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  • Study Material
  • Fundamental of Electric Drives
    • Introduction to Electrical Drives
    • Types of Electrical Drives
    • Advantages of Electrical Drives
    • Component of a Basic Electrical Drives
    • Mechanical Loads and electric drives
    • Electric Motors and Electric drives
    • Controllers and Power sources
    • Converters and electric drives
    • Ratings of Power Electronics Device
    • di/dt and dv/dt Protection
    • Speed-torque conventions
    • Multi-Quadrant operations of speed-torque characteristics
    • Constant Torque and Power Operations
    • Overview of AC and DC drives
    • Types of Loads
    • Components of Torque Loads
    • Determination of Moment of Inertia
    • Steady state stability
    • Criteria for steady state stability
    • Concept of Transient Stability of electrical drives
    • Transient Stability of a Synchronous Motor

  • DC Motor Drives
    • Dc motor drives
    • THYRISTOR D.C. DRIVES – GENERAL
    • Motor operation with converter supply
    • Motor Operation in DCM
    • Converter output impedance: overlap
    • Four-quadrant operation and inversion
    • Single-converter reversing drives
    • Double-converter reversing drives
    • Power factor and supply effects
    • CONTROL ARRANGEMENTS FOR D.C. DRIVES
    • Current control in DC motors
    • Torque control in DC motors
    • Speed control in DC motors
    • Some More cases in DC motors
    • CHOPPER-FED D.C. MOTOR DRIVES
    • Performance of chopper-fed d.c. motor drives
    • D.C. SERVO DRIVES
    • Servo Motors
    • Position control of dc motors
    • DIGITALLY CONTROLLED DRIVES
    • Damage to Electric Machines

  • Three phase induction motor drives
    • THE ROTATING MAGNETIC FIELD
    • Field produced by each phase winding
    • Production of rotating magnetic field
    • Resultant Field of an induction motor
    • Main (air-gap) flux and leakage flux
    • Magnitude of rotating flux wave
    • Excitation power and VA
    • TORQUE PRODUCTION - Rotor Construction
    • Torque Production - Slip
    • Torque Production - Rotor induced e.m.f., current and torque
    • Torque Production - Rotor currents and torque – small slip
    • Rotor currents and torque – large slip
    • Reduction of flux by rotor current
    • STATOR CURRENT-SPEED CHARACTERISTICS
    • Direct Starting of cage motors
    • Star/delta (wye/mesh) starters of motors
    • Autotransformer starter
    • Resistance or reactance starter
    • Solid-state soft starting of motors
    • RUN-UP AND STABLE OPERATING REGIONS
    • Harmonic effects – skewing
    • High inertia loads – overheating
    • Steady-state rotor losses and efficiency
    • Steady-state stability – pullout torque and stalling
    • Influence of Cage rotor in Torque-speed curve
    • Influence of Double Cage rotors in Torque-speed curve
    • Influence of Deep bar rotors in Torque-speed curve
    • Starting and run-up of slipring motors
    • INFLUENCE OF SUPPLY VOLTAGE ON TORQUE–SPEED CURVE
    • GENERATING AND BRAKING
    • Generating region – overhauling loads
    • Plug reversal and plug braking
    • Injection braking & SPEED CONTROL
    • Pole-changing motors
    • Voltage control of high-resistance cage motors
    • Speed control of wound-rotor motors
    • Power Factor Improvement - Voltage Control
    • Energy optimization - Slip energy recovery
    • Principle of operation of SINGLE-PHASE INDUCTION MOTORS
    • Capacitor-run motors
    • Split-phase motors
    • Shaded-pole motors
    • Size-Range-Scaling down – the excitation problem
    • SIMILARITY BETWEEN INDUCTION MOTOR AND TRANSFORMER
    • Ideal transformer – no-load condition, flux and magnetising current
    • Ideal transformer – no-load condition, voltage ratio
    • Ideal transformer on load
    • Real transformer – no-load condition, flux and magnetising current
    • Real transformer – leakage reactance
    • Real transformer on load – exact equivalent circuit
    • Real transformer – approximate equivalent circuit
    • Measurement of Transformer parameters
    • Significance of equivalent circuit parameters
    • Modelling the electromechanical energy conversion process
    • PROPERTIES OF INDUCTION MOTORS
    • Power balance & Torque in an Induction Motor
    • Starting and full-load relationships of an induction motor
    • Phasor diagram of induction motors
    • Dependence of pull out torque on motor parameters
    • INTRODUCTION TO INVERTER-FED INDUCTION MOTOR DRIVES
    • Comparison of Inverter fed induction motors with d.c. drive
    • Inverter waveforms of Inverter fed induction motor drives
    • Steady-state operation – Importance of achieving full flux
    • TORQUE–SPEED CHARACTERISTICS – CONSTANT V/F OPERATION
    • Limitations imposed by the inverter – constant power and constant torque regions
    • Limitations imposed by motor
    • CONTROL ARRANGEMENTS FOR INVERTER-FED DRIVES
    • Open-loop speed control
    • Closed-loop speed control
    • VECTOR (FIELD-ORIENTED) CONTROL
    • Transient torque control
    • CYCLOCONVERTER DRIVES

  • SYNCHRONOUSBRUSHLESS D.C. AND SWITCHED RELUCTANCE DRIVES
    • Synchronous Motors
    • Excited-rotor motors
    • Equivalent circuit of excited-rotor synchronous motor
    • Phasor diagram and Power-factor control
    • Starting of synchronous Motors
    • Permanent magnet synchronous motors
    • Hysteresis motors
    • Reluctance Motors
    • CONTROLLED-SPEED SYNCHRONOUS MOTOR DRIVES
    • Open-loop inverter-fed synchronous motor drives
    • Self-synchronous (closed-loop) operation
    • Operating characteristics and control
    • BRUSHLESS D.C. MOTORS
    • SWITCHED RELUCTANCE MOTOR DRIVES
    • Principle of operation of switched reluctance motor drives
    • Torque prediction and control
    • Power converter and overall drive characteristics

  • DRIVE SELECTION
    • POWER RANGE FOR MOTORS AND DRIVES
    • Maximum speed and speed range
    • LOAD REQUIREMENTS – TORQUE–SPEED CHARACTERISTICS
    • Constant-torque load
    • Inertia matching
    • Fan and pump loads
    • GENERAL APPLICATION CONSIDERATIONS of Motor Drives

  • Electric Braking
    • Introduction to Electric Braking
    • Types of Electric Braking
    • REGENERATIVE BRAKING
    • DYNAMIC BRAKING
    • COUNTERCURRENT BRAKING
    • REGENERATIVE BRAKING OF DC SHUNT MOTORS
    • REGENERATIVE BRAKING OF DC SERIES MOTORS
    • DYNAMIC BRAKING OF DC SHUNT MOTORS
    • DYNAMIC BRAKING OF DC SERIES MOTORS
    • Plugging
    • BRAKING BY TERMINAL VOLTAGE REVERSAL (TVR)
    • COUNTERCURRENT BRAKING OF DC SERIES MOTORS
    • REGENERATIVE BRAKING OF INDUCTION MOTORS
    • DYNAMIC BRAKING OF INDUCTION MOTORS
    • COUNTERCURRENT BRAKING OF INDUCTION MOTORS
    • DC Rheostatic Braking
    • Different methods of feeding dc to stator winding
    • AC Rheostatic Braking
    • Rheostatic Braking of Synchronous Motors

  • Dynamics of Electric Drive Systems
    • Introduction to Dynamics of electric Drive system
    • MOMENT OF INERTIA
    • BASIC CONCEPT OF TRAVELING TIME
    • Gears & Belts
    • Traveling time of DC motors
    • TRAVELING TIME OF INDUCTION MOTORS
    • Unloaded & Loaded Induction Motors
    • Traveling time of Synchronous Motors
    • Steady state stability of Electric Drive

  • Control of DC drives
    • Speed control of shunt or separately excited DC motors
    • Controlling speed by adding resistance
    • CONTROLLING SPEED BY ADJUSTING ARMATURE VOLTAGE
    • CONTROLLING SPEED BY ADJUSTING FIELD VOLTAGE
    • SOLID-STATE CONTROL - SINGLE-PHASE, HALF-WAVE DRIVES
    • SOLID-STATE CONTROL - SINGLE-PHASE, FULL-WAVE DRIVES
    • Continuous Armature Current
    • EFFECT OF FREEWHEELING DIODE ON DC DRIVES
    • SPEED CONTROL OF SERIES MOTOR

  • Control of AC drives
    • BASIC PRINCIPLES OF SPEED CONTROL OF INDUCTION MOTORS
    • CONTROLLING SPEED OF AN INDUCTION MOTOR USING ROTOR RESISTANCE
    • ROTOR VOLTAGE INJECTION
    • SLIP ENERGY RECOVERY
    • CONTROLLING SPEED BY THE SLIP ENERGY RECOVERY METHOD
    • TORQUE-CURRENT RELATIONSHIP IN INDUCTION MOTORS
    • Efficiency of an induction motor during slip energy recovery
    • CONTROLLING SPEED OF INDUCTION MOTOR BY ADJUSTING THE STATOR VOLTAGE
    • CONTROLLING SPEED OF INDUCTION MOTOR BY ADJUSTING THE SUPPLY FREQUENCY
    • EFFECT OF EXCESSIVELY HIGH & LOW FREQUENCIES ON INDUCTION MOTORS
    • VOLTAGE/FREQUENCY CONTROL OF INDUCTION MOTORS
    • CURRENT SOURCE SPEED CONTROL OF INDUCTION MOTORS
    • INDUCTION MOTOR WITH CONSTANT-FREQUENCY CSI
    • INDUCTION MOTOR WITH ADJUSTABLE FREQUENCY CSI

  • Piezoelectric Drives
    • Solid-state Actuators and Piezoelectric Actuators
    • Piezoelectricity
    • Nonlinearity in Piezoelectric Actuators
    • Mechanical Linkages for Piezoelectric Drives

Branch : Electrical and Electronics Engineering
Subject : Electrical drives
Unit : Three phase induction motor drives

Injection braking & SPEED CONTROL


Injection Braking:

 

Fig: 1 Torque–speed curve for d.c. injection braking of cage motor

  • Injection Braking is the most widely used method of electrical braking. When the ‘stop’ button is pressed, the 3-phase supply is interrupted, and a d.c. current is fed into the stator via two of its terminals.
  • The d.c. supply is usually obtained from a rectifier fed via a low-voltage high-current transformer. We saw earlier that the speed of rotation of the air-gap field is directly proportional to the supply frequency, so it should be clear that since d.c. is effectively zero frequency, the air-gap Weld will be stationary.
  • We also saw that the rotor always tries to run at the same speed as the field. So, if the field is stationary, and the rotor is not, a braking torque will be exerted.
  •  A typical torque–speed curve for braking a cage motor is shown in Figure 1, from which we see that the braking (negative) torque falls to zero as the rotor comes to rest.
  •  This is in line with what we would expect, since there will be induced currents in the rotor (and hence torque) only when the rotor is ‘cutting’ the flux. As with plugging, injection (or dynamic) braking is a dissipative process, all the kinetic energy being turned into heat inside the motor.

 

Speed Control:

  • To operate efficiently an induction motor must run with a small slip. It follows that any efficient method of speed control must be based on varying the synchronous speed of the field, rather than the slip.
  •  The two factors that determine the speed of the field, are the supply frequency and the pole number. The pole number has to be an even integer, so where continuously adjustable speed control over a wide range is called for, the best approach is to provide a variable-frequency supply.
  • This method is very important concerns with constant frequency mains operation, providing a choice between pole-changing, which can provide discrete speeds only, or slip control which can provide continuous speed control, but is inherently inefficient.

Questions of this topic


  • Write a short note on Injection braking of motor.

    Answer this
  • Write a short note on speed control of motor.

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