EE1F24- Rotating magnetic fields

Question 1

What determines the strength of a magnetic field?

Answer 1

Determined by the current flowing through a conductor.

Question 2

What is the magnitude of the voltage induced in each stator phase winding given by?

Answer 2

E= 4.44 kfNBmax (Volts)
E= the magnitude of the RMS phase voltage
f= Frequency
k= A constant depending on the stator magnetic circuit and the phase winding configuration
N= Effective number of turns of the stator phase winding
Bmax= the maximum air gap magnetic flux density produced by the rotor field winding

Question 3

How does flux come out of an electromagnetic body?

Answer 3

Flux comes out of an electromagnetic body at right angles.

Question 4

What is a stator in a mechnically driven rotating magnetic field?

Answer 4

Part that stays stationary, has windings attatched

Question 5

What is the effect of doubling rotor excitation current?

Answer 5

Doubling excitation current therefeore doubles flux and therefore doubles the voltage.

Question 6

What is the equation for magnetic flux linking a phase winding and phase synchronous generator given by?

Answer 6

φ=φmaxsin(ωt)
can then be differentiated to give instantaneous voltage.

Question 7

What is the equation for instantaneous voltage in a synchronous generator?

Answer 7

e=ωNφmaxcos(ωt)

Question 8

What equation gives frequency in a synchronous generator?

Answer 8

f=nsp
f=frequency
ns= synchronous speed in revolutions per second
p= pole pairs = N of poles/2

Question 9

How do we calculate rms values?

Answer 9

Divide number by root 2

Question 10

What is the power output of a rotating shaft equal to?

Answer 10

P=2πNT/60

T=torque
N= speed in rpm

Question 11

What is the equation for calculating slip?

Answer 11

Slip=(Ns-Nr)/(Ns)
Ns= synchronous speed in rpm