Lab 8fsd
Lab 8fsd
Lab 8fsd
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Procedure:
First run DC motor (Shunt) and note the direction of rotation of the motor.
Start both of them together. Measuring unit will show the values of real
power and reactive power. Measure W T (total power) by the Measuring
Unit. Also note down the value of Load Current and Load voltage when
running at rated voltage and as Induction motor. Also note down the
power factor.
At this point the speed is less than 3000 rpm. Now increase the speed of
the DC Shunt motor by increasing the applied voltage gradually so that it
becomes equal to the rated speed that is 3000 rpm. At this point the
Voltage of the DC Shunt Motor would be nearly 220V~230V.
At this speed of 3000 rpm or near it, the Induction motor is in floating
condition i.e when slip becomes zero the machines would be in floating
condition. The total active power input at that time in the motor would be
nearly zero on the measuring Unit. Again note the values of current,
voltage, power factor, active and reactive power for the floating condition
from the meters and measuring unit connected.
Now increase the speed further by changing the Applied DC Voltage from
3000 rpm to a max of 3020 rpm. At this point on forward the induction
motor becomes a generator and the values of voltage, current, active and
reactive power are again noted. Note down these readings in the table
provided. At this point, the generator is supplying energy to the WAPDA
grid.
Observations:
Synchronous Speed = N s = 3000 rpm = (120 f) / p
State of
Machine
Induction
Motor
Floating
Ind.
Generator
Line to
Line
Voltage
Line
Current
Total
Power
VL
(V)
IL
(A)
WT
(W)
(p = 2 and f = 50Hz)
Power
factor
Reactive
Power
Q
cos
Speed
Nr
(rpm)
(VAR)
Circuit Diagram:
Line Voltage VL
Measuring Unit
3 Phase AC
Voltage Supply
V L-L = 380V
From Variac
L1
L1
L2
L2
L3
L3
Line Current IL
DC Voltage Supply
0-220V
Applied Voltage
3-Phase Squirrel
Cage Induction Motor
Speed
(Tachometer)
DC Shunt Motor
Comments:
Comment on the values of Active power P in the table for three states of
Induction Machine. What does it signify?
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Discuss De-merit of Induction Generator if any?
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Induction Generator supplies Active or Reactive Energy or both to the WAPDA
Grid?
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