Electrical motors

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Published on November 14, 2007

Author: Columbia

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Slide1:  Training Session on Energy Equipment Electric Motors Presentation from the “Energy Efficiency Guide for Industry in Asia” www.energyefficiencyasia.org © UNEP 2006 Electrical Equipment/ Electric Motors Slide2:  © UNEP 2006 Training Agenda: Electric Motors Introduction Types of electric motors Assessment of electric motors Energy efficiency opportunities Electrical Equipment/ Electric Motors Slide3:  © UNEP 2006 Introduction Electromechanical device that converts electrical energy to mechanical energy Mechanical energy used to e.g. Rotate pump impeller, fan, blower Drive compressors Lift materials Motors in industry: 70% of electrical load What is an Electric Motor? Electrical Equipment/ Electric Motors Slide4:  © UNEP 2006 Introduction How Does an Electric Motor Work? Electrical Equipment/ Electric Motors (Nave, 2005) 1 2 3 4 Slide5:  © UNEP 2006 Introduction Three types of Motor Load Electrical Equipment/ Electric Motors Slide6:  © UNEP 2006 Training Agenda: Electric Motors Introduction Types of electric motors Assessment of electric motors Energy efficiency opportunities Electrical Equipment/ Electric Motors Slide7:  © UNEP 2006 Type of Electric Motors Motors are categorized on th ebasis of input supply, construction and operation principoles TEXT Classification of Motors Electrical Equipment/ Electric Motors Slide8:  © UNEP 2006 Type of Electric Motors Field pole North pole and south pole Receive electricity to form magnetic field Armature Cylinder between the poles Electromagnet when current goes through Linked to drive shaft to drive the load Commutator Overturns current direction in armature DC Motors – Components Electrical Equipment/ Electric Motors (Direct Industry, 1995) Slide9:  © UNEP 2006 Type of Electric Motors Speed control without impact power supply quality Changing armature voltage Changing field current Restricted use Few low/medium speed applications Clean, non-hazardous areas Expensive compared to AC motors DC motors Electrical Equipment/ Electric Motors Slide10:  © UNEP 2006 Type of Electric Motors Relationship between speed, field flux and armature voltage DC motors Electrical Equipment/ Electric Motors E = electromagnetic force developed at armature terminal (volt)  = field flux which is directly proportional to field current N = speed in RPM (revolutions per minute) T = electromagnetic torque Ia = armature current K = an equation constant Slide11:  © UNEP 2006 Type of Electric Motors Separately excited DC motor: field current supplied from a separate force Self-excited DC motor: shunt motor Electrical Equipment/ Electric Motors Field winding parallel with armature winding Current = field current + armature current Speed constant independent of load up to certain torque Speed control: insert resistance in armature or field current DC motors (Rodwell Int. Corporation, 1999) Slide12:  © UNEP 2006 Type of Electric Motors Self-excited DC motor: series motor Electrical Equipment/ Electric Motors DC motors (Rodwell Int. Corporation, 1999) Field winding in series with armature winding Field current = armature current Speed restricted to 5000 RPM Avoid running with no load: speed uncontrolled Suited for high starting torque: cranes, hoists Slide13:  © UNEP 2006 Type of Electric Motors DC compound motor Electrical Equipment/ Electric Motors DC motors Field winding in series and parallel with armature winding Good torque and stable speed Higher % compound in series = high starting torque Suited for high starting torque if high % compounding: cranes, hoists Slide14:  © UNEP 2006 Type of Electric Motors Motors are categorized on th ebasis of input supply, construction and operation principoles TEXT Classification of Motors Electrical Equipment/ Electric Motors Slide15:  © UNEP 2006 Type of Electric Motors Electrical current reverses direction Two parts: stator and rotor Stator: stationary electrical component Rotor: rotates the motor shaft Speed difficult to control Two types Synchronous motor Induction motor AC Motors Electrical Equipment/ Electric Motors (Integrated Publishing, 2003) Slide16:  © UNEP 2006 Type of Electric Motors Constant speed fixed by system frequency DC for excitation and low starting torque: suited for low load applications Can improve power factor: suited for high electricity use systems Synchronous speed (Ns): Electrical Equipment/ Electric Motors AC Motors – Synchronous motor Ns = 120 f / P F = supply frequency P = number of poles Slide17:  © UNEP 2006 Type of Electric Motors Most common motors in industry Advantages: Simple design Inexpensive High power to weight ratio Easy to maintain Direct connection to AC power source Electrical Equipment/ Electric Motors AC Motors – Induction motor Slide18:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors Components Rotor Squirrel cage: conducting bars in parallel slots Wound rotor: 3-phase, double-layer, distributed winding AC Motors – Induction motor Stator Stampings with slots to carry 3-phase windings Wound for definite number of poles (Automated Buildings) Slide19:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors AC Motors – Induction motor How induction motors work Electricity supplied to stator Magnetic field generated that moves around rotor Current induced in rotor Rotor produces second magnetic field that opposes stator magnetic field Rotor begins to rotate (Reliance) Slide20:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors AC Motors – Induction motor Single-phase induction motor One stator winding Single-phase power supply Squirrel cage rotor Require device to start motor 3 to 4 HP applications Household appliances: fans, washing machines, dryers Slide21:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors AC Motors – Induction motor Three-phase induction motor Three-phase supply produces magnetic field Squirrel cage or wound rotor Self-starting High power capabilities 1/3 to hundreds HP applications: pumps, compressors, conveyor belts, grinders 70% of motors in industry! Slide22:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors AC Motors – Induction motor Speed and slip Motor never runs at synchronous speed but lower “base speed” Difference is “slip” Install slip ring to avoid this Calculate % slip: % Slip = Ns – Nb x 100 Ns Ns = synchronous speed in RPM Nb = base speed in RPM Slide23:  © UNEP 2006 Type of Electric Motors Electrical Equipment/ Electric Motors AC Motors – Induction motor Relationship load, speed and torque At start: high current and low “pull-up” torque At start: high current and low “pull-up” torque At 80% of full speed: highest “pull-out” torque and current drops At full speed: torque and stator current are zero Slide24:  © UNEP 2006 Training Agenda: Electric Motors Introduction Types of electric motors Assessment of electric motors Energy efficiency opportunities Electrical Equipment/ Electric Motors Slide25:  © UNEP 2006 Assessment of Electric Motors Motors loose energy when serving a load Fixed loss Rotor loss Stator loss Friction and rewinding Stray load loss Efficiency of Electric Motors Electrical Equipment/ Electric Motors (US DOE) Slide26:  © UNEP 2006 Factors that influence efficiency Age Capacity Speed Type Temperature Rewinding Load Efficiency of Electric Motors Electrical Equipment/ Electric Motors Assessment of Electric Motors Slide27:  © UNEP 2006 Motor part load efficiency Designed for 50-100% load Most efficient at 75% load Rapid drop below 50% load Efficiency of Electric Motors Electrical Equipment/ Electric Motors (US DOE) Assessment of Electric Motors Slide28:  © UNEP 2006 Motor load is indicator of efficiency Equation to determine load: Motor Load Electrical Equipment/ Electric Motors Load = Pi x  HP x 0.7457  = Motor operating efficiency in % HP = Nameplate rated horse power Load = Output power as a % of rated power Pi = Three phase power in kW Assessment of Electric Motors Slide29:  © UNEP 2006 Three methods for individual motors Input power measurement Ratio input power and rate power at 100% loading Line current measurement Compare measured amperage with rated amperage Slip method Compare slip at operation with slip at full load Motor Load Electrical Equipment/ Electric Motors Assessment of Electric Motors Slide30:  © UNEP 2006 Input power measurement Three steps for three-phase motors Step 1. Determine the input power: Motor Load Electrical Equipment/ Electric Motors Pi = Three Phase power in kW V = RMS Voltage, mean line to line of 3 Phases I = RMS Current, mean of 3 phases PF = Power factor as Decimal Assessment of Electric Motors Slide31:  © UNEP 2006 Input power measurement Step 2. Determine the rated power: Step 3. Determine the percentage load: Motor Load Electrical Equipment/ Electric Motors Assessment of Electric Motors Slide32:  © UNEP 2006 Result Significantly oversized and underloaded Moderately oversized and underloaded Properly sized but standard efficiency Motor Load Electrical Equipment/ Electric Motors Action Replace with more efficient, properly sized models Replace with more efficient, properly sized models when they fail Replace most of these with energy-efficient models when they fail Assessment of Electric Motors Slide33:  © UNEP 2006 Training Agenda: Electric Motors Introduction Types of electric motors Assessment of electric motors Energy efficiency opportunities Electrical Equipment/ Electric Motors Slide34:  © UNEP 2006 Use energy efficient motors Reduce under-loading (and avoid over-sized motors) Size to variable load Improve power quality Rewinding Power factor correction by capacitors Improve maintenance Speed control of induction motor Electrical Equipment/ Electric Motors Energy Efficiency Opportunities Slide35:  © UNEP 2006 Reduce intrinsic motor losses Efficiency 3-7% higher Wide range of ratings More expensive but rapid payback Best to replace when existing motors fail Use Energy Efficient Motors Electrical Equipment/ Electric Motors (Bureau of Indian Standards) Energy Efficiency Opportunities Slide36:  © UNEP 2006 Electrical Equipment/ Electric Motors (BEE India, 2004) Use Energy Efficient Motors Energy Efficiency Opportunities Slide37:  © UNEP 2006 Energy Efficiency Opportunities Reasons for under-loading Large safety factor when selecting motor Under-utilization of equipment Maintain outputs at desired level even at low input voltages High starting torque is required Consequences of under-loading Increased motor losses Reduced motor efficiency Reduced power factor 2. Reduce Under-loading Electrical Equipment/ Electric Motors Slide38:  © UNEP 2006 Energy Efficiency Opportunities Replace with smaller motor If motor operates at <50% Not if motor operates at 60-70% Operate in star mode If motors consistently operate at <40% Inexpensive and effective Motor electrically downsized by wire reconfiguration Motor speed and voltage reduction but unchanged performance 2. Reduce Under-loading Electrical Equipment/ Electric Motors Slide39:  © UNEP 2006 Energy Efficiency Opportunities Motor selection based on Highest anticipated load: expensive and risk of under-loading Slightly lower than highest load: occasional overloading for short periods But avoid risk of overheating due to Extreme load changes Frequent / long periods of overloading Inability of motor to cool down 3. Sizing to Variable Load Electrical Equipment/ Electric Motors X  Motors have ‘service factor’ of 15% above rated load Slide40:  © UNEP 2006 Energy Efficiency Opportunities Motor performance affected by Poor power quality: too high fluctuations in voltage and frequency Voltage unbalance: unequal voltages to three phases of motor 4. Improve Power Quality Electrical Equipment/ Electric Motors Slide41:  © UNEP 2006 Energy Efficiency Opportunities Keep voltage unbalance within 1% Balance single phase loads equally among three phases Segregate single phase loads and feed them into separate line/transformer 4. Improve Power Quality Electrical Equipment/ Electric Motors Slide42:  © UNEP 2006 Energy Efficiency Opportunities Rewinding: sometimes 50% of motors Can reduce motor efficiency Maintain efficiency after rewinding by Using qualified/certified firm Maintain original motor design Replace 40HP, >15 year old motors instead of rewinding Buy new motor if costs are less than 50-65% of rewinding costs 5. Rewinding Electrical Equipment/ Electric Motors Slide43:  © UNEP 2006 Energy Efficiency Opportunities Use capacitors for induction motors Benefits of improved PF Reduced kVA Reduced losses Improved voltage regulation Increased efficiency of plant electrical system Capacitor size not >90% of no-load kVAR of motor 6. Improve Power Factor (PF) Electrical Equipment/ Electric Motors Slide44:  © UNEP 2006 Energy Efficiency Opportunities Checklist to maintain motor efficiency Inspect motors regularly for wear, dirt/dust Checking motor loads for over/under loading Lubricate appropriately Check alignment of motor and equipment Ensure supply wiring and terminal box and properly sized and installed Provide adequate ventilation 7. Maintenance Electrical Equipment/ Electric Motors Slide45:  © UNEP 2006 Energy Efficiency Opportunities Multi-speed motors Limited speed control: 2 – 4 fixed speeds Wound rotor motor drives Specifically constructed motor Variable resistors to control torque performance >300 HP most common 8. Speed Control of Induction Motor Electrical Equipment/ Electric Motors Slide46:  © UNEP 2006 Energy Efficiency Opportunities Variable speed drives (VSDs) Also called inverters Several kW to 750 kW Change speed of induction motors Can be installed in existing system Reduce electricity by >50% in fans and pumps Convert 50Hz incoming power to variable frequency and voltage: change speed Three types 8. Speed Control of Induction Motor Electrical Equipment/ Electric Motors Slide47:  © UNEP 2006 Energy Efficiency Opportunities Direct Current Drives Oldest form of electrical speed control Consists of DC motor: field windings and armature Controller: regulates DC voltage to armature that controls motor speed Tacho-generator: gives feedback signal to controlled Electrical Equipment/ Electric Motors 8. Speed Control of Induction Motor Slide48:  Training Session on Energy Equipment Electric Motors THANK YOU FOR YOUR ATTENTION © UNEP 2006 Electrical Equipment/ Electric Motors Slide49:  Electrical Systems/ Electric motors © UNEP 2006 Disclaimer and References This PowerPoint training session was prepared as part of the project “Greenhouse Gas Emission Reduction from Industry in Asia and the Pacific” (GERIAP). While reasonable efforts have been made to ensure that the contents of this publication are factually correct and properly referenced, UNEP does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication. © UNEP, 2006. The GERIAP project was funded by the Swedish International Development Cooperation Agency (Sida) Full references are included in the textbook chapter that is available on www.energyefficiencyasia.org

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