input Watts E x I x PF x 1.732

### Motor Application Formulas

There are four formulas related to motor horsepower, kilowatts, torque in pound-foot, or newton-meter. These formulae we are calling the Motor Application Formula.

 Horsepower =   Torque (lb-ft) x RPM                              5252 Kilowatts =           Torque (N-m) x RPM                                     9550 Torque (lb-ft) =    Horsepower x 5252                                  RPM Torque (N-m) =          Kilowatts x 9550                              RPM

#### IEC-Style Contactors and Starters Selection Guide:

Average Amperage for Given Horsepower Motor Ratings

The table below provides the average full-load currents of squirrel cage motors based on NEC (National Electrical Code) Tables 430-148, 149, and 150.

These values are given only as a guide - they may vary depending on the type of motor and manufacturer. Refer to the actual motor nameplate for full-load current values.

 HP 110 to 120 VAC 220 to 240 VAC 440 to 480 VAC Single Phase Two Phase Three Phase Single Phase Two Phase Three Phase Single Phase Two Phase Three Phase 1/10 3.0 - - 1.5 - - - - - 1/8 3.8 - - 1.9 - - - - - 1/6 4.4 - - 2.2 - - - - - 1/4 5.8 - - 2.9 - - - - - 1/3 7.2 - - 3.6 - - - - - 1/2 9.8 4.0 4.4 4.9 2.0 2.2 2.5 1.0 1.1 3/4 13.8 4.8 6.4 6.9 2.4 3.2 3.5 1.2 1.6 1 16.0 6.4 8.4 8.0 3.2 4.2 4.0 1.6 2.1 1 1/2 20.0 9.0 12.0 10.0 4.5 6.0 5.0 2.3 3.0 2 24.0 11.8 13.6 12.0 5.9 6.8 6.0 3.0 3.4 3 34.0 16.6 19.2 17.0 8.3 9.6 8.5 4.2 4.8 5 56.0 26.4 30.4 28.0 13.2 15.2 14.0 6.6 7.6 7 1/2 80.0 38.0 44.0 40.0 19.0 22.0 21.0 9.0 11.0 10 100.0 48.0 56.0 50.0 24.0 28.0 26.0 12.0 14.0 15 135.0 72.0 84.0 68.0 36.0 42.0 34.0 18.0 21.0 20 - 94.0 108.0 88.0 47.0 54.0 44.0 23.0 27.0 25 - 118.0 136.0 110.0 59.0 68.0 55.0 29.0 34.0 30 - 138.0 160.0 136.0 69.0 80.0 68.0 35.0 40.0 40 - 180.0 208.0 176.0 90.0 104.0 88.0 45.0 52.0 50 - 226.0 260.0 216.0 113.0 130.0 108.0 56.0 65.0 60 - - - - 133.0 154.0 - 67.0 77.0 75 - - - - 166.0 192.0 - 83.0 96.0 100 - 218.0 248.0 - 109.0 124.0 125 - - - - - 312.0 - 135.0 156.0 150 - - - - - 360.0 - 156.0 180.0 200 - - - - - 480.0 - 208.0 240.0 250 - - - - - 602.0 - - 302.0 300 - - - - - - - - 361.0 350 - - - - - - - - 414.0 400 - - - - - - - - 477.0 500 - - - - - - - - 590.0