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Flashcards in Basic AC Principles Deck (18)
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1

Inductance

Property of a device or circuit which opposes a change in current flow

Inductors oppose changes in current flow and therefore offer opposition to alternating current flow

2

Inductance characteristics can be increased by

Increasing the number of turns on the coil


Inserting a piece of soft iron into the coil




3

Capacitance

Property of an electrical component which is able to store energy

4

Capacitor charging

When connected to a DC circuit the capacitor charges to the max value and remains charged until the energy is released by connecting it to a complete circuit

5

Factors determining capacitance

Area of the plates - a

Distance between the plates - d

Types of dielectric - k

C = ka/d

6

Advantages of AC

Can be efficiently charged from one voltage to another using a transformer

Simpler and lighter in construction than DC machines

Can be efficiently converted to DC with a rectifier

7

RMS =

0.707 x peak

Average value = 0.637 x peak

The RMS value of AC is that which has the same heating effect as the same value as DC

8

Frequency of AC generators

=NP/60

N = speed in RPM
P= number of pairs of poles (per phase)

Periodicity = 1/freq

9

Purely resistive AC circuit

Voltage and current are in phase

All to do with power - consumed in the form heat like a DC circuit

10

Purely capacitive AC circuit

Voltage and current are out of phase by 90* - current leads voltage

Would not produce any useable power as it is out of phase

11

Capacitive reactance

In an AC circuit the capacitor is constantly charging and discharging - because of the time lag - capacitor is in constant opposition to the supply voltage

Opposition to the current flow = capacitive reactance

Inversely proportional to freq

12

Purely inductive AC circuit

Current lags behind the voltage by 90* - voltage leads

Inductor opposes changes in current flow - opposes the flow of AC

Directly proportional to freq

13

Impedance (Z)

Total opposition to current flow in an AC circuit

14

Resonant freq

XL = Xc - cancel each other out

If you control the freq to the correct level you can make it purely resistive

15

Power in an RLC AC circuit

Generally given in kilo volt amps

Power = true power/ apparent power

100% = voltage and current are in phase - true and apparent are equal

16

Reactive power

Amount of power req to overcome reactance (KVAR)

17

Apparent power

KVA = rms voltage x rms current

18

True power

KW - rms voltage x rms current x power factor