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 shortcut 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 ACAlternating 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

KilovoltAmps

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 poundfoot, or newtonmeter. These formulae we are calling the Motor Application Formula.
Horsepower = Torque (lbft) x RPM
5252

Kilowatts = Torque
(Nm) x RPM
9550

Torque (lbft) = Horsepower x 5252
RPM

Torque (Nm) = Kilowatts x 9550
RPM

IECStyle Contactors and Starters Selection Guide:
Average Amperage for Given Horsepower Motor Ratings
The
table below provides the average fullload currents of squirrel cage motors
based on NEC (National Electrical Code) Tables 430148, 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 fullload 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

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