Year 2 D4

Question 1

the effects of inductance

Answer 1

inductance is the ability of a cct component to store electrical energy in an electromagnetic field.
inductance is also expressed as the property of a cct that opposes any change of current in the circuit

Question 2

impedance

Answer 2

is the combined opposition of resistance and reactance to current flow in a cct

Question 3

the true power

Answer 3

measured in watts, in an R-L cct is all dissipated by the resistance of the cct

Question 4

reactive power

Answer 4

also called quadrature, wattless power

units VARs

Question 5

Apparent power

Answer 5

the two power components in an R-L series cct combine to form the apparent power

Question 6

Figure of merit (Q)

Answer 6

is Q = Xl/R
a coil with a high figure of merit has a large reactance compared to its resistance and relatively little power loss.
coils with a low Q value have relatively high effective resistance, and there is a large power loss when they are used

Question 7

Effects of capacitance in a DC cct

Answer 7

Capacitance is the property of a cct that opposes any change in voltage
Capacitance is the ability of a cct component to store electrical energy in an electrostatic field

Question 8

Effects of capacitance in a AC cct

Answer 8

voltage is continuously changing
the plates repeatedly charge and discharge
electrostatic field that alternates polarity at the applied Hz is established in the dielectric
counter emf is established across the plates at the same Hz as the applied voltage. this emf opposes current flow

Question 9

what is the relationship between the phase angle of a cct and its power factor

Answer 9

Cos(theta) = PF

Question 10

for analyzing AC parallel ccts

Answer 10

line voltage is used as the reference vector

Question 11

for analyzing AC series ccts

Answer 11

line current is used as the reference vector

Question 12

For R-L parallel cct

Answer 12

the current in the inductive branch is also called the quadrature current component

Question 13

how does parallel cct resonance differ from series cct resonance

Answer 13

resonant series cct current is at its max

resonant parallel cct current is at its min.

Question 14

List three reasons to correct power factor

Answer 14

Reduced energy cost
Increase in system capacity
Increase in distribution efficiency

Question 15

Why does power factor correction work using capacitors?

Answer 15

The two kinds of reactive power cancel each other out

Question 16

Power factor correction has no effect on the load itself therefore

Answer 16

the watts, volt-amps and VARs or the load itself remain unchanged.

Question 17

When installing a capacitor for power correction install it in

Answer 17

parallel with the other loads in the cct

Question 18

Nameplate of a capacitor must include

Answer 18

Voltage rating
Hz rating
kVars of correction
Phase

Question 19

What is the danger of a series connection of power factor correction?

Answer 19

Low opposition to current flow creating a series resonant cct. (not good)