Figure 5.4 - Induction motors start schemes
If switch 2 is in position "Start", the stator winding is star-connected, if in position "Work", the stator winding is delta-conneсted.
Startup is performed as following. We put a switch 2 in position "start”, then we switch-on autotransformer and fix the starting current Ist. When a motor reaches the established speed, it is necessary to move quickly a switch 2 in position "Work". Startup is finished.
After it you must switch-off autotransformer and wait, when motor stops. To switch-on autotransformer and to fix starting current at delta connection of stator windings. Make sure that
Make the conclusion of starting torque value, by measuring of the phase voltages in the star or delta connection of the stator winding
Basic results summary
Motor
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Current |
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According to the passport Irated
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Direct start Inet ( |
At rm1 Inet |
At rm2 Inet |
Start with autotransformer Inet |
At star connection Inet |
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Phase rotor |
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Short-circuited rotor |
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Control questions
1. Why is starting current higher than nominal at the startup?
2. Why is current decreased during the frequency of rotation of the motor increasing?
3. Why is starting current decreased in the induction motor having the phase rotor, when starting resistance is introduced?
4. How is the value of starting torque of motor are changed, if as the starting resistance active or inductive resistance is used?
5. How is starting torque changed in different types of induction motor startups?
6. How is acceleration of motor time is changed in depending on the start method?
Report must contain:
1. Experiments schemes and measurements and calculations results.
2. Summary of basic results.
3. The control questions answers.
Laboratory work 6 research of induction motor in unbalanced modes
Purpose of the work – to investigate working characteristics of induction motor using different types of unbalancing of rotor and stator windings.
Equipment and devices
Induction motors with phase and short-circuited rotor are investigated in this work; measuring kit “K-50”; electromagnetic ammeter (scale 10 A); three-phase rheostat at the circuit of rotor winding of induction motor with phase rotor; lamp stroboscope.
Direct current generator, regulating rheostat Rr having the resistance value about 300-400 Ohm and current about 1 A; one-phase loading rheostat; ammeter (scale to 10 A) and voltmeter (scale to 250V) of permanent-magnet system in generator armature winding.
Terminals of all equipments devices are put on the test bench.