Motor Formulas

Question 1

60xf/p

Answer 1

Synchronous speed (ns) is the speed of the rotating magnetic field

Question 2

%slip= ns-nr/ns x100

Answer 2

%slip

Question 3

Output power from horse power

Answer 3

1 Horse power is 746 w so if there is 5.36 hp then that 5.36x746 will give you your wattage

Question 4

[3xVLxILxcos€

Answer 4

Input power delta, star you divide by 3

Question 5

N=pout/pinx100%

Answer 5

Efficiency of motor

Question 6

Pext = 2xpi x n x t/60

Answer 6

Full load torque needs to be transposed to T= po x 60/ 2pi x nr

Question 7

Formula to calculate resistance in 3 heat switches (e.g electric blanket)

Answer 7

Pmed=vsquared/rmed transposed to rmed= vsquared/pmed then for low heat you double resistance and for high heat you half it

Question 8

Calculating power across a resistor

Answer 8

If it’s for eg R4 then it’s P4= I squared x r4 but to find I (current) we have to find total resistance of circuit with this formula R total =(r1 -1 +( r2 + r3)-1)-1) + r4, the -1 are all to the power of

Question 9

NR

Answer 9

Nameplate given RPM and represents the rotating field speed of the shaft

Question 10

How many poles if the question doesent give the poles?

Answer 10

4 so would make 2 pairs

Question 11

For e.g 4.0 kw on nameplate

Answer 11

Output power 4000 w

Question 12

How to calculate PF (powerfactor)

Answer 12

Voltage x current = awnser then the given wattage/ awnser

Question 13

Max voltage on secondary side of VT (voltage transformer)?

Answer 13

110v

Question 14

Common secondary current for current transformer (CT)?

Answer 14

5a or 1a mainly 5a

Question 15

Calculating power with powerfactor?

Answer 15

VphxIphxcos€

Question 16

Max Main earth conductor and bonding reading? And then for hand held appliances?

Answer 16

0.5 for main earth and 1 for appliances