2.A 3-phase motor having a star connected rotor has an induced emf of 150 volts between slip rings at standstill on open circuit. The rotor has a resistance and reactance per phase of 2 22 and 8 2 respectively. Calculate current per phase and power factor when (i) Slip rings are short circuited (ii) slip rings are connected to a star connected rheostat of 8 92 per phase

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**Problem Statement:**

A 3-phase motor having a star-connected rotor has an induced EMF of 150 volts between slip rings at standstill on an open circuit. The rotor has a resistance and reactance per phase of 2 Ω and 8 Ω, respectively. Calculate the current per phase and power factor when:

(i) Slip rings are short-circuited.

(ii) Slip rings are connected to a star-connected rheostat of 8 Ω per phase.

**Solution Approach:**

- For part (i), the calculation involves using the rotor's resistance and reactance to determine the current when the slip rings are short-circuited.

- For part (ii), the external resistance from the rheostat is included in the calculations, affecting both the current and power factor.

**Diagrams or Graphs:**

- Since this text does not contain any visuals, diagrams such as phasor diagrams or equivalent circuit diagrams would typically help illustrate the concepts of rotor circuits, equivalent impedances, and power factors in educational material. However, no specific diagrams are provided in the text.
Transcribed Image Text:**Problem Statement:** A 3-phase motor having a star-connected rotor has an induced EMF of 150 volts between slip rings at standstill on an open circuit. The rotor has a resistance and reactance per phase of 2 Ω and 8 Ω, respectively. Calculate the current per phase and power factor when: (i) Slip rings are short-circuited. (ii) Slip rings are connected to a star-connected rheostat of 8 Ω per phase. **Solution Approach:** - For part (i), the calculation involves using the rotor's resistance and reactance to determine the current when the slip rings are short-circuited. - For part (ii), the external resistance from the rheostat is included in the calculations, affecting both the current and power factor. **Diagrams or Graphs:** - Since this text does not contain any visuals, diagrams such as phasor diagrams or equivalent circuit diagrams would typically help illustrate the concepts of rotor circuits, equivalent impedances, and power factors in educational material. However, no specific diagrams are provided in the text.
Expert Solution
Step 1

Given that:

  • The 3-phase motor has star connected rotor
  • Induced EMF 150 V at a standstill on an open circuit.
  • Rotor resistance, R2= 2 ohm per phase.
  • Rotor reactance, X2= 8 ohm per phase.

Find current per phase and power factor when

  • Slip rings are short-circuited.
  • A star rheostat having 8 ohms per phase is connected to star rings.
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