Induction motor lecture Video

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AC Induction Motor Fundamentals
AC induction motors are the most common motors
used in industrial motion control systems, as well as in
main powered home appliances. Simple and rugged
design, low-cost, low maintenance and direct connection
to an AC power source are the main advantages of
AC induction motors.

Various types of AC induction motors are available in
the market. Different motors are suitable for different
applications. Although AC induction motors are easier
to design than DC motors, the speed and the torque
control in various types of AC induction motors require
a greater understanding of the design and the
characteristics of these motors.

This application note discusses the basics of an AC
induction motor; the different types, their characteristics,
the selection criteria for different applications and
basic control techniques.



A TYPICAL STATOR

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Permanent Capacitor for a Single Phase Motor Calculation

Selection of capacitance on motor capacitors

Selection of a permanent capacitor for a single phase motor implies the consideration of technical and economical aspects.

As the winding of a single phase motor can be done in very different ways (division of the winding space between the main winding and the auxiliary winding, selection of the number of winding turns and sections of the winding, and so on), it is not possible to give universal rules to determine the capacitance and the working voltage of the capacitor for a certain power of the motor.

It is then always necessary to apply the criteria established by the motor manufacturer.

However, following it is exposed a calculation procedure with the only aim of being useful for a first evaluation and give an approximate idea of the values of the permanent capacitor:

It is considered that in general, for each CV of power, a motor capacitor requires

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HOW TO CHOOSE THE RIGHT CAPACITOR

CRITERION FOR THE SELECTION OF THE RIGHT CAPACITOR:
A capacitor motor does not appear to be highly affected by the capacitance reactive power, therefore, it is not necessary to use an accurate capacitance value. It will be possible to choose a capacitance reactive power equalising the inductive-reactive power

TYPICAL CHOICE PARAMETERS:

TURNS RATIO n:
Although it is possible to choose this ratio on the basis of a large number of combinations,usually the main / auxiliary winding turns ratio is chosen in order to generate a voltage on the capacitor closest to its rated values.

VOLTAGE ON CAPACITOR VC :
The following is a formula able to approximately calculate the voltage on the capacitor. If the voltage measured at both ends of the auxiliary winding is equal to n*Vp (where Vp is the voltage measured at both ends of the main winding and n is the turns ratio), the voltage at both ends of the capacitors can be estimated as follows

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Type of single phase induction motor

Permanent-split capacitor motor
One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two phases of current displaced 90o in time. This is called a permanent-split capacitor motor in Figure below.

Fig. Permanent-split capacitor induction motor.

This type of motor suffers increased current magnitude and backward time shift as the motor comes up to speed, with torque pulsations at full speed. The solution is to keep the capacitor (impedance) small to minimize losses. The losses are less than for a shaded pole motor. This motor configuration works well up to 1/4 horsepower (200watt), though, usually applied to smaller motors. The direction of the motor is easily reversed by switching the capacitor in series with the other winding. This type of motor can be adapted for use as a servo motor, described elsewhere is this chapter.

Capacitor-start induction motor
In Figure below a larger capacitor may be used to start a single phase induction motor via the auxiliary winding if it is switched out by a centrifugal switch once the motor is up to speed. Moreover, the auxiliary winding may be many more turns of heavier wire than used in a resistance split-phase motor to mitigate excessive temperature rise. The result is that more starting torque is available for heavy loads like air conditioning compressors. This motor configuration works so well that it is available in multi-horsepower (multi-kilowatt) sizes.

Fig. Capacitor-start induction motor.

Capacitor-run motor induction motor
A variation of the capacitor-start motor (Figure below) is to start the motor with a relatively large capacitor for high starting torque, but leave a smaller value capacitor in place after starting to improve running characteristics while not drawing excessive current. The additional complexity of the capacitor-run motor is justified for larger size motors.

Fig. Capacitor-run motor induction motor.

A motor starting capacitor may be a double-anode non-polar electrolytic capacitor which could be two + to + (or - to -) series connected polarized electrolytic capacitors. Such AC rated electrolytic capacitors have such high losses that they can only be used for intermittent duty (1 second on, 60 seconds off) like motor starting. A capacitor for motor running must not be of electrolytic construction, but a lower loss polymer type.

Resistance split-phase motor induction motor
If an auxiliary winding of much fewer turns of smaller wire is placed at 90o electrical to the main winding, it can start a single phase induction motor. (Figure below) With lower inductance and higher resistance, the current will experience less phase shift than the main winding. About 30o of phase difference may be obtained. This coil produces a moderate starting torque, which is disconnected by a centrifugal switch at 3/4 of synchronous speed. This simple (no capacitor) arrangement serves well for motors up to 1/3 horsepower (250 watts) driving easily started loads.

Fig. Resistance split-phase motor induction motor.

This motor has more starting torque than a shaded pole motor (next section), but not as much as a two phase motor built from the same parts. The current density in the auxiliary winding is so high during starting that the consequent rapid temperature rise precludes frequent restarting or slow starting loads.
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starting torque of single phase induction motor

Capacitor start / induction run motors typically deliver 250 to 350 percent of full load torque when starting. Motors of this design are used in compressors and other types of industrial, commercial, and farm equipment.
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Capacitor-start single phase induction motor

Single Phase AC Induction Motors
AC single phase induction motors are classified by their start and run characteristics. An auxiliary starter winding is placed at right angles to the main stator winding in order to create a magnetic field. The current moving through each winding is out of phase by 90 degrees. This is called phase differential. After the motor has reached approximately 75% of operating speed, the auxiliary winding is disconnected from the circuit by a centrifugal switch.
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Capacitor Start / Induction Run Motors
Capacitor start / induction run motors are similar in construction to split phase motors. The major difference is the use of a capacitor connected in series to start windings to maximize starting torque.

The capacitor is mounted either at the top or side of the motor. A normally closed centrifugal switch is located between the capacitor and the start winding. This switch opens when the motor has reached about 75 percent of its operating speed.

Capacitors in induction run motors enable them to handle heavier start loads by strengthening the magnetic field of the start windings. These loads might include refrigerators, compressors, elevators, and augers. The size of capacitors used in these types of applications ranges from 1/6 to 10 horsepower. High starting torque designs also require high starting currents and high breakdown torque.

Capacitor start / induction run motors typically deliver 250 to 350 percent of full load torque when starting. Motors of this design are used in compressors and other types of industrial, commercial, and farm equipment.

Capacitor start induction run motors of moderate torque values are used on applications that require less than 175 percent of the full load. These are used with lighter loads like fans, blowers, and small pumps.
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Capacitor-start single phase induction motor vedio

Factors Affecting of an Ac Induction Motor Design

Factors Affecting the Design of an

Ac Electric Induction Motor1

Author: Baljeet

Factors affecting the Design of an ac electric induction motor

Design of an ac electric motor is directly affected by the length of the air gap. Ampere Conductors value also affects the design of an ac electric motor.

The value of average flux density over the air gap of an ac electric motor also affects the design of an ac electric motor. The size or dimensions of an ac electric motor depend upon the speed of an ac electric motor. It can also be said that the volume of active parts of an ac electric motor varies inversely as the speed of an ac electric motor. The value of output co-efficient is directly responsible for the dimensions of an ac electric motor. In other words the volume of active parts of an ac electric motor is inversely proportional to the value of output co-efficient of the ac electric motor.

The total flux around the armature (or stator of an ac electric motor) periphery at the air gap is called the total magnetic loading. While total electric loading is the total number of ampere conductors around the armature (or stator of an ac electric motor) periphery. Since the output coefficient of an ac electric motor is proportional to the product of specific magnetic and specific electric loading of an ac electric motor, we conclude that the size and hence the cost of ac electric motor decreases if increased values of specific magnetic and electric loading are used. The flux density in iron parts of an ac electric motor is directly proportional to the average flux density in the air gap of the ac electric motor. In a well designed ac electric motor the maximum density occurs in the teeth of the ac electric motor and therefore let us relate the flux density in the teeth with flux density in the air gap of ac electric motor.

The magnetizing current of an ac electric motor is directly proportional to the mmf required to force the flux through the air gap and the parts of the ac electric motor. The mmf required for the air gap of an ac electric motor is directly proportional to the gap flux density i.e. the specific magnetic loading of an ac electric motor. The consideration of magnetizing current is very important in ac electric induction motor(s) as an increased value of magnetizing current means of a low operating power factor of ac electric motor. Therefore specific magnetic loading in the case of ac electric induction motor(s) is lower than that in dc electric motor(s).

The core loss in any part of the magnetic circuit of an ac electric motor is directly proportional to the flux density for which the ac electric motor is going to be designed. Thus a large value of specific magnetic loading in an ac electric motor indicates an increased core loss in ac electric motor and consequently a decreased efficiency of ac electric motor and an increased temperature rise of ac electric motor. In case of high frequency ac electric motor, specific magnetic loading must be reduced in order to get lower iron losses in ac electric motor so that reasonable values of efficiency may be maintained in an ac electric motor. The maxmium temperature rise of an ac electric motor is determined by the type of insulation material used in the ac electric motor. If the cooling co-efficient of the ac electric motor is small, a high value of specific loading may be used in the ac electric motor.

About the Author:

Softbit provides CAD/CAM software packages for Electrical Machine Design, Industrial Automation products such as Remote Data Logger. Company aims to satisfy the current and future needs of its valued clients. We strive for customer’s satisfaction; our aim is technology dedication & continual improvements. http://www.softbitonline.com/ ac electric motor

Article Source: http://www.articlesbase.com/business-articles/factors-affecting-the-design-of-an-ac-electric-induction-motor1-222242.html

Factors affecting the speed-torque characteristics of an Induction motor :

The speed-torque characteristics are affected by various factors like applied voltage, R2’ and frequency.

(a) Applied voltage : We know that T µ V2. Thus not only the stationary torque but also the torque under running conditions changes with change in supply voltage.

(b) Supply frequency : The major effect of change in supply frequency is on motor speed. The starting torque is reduced with increase in frequency.

(c) Rotor resistance : The maximum torque produced does not depend on R2’. However, with increase in R2’, the starting torque increases. The slip at which Tmax is reached increases too which means that Tmax is obtained at lower motor speeds
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Energy-Efficient Motors Motors

Energy-Efficient Motors

Efficiency is an important factor to consider when buying or rewinding an electric motor. This Technical Brief answers some frequently asked questions about how to obtain the most efficient motor at the lowest price while avoiding some common problems.
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Energy Savings by means of Energy Efficient Electric Motors
Abstract
The electric motors consume a significant amount of
electricity in the industrial and in the tertiary sectors of
the European Union. Because of its simplicity and
robustness the three-phase squirrel-cage induction motor
is the prime mover of the modern industry. The electricmotor
manufacturers are seeking methods for improving
the motor efficiencies, which resulted in a new
generation of electric motors that are known as energyefficient
motors.

This paper deals with energy conservation by
installing energy efficient motor (EEM) instead of
standard efficiency motor. This transition becomes a
necessity as a direct result of limitation in energy sources
and escalating energy prices. In the end of this analysis,
there are different practical cases in where EEM is
compared with standard motors and rewound motor. In
all these cases energy savings can be achieved and the
simple payback is less of five years. So, it is very
interesting the implementation of EEM in the industry.

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A Novel Analysis of Energy Efficiency Motors and Power Controllers

Author: s.sankar

A novel analysis of energy efficiency motors and power controllers

Voltage Control

Voltage alone can be used as a source of intelligence when the switched capacitors are applied at point where the circuit voltage decreases as circuit load increases. Generally, where they are applied the voltage should decrease as circuit load increases and the drop in voltage should be around 4 – 5 % with increasing load.

Voltage is the most common type of intelligence used in substation applications, when maintaining a particular voltage is of prime importance. This type of control is independent of load cycle. During light load time and low source voltage, this may give leading PF at the substation, which is to be taken note of. KILOVAR Control

Automatic Power Factor Control Relay

It controls the power factor of the installation by giving signals to switch on or off power factor correction capacitors. Relay is the brain of control circuit and needs contactors of appropriate rating for switching on/off the capacitors.

There is a built-in power factor transducer, which measures the power factor of the installation and converts it to a DC voltage of appropriate polarity. This is compared with a reference voltage, which can be set by means of a knob calibrated in terms of power factor.

When the power factor falls below setting, the capacitors are switched on in sequence. The relays are provided with First in First out (FIFO) and First in Last Out (FILO) sequence. The capacitors controlled by the relay must be of the same rating and they are switched on/off in linear sequence. To prevent over correction hunting, a dead band is provided. This setting determines the range of phase angle over which the relay does not respond; only when the PF goes beyond this range, the relay acts. When the load is low, the effect of the capacitors is more pronounced and may lead to hunting. Under current blocking (low current cut out) shuts off the relay, switching off all capacitors one by one in sequence, when load current is below setting. Special timing sequences ensure that capacitors are fully discharged before they are switched in. This avoids dangerous over voltage transient. The solid state indicating lamps (LEDS) display various functions that the operator should know and also and indicate each capacitor switching stage.

Intelligent Power Factor Controller (IPFC)

This controller determines the rating of capacitance connected in each step during the first hour of its operation and stores them in memory. Based on this measurement, the IPFC switches on the most appropriate steps, thus eliminating the hunting problems normally associated with capacitor switching.

Energy Efficient Motors
Minimising Watts Loss in Motors

Improvements in motor efficiency can be achieved without compromising motor performance - at higher cost - within the limits of existing design and manufacturing technology.

From the Table .1, it can be seen that any improvement in motor efficiency must result from reducing the Watts losses. In terms of the existing state of electric motor technology, a reduction in watts losses can be achieved in various ways.

All of these changes to reduce motor losses are possible with existing motor design and manufacturing technology. They would, however, require additional materials and/or the use of higher quality materials and improved manufacturing processes resulting in increased motor cost.

Energy Efficient Motor

Table 1

Thus energy-efficient electric motors reduce energy losses through improved design, better materials, and improved manufacturing techniques. Replacing a motor may be justifiable solely on the electricity cost savings derived from an energy-efficient replacement. This is true if the motor runs continuously, power rates are high, the motor is oversized for the application, or its nominal efficiency has been reduced by damage or previous rewinds. Efficiency comparison for standard and high efficiency motors is shown in Figure 2.

Fig.2

Technical aspect of energy efficiency motors

Energy-efficient motors last longer, and may require less maintenance. At lower temperatures, bearing grease lasts longer; required time between re-greasing increases. Lower temperatures translate to long lasting insulation. Generally, motor life doubles for each 10°C reduction in operating temperature.

Select energy-efficient motors with a 1.15 service factor, and design for operation at 85% of the rated motor load.

Electrical power problems, especially poor incoming power quality can affect the operation of energy-efficient motors.

Speed control is crucial in some applications. In polyphase induction motors, slip is a measure of motor winding losses. The lower the slip, the higher the efficiency. Less slippage in energy efficient motors results in speeds about 1% faster than in standard counterparts.

Starting torque for efficient motors may be lower than for standard motors. Facility managers should be careful when applying efficient motors to high torque applications.

Soft Starter

When starting, AC Induction motor develops more torque than is required at full speed. This stress is transferred to the mechanical transmission system resulting in excessive wear and premature failure of chains, belts, gears, mechanical seals, etc. Additionally, rapid acceleration also has a massive impact on electricity supply charges with high inrush currents drawing +600% of the normal run current.

Soft Starter

The use of Star Delta only provides a partial solution to the problem. Should the motor slow down during the transition period, the high peaks can be repeated and can even exceed direct on line current. Soft starter (see Figure 10.5) provides a reliable and economical solution to these problems by delivering a controlled release of power to the motor, thereby providing smooth, stepless acceleration and deceleration. Motor life will be extended as damage to windings and bearings is reduced. Soft Start & Soft Stop is built into 3 phase units, providing controlled starting and stopping with a selection of ramp times and current limit settings to suit all applications

Soft Starter: Starting current, Stress profile during starting

Advantages of Soft Start –

Less mechanical stress

Improved power factor

Lower maximum demand

Less mechanical maintenance

About the Author:

Assistant professor in lord venkateswara engineering college.I am doing phd in sathyabama university, Tamil Nadu,India.

Article Source: http://www.articlesbase.com/electronics-articles/a-novel-analysis-of-energy-efficiency-motors-and-power-controllers-770964.html

What is an Energy-Efficient Motor?

Motor efficiency is the ratio of mechanical power output to the electrical power input, usually expressed as a percentage. Energy-efficient motors use less energy. Because they are manufactured with higher quality materials and techniques, they usually have higher service factors and bearing lives, less waste heat output, and less vibration, all of which increase reliability. This is often reflected by longer manufacturer’s warranties.
To be considered energy-efficient, a motor’s performance must equal or exceed the nominal full-load efficiency values provided by the National Electrical Manufacturer’s Association (NEMA) in their publication MG-1. The Energy Policy Act of 1992 (EPACT) required most general purpose motors between 1 and 200 horsepower for sale in the U.S. to meet these NEMA standards by October 24, 1997.

What Efficiency Value Should I Use?
When comparing two motors, be sure to use a consistent measure of efficiency. "Nominal" efficiency is best. This value is obtained through standardized testing. "Minimum" or "guaranteed" efficiency is slightly lower to take into account typical variations in efficiency within a population of motors.

When Should I Consider an Energy-Efficient Motor?
Assuming 6 cents per kWh electricity cost and a payback criteria of 2 years, most motors should be replaced with an energy-efficient model if they operate over 4,000 hours per year. In general, energy-efficient motors should be considered in the following circumstances:
New installations, both separate and as part of packages such as HVAC systems
When major modifications are made to a facility or a process
Instead of rewinding older, standard-efficiency motors
As part of a preventive maintenance or energy conservation plan
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AC Induction Motor Design Software

Electric Motor Design Software
AC Induction

FEATURES
- Microsoft ® Windows™ based program
- Analysis tool used in design of Poly Phase and Single Phase Motors,
including Capacitor Start, PSC and Split Phase
- Computes all relevant motor parameters
- Allows printing of inputs, outputs & graphs
- Multi-window tasking
- Important constants built into program
- Variable definitions instantly available on screen
- Reduces development cycle time and cost
- Instantly check effects of design change
- Maximizes material usage
- On-line design tips
- Reduce number of prototype iterations

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Ac Electric Motor Design – Software1

Author: Baljeet

AC Electric Motor Design - Software


Softbit presents an easy way to design LT, 3 ph, TEFC, squirrel cage ac electric motors with the help of "AC Electric Motor Design Software". You just need to enter a few preliminary inputs and click a button. What you get is an output "Design Sheet" containing more than 100 output parameters required to build an ac squirrel cage electric motor. You can start to design from a small fractional horse power ac electric motor to a 200 hp ac electric motor using this design software. Higher hp modules are also available on request. You have the options to change any of the values from output design data to match your specifications and need. With the change in any of these values, the remaining parameters change automatically, without affecting the output design and performance of the motor.

What you can Change

You can change any parameter from the design data sheet like no. of slots, type of cage, material of cage conductor (Al or Cu), length of stator, bore of stator, core type / material, rotor dimensions, stator length, shaft diameter, shaft length, supply voltage etc.,. to get a better and most suited design for your requirement. Accordingly motor winding data will also change.

Why to change the output parameter

What ever results you get through this design software are as per calculations done using the formulae used to design a squirrel cage ac electric induction motor. Now suppose you get a rotor diameter as X and rotor length as Y but the job and place do not permit you to use these dimensions of rotor or say motor then you just change the value of either X or Y to best suit your requirement and all the related output parameters will change automatically. So you can customize the design as per yours, your client's or job's requirement.

Values you need to enter at the start

When you start designing a squirrel cage ac electric motor, certain preliminary values are required to be fed to the software to give the out put parameters. So you need to enter - capacity of motor in hp / kw, poles, supply voltage, rpm, frequency and certain more that the software will ask you at the time of start.

About The Software

The software has been developed keeping in mind to give our design engineers and professionals more flexibility while they are designing a squirrel cage ac electric motor. This window based software is very much user friendly. It gives you numerical, pictorial and graphical out puts to easily understand various design data values. It is flexible enough so that you can change any output design data value as per your requirement and get the changed values instantly, without affecting the final design and performance of motor. Its worth buying as it saves time, energy, gives more accurate results in shortest time, data comparison easy.

Factors affecting the Design of an ac electric induction motor

"An electric motor converts electrical energy into rotating mechanical energy or an electric motor is a machine that converts electrical energy into rotating mechanical energy. AC electric motor works on the principle of electro - magnetic induction".

Who Should Buy?

Every professional linked with motor design, QC, production, purchase, maintenance, repairer & re-builders, training professionals, engineering students, end users of electric motors must posses this motor design software.

Price v/s Benefits

This software is developed for the engineers with an aim to get high productivity and easy to learn features, with full documentation that includes extensive information on machine theory and design. Motor design with this simulation is interactive and fast. However, this software does not do the engineer's job. It is simply a specialized calculating tool to assist the design engineers with initial sizing and preliminary design of a motor by providing a simple intuitive interface and quick simulation.

About the Author:

Softbit provides CAD/CAM software packages for Electrical Machine Design, Industrial Automation products such as Remote Data Logger. Company aims to satisfy the current and future needs of its valued clients. We strive for customer’s satisfaction; our aim is technology dedication & continual improvements. http://www.softbitonline.com/ Power transformer design

Article Source: http://www.articlesbase.com/business-articles/ac-electric-motor-design-software1-222240.html

The Workings of a DC Motor and Interactive Animation

The Workings of a DC Motor
By David Urmann

Electric motors are all around us. In our homes alone, nearly all mechanical and electrical movement you see around is brought about by a DC (direct current) electric motor and AC (alternating current) electric motor.

It was in 1873 that Zénobe Gramme created the contemporary DC electric motor. Gramme linked his devised dynamo to another apparatus and steered it like a motor. His invention, the Gramme device, was the first electric motor that pulled off in the field.

Two good examples of electric DC inventions are the innovative ball-bearing motor and the unusual homo polar motor that Michael Faraday created.

In general, a simple DC electric motor consists of six basic parts. These are the rotor or armature, brushes, axle, commutator, field magnet, and DC power supply. An electric motor is powered by magnets that employ magnet fields to produce torque, setting the motor in motion. Those who previously played with magnets are familiar with the elementary principle of magnets, that similar poles repel and opposites attract. The repelling and attracting electromagnetic forces inside an electric motor make the DC motor to create rotating motion.

Magnets are polarized, with a negative and a positive section. Even with comparatively puny magnets, the repulsion of like poles and the attraction of opposite poles are evident. Direct current electric motor utilizes these components to virtually transform electrical current into shifting movement.

A DC electric motor needs at least one electromagnet. An electromagnet serves as the source of an electric motor and it changes the electricity flow as the motor moves, altering its polarization in order to maintain the operation of the motor. The other magnetic fields are either electromagnets or permanent magnets. The electromagnet is typically to be found in the motor's hub and rotates in the permanent magnets.

A DC electric motor features coils of wire that go around in a magnetic field. The coil is placed in a fixed magnet. The electric flow in the coil is delivered by means of two brushes that produce moving connections with a split ring. The forces applied on the coils of wire initiate for a movement or torque on the coil. The coil also acts as a tiny magnetic dipole.

To better understand and imagine a simple DC electric motor, picture a wheel split into two between two magnets. In this case, the DC motor's wheel is the electromagnet. The two permanent outer magnets are the negative and the positive. Now, suppose that the right magnet is positive and the left magnet is negative.

The coils of wire on the wheel of the DC motor are being brought in with electric flow and this current ignites a magnetic drive. In order to cause the DC motor to twist and more, the wheels on the permanent positive magnet have to be positively charged and the negative permanent magnet have to be negatively charged as well. And, since opposite charges attract and similar charges repel, the wheel shifts in order for its negative piece turns over around to the right and the positive section of the wheel moves to the left. The magnetic force enables the wheel to spin thus, the movement is utilized to perform and operate.

The consistency and straightforward pattern of DC motors make it an ideal option for countless various purposes. DC motors are largely employed for multiple applications such as remote control cars and electric razors.

For more information on DC Electric Motors and Online Electric Motor Repair Advice please visit our website.

Article Source: _http://EzineArticles.com/?expert=David_Urmann

DC Motors Principles of operation and interactive animation
In any electric motor, operation is based on simple electromagnetism. A current-carrying conductor generates a magnetic field; when this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite (North and South) polarities attract, while like polarities (North and North, South and South) repel. The internal configuration of a DC motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion.
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AC Motor Calculation

AC Motor Calculation

Calculate the Full Load Current of AC Motor

INDUCTION MOTORS ANALYSIS

Equivalent circuits of three-phase induction motor

Estimation of Induction Motor Parameters

Estimation of Induction Motor Parameters Program

Power and Efficiency

Power flow in an Induction motor

Losses and Efficiency of Induction Motor

Program

Calculation Equivalent of induction motors program

Guidelines For Performing Infrared Inspections Of Motor Control Centers

By Josh L. White

The Motor Control Center

The MCC enclosure protects personnel from contact with current carrying devices, and it protects the components from various environmental conditions. It is important that the enclosure is mounted to assure accessibility so that qualified personnel (such as a trained thermographer) can open the panel under load. There are different classes and types of MCCs, but generally speaking, an MCC looks like a row of file cabinets with each cabinet representing an MCC section. The drawers of the file cabinet represent the plug-in units that contain the motor control components. Three phase power is distributed within the MCC by bus bars, large metal current carrying bars. The horizontal bus provides three-phase power distribution from the main power supply. Vertical bus in each section is connected from it to individual MCCs. Bracing and isolation barriers are provided to protect against fault conditions. The plug-in units of an MCC have power stabs on the back to allow it to be plugged into the vertical power bus bars of the structure.

Beginning Your MCC Infrared Inspection

Before opening the panel or door on a motor controller, prescan the enclosure to assure a safe opening condition. If excessive heat appears on the surface of the door, extra care should be taken when opening it. The thermographer or escort may decide to note the condition as unacceptable and not take a chance on opening it under load. Once the unit is open, begin with both an infrared and a visual inspection to assure no dangerous conditions exist. Be systematic while conducting the infrared inspection. Remember the system must be under load to conduct the inspection. Work from left to right or follow the circuit through carefully, inspecting all of the components. Look for abnormal thermal patterns caused by high-resistance connections, overloads, or load imbalances. In three-phase systems this can be accomplished by comparing phases. Adjust the level and span on the infrared system to optimize the image. Proper adjustment will identify primary and secondary anomalies. The bus stabs and the connections to the main are important inspection points that are often overlooked or misdiagnosed. The incoming connection to the main horizontal bus is usually located behind a cover or panel that is not hinged. These are typically bolted connections and may have parallel feeders. The bus stab connections on the back of the plug-in units are more difficult to inspect. The thermographer does not have direct view of the connection, and the first indication of a problem can be seen on the incoming conductors feeding the breaker or fused disconnect. Remember, even small temperature rises identified at this point could mean serious problems.

Motor Starters and Motor Controllers

The purpose of the motor starter is to protect the motor, personnel, and associated equipment. Over 90% of the motors used are AC induction motors, and motor starters are used to start and stop them. A more generic term would identify this piece of equipment as a motor controller. A controller may include several functions, such as starting, stopping, overcurrent protection, overload protection, reversing, and braking. The motor starter is selected to match the voltage and horsepower of the system. Other factors used to select the starter include: motor speed, torque, full load current (FLC), service factor (SF), and time rating (10 or 20 seconds).

Understanding the thermal patterns of this equipment is critical to a successful inspection. Also correctly identifying the source of the anomaly can make recommendations more valuable.

Motors may be damaged or their life significantly reduced if they operate continuously at a current above full load current. Motors are designed to handle in-rush or locked rotor currents without much temperature increase, providing there is a limited duration and a limited number of starts. Overcurrents up to locked rotor current are generally caused by mechanical overloading of the motor. The National Electric Code (NEC) describes overcurrent protection for this situation as "motor running overcurrent (overload) protection." This can be shortened to overload protection. Overcurrents caused by short circuits or ground faults are dramatically higher than those caused by mechanical overloads or excessive starts. The NEC describes this type of overcurrent protection as "motor branch-circuit short-circuit and ground-fault protection." This can be shortened to overcurrent protection. The four common varieties of motor starters are: across-the-line, the reversing starter, the multispeed starter, and the reduced voltage starter. Motor starters are generally comprised of the same types of components. These include a breaker or fused disconnect, contactor and overloads. There may also be additional components, including control circuitry and a transformer. Understanding the thermal patterns of this equipment is critical to a successful inspection. Also correctly identifying the source of the anomaly can make recommendations more valuable.

Overcurrent Protection

NEC requires overcurrent protection and a means to disconnect the motor and controller from line voltage. Fused disconnects or thermal magnetic circuit breakers are typically used for overcurrent protection and to provide a disconnect for the circuit. A circuit breaker is defined in NEMA standards as a device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself when properly applied within its rating. If we look at a cutaway of a breaker, we can identify potential connection problems. The line side and load side lugs are the most common source of abnormal heating, but many breakers have a second set of bolted connections on the back of the breaker. Heat from this connection can be misdiagnosed as the main lug. There are also internal contacts where current flow is interrupted by exercising the component. These contacts experience arcing each time the breaker is opened. An arc is a discharge of electric current jumping across an air gap between two contacts. Arcs are formed when the contacts of a circuit breaker are opened under a load. Arcing under normal loading is very small compared to an arc formed from a short circuit interruption. Arcing produces additional heat and can damage the contact surfaces. Damaged contacts can cause resistive heating. Thermal patterns from these poor connections appear as diffuse heating on the surface of the breaker. In addition, there are several types of breakers that have internal coils used for circuit protection. These coils have heat associated with them and can appear to be an internal heating problem, when in fact, it is a normal condition.

Fused Disconnects

Fused disconnects are used to provide over-current protection for motor in the same manner as a breaker. Instead of opening contacts, fuses fail opening the circuit. When overcurrent protection is provided by fuses, a disconnect switch is required for manual opening of the circuit. The disconnect switch and fuse block are typically one assembly. The hinge and blade connections on the switch are a typical source of overheating. High resistance from overuse or underuse is usually the cause. Fuse clips are also a weak connection point for some disconnect designs. Different types or manufacturers of fuses of the same amperage may produce different thermal signatures. While different size or amperage fuses will also have a different thermal pattern, fuse bodies may appear warmer than the rest of the circuit due to conductor size.

Contactors

Starters are made from two building blocks, contactors and overload protection. Contactors control the electric current flow to the motor. Their function is to repeatedly establish and interrupt an electrical power circuit. A contactor can stand on its own as a power control device, or as part of a starter. Contactors operate electromechanically and use a small control current to open and close the circuit. The electromechanical components do the work, not the human hand, as is the case with a knife blade switch or a manual controller. The sequence of operation of a contactor is as follows: first, a control current is applied to the coil; next, current flow into the coil creates a magnetic field which magnetizes the E-frame making it an electromagnet; finally, the electromagnet draws the armature towards it, closing the contacts. A contactor has a life expectancy. If the contactor contacts are frequently opened and closed, it will shorten the life of the unit. As the contacts are exercised, an electrical arc is created between the contacts. Arcs produce heat, which can damage the contacts. Contacts eventually become oxidized with a black deposit. This black deposit may actually improve the electrical connection between the contacts by improving the seat, but burn marks, pitting, and corrosion indicate it is time to replace the contacts. The following thermal patterns are associated with contactors. The coil of the contactor is usually the warmest part of the unit. High temperatures may indicate a breakdown of the coil. Line side and load side lug connections may show high resistance heating from poor connections. Heating from burned and pitted contacts may be thermally "visible" on the body of the contactor.

Overload Protection

The ideal motor overload protection is a unit with current sensing capabilities similar to the heating curve of the motor. It would open the motor circuit when full load current is exceeded. Operation of this device would allow the motor to operate with harmless temporary overloads, but open up when an overload lasts too long.

Typical thermal problems in overloads are found in the connections to the contactor, overload relay, or motor.

This protection can be provided by the use of an overload relay. The overload relay limits the amount of current drawn to protect the motor from overheating. It consists of a current sensing unit and a mechanism to open the circuit. An overload relay is renewable and can work for repeated trip and reset cycles. Overloads, however, do not provide short circuit protection. The melting alloy (or eutectic) overload relay consists of a heater coil, a eutectic alloy, and a mechanical mechanism to activate a tripping device when an overload occurs. The relay measures the temperature of the motor by monitoring the amount of current being drawn. This is done indirectly through a heater coil, which under overload conditions, melts a special solder allowing a ratchet wheel to spin free and open the contact. A bimetallic thermal overload uses a U-shaped bimetal strip. In an overload condition heat will cause the bimetal to deflect and open a contact. The solid state overload relay does not generate heat to cause a trip. Instead, it measures current or a change in resistance. The advantage of this method is that the overload relay doesn't waste energy generating heat and doesn't add to the cooling requirements of the panel. Normal heating for an overload may look like a thermal anomaly. Heat generated in the coil or bimetal may look like a connection problem. Typical thermal problems in overloads are found in the connections to the contactor, overload relay, or motor.

Starters

Starters are the combination of a controller, usually a contactor and an overload relay. The above descriptions of the individual components apply to the starter systems. Reduced voltage starters are used in applications that involve large horsepower motors. They are used to reduce the in-rush current and limit the torque, and thus the mechanical stress on the load. The components of this type of starter should be inspected as the motor steps up to speed. A separate low-voltage starter circuit is used to step the motor up to speed. Once at operating speed, these components are de-energized.

Completing Inspections

Remember that primary anomalies are the problems that readily stand out while secondary anomalies may require that primary anomalies be adjusted into saturation to allow for the identification of a secondary anomaly. For example, different fuse types and sizes will cause different thermal signatures as will overload relays that are sized differently within the same circuit. Anomalies like this should be identified and reported. Also note that when evaluating the severity of a problem, temperature is just one variable. All of the parameters involved with the severity of the anomaly should be considered. To improve temperature measurements, avoid low emissive surfaces. Look for cavity radiators or highly emissive insulation on conductors. Measure loads where component sizing, overloading, or load imbalances are observed. Beware of the effects of wind or convection on components. Note ambient temperatures, large thermal gradients, and the source of heating. Safety should be the top consideration.

Conclusion

Knowing the equipment under inspection allows for the correct identification of problems that could be misdiagnosed or overlooked. Analyzing unfamiliar thermal patterns on a component is easier when equipment design is reviewed. More precise repair recommendations can also be made. Locating temperature differences qualitatively or quantitatively is the real benefit of infrared thermography. Knowing where to look for these temperature differences comes from knowledge of the equipment, and knowledge of the equipment will make a better thermographer.

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The Difference Between AC and DC Electric Motors

The Difference Between AC and DC Electric Motors
By John Francis

There are two main types of electric motors. There are direct current or DC and alternating current or AC motors. The reference of DC or AC refers to how the electrical current is transferred through and from the motor. Both types of motors have different functions and uses. Dc motors come in two general types. They can have brushes or be brushless. AC motors, as well, come in two different types. They can be two phase or three phase. The differences in DC and AC motors are sometimes subtle, but these differences are what make one types better for a certain use.

Direct current or DC electric motors work for situations where speed needs to be controlled. DC motors have a stable and continuous current. DC motors were the first and earliest motors used. They were found, however, to not be as good at producing power over long lengths. Electric companies found using DC motors to generate electric did not work because the power was lost as the electric was transmitted. Brush DC motors use rings that conduct the current and form the magnetic drive that powers the rotor. Brushless DC motors use a switch to produce the magnetic drive that powers the rotor. Direct current motors are often found in appliances around the home.

Alternating current or AC electric motors are used differently based on what type of AC motor it is. Single phase AC motors are known as general purpose motors. They work well in many different situations. These AC motors work great for systems that are hard to start because they need a lot of power up front. Three phase, also called polyphase, AC motors are usually found in industrial settings. These motors also have high starting power built transmit lower levels of overall power. AC power gets its name from the fact that it alternates in power. The amount of power given off by an AC motor is determined by the amount of power needed to operate the system.

DC and AC electric motors are found everywhere from the home to the car to industrial plants. Motors are important to everyday life. Dc motors were introduced and caused a great revolution in the way many things are done. When AC motors came on the market the way motors were looked at changed because of their amazing starting power potential. DC motors and AC motors are different in many ways, but they still both are usede to power the world. http://electricmotors-hq.com Everything you need to know about electric motors from their history to buying new and used.
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Differences in AC Motor Controls

Differences in AC Motor Controls
By Mike Imprixis

Every AC motor needs to be accompanied with an efficient motor controller to ensure proper functioning. Installing such a control system can prove to be beneficial as it can serve you in a number of ways. It may include a single device or a group of devices that manage the entire working of the motors in a preset manner.

These efficient motor controllers have different functionalities for different motor types. AC induction motors primarily induce current into the rotor windings without being physically connected to the stator windings. The induction motor drives uniquely feature electrical isolation and self-protection against faults. They usually comprise a device programmer, in-circuit debugger, motor control development board, a high voltage motor and a 3-phase or 1-phase high voltage power module. Usually, most of the industrial applications call for three-phase windings. This is because these motors allow variable speed control and considerable power in any kind of setting.

Sophisticated AC motor controllers are commonly referred to as motor drives. They balance the signal type with the control signals. The signal type is either analog or digital like power and voltage signals. The controllers can also work for power conversion, increasing the signal waves and sequencing the waveforms. You can fit in these motor drives in diverse types of AC motors.

The synchronous motors are those, which operate at a constant level of speed up to the full load. They do not slip in order to produce torque. These motors are driven by inverter controllers and feature a huge list of functions such as electro-mechanical braking, electronic power assisted steering, motor torque regulation, and many more. You can choose them for several industrial and automotive applications, so as to ensure the highest productivity for your machines.

Among the extensive collection of AC motor controls, the vector drive motors can control both the voltage and the frequency in an independent way. This eventually results in low-torque turnouts. The pole changing motor controls, suited to the synchronous AC motors, takes care of the pole number. This is a way to alter the number of poles in the primary winding.

Another variety of synchronous motor control includes the AC servo motor controls that make use of brushless commutation with necessary feedback. The most prevailing technologies utilize the concepts of moving coil, switched reluctance designs and moving magnets. You need to study your requirements well in order to purchase the most suitable controls for your motors. Some of the designs use encoders and resolvers to get adequate feedback regarding speed and position.

Inverter drives constitute a very common type of motor control system. They convert inputs in AC power to outputs with DC power. Again, if you require motor controls with very high frequency, then you can choose from a wide array of high frequency drives. These drives are used to supply power to the AC motors at substantially high frequency, as compared to the common power applications. You can also opt for the variable speed drives that serve you by adjusting and controlling the speeds of your motors.

An AC motor performs optimally through the controlled usage of electric power and sufficient savings on the expenditure of the owners. These motors were invented for the purpose of applying the system of alternate current transmission, in order to give an overall voltage control. If you own a medium or big cap factory, installing these motors can be quite cost saving. They provide efficient generation and distribution of electric power over long distances.

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Running 3-phase motors with 1-phase

Three-phase motors will run on single phase as readily as single
phase motors. The only problem for either motor is starting.
Sometimes 3-phase motors are purchased for use on single phase
if three-phase provisioning is anticipated. The power rating needs
to be 50% larger than for a comparable single phase motor to
make up for one unused winding. Single phase is applied to a pair
of windings simultanous with a start capacitor in series with the
third winding. The start switch is opened in Figure below upon
motor start. Sometimes a smaller capacitor than the start capacitor
is retained while running.

Starting a three-phase motor on single phase.

The circuit in Figure above for running a three-phase motor on
single phase is known as a static phase converter if the motor
shaft is not loaded. Moreover, the motor acts as a 3-phase
generator. Three phase power may be tapped off from the three
stator windings for powering other 3-phase equipment. The
capacitor supplies a synthetic phase approximately midway 90o
between the 180o single phase power source terminals for
starting. While running, the motor generates approximately
standard 3-φ, as shown in Figure above. Matt Isserstedt shows
a complete design for powering a home machine shop.

Self-starting static phase converter. Run capacitor = 25-30µF per HP.

Adapted from Figure 7, Hanrahan

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Losses and Efficiency of Induction Motor

A. Definition of energy efficiency

Efficiency is the ratio of mechanical energy output divided by
the electrical energy input. There are different efficiency definitions
that describe the relationship between a motor’s rating and
efficiency test results:

- Tested. This refers to the efficiency measured by testing that
specific motor.

- Nominal or Average Expected. Nominal values are the average
values obtained after testing a sample population of the motor model.

- Nameplate. This refers to the efficiency measured by a specific
standard.

- Minimum. These values are intended to represent the lowest point in
the bell curve of motor efficiency distribution.

- Apparent Efficiency. This is the product of a motor’s efficiency and
power factor.

Figure 2.1 – Typical energy flow of standard motors

B. Motor Losses
Energy losses are the determining factor in motor
efficiency. These losses can be divided in five classes:

Classes of Motor Energy Losses

The main difference between the standards emerges
from the way in which the additional load losses, is
treated. The IEC 34.2 standard assumes a standard value
for the additional load losses at rated load of 0.5% of the
input power. The new proposed IEC 61972 standard
gives two possibilities for the assessment of the
additional losses. The first one is a determination by
means of the measured output power, as in the IEEE 112-
B; the second one gives a fixed amount to every machine
of the same rated power. The Japanese JEC standard 37
completely neglects the additional load losses.

Source
http://www.icrepq.com/icrepq-08/352-mantilla.pdf

Paper

Genetic Algorithms in Induction Motor Efficiency

Determination

Many current techniques of calculating induction motor efficiency

are difficult, expensive, or inaccurate in the field. Induction motors

consume a large percentage of the electricity used in the US.

Accurate calculations of the efficiency of these motors would allow

savings in both energy and cost. One major obstacle in the

calculation of efficiency is that it is often difficult to measure the

output power accurately and safely while the motor is running,

say in a factory. It would be of interest to find a way to estimate

the output power using only easily measured quantities, such as

input current and voltage.

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Effective Estimation of Induction Motor Field Efficiency

Based on On-site Measurements
ABSTRACT
This paper proposes the effective technique for
estimating efficiency of existing three-phase induction
motors in the field. This technique focuses on the
operating efficiency of motors without the need for
removing the motors and without the need for measuring
the output power or torque. This paper describes the use
of a few sets of data (voltage, current, power, speed)
measured from the motor (on-site) coupled with the
genetic algorithms for evaluating the motor parameters
instead of using the no-load and blocked rotor test results.
Once these parameters are known it is possible to obtain
the estimated efficiency of the motor. To illustrate how
well the estimated efficiency match that of the calculated
obtained from the standard evaluations, the results of
various induction motors rating 10 up to 100 hp are
presented. Test results indicate that this proposed
technique has a high accuracy, and then it could be
suitable for conducting on-site energy audits of existing
motors in order to support a decision to replace operating
motors with a higher-efficiency model.

more pdf

Power flow in an Induction motor

The exact equivalent circuit model of an Induction motor is

where

R1 is the stator resistance per phase

X1 is the stator reactance per phase

R2' is the equivalent rotor resistance referred to stator per phase

X2' is the equivalent rotor reactance referred to stator per phase

Rc is the resistance representing core losses

Xm is the magnetizing reactance per phase

V1 is the per phasesupply voltage to the stator
s is the slip of the motor

Power flow in an Induction motor

From the circuit, we see that the total power input to the rotor Pg is
The power flow diagram is-

Source
http://powerlearn.ece.vt.edu/modules/PE2/index.html

How the efficiency of induction motor is measured?

Abstract
The efficiency is of paramount importance nowadays due
to increasing electrical energy demand, increasing awareness of
environmental problems as greenhouse effects and increasing
fossil fuel prices.

This paper tries to show the different results between the
standards for efficiency evaluation and the necessity of
harmonization worldwide. Then, it is going to be explained the
different standards for measurement of efficiency, and the main
differences between the standards (IEEE 112, IEC 60034-2 and
JEC-37).

To complete this study, it is going to be described the steps
in order to estimate efficiency on the jobsite and expressed the
different efficiency labels motors.

Figure 2.1 – Typical Power flow of standard motors

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