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2nd Period Electrican > Theory > Flashcards

Theory Flashcards

1
Q

Factors on EMF generation/ Faraday’s Law

A

-density of magnetic flux
-length of conductor within magnetic field
-rate at which conductor cuts lines of magnetic force

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2
Q

Maximum cutting rate

A

90 degrees

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3
Q

Components of AC sine wave

A

-One positive alternation (0 to 180)
-One negative alternation (180 to 360)

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4
Q

Frequency

A

-number of electrical cycles per second
-symbol (f)
-unit of measurement (hertz)
-symbol of hertz (hz)
-time to complete one cycle (time period)

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5
Q

Frequency formula

A

f= (p x n)/120

f=(pp x r/min)/60

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6
Q

Maximum values at sine waves

A

+V at 90 degrees
-V at 270 degrees

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7
Q

Instantaneous values of a cycle

A

e=Emax x sine of angle

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8
Q

Effective Value/RMS value

A

Emax = E RMS / 0.707

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9
Q

Impedance on AC circuit

A

Resistance
Inductive Reactance
Capacitive Reactance

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10
Q

Inductance

A

Property of a circuit that opposes change of current
through a counter EMF
(L)
unit of measurement: Henry

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11
Q

Inductive reactance

A
  • Current limiting property of an inductor of a circuit
    (XL)
  • measured in Ohms

XL = 2 pi f L

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12
Q

Factors on AC resistance

A
  • DC ohmic value
  • Iron losses
  • Dielectric losses
  • Skin Effect
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13
Q

Iron Losses

A
  • Hysteresis loss and Eddy current loss
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14
Q

Hysteresis loss

A
  • energy it takes to overcome molecular friction due to reversing polarity
  • use an alloy that contains Silicon for the core and armature
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15
Q

Eddy Current loss

A
  • circulating current induced in magnetic material that is adjacent to an AC circuit
  • use laminations in the core and armature, less induced voltage
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16
Q

Dielectric loss

A
  • energy loss to circuit due to voltage stress of a conductor
  • greater at high voltage
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17
Q

Skin Effect

A
  • tendency of AC to flow towards conductors surface
  • effective area of conductor is reduced, resistance increases
  • problem at high frequency
  • allows transmission lines to have a steel core
18
Q

Inductor

A
  • an insulated wire wrapped around a core
  • coil, solenoid, reactor
19
Q

Factors that affect Inductance

A

L= (N^2 u A)/l

N(number of turns of a conductor)
u(permeability of core material)
A(cross-sectional area)
l(length of core’s magnetic path)

20
Q

Mutual Induction

A
  • emf generated in one conductor by a change of flux around a separate circuit
21
Q

Lenz’s Law

A
  • induced voltage attempts to force electron in one direction
21
Q

Self Induction

A
  • emf generated by a change of flux around a conductor
22
Q

Left Hand Rule

A
  • thumb points towards core
  • forefinger points to direction of magnetic field
  • middle finger points of of page, cemf
23
Q

Factors that affect CEMF

A
  • inductance of coil
  • rate of change of current

cemf= (change in current / change in time) x inductance

24
Q

Time Constants of inductive circuits

A

T= L/R

  • takes 5 time constants to reach steady value
  • one time constant = 63.2%
25
Q

Discharge Resistor

A
  • placed in parallel to coil
  • reduces inductive kick
  • reduces arcing
26
Q

Inductive Circuits

A

Current lags voltage by 90 degrees

27
Q

Reactive Power/ Quadrature Power

A

Qxl = Vx x Ix

Qxl = I^2 XL

28
Q

Capacitor Construction

A

2 plates of conducting material seperated by a insulating material called dielectric

29
Q

Non polarized Capacitors

A

Air
Oil filled
paper, tubular
plastic film
mica
ceramic disc

30
Q

Capacitor applications

A

Timer
Rectifier smoothing and filtering
Power factor correction
Motor starting

31
Q

Capacitance

A

capacitor ability to store charge
measured in micro farads

32
Q

Factors that affect Capacitance

A

Area of plate
distance between plates
type of dielectric material

33
Q

Dielectric Constant

A

Rating of dielectric insulating material’s ability to polarize and store charge compared to air

34
Q

Dielectric Strength

A

Ability to withstand volatge
kV/mm

35
Q

Electric Charge

A

Q= I x t
C= Q / V

36
Q

Time Constants in Capacitive circuits

A

T= R x C

37
Q

Capacitive reactance

A

Xc = 1/( 2 pi f C)

38
Q

Capacative phasor relationship

A

current leads voltage by 90 degrees

39
Q

Series AC Circuits

A

Total Resistance Rt =R1 + R2 +R3 …
Total Inductance Reactance XLt = XL1 + XL2 + XL3 …
Total Capacitive Reactance XCt = XC1 + XC2 + XC3 ..

2nd Period Electrican (4 decks)

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