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Determination of Induction-Motor Parameters

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Determination of Induction-Motor Parameters DC Test Determines R1 Connect any two stator leads to a variable-voltage DC power supply Adjust the power supply to ... – PowerPoint PPT presentation

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Title: Determination of Induction-Motor Parameters

1
Determination of Induction-Motor Parameters
• DC Test
• Determines R1
• Connect any two stator leads to a
variable-voltage DC power supply
• Adjust the power supply to provide rated stator
current
• Determine the resistance from the voltmeter and

2
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3
For a Y-Connected Stator
4
For a Delta-Connected Stator
5
Determination of Induction-Motor Parameters
• Blocked-Rotor Test
• Determine X1 and X2
• Determines R2 when combined with data from the DC
Test
• Block the rotor so that it will not turn
• Connect to a variable-voltage AC supply and
adjust until the blocked-rotor current is equal
to the rated current

6
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7
Simplified Equivalent Circuit
Neglect the exciting current under blocked-rotor
conditions remove the parallel branch
8
IEEE test code recommends that the blocked-rotor
test be made using 25 rated frequency with the
test voltage adjusted to obtain approximately
rated current. A 60-Hz motor would use a 15-Hz
test voltage. The calculated reactance is
corrected to 60-Hz by multiplying by
60/15. Calculated resistance is correct.
9
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10
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11
How Is the Blocked-Rotor Impedance Divided?
If the NEMA-design letter of the motor is known,
use Table 5.10 to divide the impedances.
Otherwise, divide the impedances equally.
12
Determination of Induction-Motor Parameters
• Determine the magnetizing reactance, XM and
combined core, friction, and windage losses.
• Connect as for blocked-rotor test (next slide).
• The rotor is unblocked and allowed to run
unloaded at rated voltage and rated frequency.

13
Electrical connection for the No-Load Test is the
same as for the Blocked-Rotor Test
14
Determination of Induction-Motor Parameters
• At no-load, the speed is very close to
synchronous speed the slip is 0, causing the
current in R2/s to be very small, and will be
ignored i the calculations.
• IMgtgtIfe, so I0 IM.

15
The equivalent circuit for the no-load test is
shown.
Ignore
16
Substitute X1 from the blocked-rotor test to
determine the value of XM.
17
Example 5.16
• The following data were obtained from no-load,
blocked-rotor, and DC tests of a three-phase,
wye-connected, 40-hp, 60-Hz, 460-V, design B
induction motor whose rated current is 57.8A.
The blocked-rotor test was made at 15 Hz.

18
36.2V Vline 460.0V VDC 12.0V Iline
58.0A Iline 32.7A IDC 59.0A P3phase
2573.4W P3phase 4664.4W
a) Determine R1, X1, R2, X2, XM, and the combined
core, friction, and windage loss. b) Express the
no-load current as a percent of rated current.
19
Convert the AC test data to corresponding phase
values for a wye-connected motor.
20
Determine R1
Determine R2
21
Determination of X1 and X2
From Table 5.10, for a design B machine, X1
0.4XBR,60 0.4(1.0182) 0.4073?/phase X2
0.6XBR,60 0.6(1.0182) 0.6109/phase
22
Determination of XM
23
Determination of combined friction, windage, and
core loss
b) Express the no-load current as a percent of
rated current.