Skip to the content

onlineexamguide

  • Home
  • Courses
  • Engineering Study Materials
    • Electrical Engineering
    • Mechanical Engineering
    • Automobile Engineering
    • Civil Engineering
    • Computer Science Engineering
    • Chemical Engineering
  • Online Exam
    • Aptitude Tricks
    • Computer Knowledge
    • Logical Reasoning Tricks
    • Networking
  • Ghatna Chakra
  • Register
    • Instructor Registration
    • Student Registration
  • User Login
  • Home
  • Courses
  • Engineering Study Materials
    • Electrical Engineering
    • Mechanical Engineering
    • Automobile Engineering
    • Civil Engineering
    • Computer Science Engineering
    • Chemical Engineering
  • Online Exam
    • Aptitude Tricks
    • Computer Knowledge
    • Logical Reasoning Tricks
    • Networking
  • Ghatna Chakra
  • Register
    • Instructor Registration
    • Student Registration
  • User Login

Schrage Motor

Schrage Motor

Table of Contents

  • What is Schrage Motor
  • Operation Principle of Schrage Motor
  • Speed Control of Schrage Motor
    • Case 1: When Ej is in phase opposition to sE2
    • Case 2: When Ej is in phase with sE2
  • Power Factor Control
  • Characteristics of Schrage Motor
  • Schrage Motor Application

Schrage Motor

What is Schrage Motor

Schrage motor is Essentially a Frequency Converter and wound rotor Induction motor Combined. An Inverted Polyphase Induction motor can be used to describe the Schrage motor. Schrage motor’s primary winding, in Contrast to an Induction motor, is located on the rotor. Three slip rings are used to provide the primary with a three phase supply. The stator has the secondary winding. A third type of winding, known as Tertiary winding, is in addition to primary and Secondary Windings and is connected to the Commutator.

The primary and Tertiary are Mutually coupled and housed in the same rotor slots. Three sets of movable brushes, A1A2, B1B2, and C1C2, join the commutator to the secondary winding terminals. A wheel located at the motor’s back can be used to adjust the brush position. The Injected emf into the secondary winding, which is necessary for speed and power factor control, is determined by the angle between the brushes.

Schrage Motor

Operation Principle of Schrage Motor

A rotating field is created at a standstill as a result of three phase currents flowing in the primary winding. With a synchronous speed of ns, this rotating field abrades the secondary.
The rotor will therefore rotate in a way that opposes the cause, which is to cause slip frequency emfs to enter the secondary, in accordance with Lenz’s law. As a result, the rotor rotates in the opposite direction to the synchronously rotating field. The air gap field is currently rotating with respect to the secondary at a slip speed of ns – nr. The emf that the stationary brushes have collected is therefore at slip frequency and suitable for injection into secondary.

Speed Control of Schrage Motor

By adjusting the injected emf into the motor, which is controlled by altering the angular displacement between the two brushes, the speed of a schrage motor can be changed. Let’s first examine the speed control in WRIMs using the injected emf method in order to comprehend the speed control of the Schrage motor.

Consider the following rotor circuits (values are only for illustration purpose).

Speed Control of Schrage Motor


Let initially electrical torque (Te) = load torque (Tl) = 2Nm
Rotor current Ir = 2A.
Let sE2 = slip emf induced in the rotor ckt.
And Ej = emf injected in the rotor ckt.

Case 1: When Ej is in phase opposition to sE2

Speed Control of Schrage Motor 1


Now the rotor current becomes Ir = 1A. Therefore Te < Tl due to which motor decelerates. Therefore ωr decreases. That implies slip increases. Therefore ωr decreases till sE2 becomes 15V and Ir = 2A i.e till Te = Tl again.

Case 2: When Ej is in phase with sE2

Speed Control of Schrage Motor 2


Now the rotor current becomes 3A. Therefore Te > Tl due to which motor accelerates. Therefore ωr increases. That implies slip decreases. Therefore ωr increases till sE2 becomes 5V and Ir = 2A i.e till Te = Tl again.

The injected emf needs to be in phase with the rotor’s slip emf in order to increase speed, as can be seen from the analysis above. The slip emf in the rotor should be out of phase with the injected emf in order to slow down the speed.
We will now examine the speed control of the Schrage motor based on the aforementioned principles.


Speed Control of Schrage Motor

In the above figure
E20 = standstill emf induced in the secondary.
sE20 = induced emf at any slip s.
a, b = brush terminals.

Both brushes in Fig. (a) are short-circuited because they are both connected to the same commutator segment. In this instance, no injected emf exists. Rotor spins at a speed that is nearly synchronous as a result.
In figure (b), the brushes a and b are separated by an angle θ such that the secondary winding axis and the tertiary winding axis are parallel to each other. The injected emf Ej is now in phase opposition to E20 when we trace the path BAabB. Therefore, according to the principles mentioned above, the motor’s speed should be lower than it was in case a. The motor therefore runs at sub-synchronous speeds.

i.e. nr < ns.
In fig(c) the brush positions are interchanged. Now on tracing the path BAabB we find that the injected emf is in phase with the standstill emf E20. Therefore speed of motor should increase from what it was in case a. Hence the motor operates at super synchronous speed i.e. nr > ns.
For any brush separation θ the injected emf is given by

brush separation θ the injected emf


From the equation it can be seen that minimum value of injected emf Ej = 0 at θ = 0 (i.e. when the brushes are short circuited). And maximum value of injected emf is Ej = Ejmax at θ = 90 degrees (i.e. when the brushes are one pole pitch apart).

Power Factor Control

Power Factor Control


An angular displacement of ρ is added between the secondary and tertiary winding axes in order to improve power factor. Now, flux φ moves an additional angular distance of ρ degrees before cutting the tertiary winding axis. Because of this, the emf phasor-Ej in case a lags the emf phasor-Ej in case b by an angle ρ of.
The two cases’ phasor diagrams are displayed below.


Schrage Motor phasor diagram


The phasor diagram has been constructed based on the following equations:


I2 lags I2Z2 by some angle θ. I2’ is draw opposite to I2. The resultant of I2’ and magnetizing current I0 gives the primary current I1.
From the phasor diagram it is clear that if the tertiary winding axis and secondary winding axis are displaced by an angle ρ then power factor improves.

Characteristics of Schrage Motor

If we apply KVL to secondary circuit then we get

Characteristics of Schrage Motor


Under no load conditions I2 value is very small and hence the can be neglected.
Therefore we have,


Where, s0 is the no load slip

no load slip

Where,
Ejmax is the transformer emf induced in the Tertiary winding.
φm = max flux linkage
fs = supply frequency
Z = number of conductors in tertiary
A = number of parallel paths
Also


Where,
E20 = the transformer emf induced in the secondary.
N2’ = effective number of turns in the secondary
Now on substituting these values in the expression of no load slip we get

expression of no load slip


This implies values of slip depend completely on machine constants and the brush separation.



This demonstrates that depending on the phase of the injected emf, two different speeds are possible at no load. By changing the brush separation, it is possible to control the magnitude of these speeds.
when there is load


magnitude of these speeds



Schrage Motor Application

Utilised in drives that need variable speed, such as those for conveyors, fans, centrifugal pumps, and cranes.

Write a comment Cancel reply

You must be logged in to post a comment.

*
  • प्रवासन के लिए अंतर्राष्ट्रीय संगठन की पहली महिला महानिदेशक एमी पोप (Amy Pope) किस देश से हैं?

  • उत्तर – अमेरिका

  • किस केंद्रीय मंत्रालय ने ‘मेरी LiFE, मेरा स्वच्छ शहर’ अभियान शुरू किया?

  • उत्तर – आवास और शहरी मामलों के मंत्रालय

  • किस देश में अत्यधिक रोगजनक एवियन इन्फ्लुएंजा (Highly Pathogenic Avian Influenza – HPAI) की पुष्टि हुई है?

  • उत्तर – ब्राजील

  • किस संस्था ने ‘राष्ट्रीय ऊर्जा प्रबंधन केंद्र’ (National Energy Management Centre) की स्थापना की है?

  • उत्तर – REMC लिमिटेड

  • किस संस्था ने ‘World Tourism Barometer’ रिपोर्ट जारी की?

  • उत्तर – UNWTO

  • ‘साइबर सुरक्षित भारत’ किस संस्था/केंद्रीय मंत्रालय की पहल है?

  • उत्तर – इलेक्ट्रॉनिक्स और आईटी मंत्रालय

  • हाल ही में ख़बरों में रहा ‘प्रोजेक्ट-स्मार्ट’ किस केंद्रीय मंत्रालय से संबंधित है?

  • उत्तर – शहरी मामले मंत्रालय-रेलवे मंत्रालय

  • किस राज्य/केन्द्र शासित प्रदेश ने ‘जगन्नानकु चेबुदम कार्यक्रम’ (Jaganannaku Chebudam Programme) का शुभारंभ किया?

  • उत्तर – आंध्र प्रदेश

  • किस देश द्वारा प्रथम चीन-मध्य एशिया शिखर सम्मेलन (China-Central Asia Summit) की मेजबानी की जाएगी?

  • उत्तर – चीन

  • किस संस्था ने ‘Race to Net Zero’ शीर्षक से एक रिपोर्ट जारी की?

  • उत्तर – UN ESCAP

Recent Posts

  • CONSTRUCTION OF Cables & Selection
  • Ferranti Effect in transmission line
  • Insulator
  • String Efficiency
  • Corona Effect in Overhead Transmission Line
  • Types of Conductor
  • Proximity Effect
  • Skin Effect
  • What is GMD and GMR in Transmission Lines
  • Synchronous Reluctance Motor
  • Pass by Value and Pass by Reference in Java
  • JAVA Methods
  • BLDC Motor
  • OOPS Concepts in Java
  • Command line argument in JAVA

onlineexamguide

onlineexamguide.com is the ultimate guide that will keep you updated about almost every Exam & Interviews . We aim to provide our readers with an informative details that have been occurring in Examination . Here at onlineexamguide.com , we focus on delivering our readers with the latest exam Pattern Mock test

We Provide Free online test to practice for Competitive exams , Online Exam, Entrance and Interview. Learn and Practice online test for Free and Prepare for your exam online with us

Quick links

  • About us
  • Privacy Policy
  • Instructor Registration
  • Student Registration
  • Java Programming
  • C programming
  • C++ programming
  • Aptitude Tricks

Follow us

Free Online Mock Test

  • UPTET PRIMARY Online Test Series
  • Super TET Mock Test in Hindi 2023
  • CTET Mock Test 2022 Paper 1
  • SSC CHSL Online Mock Test
  • SSC MTS Mock Test 2023
  • SSC CGL Mock Test
  • SSC GD Mock Test
  • ccc online test

Search

Learn and Earn

Register as Instructor - Create and sell online courses and coaching services with the best online platform onlineexamguide.com . Build a course, build a brand, earn money

Contact us

For any queries

Email us on - admin@onlineexamguide.com

We will response fast as much as we can
Copyright © 2023 onlineexamguide.com - All Rights Reserved.
error: Content is protected !!

Insert/edit link

Enter the destination URL

Or link to existing content

    No search term specified. Showing recent items. Search or use up and down arrow keys to select an item.