Reference no: EM131069772
Requirements
- Students need to attend one laboratory session, as per the group timetable, where they will be given all the necessary instructions how to do measurements relevant for the assignment.
- Prepare a brief report (preferably word edited) to include explicit responses to the questions below, and hand it in to the FEE Office in Ellison Building, room B201 by Thursday, 29 April 2016. Please use this Word file as a template and add the required number of answer sheets as appropriate. Make sure you populate the sections on the cover page above (e.g. name, ID, your bench number when you did your lab session, as well as the submission date).
- In case of late submission without a proven good cause, your assignment will incur fail or zero mark. In the event that you submit the assignment late but with a genuine reason, you must complete a late submission form available from the FEE office referenced above, and then have it authorised/signed by the module tutor.
Tasks
1. From your test results, determine the machine synchronous speed and the number of poles.
2. The example cage induction machine was started using a variable voltage supply at 50 Hz.
a. What is the main reason for adopting such a starting procedure as opposed to dead-on-line start, and especially with larger machines?
b. State alternative electro-mechanical and power electronics starters (at least one configuration for each) which can be used for the same purpose. What are the main advantages of the latter over the former?
c. Identify the common problem of fixed frequency operation of the motor with respect to the starting torque and current?
3. If the same 415 V, Y-connected machine was Δ-connected (as you did in your experiments), what maximum voltage could be applied to its terminals to prevent the current over-loading? Compare (in relative sense) the line current and torque values for the two winding connections of the motor for a given speed?
4. Tabulate your measurements (similarly to the table on page 8 of the lab sheets) showing the following performance parameters: line current, 3-phase electrical power, power factor, load torque (the measurements may necessarily differ from the values in the above table), speed, calculated slip in motoring mode, and speed and electro-magnetic power predictions for the machine operated as a generator at the same absolute slip and shaft torque values as in motoring mode.
5. Using Excel spreadsheets or similar software available in the computer rooms or elsewhere, present graphically the following operating characteristics of the motor in terms of torque: speed, current, power factor, input power and slip (two plots/figure for each, one for Y and one for Δ connection for comparison).
6. Using the approximate equivalent circuit, show that the machine electro-magnetic torque is proportional to slip in the low slip region, and verify this linear relationship by the corresponding experimental plot(s) above.
7. In your experiments, 3-phase power has been measured using two single phase watt-meters connected as illustrated in Fig. 4 of the lab sheets (this is known as the ‘two-wattmeter method' in the literature). Using phasor diagrams, an expression for instantaneous power, or applying any other approach you consider appropriate, explain how is this possible and why?
Attachment:- assign.rar