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Technology Training for tomorrows world

Interactive Discovery Software

Electricity & Electronics

Control & Instrumentation

Process Control

Mechatronics

Telecommunications

Electrical Power & Machines

Test & Measurement

Powerframes

ElectricalMachines

Student'sManual

60-070-CS-S

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Powerframes

Electrical Machines

Students Manual

60-070-CS-S

(Also covers Series Universal Motor 60-070-SUMand Synchronous Machine 60-070-SMC Options)

Feedback Instruments Ltd, Park Road, Crowborough, E. Sussex, TN6 2QR, UK.Telephone: +44 (0) 1892 653322, Fax: +44 (0) 1892 663719.

email: [email protected] website: http://www.fbk.com

Manual: 60-070-CS-S Ed01 122006 Printed in England by Fl Ltd, CrowboroughFeedback Part No. 116060070CSS

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Notes

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PowerframesELECTRICAL MACHINESSTUDENTS MANUAL Preface

60-070-CS-S i

THE HEALTH AND SAFETY AT WORK ACT 1974

We are required under the Health and Safety at Work Act 1974, to make available to users of this equipment certain informationregarding its safe use.

The equipment, when used in normal or prescribed applications within the parameters set for its mechanical and electrical performance,should not cause any danger or hazard to health or safety if normal engineering practices are observed and they are used in accordancewith the instructions supplied.

If, in specific cases, circumstances exist in which a potential hazard may be brought about by careless or improper use, these will bepointed out and the necessary precautions emphasised.

While we provide the fullest possible user information relating to the proper use of this equipment, if there is any doubt whatsoever aboutany aspect, the user should contact the Product Safety Officer at Feedback Instruments Limited, Crowborough.

This equipment should not be used by inexperienced users unless they are under supervision.

We are required by European Directives to indicate on our equipment panels certain areas and warnings that require attention by theuser. These have been indicated in the specified way by yellow labels with black printing, the meaning of any labels that may be fixed tothe instrument are shown below:

CAUTION -RISK OFDANGER

CAUTION -RISK OF

ELECTRIC SHOCK

CAUTION -ELECTROSTATIC

SENSITIVE DEVICE

Refer to accompanying documents

PRODUCT IMPROVEMENTSWe maintain a policy of continuous product improvement by incorporating the latest developments and components into our equipment,even up to the time of dispatch.

All major changes are incorporated into up-dated editions of our manuals and this manual was believed to be correct at the time ofprinting. However, some product changes which do not affect the instructional capability of the equipment, may not be included until it isnecessary to incorporate other significant changes.

COMPONENT REPLACEMENT

Where components are of a Safety Critical nature, i.e. all components involved with the supply or carrying of voltages at supplypotential or higher, these must be replaced with components of equal international safety approval in order to maintain full equipmentsafety.

In order to maintain compliance with international directives, all replacement components should be identical to those originally supplied.

Any component may be ordered direct from Feedback or its agents by quoting the following information:

1. Equipment type

3. Component reference

2. Component value

4. Equipment serial number

Components can often be replaced by alternatives available locally, however we cannot therefore guarantee continued performanceeither to published specification or compliance with internationalstandards.

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PowerframesELECTRICAL MACHINESSTUDENTS MANUAL Preface

ii 60-070-CS-S

OPERATING CONDITIONS

This equipment is designed to operate under the following conditions:

Operating Temperature 10C to 40C (50F to 104F)

Humidity 10% to 90% (non-condensing)

DECLARATION CONCERNING ELECTROMAGNETIC COMPATIBILITYShould this equipment be used outside the classroom, laboratory study area or similar such place for which it is designed and sold thenFeedback Instruments Ltd hereby states that conformity with the protection requirements of the European Community ElectromagneticCompatibility Directive (89/336/EEC) may be invalidated and could lead to prosecution.

This equipment, when operated in accordance with the supplied documentation, does not cause electromagnetic disturbance outside itsimmediate electromagnetic environment.

COPYRIGHT NOTICE

Feedback Instruments LimitedAll rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by anymeans, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Feedback Instruments Limited.

ACKNOWLEDGEMENTSFeedback Instruments Ltd acknowledge all trademarks.

IBM, IBM - PC are registered trademarks of International Business Machines.

MICROSOFT, WINDOWS XP, WINDOWS 2000, WINDOWS 98, WINDOWS 95, WINDOWS 3.1 and Internet Explorer are registeredtrademarks of Microsoft Corporation.

WARNING:

This equipment must not be used in conditions of condensing humidity.

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PowerframesELECTRICAL MACHINESSTUDENTS MANUAL Foreword

60-070-CS-S iii

PURPOSE

This manual provides practical assignments to support the use of this trainer as a teaching aid.Each assignment consists of exercises which, when performed, allow the students to discover forthemselves the practical aspects of a particular subject. Results obtained are entered into tablesand, if necessary, plotted on graph paper. Provided at the front of each assignment is any relevanttheory pertaining to the subject and/or references to further reading.

CONTENT

This manual comprises:

Chapter 1 - Description. Provides an overview of the Electrical Machines trainer, includingpower supply safety features, system frame construction, and an introduction to theequipment.

Chapter 2 - Preliminary Checks. Provides information about installation, inspection, earthprotection and the Module Utility Sheets.

Chapter 3 - Assignments. Consists of practical assignments that can be performed by thestudent.

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PowerframesELECTRICAL MACHINESSTUDENTS MANUAL Foreword

iv 60-070-CS-S

Notes

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PowerframesELECTRICAL MACHINESSTUDENTS MANUAL Contents

60-070-CS-S TOC-1

TABLE OF CONTENTS

FOREWORD

CHAPTER 1 Systems Description

CHAPTER 2 Preliminary Checks

CHAPTER 3 Assignments

Assignment 1 dc Shunt Motor and FamiliarisationPracticals

1.1 - Speed / Torque Characteristics

1.2 - Effect of Field Current on Speed/Torque Characteristics

Assignment 2 dc Series Motor

Practicals


2.2 - Speed / Applied Voltage Characteristics

Assignment 3 dc Compound Wound MotorPracticals


3.2 - Effect of Field Current on Speed/Torque characteristics

Assignment 4 dc Separately Excited Motor

Practicals


4.2 - Effect of Field Current on Speed/Torque Characteristics

Assignment 5 dc Shunt Generator

Practicals

5.1 - Effect of Field Current on Output Voltage

5.2 - Effect of Generator Speed on Output Voltage

5.3 - Effect of Resistive Load on Output Voltage and Power

Assignment 6 dc Compound Generator

Practicals

6.1 - Effect of Load Current on Output Voltage

6.2 - Effect of Speed on Output Voltage for Different Load Values

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TOC-2 60-070-CS-S

Assignment 7 dc Separately Excited Generator

Practicals

7.1 - Effect of Field Current on Output Voltage

7.2 - Effect of Load Current on Output Power and Output Voltage

7.3 - Effect of Generator Speed on Output Voltage

Assignment 8 Single Phase Induction Motor - Capacitor Start

Practical

8.1 - Speed / Torque and Efficiency Characteristics

Assignment 9 3-Phase Squirrel Cage Induction Motor

Practicals

9.1 - Speed / Torque Characteristics - Star connection

9.2 - Speed / Torque Characteristics - Delta Connection

OPTIONS

60-070-SUM

Assignment 10 Series Universal Motor

Practicals

10.1 - Motor Characteristics with dc Supply

10.2 - Motor Characteristics with ac Supply

60-070-SMCAssignment 11 3-Phase Synchronous Generator Open & Short Circuit

Characteristics

Practicals

11.1 - Open Circuit Characteristic

11.2 - Short Circuit Characteristic

11.3 - Effect of Speed Variation on Output Voltage and Frequency

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60-070-CS-S TOC-3

OPTIONS (continued)

60-070-SMC

Assignment 12 Voltage Regulation of a 3-Phase Generator

Practicals

12.1 - Voltage Regulation with Resistive Load

12.2 - Voltage Regulation with Inductive Load (Using Option 60-070-ECT)

12.3 - Voltage Regulation with Capacitive load (Using Option 60-070-ECT)

Assignment 13 Synchronisation Procedure and Motor Operation of a 3-PhaseSynchronous Machine

Practicals

13.1 - Synchronising a Three Phase Synchronous Generator

13.2 - Power Factor Control of a Three Phase Synchronous Motor

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TOC-4 60-070-CS-S

Notes

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Powerframes Chapter 1ELECTRICAL MACHINESSTUDENTS MANUAL Systems Description

60-070-CS-S 1-1

1 Systems Description

1.1 Introduction

The 60-070 forms the core part of one of the Powerframes range of electrical machines trainers,that has been designed to allow the properties of dc motors and generators, single and threephase ac machines to be investigated. The measurement of these properties is accomplishedusing virtual or conventional instrumentation.

Power supplies, electrical loading and virtual instrumentation are all provided in the form of panels

which are mounted into a purpose-designed, bench-standing frame. The panels can be arranged inan order convenient to the user as they can easily be slotted in and out of the frame.

To enable the assignments contained in this manual to be easily followed, the layout of the panelswithin the frame has been pre-determined.

The courseware provided in this manual assumes that a complete trainer is available. Theassignments have been organised such that they can be carried out with systems that use eithervirtual or conventional instrumentation. Check your product to determine the type beforecommencing assignments for instrumentation supplied.

1.2 Power Supply Safety Features

The Universal Power Supply 60-105 comes complete with a 3-phase circuit breaker to ensuremains supplies are automatically disconnected in the event of a current overload occurring or aninadvertent interruption of the ac mains supply. It is recommended that the 3-phase mains supplyto this unit is connected via an earth leakage circuit breaker (such as Feedback 60-140-1).

An emergency power off pushbutton is also provided which allows an operator to disconnect allsupplies from the unit and frame equipment in the event of an emergency.

Variable ac and dc supply outputs are provided which are protected by a current operated circuitbreaker. A fixed dc supply is available which is protected by a fuse.

All power connections for assignment work are made using 4 mm output shrouded plug leads.

1.3 System Frame Construction

The system frame (91-200) is constructed using captive nut and bolt fixings as shown in theAssembly Instructions - Frame System drawing (Figure 1-1). Ensure all bolts including the bolts

securing the frame feet , as shown in the side view of Figure 1-1, are fully tightened beforeloading the frame with equipment.

WARNING:

All un-powered frame mounted units are provided with earth terminals on the front and/or backwhich must be connected to a protective earth point that is provided on all power supply units,using the earth leads supplied.

WARNING:If the frame system fixings are not fully tight before equipment is mounted, the frame could beunstable or collapse with consequent damage to equipment and personnel.

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1-2 60-070-CS-S

Figure 1-1: System Frame Fixings Location

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60-070-CS-S 1-3

1.4 Equipment

The core system of the Electrical Machines trainer is shown in Figure 1-2 with virtualinstrumentation and Figure 1-3 with conventional instrumentation. It comprises:

Universal Power Supply 60-105

dc Compound Wound Motor 63-120

Single Phase Induction Motor - capacitor start, induction run 64-110

Three Phase Induction Motor - squirrel cage, dual voltage 64-501

Dynamometer incorporating a Tachogenerator 67-530

Torque & Speed Control Panel 68-441

Switched Three Phase Resistance Load 67-142

Shaft Coupling and Key 68-703

System Frame 91-200

Standard Set of Patch Leads 68-800

Machine Guards 91-270

The system may have one of the following:

Multichannel I/O Unit 68-500

Software Pack CD 68-912-USB

VirtualInstrumentation(Option

60-070-VIP)

or

Two Voltmeter and Ammeter panels 68-110

Single and Three Phase Measurements

68-100

ConventionalInstrumentation

(Option60-070-CI1)

For a more detailed description of the individual units supplied, please consult the Utilities Manual60-070-UM and the relevant product number that can be found on a label fixed to the rear panel ofthe instrument.

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1-4 60-070-CS-S

Figure 1-2: Layout with Virtual Instrumentation

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60-070-CS-S 1-5

Figure 1-3: Layout with Conventional Instrumentation

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1-6 60-070-CS-S

1.5 Core System Panels

1.5.1 Universal Power Supply 60-105

The power supplies in the 60-070 series are provided by a Universal Power Supply 60-105.

The power supply is designed to be fitted between the two narrow rails of the frame in the lowestarea of the frame.

The Universal Power Supply 60-105 receives a three phase input from the mains supply and inputconnections are hard wired at the rear of the unit. After being connected to the unit 60-105, the

supply is protected via a three phase circuit breaker which when closed provides power to threephase variable and fixed ac outputs and variable and fixed dc outputs (as indicated by a greenpower on indicator light). An emergency power off pushbutton is provided which allows anoperator to remove all supply outputs from the panel and other units supplied from it. The supplyoutputs can be re-established by releasing the emergency power off button (turn clockwise torelease) and resetting the lever switches on the circuit breaker to up (on) position.

1.5.2 Three Phase Resistive Load 67-142

The Three Phase Resistive Load 67-142 unit provides a wide range of resistance variation makingit ideally suited to the testing of electrical circuits, transformers and electrical machines.

Three resistance banks are provided for three phase applications; however, they may be used inseries or parallel to provide the value required.

Note that the resistors in each section are identified with references R1, R2, R3 etc. Thesereferences will be used in the assignments to select specific resistances.

1.5.3 Torque & Speed Control Panel 68-441

The 68-441 Torque & Speed Control Panel in conjunction with the Dynamometer 67-530, inTorque Mode provides a system for applying loads to a motor, allowing the performanceparameters of the motor to be measured.

In Speed Mode the panel allows a generator to be driven at a desired speed, allowing theperformance parameters of the generator may be measured.

1.6 Virtual Instrumentation 60-070-VIP

1.6.1 Multichannel I/O 68-500

The Multichannel I/O 68-500 unit allows a number of different parameters associated with theoperation of the motors and generators to be measured with a Virtual Instrumentation system.Used with a PC, the software provides on-screen ac and dc voltmeters and ammeters, dcwattmeter, single and three phase wattmeters, ac phase meter, ac power meter, ac frequencymeter and single and three phase power factors. Torque and speed measurements can also bedisplayed when the 68-441 Torque & Speed Control Panel is connected.

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60-070-CS-S 1-7

The system requires the following:

Virtual instrumentation software 68-912-USB,

PC interface hardware,

PC with a minimum specification of 700 MHz, Pentium 3, 512 MB of memory, USB1 portand Windows 2000 or XP operating systems.

For further information, see the Powerframes Virtual Instrumentation 60-070-VIP manual.

1.7 Conventional Instrumentation 60-070-CI1

As an alternative to the use of virtual instrumentation, the 60-070-CI1 provides the followingconventional instruments:

2 x 68-110 dc voltmeter and ammeter panels

1 x 68-100 Electronic Single and Three Phase Measurements panel. This is aprogrammable industrial standard unit and the user is referred to its accompanying manualfor operating information.

WARNING:High voltages are present on front panel sockets. Ensure that only the 4 mm shroudedplug leads provided are used for all power connections to prevent exposure to the hazardof electric shock.

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1-8 60-070-CS-S

Notes

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Powerframes Chapter 2ELECTRICAL MACHINESSTUDENTS MANUAL Preliminary Checks

60-070-CS-S 2-1

2 Preliminary Checks

2.1 Installation

Hardware installation instructions are provided in the Powerframes Installation and CommissioningManual 60-070-IC. For Virtual Instrumentation software installation and associated hardwareinstallation, refer to manual 60-070-VIP.

2.2 Inspection

Prior to use, check all equipment for mechanical damage and for any loose fittings, and securethese.

2.3 Earth Protection

Ensure all non-powered modules such a Three Phase Resistive Load 67-142 are earthed throughthe supply by connecting all module earth terminals (normally situated on the back of each module)to any one of the earth terminals situated on the back of the Universal Power Supply 60-105 usingthe earth leads supplied.

Powered modules such as the Multichannel I/O Unit 68-500 are directly supplied with power andare earthed through the supply.

A protective earth terminal on the front panel of the power supply unit is provided to allowconnection to non-direct mains powered equipment such as electrical machines, transformers etcthat are bench-standing.

2.4 Specification

Specification details and safety aspects of the individual modules are provided in Module Utility

Sheets which are provided with the equipment and in the Powerframes Utilities Manual60-070-UM.

WARNING:If the frame system fixings are not fully tight before equipment is mounted, the frame could beunstable or collapse with consequent damage to equipment and personnel. See Chapter 1 forfurther information.

WARNING:

All non-direct powered panels must be earthed to the main power supply, 60-105, using theearth leads supplied.

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Powerframes Chapter 2ELECTRICAL MACHINESSTUDENTS MANUAL Preliminary Checks

2-2 60-070-CS-S

Notes

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Powerframes Chapter 3ELECTRICAL MACHINESSTUDENTS MANUAL Assignments

60-070-CS-S 3-1

3 Assignments

3.1 Introduction

This chapter contains assignments for Electrical Machines supplied with the core system 60-070and for the extension options of the Synchronous Machine and Series Motor.

The assignments are designed to demonstrate the behaviour of a number of typical ac and dcmotors and generators under various conditions. They enable you to investigate and record theeffect of varying the motor or generator parameters such as field current, armature current, speed,

applied load torque etc.In all cases calculations are made, the results are evaluated and conclusions are drawn.

The assignments are:

1. dc Shunt Motor and Familiarisation

2. dc Series Motor

3. dc Compound Wound Motor

4. dc Separately Excited Motor

5. dc Shunt Generator

6. dc Compound Generator

7. dc Separately Excited Generator

8. Single Phase Induction Motor - Capacitor Start/Induction Run

9. 3-Phase Squirrel Cage Induction Motor

Additional assignments available with the various optional machines.

10. Series Universal Motor (Option 60-070-SUM)

11. 3-Phase Synchronous Generator Open & Short Circuit Characteristics(Option 60-070-SMC)

12. Voltage Regulation of 3-Phase Synchronous Generator (Option 60-070-SMC)

13. Synchronisation Procedure and Motor Operation of a 3-Phase Synchronous Machine(Option 60-070-SMC)

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Powerframes Chapter 3ELECTRICAL MACHINESSTUDENTS MANUAL Assignments

3-2 60-070-CS-S

3.2 Assignment Composition

Each assignment comprises:

An Introduction giving theory relevant to the assignment as a whole.

Practicals, which contain operating procedures, and exercises pertaining to the resultsobtained. For each practical, a circuit diagram is provided (see below), and, for the morecomplex circuits, the patching diagram is also given.

Results tables for each practical in which measured data is recorded.

Typical results and answers which provide completed tables and graphs, and answers toall questions are provided the Reference Manual 60-070

3.3 Wiring Diagrams

In Assignment 1, wiring and circuit diagrams are given for both Conventional Instrumentation andVirtual Instrumentation equipment set ups.

After this assignment, the student should be familiar with interpreting the circuit diagram such thatthe various equipment meters, power supply motor etc can be interconnected without fully detailedinformation. Wiring diagrams are shown only for the more complex circuits, or where new items ofequipment are being introduced which have not been used in previous assignments.

3.4 Trainer Versions (230 V and 120 V)The practicals provided in each assignment cover both 230 V and 120 V versions of the trainer.

Check your product for the version in use.

Where parameters specific to an appropriate trainer version are given within a practical, theyappear in a table adjacent to the associated step of the practical procedure.

Results tables are given at the end of the assignment for both versions (230 V and 120 V) of thetrainer.

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Powerframes Assignment 1ELECTRICAL MACHINESSTUDENTS MANUAL dc Shunt Motor and Familiarisation

60-070-CS-S 3-1-1

1 dc Shunt Motor and Familiarisation

1.1 Assignment Information

1.1.1 Objectives

When you have completed this assignment you will:

be familiar with the trainer.

understand the principles of dc motor operation.

be aware of the parameters used to measure dc motor performance.

know where to use a dc shunt motor.

1.1.2 Knowledge Level

Before you start this assignment:

you should have a clear understanding of voltage and current in dc circuits.

you should be familiar with the procedures associated the Machine Shaft Covers andCoupling (see Appendix A).

if you have a Virtual Instrumentation System, you should be familiar with its use and itsconnections to a dynamometer.

For details on the connections between the PC, the 68-441 Torque & Speed Control Paneland the 68-500 Multichannel I/O Unit, see Virtual Instrumentation System manual -60-070-VIP. See also this manual for details of the Virtual Instrumentation software68-912-USB and Machine Loading and Testing System.

1.1.3 Practicals

1. Speed / torque relationshipArmature current / output torque relationship,Armature voltage / speed relationship,Efficiency

2. Field current / shaft speed relationship

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3-1-2 60-070-CS-S

1.2 Theory

1.2.1 Introduction

A shunt connected motor has its armature and field windings connected in parallel across the dcsupply. Figure 3-1-1 shows the equivalent circuit of a dc shunt machine.

Figure 3-1-1: Equivalent Circuit of a dc Shunt Machine

where V is the voltage applied to the terminals

E is the motional or back EMF

L is the self inductance of the field winding

is the flux in the armature circuit

The magnitude of E is proportional to the flux and speed

NKEE

= Eq 1

where N is the speed, KE a constant referring to the field windings.

The armature current is given by

a

aR

EVI

= Eq 2

where Ra the is resistance of the armature and Ia the current through the armature.

NOTES:

Practicals cover both 230 V and 120 V versions of the trainer.

Where parameters specific to an appropriate trainer versions are given within a practical, theyappear in a table adjacent to the associated step of the practical procedure.

Results tables are given at the end of the assignment for both versions (230 V and 120 V) of thetrainer.

This assignment contains both wiring and circuit diagrams, and is designed to familiarise youwith the equipment for use with dc motors and generators.

Subsequent dc motor and generator assignments will only contain the circuit diagram, as bythen it is expected that you will be able to wire the equipment yourself from the circuit diagram.

The wiring and circuit diagrams are shown for both virtual and conventional instrumentation.

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60-070-CS-S 3-1-3

The torque produced on the rotor is proportional to the flux and the armature current.

aTIKT = Eq 3

Where KT is a constant relating to the armature winding.

Under steady state ideal (light running) conditions if we assume there is no friction or other lossesin the motor, the torque is zero, and hence from Eq 3 the armature current Iais zero. This implies,from Eq 2 that:

NKEVE== Eq 4

From Eq 4 it can be seen that if the magnetic flux is reduced (i.e. the field is weakened), the speedwill correspondingly increase in inverse proportion, until the motor is again at a higher equilibriumspeed.

Consider how the speed varies with an increase in load, if the terminal voltage is kept constant.

When subjected to an increase in torque, the flux in a shunt motor is virtually independent of thearmature current. Therefore the armature current increases proportionally with torque, leading to afall in motional EMF, which causes the speed to fall linearly with increasing torque.

Flux is proportional to the field current, hence speed can be controlled by the field current, if theterminal voltage is kept constant.

The practicals in this assignment will demonstrate the basic laws governing the behaviour of theshunt motor and will investigate the relationships between applied armature voltage, field strengthand motor torque and speed.

1.2.2 Efficiency

Input power to the motoraaffiIVIVP += Eq 5

Output power from the motor60

TN2Po

= Eq 6

Efficiency %100InPower

OutPower

= %100IVIV

60

TN2

aaff

+

Eq 7

where Vfand Ifare the voltage across and the current through the field winding.

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3-1-4 60-070-CS-S

1.3 Content

The practicals in this assignment familiarise the student with the trainer and provide an introductionto dc shunt motors.

1.4 Equipment Required

Universal Power Supply 60-105.



Dynamometer Machine 67-530



System Frame 91-200


Either:



Virtual

Instrumentation(Option

60-070-VIP)

or

Two Voltmeter and Ammeterpanels

68-110ConventionalInstrumentation(Option

60-070-CI1)

NOTES:

Refer to the Virtual Instrumentation System manual 60-070-VIP for the setting up of thevirtual instrumentation voltmeters, ammeters etc, and the use of Set-Up files.

Do refer to the Help information in the 68-500-USB software.

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60-070-CS-S 3-1-5

1.5 Circuit Diagrams and Wiring

Figure 3-1-2: Virtual Instrumentation Wiring

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3-1-6 60-070-CS-S

Figure 3-1-3: Conventional Instrumentation Wiring

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60-070-CS-S 3-1-7

Figure 3-1-4: Circuit Diagram with resistance shorting link fitted

1.6 Preliminary Set-up

Switch off all power by setting the 3 phase circuit breaker with no volt releaseon the UniversalPower Supply 60-105 to the off position.

Make up connections shown in Figure 3-1-2 and Figure 3-1-4 for Virtual Instrumentation andFigure 3-1-3 and Figure 3-1-4 for Conventional Instrumentation.

If you have Virtual Instrumentation and access to an Excel Spreadsheet you can use the facilityin the 68-912-USB software to save and store sets of results, import them directly into Excel,automatically calculate results and draw graphs. (See the manual - Virtual Instrumentation Pack60-070-VIP, Appendix A).

NOTE:

The circuit diagram shows both virtual and conventional instrumentation.

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3-1-8 60-070-CS-S

1.7 Control Settings

67-142 Resistance Box Fit the link, which shorts out the resistance box, and check that all theresistance switches are switched on (see Figure 3-1-5).

60-105 Power Supply Turn the variable output voltagecontrol to 0% on the UniversalPower Supply 60-105 and then switch off all power by opening the3 phase circuit breaker with no volt releasecircuit breaker.

68-441 Switch off the main ac power using the green on/off button.

Set the constant speed or torqueand the torque proportional tospeedcontrol to their most anti-clockwise positions.

Connect the dynamometer to the torque mode socket.

Set the demand voltageswitch to +ve.

Press the powerpushbutton which illuminates green.

Press the dynamometer poweron button so that the adjacent redLED is lit.

68-912-USB Software For Virtual Instrumentation, switch on the PC and start the VirtualInstrumentation Software 68-912-USB (see manual 60-070-VIP).

SAFETY NOTES

1. Do NOT leave the 68-441 powered up with the test motorNOT rotating and with a load demand. This will cause the

dynamometer motor to overheat which may lead topermanent damage.

2. In circumstances when the dynamometer is not being usedfor a period longer than 5 minutes, press the dynamometerpower off button. When ready to continue with theassignment, press the dynamometer power on buttonbringing power back on to the system.

3. Do NOT under any circumstances allow an open circuit inthe 67-142 resistance box, when conducting motor testsrequiring a resistance in series with the field winding. Thiswill collapse the field to zero and lead to the motor running

away at high speed. Always ensure the link is insertedwhen the resistance is not required, and that the resistanceswitches are never all set to off.

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60-070-CS-S 3-1-9

1.8 Practical 1.1 - Speed / Torque Characteristics

Product Version

230 V 120 V

On the 60-105 unit, ensure the variable output voltagecontrol is set to 0%and then set the circuit breaker switch to the on position. Power is nowavailable as indicated by the power ongreen indicator being illuminated.

On the 60-105, increase the variable output voltagecontrol, until the motorspeed is about 3200 rpm with a maximum voltage of .......................... 220 V dc 120 V dc

Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the readings listed for values of the applied torquefrom the minimum to a maximum of 1.2 Nm in increments of 0.1 NmEnter them into a table similar to that given in Practical 1.1 Results Table atthe end of this assignment. Results are required for the followingparameters:

Armature Volts (V1)

Field Volts (V2)

Armature Current (I1)

Field Current (I2)

Torque Nm

Speed rpm

Note: Should the readings fluctuate significantly when approaching themaximum torque values, record the meter readings for the highest

sustainable torque in the appropriate line and column of your results table

Switch off all power from the Universal Power Supply 60-105 by setting thecircuit breaker to off.

1.8.1 Exercise 1.1

Calculate the input power, output power and efficiency from Eq 5, 6, and 7and enter them in the table.

Draw graphs of speed, armature current and efficiency vs torque, using theaxes suggested by those shown in Practical 1.1 Results Table.

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3-1-10 60-070-CS-S

1.8.2 Questions

Question 1 What do you notice about the shape of the armature current vs torquegraph? Compare with Eq 3.

Question 2 What do you notice about the slope of the speed vs torque graph?

Question 3 What do you notice about the slope of the efficiency vs torque graph?

Question 4 List as many factors you can to account for the efficiency being lessthan 100%. Which of these will increase as the torque increases andwhich will decrease?

1.9 Practical 1.2 - Effect of Field Current on Speed/Torque Characteristics

Reset the control settings as previously described with the followingdifferences. Remove the link across the resistor box shown by the dottedline in Figures 3-1-2 to 3-1-5.

Figure 3-1-5

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60-070-CS-S 3-1-11

Product Version

230 V 120 V

Now set the resistance panel to change the motor field resistance to anew value so that results can be found for the Set 2 column of your table

182All resistors

on.All sectionsconnected

in parallel.

1.9.1 Practical

On the 60-105 unit, ensure the variable output voltagecontrol is set to0% then set the 3 phase circuit breakerto the on position.

On the 60-105 unit, increase the variable output voltagecontrol, until themotor speed is about 3200 rpm with a maximum voltage of 220 V dc 120 V dc

A Using either the PC Virtual Instrumentation Software or

conventional instrumentation, take the following readings forvalues of the applied torque from the minimum possible value to1.2 Nm, in increments of 0.1 Nm and enter them into the Set 2column of a copy of the appropriate Practical 1.2 Results Table(230 V or 120 V product version) at the end of this assignment.

Field Current (I2)

Torque Nm

Speed rpm

B On the 60-105, turn the variable output voltagecontrol to 0%.Switch off all power by setting the circuit breaker to the offposition.

Now set the resistance panel to change the motor field resistance to anew value so that results can be found for the Set 3 column of your table.

316R1, R4 and

R7 on.All sectionsconnectedin parallel

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3-1-12 60-070-CS-S

Using this new value for the resistance in series with the field winding,which will have the effect of reducing the field current, follow the samesequence of operations you previously carried out between:

AandB

entering your results into the Set 3 column of a copy of the appropriatePractical 1.2 Results Table (230 V or 120 V product version).

Finally enter the corresponding values from your copy of Practical 1.1Results Table (230 V or 120 V product version) into the Set 1 column ofyour copy of the appropriate Practical 1.2 Results Table (230 V or 120 Vproduct version).

1.9.2 Exercise 1.2

Draw a graph of speed vs torque for each of the three values of the fieldcurrent using the axes suggested by that given in Practical 1.2 ResultsTable (230 V or 120 V product version). Compare your results with thetheoretical predictions at the beginning of this assignment.

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Powerframes Assignment 1ELECTRICAL MACHINESSTUDENTS MANUAL Results Tables

60-070-CS-S 3-1-13

1.10 Practical 1.1 - Results Tables and Graphs (230 V Product Version)

ArmatureVoltage V1

(V)

FieldVoltage V2

(V)

Armature

Current I1(A)

Field

Current I2(A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

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3-1-14 60-070-CS-S


ArmatureVoltageV1 (V)

FieldVoltageV2 (V)

ArmatureCurrent

I1 (A)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

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60-070-CS-S 3-1-15


Set 1: No resistance in serieswith field winding

Set 2: 182 Resistance inseries with field winding

Set 3: 317 Resistance inseries with field winding

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

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3-1-16 60-070-CS-S

Practical 1.2 - Results Tables and Graphs (120 V Product Version)

Set 1: No resistance in serieswith field winding

Set 2: Resistance inseries with field winding

Set 3: Resistance inseries with field winding

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

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Powerframes Assignment 2ELECTRICAL MACHINESSTUDENTS MANUAL dc Series Motor

60-070-CS-S 3-2-1

2 dc Series Motor


2.1.1 Objectives


appreciate the different characteristics between a dc series motor and dc shunt motor.


know suitable applications for dc series and shunt motors.



you should have completed Assignment 1.



if you have a Virtual Instrumentation System, you should be familiar with its use and itsconnections to a dynamometer. (Refer to the 60-070-VIP manual for details on theequipment interconnection and software operation.)

2.1.3 Practicals

1. Speed / torque relationshipArmature current / output torque relationshipArmature voltage / speed relationshipEfficiency

2. Relationship of speed to applied voltage

NOTES:


Where parameters specific to an appropriate trainer version are given within apractical, they appear in a table adjacent to the associated step of the practicalprocedure.

Results tables are given at the end of the assignment for both versions (230 V and120 V) of the trainer.

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3-2-2 60-070-CS-S

2.2 Theory

2.2.1 Introduction

A series connected dc motor has its armature and field windings connected in series across a dcsupply. Figure 3-2-1 shows the circuit for a dc series machine.

Figure 3-2-1: Equivalent Circuit of a dc Series Machine

where V is the voltage applied to the terminals

E is the motional or back EMF

Ra is the inherent armature resistance

Rs is an external resistance added in series with the armature.

The magnitude of E is proportional to the flux and speed.

NKE E= Eq 1

Where N is the speed and KE is a constant referring to the field windings.

The armature current is given by:

EVIR aa = Eq 2

The flux is proportional to the field current (until the effects of magnetic saturation take place),which, for a series motor, is equal to the armature current

afff IKIK==

Eq 3

where TK is a constant related to the field windings.

The speed of the motor can be controlled by adding a variable resistor in series with the armaturewinding resistance. Increasing the value of the resistor will increase the voltage drop across it, thiswill cause a drop in the motor terminal voltage and hence a reduction in the speed of the motor asthe motional EMF reduces to balance the loss of terminal voltage.

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60-070-CS-S 3-2-3

Torque produced on the rotor is proportional to the flux density. It can be proved that.

aT IKT = Eq 4

Where Ia is armature current and KT is a constant relating to the armature winding.

2

aIKT = Eq 5

where K is a constant of proportionality.

Thus the torque is proportional to the square of the armature current. The current varies inversely

with speed due to the low value of the back EMF at low speeds and hence the series motor has ahigh torque at low speeds. This makes it suitable for use in traction applications.

From Eq 1, Eq 2 and Eq 3

)NKR(IV 1aa += Eq 6

and from Eq 5, (assuming that V is constant after allowing for the very small voltage drop acrossthe field winding)

2

1

1a

3

)NKR(

1KT

+

= Eq 7

where 1K and 3K are constants.

At large values of the speed N, Ra

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3-2-4 60-070-CS-S

2.3 Content

The practicals in this assignment investigate the operation of a dc series motor.







System Frame 91-200


Either:




60-070-VIP)

or



60-070-CI1)

NOTES:



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60-070-CS-S 3-2-5


Figure 3-2-2: Circuit Diagram


Switch off all power by setting the 3 phase circuit breakeron the Universal Power Supply 60-105to the off position.

Make up connections shown in the circuit diagram in Figure 3-2-2.


NOTE:

The circuit diagram shows for both virtual and conventional instrumentation.

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3-2-6 60-070-CS-S


60-105 Power Supply Turn the variable output voltagecontrol to 0%. Switch off the3 phase circuit breaker.


Set the two rotary controls to their most anti-clockwise positions.





SAFETY NOTES:

1. Do NOT leave the 68-441 powered up with the test motorNOT rotating and with a load demand. This will cause thedynamometer motor to overheat which may lead to permanentdamage.

2. In circumstances when the dynamometer is not being used fora period longer than 5 minutes, press the dynamometer power

off button. When ready to continue with the assignment, pressthe dynamometer power on button bringing power back on tothe system.



The series motor is always a difficult motor to make measurements on,since on light loads it will tend to run at very high speed (theoretically infinitespeed at no load) and with any increase in load the speed initially reducesrapidly to a lower value until the additional load can be sustained.

With increasing load the torque output increases rapidly as does armaturecurrent, the current and torque theoretically being infinite at zero speed.

With this type of characteristic it is possible only to obtain a portion of theoverall characteristic torque/speed curve.

On the 60-105 unit, set the 3 phase circuit breakerto the on position.

Product Version

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60-070-CS-S 3-2-7

230 V 120 V

Using the variable output voltagecontrol on the 60-105, raise the dc supplyvoltage to the motor to 160 V dc 80 V dc

You will notice that as the supply voltage is applied the motor shaft speed isincreasing rapidly to a point where it exceeds 5000 rpm. This speed isoutside the measuring range of the instrumentation and will need to bereduced before measurements can be made.

Slowly reduce the dc supply voltage until the motor speed is 4950 rpm.

This will be the initial value of speed and supply voltage to carry out thefollowing test.

Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the readings listed for values of the applied torquefrom the minimum to a maximum of 1 Nm in increments of 0.1 NmEnter them into a table similar to that given in Practical 2.1 Results Table(230 V or 120 V product version) at the end of this assignment. Record thefollowing:

Motor Voltage (V1)

Motor Current (I1)

Torque Nm

Speed rpm

Note: Maintain the applied voltage as constant as possible throughout thetest.

Be sure that as you increase the torque you allow enough time for the shaft

speed to settle before taking your readings.

Turn the variable output voltagecontrol to 0% on the Universal PowerSupply 60-105 and then switch off the 3 phase circuit breaker.

2.8.1 Exercise 2.1

Calculate the input power, output power and efficiency from Eq 8, 9 and 10and enter them in the table.


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3-2-8 60-070-CS-S

2.9 Practical 2.2 - Speed / Applied Voltage Characteristics

Product Version

230 V 120 V


Increase the variable output voltagecontrol on the 60-105 until the speedof the motor is 4950 rpm. The voltage should be the same as that

determined in Practical 2.1. Ensure that the torque applied is at theminimum. There will always be some torque due to the load imposed bymotor losses and the effect of the dynamometer motor being attached.

Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, Take the following readings:

Motor Voltage (V1)

Speed - rpm

reducing the voltage by ..

Enter the readings in to a copy of the appropriate Practical 2.2 ResultsTable (230 V or 120 V product version). Note the minimum value of thetorque.

20 Volt

stepsdown to20 V

10 Volt

stepsdown to10 V

Turn the variable output voltagecontrol to 0% on the Universal PowerSupply 60-105 and then switch off all power by setting the 3 phase circuitbreakerto the off position.

2.9.1 Exercise 2.2

Draw a graph of speed against applied motor voltage using the axessuggested by those shown in Practical 2.1 Results Table.

2.9.2 Questions

Question 1 What are the main differences between the torque/speed curves forthe shunt and series connected motor?

Question 2 What do you notice from the shape of the speed versus applied motorvoltage curve? Are your deductions in accordance with Eq 6?

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60-070-CS-S 3-2-9


Motor VoltageV1 (V)

Motor Current

I1 (A)

Torque(Nm)

Speed(rpm)

Input Power(W)

Output Power(W)

Efficiency(%)

0

1000

2000

3000

4000

5000

6000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Speed(rpm)

M

otorCurrent(A)

E

fficiency(%)

Torque (Nm)

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3-2-10 60-070-CS-S


Motor VoltageV1 (V)

Motor Current

I2 (A)

Torque(Nm)

Speed(rpm)

Input Power(W)

Output Power(W)

Efficiency(%)

0

1000

2000

3000

4000

5000

6000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Speed(rpm)

M

otorCurrent(A)

E

fficiency(%)

Torque (Nm)

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60-070-CS-S 3-2-11


Speed(rpm)

Motor Voltage(V)

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3-2-12 60-070-CS-S


Speed(rpm)

Motor Voltage(V)

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Powerframes Assignment 3ELECTRICAL MACHINESSTUDENTS MANUAL dc Compound Wound Motor

60-070-CS-S 3-3-1

3 dc Compound Wound Motor


3.1.1 Objectives


appreciate the difference between series dc motors and shunt motors, and the combinationcompound motor.


know the connection and behaviour of differential and cumulative compound motors.







3.1.3 Practicals


2. Torque / Speed and Field Current relationship

NOTES:




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3-3-2 60-070-CS-S

3.2 Theory

The dc compound wound motor is fundamentally a combination of series and shunt connected dcmotors. The series winding is arranged so its magnetomotive force either assists or opposes thatof the shunt. This makes it possible to attain a selection of torque/speed characteristics. Byadjusting the relative strengths and ratios of the windings, it is possible to obtain anycharacteristics of the shunt and series motors. In most compound motors, however, most of themagnetomotive force is produced by the shunt winding.

3.2.1 Differential dc compound wound motor

The differential dc compound wound motor has the series winding opposing the shunt. Any

increase in current results in a weakening of the field and a reduction in torque per ampere.However, this connection is not used in practise as it is inherently unstable when loaded.

3.2.2 Cumulative dc compound wound motor

The cumulative dc compound wound machine has the series winding reinforcing the shunt. This isshown in Figure 3-3-1.

Figure 3-3-1: Equivalent Circuit of a dc Compound Wound Machine

When subjected to an increase in load, the resultant increase in armature current in the series fieldcauses an increase in flux. This increases the torque per ampere.

Therefore there is a greater drop in speed with increase in torque than in the shunt connectedmotor.

The torque/speed characteristics of the cumulative compound motor can also be varied by the useof a resistance in series with the shunt winding.

3.2.3 Efficiency

Input power to the motoraaffiIVIVP += Eq 1


NT2Po

= Eq 2


OutPower

= %100IVIV

60

NT2

aaff

+

Eq 3


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60-070-CS-S 3-3-3

3.3 Content

The practicals in this assignment investigate the operation of a cumulative dc compound woundmotor.








System Frame 91-200


Either:




60-070-VIP)

or



60-070-CI1)

NOTES:



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3-3-4 60-070-CS-S







NOTE:


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60-070-CS-S 3-3-5


67-142 Resistance Box Fit the link, which shorts out the resistance box, and check that all theresistance switches are switched on. See Figure 3-3-3.





Set the demand voltageswitch to +ve.Press the powerpushbutton which illuminates green.


SAFETY NOTES:


2. In circumstances when the dynamometer is not being used fora period longer than 5 minutes, press the dynamometer poweroff button. When ready to continue with the assignment, pressthe dynamometer power on button bringing power back on tothe system.

3. Do NOT under any circumstances allow an open circuit in the67-142 resistance box, when conducting motor tests requiringa resistance in series with the field winding. This will collapsethe field to zero and lead to the motor running away at highspeed. Always ensure the link is inserted when the resistanceis not required, and that the resistance switches are never allset to off.


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3-3-6 60-070-CS-S


Product Version

230 V 120 V


Using the variable output voltagecontrol on the 60-105, increase thesupply until the motor speed is about 3200 rpm not exceeding the voltage of

.. 220 V dc 120 V dc

Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the following readings for values of the applied torquefrom the minimum to 1.2 Nm in increments of 0.1 Nm and enter them into acopy of the appropriate Practical 3.1 Results Table (230 V or 120 V productversion). Record these values:

Armature Volts (V2)

Field Volts (V1)


Field Current (I1)

Torque Nm

Speed rpm


Turn the variable output voltagecontrol to 0% on the Universal Power

Supply 60-105 and then switch off the 3 phase circuit breaker.

3.8.1 Exercise 3.1

Calculate the input power, output power and efficiency from Eq 1, 2, and 3and enter them in the table.


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60-070-CS-S 3-3-7

3.9 Practical 3.2 - Effect of Field Current on Speed/Torque characteristics

Product Version

230 V 120 V

Reset the control settings as previously described with the followingdifferences.

Remove the link across the resistor panel shown as a dotted line inFigure 3-3-3.

Figure 3-3-3

Set all of the switches on the resistor panel 67-142 to the on position asshown in Figure 3-3-3, and link the resistor arrays in parallel to give aresistance in series with the field coil of .. 182

3.9.1 Practical


Using the variable output voltagecontrol, increase the supply until themotor speed is about 3200 rpm not exceeding the voltage of ... 220 V dc 120 V dc

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3-3-8 60-070-CS-S

Product Version

230 V 120 V

A Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the following readings for values of the appliedtorque from the minimum to 1.2 Nm, in increments of 0.1 Nm andenter them into the column Set 2 of a copy of the appropriate

Practical 3.2 Results Table (230 V or 120 V product version).

Record in your table the following:

Field Current I2

Torque Nm

Speed rpm

B On the 60-105, turn the variable output voltagecontrol to 0% and

then switch off the circuit breaker.

Now set the resistance panel 67-142 to give the resistance in series withthe field winding of.

317

R1, R4,

R7 to

on.

All other

values

switched

to off

Using this new value for the resistance in series with the field winding,

follow the same sequence of operations you previously carried out between:

A and B

entering your results into the column Set 3 of a copy of the appropriatePractical 3.2 Results Table (230 V or 120 V product version).

Finally enter the corresponding values from your copy of Practical 3.1Results Table (230 V or 120 V product version) into the column Set 1 ofyour copy of the appropriate Practical 3.2 Results Table (230 V or 120 Vproduct version).

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60-070-CS-S 3-3-9

3.9.2 Exercise 3.2

Draw a graph of speed vs torque for each of the three values of the fieldcurrent using axes suggested by that given in Practical 3.2 Results Table(230 V or 120 V product version).

Compare your results with the theoretical predictions at the beginning of thisassignment.

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3-3-10 60-070-CS-S



ArmatureCurrent

I2 (A)

FieldVoltageV1 (V)

FieldCurrent

I1 (A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

Torque (Nm)

2400

2500

2600

2700

2800

2900

3000

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.5

1

1.5

2

2.5

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

Armature

Current(A)

Spee

d(rpm)

Efficiency(%)

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60-070-CS-S 3-3-11



ArmatureCurrent

I2 (A)

FieldVoltageV1 (V)

FieldCurrent

I1 (A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

Torque (Nm)

2400

2500

2600

2700

2800

2900

3000

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.5

1

1.5

2

2.5

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

ArmatureCurrent(A)

Spe

ed(rpm)

Efficiency(%)

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3-3-12 60-070-CS-S


Field Current

I2 = amps

Field Current

I2 = amps

Field Current

I2 = amps

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Set 1 Set 2 Set 3

2200

2300

2400

2500

2600

2700

2800

2900

3000

3100

3200

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Torque (Nm)

Speed(r

pm)

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60-070-CS-S 3-3-13


Field Current

I2 = amps

Field Current

I2 = amps

Field Current

I2 = amps

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Set 1 Set 2 Set 3

2200

2300

2400

2500

2600

2700

2800

2900

3000

3100

3200

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Torque (Nm)

Speed

(rpm)

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3-3-14 60-070-CS-S

Notes

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Powerframes Assignment 4ELECTRICAL MACHINESSTUDENTS MANUAL dc Separately Excited Motor

60-070-CS-S 3-4-1

4 dc Separately Excited Motor


4.1.1 Objectives


appreciate the difference between series dc motors and shunt motors, and the separatelyexcited motor.


know some of the applications for this type of motor.







4.1.3 Practicals


2. Torque / Speed and Field Current relationship

NOTES:




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3-4-2 60-070-CS-S

4.2 Theory

The dc separately excited motor has the field circuit supplied from a different source to thearmature circuit. This is illustrated in Figure 3-4-1.

Figure 3-4-1: Equivalent Circuit for a dc Separately Excited Motor

Since the flux is proportional to field current, the flux in the following equation can be considered aconstant, along with the torque constant KT.

aTIK=T Eq 1

Thus the armature current is directly proportional to the torque for any given value of flux. Thearmature current depends on the difference between the armature supply voltage and the motorsback EMF, E.

NKE E= Eq 2

Hence for a constant supply voltage the motors back EMF is directly proportional to speed.

By varying the current, and hence the flux in the field circuit a range of torque/speed characteristicscan be obtained for the separately excited dc motor.

There are two ways the field current can be altered.

1. A variable resistor can be added in series with the field circuit.

2. Variation of the field circuit supply voltage.

4.2.1 Efficiency

Input power to the motor aaffi IVIVP += Eq 3


NT2Po

= Eq 4


OutPower

= %100IVIV

60

NT2

aaff

+

Eq 5


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60-070-CS-S 3-4-3

4.3 Content

The practicals in this assignment investigate the operation of a dc separately excited motor.








System Frame 91-200


Either:



VirtualInstrumentation

(Option60-070-VIP)

or



60-070-CI1)

NOTES:Refer to the Virtual Instrumentation System manual 60-070-VIP for the setting up of thevirtual instrumentation voltmeters, ammeters etc, and the use of Set-Up files.


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3-4-4 60-070-CS-S







NOTE:


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60-070-CS-S 3-4-5


67-142 Resistance Box Fit the link, which shorts out the resistance box, and check that all theresistance switches are switched on.See Figure 3-4-3.








SAFETY NOTES:


2. In circumstances when the dynamometer is not being used fora period longer than 5 minutes, press the dynamometer poweroff button. When ready to continue with the assignment, pressthe dynamometer power on button bringing power back on tothe system.

3. Do NOT under any circumstances allow an open circuit in the67-142 resistance box, when conducting motor tests requiring

a resistance in series with the field winding. This will collapsethe field to zero and lead to the motor running away at highspeed. Always ensure the link is inserted when the resistanceis not required, and that the resistance switches are never allset to off.


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3-4-6 60-070-CS-S


Product Version

230 V 120 V


Increase the variable output voltagecontrol on the 60-105, until the motorspeed is about 3200 rpm not exceeding the values . 220 V dc 120 V dc

Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the following readings for values of the applied torquefrom the minimum to 1.2 Nm in increments of 0.1 Nm and enter them into atable similar to that given in Practical 4.1 Results Table.Record the values:

Armature Volts (V1)

Field Volts (V2)


Field Current (I2)

Torque Nm

Speed rpm


Turn the variable output voltagecontrol to 0% on the Universal PowerSupply 60-105 and then switch off the 3 phase circuit breaker.

4.8.1 Exercise 4.1

Calculate the input power, output power and efficiency from Eq 3, 4 and 5and enter them in the table.

Draw graphs of speed, armature current and efficiency vs torque,suggested by those shown in Practical 4.1 Results Table.

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60-070-CS-S 3-4-7

4.9 Practical 4.2 - Effect of Field Current on Speed/Torque Characteristics

Product Version

230 V 120 V

4.9.1 Control Settings

Reset the control settings as previously described with the followingdifferences. Remove the link across the resistor panel shown as a dotted

line in Figure 3-4-3.

Figure 3-4-3

Set all of the switches on the resistor panel 67-142 to the on position asshown in Figure 3-4-3, and link the resistor arrays in parallel to give aresistance in series with the field coil of . 182

4.9.2 Practical


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3-4-8 60-070-CS-S

Product Version

230 V 120 V

Increase the variable output voltagecontrol on the 60-105 to approximatelythe listed value, so that the motor speed is about 3200 rpm not exceedingthe voltage 220 V dc 120 V dc

A Using either the PC Virtual Instrumentation Software or conventionalinstrumentation, take the following readings for values of the appliedtorque from the minimum to 1.2 Nm, in increments of 0.1 Nm andenter them into the Set 2 column of a copy of the appropriatePractical 4.2 Results Table (230 V or 120 V product version).Record values of:

Field Current (I2)

Torque Nm

Speed rpm


B Turn the variable output voltagecontrol to 0% on the UniversalPower Supply 60-105 and then switch off the 3 phase circuitbreaker.

Now set the resistance panel to give the resistance values listed in serieswith the field winding, by making the following switch selections

317

Switch

on R1,

R4 & R7

only.

Using this new value for the resistance in series with the field winding,which will have the effect of reducing the field current, follow the samesequence of operations you previously carried out between:

A and B

entering your results into the Set 3 column of a copy of the appropriatePractical 4.2 Results Table (230 V or 120 V product version).

Finally enter the corresponding values from your copy of Practical 4.1Results Table (230 V or 120 V) into the Set 1 column of your copy of the

appropriate Practical 4.2 Results Table (230 V or 120 V product version).

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60-070-CS-S 3-4-9

4.9.3 Exercise 4.2

Draw a graph of speed vs torque for each of the three values of the fieldcurrent using the axes suggested by that given in Practical 4.2 ResultsTable (230 V or 120 V product version).

Compare your results with the theoretical predictions at the beginning of thisassignment.

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3-4-10 60-070-CS-S



ArmatureCurrent

I1 (A)

FieldVoltageV2 (V)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

2700

2750

2800

2850

2900

2950

3000

3050

3100

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0

0.5

1

1.5

2

2.5

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Speed(re

v/min)

ArmatureC

urrent(A)

Efficienc

y(%)

Torque (Nm)

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60-070-CS-S 3-4-11



ArmatureCurrent

I1 (A)

FieldVoltageV2 (V)

FieldCurrent

I2 (A)

Torque(Nm)

Speed(rpm)

InputPower

(W)

OutputPower

(W)

Efficiency(%)

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3-4-12 60-070-CS-S


Field Current

I2 = amps

Field Current

I2 = amps

Field Current

I2 = amps

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Set 1 Set 2 Set 3

2500

2700

2900

3100

3300

3500

3700

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Speed(rpm)

Torque (Nm)

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60-070-CS-S 3-4-13

Practical 4.2 - Results Tables and Graphs (120 V Product Version)

Field Current

I2 = amps

Field Current

I2 = amps

Field Current

I2 = amps

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Torque(Nm)

Speed(rpm)

Set 1 Set 2 Set 3

2500

2700

2900

3100

3300

3500

3700

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Speed(rpm)

Torque (Nm)

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3-4-14 60-070-CS-S

Notes

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Powerframes Assignment 5ELECTRICAL MACHINESSTUDENTS MANUAL dc Shunt Generator

60-070-CS-S 3-5-1

5 dc Shunt Generator


5.1.1 Objectives


be familiar with the trainer.

understand the principles of dc generator operation.

be aware of the parameters used to measure dc motor generator performance.

know the connection and characteristic of a dc shunt generator.







5.1.3 Practicals

1. Effect of field current on the output of a shunt connected dc generator (open circuitcharacteristic).

2. Effect of generator speed on the output of a shunt connected dc generator (opencircuit characteristic).

3. Load voltage/current characteristic of a shunt connected dc generator.

NOTES:




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3-5-2 60-070-CS-S

5.2 Theory

A shunt connected generator has its armature and field windings connected in parallel across thedc output terminals.

Figure 3-5-1 shows the equivalent circuit for a dc shunt machine connected as a generator.

Figure 3-5-1: Equivalent Circuit of a Shunt Connected dc Generator

E is the generated EMF

Ra is the inherent resistance of the armature winding

V is the output voltage.

The initial excitation of a dc generator is dependent on the existence of a small residual flux. Whenthe armature is rotated the residual flux induces a small EMF producing a current which eitherincreases or decreases the flux in the magnetic circuit depending on its direction. If the residual

flux is not present or produces a current which causes a decrease in flux then it is necessary toseparately excite the winding for a few seconds using an external dc supply.

The generated EMF causes current to flow through the circuit. The current If flowing through thefield winding increases the magnetic field which increases the induced EMF and current. Thisprocess continues until the magnetic field reaches its maximum value.

The magnitude of the generated EMF, E, is proportional to the flux and speed.

aaRIVE += Eq. 1

For a given machine

NKEE= Eq. 2

where N is the speed and KE is a constant referring to the particular machine.

Hence for a constant speed the generated EMF is proportional to the flux.

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60-070-CS-S 3-5-3

5.3 Content

The practicals in this assignment investigate the operation of a dc shunt generator.



dc Compound Wound Machine 63-120





System Frame 91-200


Either:



VirtualInstrumentation

(Option60-070-VI

Documents

gre paper 0f 2013