All About Circuits Forum 3 phase induction motor Lab
 Register Blogs FAQ Members List Today's Posts Search Today's Posts Mark Forums Read

 Homework Help Stuck on a textbook question or coursework? Cramming for a test and need help understanding something? Post your questions and attempts here and let others help.

#1
10-04-2011, 10:08 AM
 Jess_88 Senior Member Join Date: Apr 2011 Location: Australia Posts: 174
3 phase induction motor Lab

Hey guys

I'm having some trouble with what I need to determine from the measurements made in my lab.

I'll copy all of my lab procedure and parameters to avoid as much confusion as possible.

The objective of this experiment is to investigate various methods of induction motor speed control. How the standard motor characteristics are affected by the different methods of speed control, so as to allow informed decisions on the best type of control for a given application The Experiment includes:
• Variable stator voltage control
• Rotor resistance control
• Frequency control

VARIABLE STATOR SUPPLY VOLT AGE (DEL T A CONNECTED)
1) Ensure the cage induction motor is Delta connected and the dynamometer is cumulatively compounded with minimum excitation.

2) Set the panel autotransformer to the 440 V tap. Switch the motor on and record the no-load speed and line current.

3) Set the dynamometer load to 10 N and record the induction motor line current and speed. (Note: Torque arm length is 0.25m)

4) Switch off the motor. Set the panel autotransformer to the next voltage level tap down and repeat steps 1 & 2

5) Repeat the above steps for successive voltage level taps down to the 220V tap.

6) Plot on a common graph Speed V Voltage for Delta connections Loaded and on No Load.

MY RESULTS

VARIABLE STATOR SUPPLY VOLTAGE (STAR CONNECTED)
1)Ensure the cage induction motor is Star connected and the dynamometer is cumulatively compounded with minimum excitation.

2) Set the panel autotransformer to the 440 V tap. Switch the motor on and record the no-load speed and line current.

3) Set the dynamometer load to 10 N and record the induction motor line current and speed. (Note: Torque arm length is 0.25m)

4) Switch off the motor. Set the panel autotransformer to the next voltage level tap down and repeat steps 1 and 2

5) Repeat the above three steps for successive voltage level taps down to the 220V tap.

6) Plot on a the same common graph Speed V Voltage for Star connections Loaded and on No Load so that a comparison can be made with the Delta connection.

My results

note- the results in red i think my be incorrect... maybe

VARIABLE ROTOR RESISTANCE. (DELTA CONNECTED)
1) Ensure the Wound Rotor Induction motor is Delta connected and the dynamometer is cumulatively compounded with minimum excitation.

2) Adjust the rotor resistance set to the first position. Switch the motor on and record the no-load speed and line current. Repeat for all rotor resistance positions.

3) Set the dynamometer load to 20 N and record the induction motor line current and speed. Repeat for all rotor resistance positions.

4) Plot a graph of resistor position Vs Speed for both no load and load and comment on the characteristic produced.

My results

VARIABLE VOLTAGE VARIABLE FREQUENCY CONTROL
1) Ensure the cage induction motor is Star connected.

2) Connect the inverter input terminals to the three phase supply on the panel and its output terminals to the motor with the power analyser set to measure
frequency. This is on voltage current and hertz range with the voltage inputs set on motor line to line voltage.

3) Vary the inverter frequency from 25 Hz to 60 Hz in steps of 5 Hz. Record frequency, speed, voltage and line current for each step.

4) Calculate the synchronous speed and slip for each test.

5) Plot a graph of Frequency Vs Speed of the motor and comment on the result.

So here is my confusion. Can I really determine anything from plotting Voltage against speed? Should I be tying to determine the equivalent circuit???
I am guessing I need to determine the torque induced for each test, then plot that agains Ns to determine the motor class. Then I can determine the motor application right?

How can I calculate the slip without the rated speed???

Let me know if you want to see my graphs.

thanks guys
__________________
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
-Archimedes
#2
10-04-2011, 10:10 AM
 Jess_88 Senior Member Join Date: Apr 2011 Location: Australia Posts: 174

My results from VARIABLE VOLTAGE VARIABLE FREQUENCY CONTROL

note - sync speed was calculated from Ns = (120*f)/4
__________________
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
-Archimedes
#3
10-04-2011, 11:04 AM
 strantor Senior Member Join Date: Oct 2010 Location: Houston tx Posts: 3,581

Quote:
 Originally Posted by Jess_88 4) Calculate the synchronous speed and slip for each test. 5) Plot a graph of Frequency Vs Speed of the motor and comment on the result. How can I calculate the slip without the rated speed??? Let me know if you want to see my graphs. thanks guys
 The Following User Says Thank You to strantor For This Useful Post: Jess_88 (10-04-2011)
#4
10-04-2011, 12:05 PM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,924

Keep in mind that in Australia the mains frequency is 50Hz.
 The Following User Says Thank You to t_n_k For This Useful Post: Jess_88 (10-04-2011)
#5
10-04-2011, 12:41 PM
 strantor Senior Member Join Date: Oct 2010 Location: Houston tx Posts: 3,581

Quote:
 Originally Posted by t_n_k Keep in mind that in Australia the mains frequency is 50Hz.
doh! missed that

EDIT: despite that oversight, he's still running above synchronous speed at 50Hz in variable frequency test, so something still doesn't add up.

EDIT 2; should still double RPM when in star
 The Following User Says Thank You to strantor For This Useful Post: Jess_88 (10-04-2011)
#6
10-04-2011, 01:57 PM
 Jess_88 Senior Member Join Date: Apr 2011 Location: Australia Posts: 174

Is difference in expected results maybe because the torque arm length is 0.25m for all tests but the variable voltage variable frequency control test???
__________________
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
-Archimedes
#7
10-04-2011, 02:17 PM
 strantor Senior Member Join Date: Oct 2010 Location: Houston tx Posts: 3,581

Quote:
 Originally Posted by Jess_88 Is difference in expected results maybe because the torque arm length is 0.25m for all tests but the variable voltage variable frequency control test???
No, I thought 1.1, 1.3, and 3.1 were no-load tests. if 1.1 & 1.3 were no-load, and 3.1 was with a load, then that means the error is even greater than I thought.
 The Following User Says Thank You to strantor For This Useful Post: Jess_88 (10-04-2011)
#8
10-04-2011, 02:26 PM
 Jess_88 Senior Member Join Date: Apr 2011 Location: Australia Posts: 174

sorry, my mistake (I feel silly). Yeah data from table 1.1, 1.3 and 2.1 are no load. As for Table 3.1... I'm a bit confused (I can't remember applying a load). Shouldn't the variable voltage variable frequency control test be done without a load?
goodness me... I feel like I could be in trouble. I was sure I was making my measurements correctly
__________________
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
-Archimedes
#9
10-04-2011, 03:16 PM
 strantor Senior Member Join Date: Oct 2010 Location: Houston tx Posts: 3,581

Quote:
 Originally Posted by Jess_88 sorry, my mistake (I feel silly). Yeah data from table 1.1, 1.3 and 2.1 are no load. As for Table 3.1... I'm a bit confused (I can't remember applying a load). Shouldn't the variable voltage variable frequency control test be done without a load? goodness me... I feel like I could be in trouble. I was sure I was making my measurements correctly
well if you did all the other tests with & without a load, I would expect you would do the variable voltage variable frequency test both with and without a load as well. So are you missing a table of data?

I'm slightly confused myself now; I think the key (or part of it) lies in the voltage output of the transformer. I was using the numbers from the variable frequency variable voltage test (444V @ 60Hz) to determine what your RPM would be in the other tests, but then learned that those were 50Hz tests, so now I don't have much to go on. I strongly suspect that you flubbed some measurements in the variable frequency variable voltage test.
 The Following User Says Thank You to strantor For This Useful Post: Jess_88 (10-05-2011)
#10
10-04-2011, 04:05 PM
 GetDeviceInfo Senior Member Join Date: Jun 2009 Location: Canada Posts: 1,501

I personally don't see any problems with your results. Yes, the graphs are a quick visual reference to the spectrum.

why would rpm double going from delta to star?

I agree that a loaded test should have been performed for variable frequency.

If I'm not mistaken, the intent of the exercise is to realize speed regulation over the varying methods.
__________________
I get all the news I need on the weather report
 The Following User Says Thank You to GetDeviceInfo For This Useful Post: Jess_88 (10-05-2011)

 Tags induction, lab, motor, phase

 Related Site Pages Section Title Worksheet AC motor theory Textbook AC commutator motors : Ac Motors Worksheet AC generator theory Textbook Selsyn (synchro) motors : Ac Motors Textbook Other specialized motors : Ac Motors Textbook Wound rotor induction motors : Ac Motors Textbook Tesla polyphase induction motors : Ac Motors Textbook Stepper motors : Ac Motors Textbook Reluctance motor : Ac Motors Textbook Synchronous Motors : Ac Motors

 Similar Threads Thread Thread Starter Forum Replies Last Post dec335 The Projects Forum 4 10-13-2010 11:34 AM tgovender0 General Electronics Chat 0 03-03-2010 11:06 AM aardbearst General Electronics Chat 6 12-12-2009 07:57 PM resilient General Electronics Chat 0 04-30-2009 08:39 AM mksa Homework Help 2 05-09-2006 05:41 AM

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Electronics Forums     General Electronics Chat     The Projects Forum     Homework Help     Electronics Resources Software, Microcomputing, and Communications Forums     Programmer's Corner     Embedded Systems and Microcontrollers     Computing and Networks     Radio and Communications Circuits and Projects     The Completed Projects Collection Abstract Forums     Math     Physics     General Science All About Circuits Commmunity Forums     Off-Topic     The Flea Market     Feedback and Suggestions

All times are GMT. The time now is 09:37 PM.