The method
Before using the result
- AC induction-machine kinematics. Pole count must be even; a negative slip indicates supersynchronous operation, not ordinary motoring.
Worked examples
These original training examples illustrate the method for Third-Class Electric Chief Engineer 電験三種 (Theory/Power/Machine/Law). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Link supply frequency and pole count to synchronous speed, then interpret rotor slip. Recognise supersynchronous operation from the sign of the calculated slip.
- Frequency (Hz)
- 50
- Pole count
- 4
- Rotor speed (rpm)
- 1,440
- Ns = 120 × 50 / 4 = 1500 rpm.
- Slip = (1500 − 1440) / 1500.
- Synchronous speed: 1,500 rpm
- Slip: 4 %
2. Comparison example
Compare a different supplied condition using the same method. For Denken Exam, the important check is that the input meaning, units and method assumptions still match the problem.
- Frequency (Hz)
- 50
- Pole count
- 4
- Rotor speed (rpm)
- 1,470
- Ns = 120 × 50 / 4 = 1500 rpm.
- Slip = (1500 − 1470) / 1500.
- Synchronous speed: 1,500 rpm
- Slip: 2 %
Check your understanding
1. Which relationship is used?
Synchronous speed Ns = 120f/p; slip = (Ns−N)/Ns.
2. Which assumption should you check first?
AC induction-machine kinematics. Pole count must be even; a negative slip indicates supersynchronous operation, not ordinary motoring.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
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