ESSENTIAL FORMULAS FOR MOTOR ENGINEERING



Essential Formulas for Motor Engineering

Motor Engineering is a vital part of Engineering sector. There is no industry where motor is not using; from utility to machinery keep it run motor is mandatory. 

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

Yes friends, to solve the problems some time quick and short-cut formula is very effective. That is the main reasons today's presentation on very easy and basic formula related to motor which we called Essential Formula for Motor engineering.

We know, You who are engaged with motor engineering know these formula very well, but some time memory lost. Hope this will help like a friends.

Ohm's Law

Ohm's Law Easy Use


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










Three Phase Values

Just memorise the value 1.732 which comes from square root of 3; multiply with this value to get three value from 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 formula related to motor horse power, kilowatts, torque in pound-foot or newton-meter. These formula we are calling 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 Amperages 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

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