AC Theory

Question 1

Negative multiplication is a phase rotation of ___ degrees.

Answer 1

180

Question 2

What are the units for the three kinds of power (apparent, reactive, active?)

Answer 2

Apparent = VA (Volt-Amps) Active = W (Watts) Reactive = VARs (Volt-Amps-Reactive)

Question 3

Inductors are (positive/negative) ‘j’ operator Capacitors are (positive/negative) ‘j’ operator

Answer 3

Inductors = positive Capacitors = negative

Question 4

In vector notation, Power = ?

Answer 4

P = V x I (conjugate)

Question 5

In a capacitor, the current (leads / lags) the voltage waveform.

Answer 5

leads

Question 6

The ‘a’ operator phase-shifts by ___ degrees. a^2 = ___ degrees

Answer 6

120; a^2 = 240

Question 7

What are symmetrical components?

Answer 7

A way of expressing tricky unbalanced phasors in a set of balanced, symmetrical components: - positive sequence - negative sequence - zero sequence

Question 8

Why are symmetrical components important in power protection?

Answer 8

Method of calculating complicated unbalanced fault currents.

Question 9

Write the equation for a positive-sequence symmetrical component.

Answer 9

Question 10

A balanced, three-phase fault has (positive/negative/zero) symmetrical components.

Answer 10

Positive

Question 11

An unbalanced, phase-to-phase fault has (positive/negative/zero) sequence symmetrical components.

Answer 11

Positive and negative.

Question 12

A single-phase to earth fault has (positive/negative/zero) sequence symmetrical components.

Answer 12

all three

Question 13

In all faults, the driving source is a (positive/negative/zero) sequence voltage.

Answer 13

Positive

Question 14

Draw the power, voltage and current waveforms for a balanced, single-phase system with a power factor of 1.

Answer 14