1
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Give reason : The
alternating waveform is called as sinusoidal waveform.
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Sinusoidal waveform
- The induced emf in the coil varies with the sine
function of the time angle ωt therefore the alternating waveform is called as
sinusoidal waveform.
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2
|
Explain the
following terms : Waveform , Amplitude
and Frequency
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Waveform
- The shape of the
instantaneous value of alternating quantity ( voltage or current ) is
represented on Y – axis and time on X – axis is called waveform of the
alternating quantity.
Amplitude
- The maximum ( Positive
or Negative ) value of an alternating quantity is called as amplitude.
Frequency ( f )
- The numbers of
cycle per second of an alternating quantity is called as frequency.
- Its unit is cycle
per second or Hertz ( Hz ).
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3
|
Explain the
following terms : Cycle , Instantaneous value and Time period
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Cycle
- One complete set of
positive and negative cycle of an alternating quantity is called as cycle.
Instantaneous value
- The value of
alternating quantity at given instant (or time) is called as instantaneous
value.
Time period (T)
- It is defined as
the time required to complete one cycle of an alternating quantity.
- It is measured in second.
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4
|
Explain the
following terms : Peak value , Average or mean value , Effective or RMS value
and Form factor
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Peak Value
- The maximum value
of positive or negative half cycle of symmetrical waveform of an alternating
quantity is called as peak value.
Average or mean value
- It is DC quantity which
transfers the same charge in a given circuit as is transferred by the
alternating quantity during the same time.
Effective or RMS value
- The RMS value of an
alternating quantity is defined as the value of direct current which when
flowing through a given circuit for a given time produces the same heat as
that is produced by alternating quantity when flowing through the same
circuit for the same time.
Form factor ( Kf )
- It is defined as
the ratio of the RMS value to the average value of an alternating quantity.
Form factor = RMS
value / Average value
- The value of form
factor for sinusoidal alternating quantity is 1.11
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5
|
Explain the term :
Complex waveform
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Complex Waveform
- It is composed of
fundamental waveform and number of other harmonics waveform.
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6
|
What is frequency
of the fundamental harmonic?
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50 Hz
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7
|
At which condition,
the complex waveform does not contain distortion?
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Distortion in the Complex waveform
- When the two halves of the
complex wave are identical in shape there is no distortion in the output
waveform. It is only possible when only odd harmonics ( 3rd , 5th
, 7th etc ) are present.
- When
the two halves of the complex wave are not identical in shape, there is
distortion in the output waveform. It is only possible when only even
harmonics ( 2nd , 4th , 6th etc ) are
present.
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8
|
State the frequency
of the 5th harmonics if the fundamental frequency 50 Hz?
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The frequency of the 5th harmonics is 250 Hz.
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9
|
State the speed of
the 5th harmonics if the fundamental waveform rotates at Ns RPM.
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The speed of the 5th harmonics is Ns / 5 RPM.
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10
|
State other name of
the RMS current.
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Effective / virtual current
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11
|
Which method is
used to find out RMS value of the alternating quantity?
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Method to find out RMS quantity
- Mid – ordinate method
- Analytical method
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12
|
State the average
value of the complete symmetrical alternating voltage.
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Zero
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13
|
Write the equation
of the RMS voltage, average voltage and form factor for sinusoidal and half
wave rectified voltage
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Sinusoidal voltage
- RMS voltage : Im / √ 2
- Average
voltage : 2Im / π
- Form factor : 1.11
Half wave rectified voltage
- RMS voltage : Im
/ 2
- Average
voltage : Im / π
- Form
factor : 1.57
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14
|
Describe the
importance of the amplitude or crest factor.
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Importance of amplitude factor
- The dielectric stress on
the insulation depends upon maximum voltage therefore the amplitude factor
is importance during testing of dielectric insulation.
- The iron loss depends upon
maximum flux density not RMS flux density therefore the amplitude factor
greatly affect the value of the iron loss.
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15
|
Why alternating
supply is not used for charging batteries?
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The alternating supply
consists of both positive and negative half cycle therefore the charging of
battery is done during positive half cycle and it will discharge during
negative half cycle.
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16
|
State the RMS and
average value of symmetrical rectangular waveform.
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The RMS value and
average value of symmetrical rectangular waveform is one.
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17
|
An alternating
current of peak value is 50.0 Amp. If this current is passing through ( a )
Moving coil ammeter ( b ) Moving iron ammeter. What is indication on these
meters?
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- The Moving coil
ammeter indicates average value of an alternating quantity. Therefore the
meter indicates Zero reading
for sinusoidal alternating current of peak value 50.0 amps.
- The moving iron
ammeter indicates RMS value of an alternating quantity.
- Therefore the meter
indicates = RMS value of current = 0.707 × Maximum value of current = 0.707 × 50 = 35.35 Amp
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18
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Which parameters
affect the value of self inductance or back emf of the inductive coil?
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The self inductance
of the inductive coil is affected by
- Rate of change of
current and
- Inductance of the
coil : E = – L ( di / dt )
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19
|
Give reason : The
power loss in the pure resistive circuit never becomes zero.
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The instantaneous
value of voltage and current are always either either negative or both
positive therefore the power loss never becomes zero.
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20
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Explain : Pure
inductive coil
|
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Pure inductive coil
- It is coil in which no ohmic resistance and no power
loss. It is only consider for theory point of view.
- Practically the pure inductance
is not possible.
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