# Synchronous Machines BTEE-501 Sept 2020 B.Tech EE PTU Paper

## Download Previous Year PTU University Question Paper of Synchronous Machines 5th Sem BTEE-501 B.Tech EE PTU Sept 2020 Paper

**B.Tech.** **(EE-2011 Batch)**

## SYNCHRONOUS MACHINES

### Subject Code : BTEE-501 M.Code : 70554

## Download Previous Year PTU University Question Paper of Asynchronous Machines 4th Sem BTEE-401 B.Tech EE PTU Nov 2018 Paper

### Time : 2 Hrs. Max. Marks : 30

#### INSTRUCTIONS TO CANDIDATES :

1. Attempt any FIVE question(s), each question carries 6 marks.

## Synchronous Machines 5th Sem BTEE-501 B.Tech EE PTU Sept 2020 Paper

** SECTION-A**

#### 1. Draw and explain equivalent circuit and phasor diagram of an alternator.

2. Derive pitch factor. Discuss the effect of harmonics on this factor. Also discuss the

necessity of chording the armature windings.

#### 3. Explain two reaction theory of salient pole machines. 4. Write a note on following :

a) Transient reactance of synchronous machines

b) Rating of Alternator is in kVA not in kW. Explain why.

#### 5. Explain with the help a neat sketch the construction and working of Reluctance type Single

phase synchronous motor.

6. Discuss EMF method for calculating voltage regulation of an alternator.

7. What are the conditions of parallel operation of alternators? Also state advantages of the

parallel operation.

8. Explain why a three phase synchronous motor is not self starting. Describe two methods

used to start this motor.

**Note:** Any student found attempting answer sheet from any other person(s), using incriminating material or involved in any wrong activity reported by evaluator shall be treated under UMC provisions.

Student found sharing the question paper(s)/answer sheet on digital media or with any other person or any organization/institution shall also be treated under UMC.

Any student found making any change/addition/modification in contents of scanned copy of answer sheet and original answer sheet, shall be covered under UMC provisions.

#### Explain equivalent circuit and phasor diagram of an alternator.

#### Pitch factor.

#### Discuss the effect of harmonics on this factor.

#### Discuss the necessity of chording the armature windings.

#### Two reaction theory of salient pole machines.

#### a) Transient reactance of synchronous machines

#### b) Rating of Alternator is in kVA not in kW. Explain why.

#### Construction and working of Reluctance type Single phase synchronous motor.

#### EMF method for calculating voltage regulation of an alternator.

#### Conditions of parallel operation of alternators? Also state advantages of the parallel operation.

#### Why a three phase synchronous motor is not self starting.

#### Describe two methods

used to start this motor.

#### Explain Why does a 3-phase induction motor always run at a speed less than the synchronous speed.

###### Asynchronous Machines 4th Sem BTEE-401 B.Tech EE PTU Nov 2018 Paper Click Here

#### 3-phase induction motor crawls near half synchronous speed. Give the reasons.

#### 3-phase cage rotor induction motor has a full load slip at 4%. The standstill current at rated voltage is 6.5 times full load current. Find auto transformer tapping to give full load torque at starting and also find line current at starting.

#### How the stationary, pulsating m.m.f. wave of a single phase induction motor can be considered as equivalent to two equal but oppositely rotating m.m.f. waves.

#### Constructional features and working of stepper motor.

#### Various methods of excitation of induction generator.

##### Asynchronous Machines 4th Sem BTEE-401 B.Tech EE PTU Nov 2018 Paper Click Here

#### 1100 V, 50 Hz star connected induction motor has a star connected slip-rings rotor with a transformation ratio of 3.8 the rotor resistance per phase is 0.012 Ohm. and leakage inductance is 0.8 mH per phase. Neglect’ stator impedance.

#### (a) the rotor starting current per phase with slip rings short circuited,

#### The rotor power factor at starting

#### External resistance per phase to obtain a starting current of 100A in the stator.

#### The rotor current at 4% slip.

#### How the equivalent circuit of an ordinary polyphase induction motor is also applicable to deep-bar induction motors.

#### Working of universal motor and draw its phasor diagram.

##### Asynchronous Machines 4th Sem B.Tech EE PTU Nov 2018 Paper **Contact Us**

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### Time : 2 Hrs. Max. Marks : 30

#### INSTRUCTIONS TO CANDIDATES :

1. Attempt any FIVE question(s), each question carries 6 marks.

#### 4-pole, 3-phase, 50 Hz induction machine, the slip-rings of the machine are open- circuited. The frequency of the voltage across slip-rings is 75 Hz. Find the speed at which the rotor is driven.

#### No-load speed of a 3-phase 50 Hz induction motor is 1485 rpm. Find the number of alterations per minute which the rotor emf will make and the speed of rotor mmf with respect to rotor wound.

#### Stator of a 4-pole, 3-phase induction machine is supplied from 3-phase, 50 Hz supply and a prime-mover drives its rotor at a speed of 750 rpm. The slip-rings of the machine are open-circuited. Find the frequency of the voltage across any two slip-rings.

#### Limitations of induction generator.

#### Condition for maximum torque in a 3-phase induction motor.

#### Rotating fields of the stator and rotor are stationary with respect to each other.

#### What happens to a 3-phase induction motor if one of its three supply-leads gets disconnected.

#### 6-pole, 50 Hz single-phase induction motor runs at a speed of 900 rpm. Calculate the frequency of current in the cage rotor.

#### 3-phase induction motor, maximum torque of 100 Nm occurs at a slip of 10%. Calculate the torque at a slip of 5%.

#### Explain Why does a 3-phase induction motor always run at a speed less than the synchronous speed.

### Synchronous Machines 5th Sem BTEE-501 B.Tech EE PTU Sept 2020 Paper Click Here

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