Electrical Principles Part B

How is EMF generated in an AC sine wave and what factors affect it?

Requires relative motion between conductor and magnetic field

Factors:

Density of magnetic flux

Length of conductor in magnetic field

Cutting angle (90° = max EMF)

Moving parallel to field = minimum EMF

What defines a completed AC cycle and alternation?

1 positive and 1 negative alternation = 1 cycle

1 alternation = 180° of a sine wave

How does the cutting angle of a conductor affect EMF generation?

0°: no EMF generated

45°: medium EMF

90°: maximum EMF (peak, Emax, Epk)

What is an alternator and how does it relate to frequency in AC generation?

Alternator: AC generator

If spinning at 60 RPM, produces 60 Hz (cycles/sec)

What is the relationship between mechanical and electrical degrees in an alternator?

360 mechanical degrees = 1 shaft revolution

360 electrical degrees = conductor passes 2 poles

e.g., 4-pole machine: 180 mech. deg. = 360 electrical deg

How is the frequency of an AC alternator calculated?

Based on:

of poles
RPM (shaft speed)

Equations:

Hz = pole pairs × RPM / 60

Hz = poles × RPM / 120 (more commonly used)

What is the difference between instantaneous and effective AC voltage values?

Instantaneous: EMF at a specific time

Effective (RMS): peak × 0.707

RMS = √mean of square of all instantaneous values

RMS = sin(45°) = 1/√2

Why is effective (RMS) voltage used for AC?

Helps compare AC to equivalent DC voltage

Example: 100VAC RMS ≈ 100VDC

What are the three main components of AC impedance?

Resistance (R): restricts electron flow

Inductance (Xl): restricts rate of change of current

Capacitance (Xc): restricts rate of voltage change (charges/discharges in AC)

How is impedance defined and how is it measured?

Impedance (Z): combination of R, Xl, and Xc

Measured in ohms

Cannot be directly measured—only calculated

Why does AC create more effective resistance than DC in the same coil?

AC effective resistance > DC due to energy losses
AC effective resistance cannot be measured with multimeter, need a wattmeter to measure it

What factors contribute to AC resistance in a circuit?

-Eddy Current Loss (Iron Loss):

Circulating currents in metal

Reduced via laminated iron cores

-Hysteresis Loss:

Energy to flip magnetic polarity

Reduced using silicon

-Dielectric Loss:

Insulation distortion from field

-Skin Effect:

Electrons move to conductor surface

Reduces effective conductive area

-DC Ohmic Resistance:

Can only be measured with an ohmmeter