Flashcards in Basic AC Principles Deck (18)

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1

## Inductance

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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

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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

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Area of the plates - a

Distance between the plates - d

Types of dielectric - k

C = ka/d

6

## Advantages of AC

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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 =

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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

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=NP/60

N = speed in RPM

P= number of pairs of poles (per phase)

Periodicity = 1/freq

9

## Purely resistive AC circuit

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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

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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

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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

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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

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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

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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