Different types of Induction Motor

Different types of Induction Motor

SINGLE PHASE INDUCTION MOTOR

1.    Split phase induction motor

There are various types of self-starting motors, known as split phase motors. Such motors have a starting winding displaced 90 electrical degrees from the main or running winding. In some types, the starting winding has a fairly high resistance, which causes the current in this winding to be out of phase with the current in the running winding. This condition produces, in effect, a rotating field and the rotor revolves. A centrifugal switch disconnects the starting winding automatically, after the rotor has attained approximately 25 percent of its rated speed.

2.    Capacitor start induction motor

With the development of high capacity electrolytic capacitors, a variation of the split phase motor, known as the capacitor start motor, has been made. Nearly all fractional horsepower motors in use today on refrigerators, oil burners, and other similar appliances are of this type. In this adaptation, the starting winding and running winding have the same size and resistance value. The phase shift between currents of the two winding is obtained by using capacitors connected in series with the starting winding.

3.    Capacitor start capacitor run induction motor

A variation of the capacitor-start motor 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.

4.    Shaded pole induction motor

The first effort in the development of a self-starting, single phase motor was the shaded pole induction motor. This motor has salient poles, a portion of each pole being encircled by a heavy copper ring. The presence of the ring causes the magnetic field through the ringed portion of the pole face to lag appreciably behind that through the other part of the pole face. The net effect is the production of a slight component of rotation of the field, sufficient to cause the rotor to revolve. As the rotor accelerates, the torque increases until the rated speed is obtained. Such motors have low starting torque and find their greatest application in small fan motors where the initial torque required is low. 

THREE PHASE INDUCTION MOTOR

5.    Squirrel cage induction motor

Three-phase squirrel-cage motor are made of squirrel cage rotor in which copper bar are used and shorted at both end by copper ring. Three-phase squirrel-cage induction motors are widely used in industrial drives because they are rugged, reliable and economical.

6.    Slip ring induction motor

A wound-rotor motor is a type of induction motor where the rotor winding are connected through slip rings to external resistances. Adjusting the resistance allows control of the speed/torque characteristic of the motor. Wound-rotor motors can be started with low inrush current, by inserting high resistance into the rotor circuit; as the motor accelerates, the resistance can be decreased.

Compared to a squirrel-cage rotor, the rotor of the slip ring motor has more winding turns; the induced voltage is then higher, and the current lower, than for a squirrel-cage rotor. During the start-up a typical rotor has 3 poles connected to the slip ring. Each pole is wired in series with a variable power resistor. When the motor reaches full speed the rotor poles are switched to short circuit. During start-up the resistors reduce the field strength at the stator. As a result the inrush current is reduced. Another important advantage over squirrel-cage motors is higher starting torque.

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Why LT motors are delta connected and HT motors are star connected?

Why LT motors are delta connected and HT motors are star connected?

• There is both reason technical and commercial.

1.     In star, phase current is same as line current. But phase voltage is 1/1.732 times line voltage. So insulation required in case of HT motor is less.

2.     The starting current for motors is 6 to 7 times full load current. So start-up power will be large if HT motors are delta connected. It may cause instability (voltage dip) in case small Power system. In starred HT motor starting current will be less compared to delta connected motor. So starting power is reduced. Starting torque will also be reduced. (It will not be a problem as motors are of high capacity.)

3.    Also as current is less copper (Cu) required for winding will be less.

4.    LT motors are delta connected.

1.    Insulation will not be problem as voltage level is less.

2.    Starting current will not be problem as starting power in all will be less. So no problem of voltage dips.

3.    Starting torque should be large, as motors are of small capacity.

LT motors have winding delta connected.

1. In case it is having star delta starter than they are started as Star connected motor.

2. After it attains 80% of synchronous speed the changeover takes place from star to original configuration    delta.

3. In star the voltages across the winding are lesser that is 1/1.732 times that available in delta so current    is limited.

4. When it goes to delta again voltage is full line voltage so current increase even though it is lesser than     the line current it remains higher than the line current drawn in star connection at reduced voltage. So       cables for motor are sized for this current that is what it draws in delta connection.

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Brief Idea of Induction Motor

Brief Idea of Induction Motor

Induction motor: is an energy conversion device that converts electrical energy into useful rotational kinetic energy, it is an application of the Faraday's law of induction.

Sectional View

3-ph Induction Motor

 

Drawing of Induction Motor

Induction motor are the most commonly used motors in many applications. These are also called as Asynchronous Motors, because an Induction motor always runs at a speed lower than synchronous speed. Synchronous speed means the speed of the rotating magnetic field in the stator.

An Induction motor has basically two parts – Stator and Rotor

The Stator is made up of a number of stamping with slots to carry three phase winding. It is wound for a definite number of poles. The winding are geometrically spaced 120 degrees apart. Two types of rotors are used in Induction motors - Squirrel-cage rotor and Wound rotor. 

 

A squirrel-cage rotor consists of thick conducting bars embedded in parallel slots. These bars are short-circuited at both ends by means of short-circuiting rings.

A wound rotor has three-phase, double-layer, distributed winding. It is wound for as many poles as the stator. The three phases are wyed internally and the other ends are connected to slip-rings mounted on shaft with brushes resting on them. The brushes are connected to an external resistance that does not rotate with the rotor and can be varied to change the N-T characteristics. 

In fact an Induction motor can be compared with a transformer because of the fact that just like a transformer it is a singly energized device which involves changing flux linkages with respect to a primary(stator) winding and secondary(rotor) winding.

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Air Insulated Switch-gear VS Gas Insulated Switch-gear

Air Insulated Switch-gear VS Gas Insulated Switch-gear

Gas Insulated Switch-Gear

Air Insulated Switch-Gear

Limitations of Air Insulated Switchgears (AISs)

• Large dimensions due to statutory clearances & poor dielectric strength of air
• Insulation deterioration with ambient conditions and susceptibility to pollutants
• Wastage of space above
• Life of steel structures
• Seismic instability
• Large planning and execution time
• Grounding-mat is essential for containing touch and step potentials
• Hot line washing and regular maintenance of the substation is essential, requires more spares inventory and man-power

Advantages of GISs over AISs

• Compact space-saving design
• Minimal operating cost
• Minimal weight by lightweight construction
• Safe encapsulation
• Environmental compatibility
• Economical transport
• Reliability
• Smooth and efficient installation and commissioning

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Every Challenge Is An Opportunity

Edison, one of Europe’s oldest power companies, which was founded in 1884 in Milano, owns the Fontanamora hydroelectric plant that generates three megawatts (MW) of renewable power from turbines and auxiliary machinery. The plant is situated at Lombardy by a fast-flowing river at the bottom of a steep gorge. Lombardy lies in the north of the country, sharing a border with Switzerland.

As the second energy company in Italy, and a European leading operator with operations in the supply, production and sales of electric power and hydrocarbons (natural gas and crude oil), Edison has a strong focus on renewable generation. It has 7.7 giga watts (GW) of installed renewable capacity, comprising hydroelectric, wind, solar, thermometric plants and a biomass system.

The challenge

At the beginning of 2013, Edison decided to undertake a complete revamp of the plant, with the project including also the step-up of the voltage level of connection to the electricity grid, from medium to high voltage. The customer decided to replace the previously installed switch gear with a new product featuring the latest in switching technology: ABB's PASS hybrid switch gear module, rated at 72.5 kilo volts (kV).

The project was challenging both technically and from an installation perspective, as access to the powerhouse is only possible by way of a steep, narrow stairway down the side of the gorge. Entrance to the powerhouse is small, and the room available for installing switch gear is only three square meters wide.

Solution with innovative design

To cope with these difficult space challenges, ABB leveraged its expertise in switch gear design to supply a hybrid module that integrates a circuit breaker and two dis-connectors, plus current and voltage transformers – and the control and protection relay in a single unit. 

Plug-in cable terminals instead of traditional air-insulated bushings were deployed to further reduce the module's size, enabling it to fit it in the reduced space of the Fontanamora powerhouse.

Innovative logistics

To overcome the narrow stairway and minimise transport risks, the installation team secured the PASS hybrid module with special harness straps – and lowered it down into the gorge with a crane. The preassembled unit arrived on site pretested for high-voltage and ready for installation, which took four days. There was no need for the additional equipment typically needed to perform on-site high-voltage tests, so the ABB PASS hybrid module could be put into service without delay, saving time and costs.

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RENEWABLE ENERGY DEMAND IN EUROPE REACHES RECORD LEVELS

RENEWABLE ENERGY DEMAND IN EUROPE REACHES RECORD LEVELS

The demand for renewable electricity in Europe, documented with Guarantees of Origin (GO), continued to grow in 2015. The growth is up more than 8% from 2014 and surpassed 340 TWh. Behind this growth are thousands of businesses and millions of households in numerous European countries – voluntarily purchasing renewable electricity documented with Guarantees of Origin.

The market has seen a steady increase in national participants but is still dominated by a select number of countries. The five countries that consume the most renewable energy are Germany, Sweden, Switzerland, the Netherlands and Italy. Together they demand ¾ of the renewable energy used in Europe. The Netherlands is the fastest growing market. From 2014 to 2015 it has grown by a brisk 12%, and consumed more than 42.5 TWh in 2015. Germany is still the largest market with a total volume of 87 TWh in 2015.

The marketplace for Guarantees of Origin is steadily growing in terms of countries, with more than 20 countries actively working with AIB (Association of Issuing Bodies) and fully using EECS, the common European market standard.

Norway, Austria, Finland, Denmark, France and Belgium today make up the next group of countries – each with a steady market demand between 10 and 35 TWh annually. The rest of the national markets are still fairly immature, and together represent only a smaller share of the total market demand.

The AIB statistics include only GOs based on the EECS standard. There are still countries with national certificate markets that have yet to adopt the EECS standard. These markets total more than 100 TWh of additional market demand. This pushes the actual market volume beyond 440 TWh.

United Kingdom and Spain – will they join the European market in 2016?

The development in 2015 follows a record-breaking 2014, during which the market experienced a 27.6 % growth and an all-time high, 314 TWh demand for renewable electricity. Moreover, for the first time since 2011, there was a real balance between supply and demand.

With the UK, Spain and a few smaller countries considering joining AIB, and adopting the EECS standard, there is much discussion and uncertainty concerning how this will affect the market. Both the UK and Spain are countries with a sizable renewable energy generation, as well as a corporate sector that can have strong demand for renewable energy. Wholesale prices have risen significantly the last part of 2015. The question market-players and consumers are voicing is “Will the inclusion of new markets give additional push to the upward price development?”

The European demand for renewable electricity documented by Guarantees of Origin now constitutes more than 13% of all electricity consumption in Europe (ca. 3,200 TWh) and approximately 40% of all electricity generated from renewable sources in Europe (ca. 1,100 TWh).

The above is a commentary based on figures published by AIB (Association of Issuing Bodies).

ECOHZ offers renewable energy solutions to electricity providers, businesses and organizations across Europe, North America and Asia – providing renewable electricity, from a wide range of sources, regions and qualities. Renewable electricity is documented by Guarantees of Origin in Europe, RECs and Green-e in the US, and International RECs (I-REC) in selected Asian markets. ECOHZ also provides a new and innovative solution – GO² – combining renewable energy purchases with the financing and building of new renewable power generation. Companies choosing documented renewable energy can reduce their carbon footprint and improve their sustainability ratings. ECOHZ is among the leading independent suppliers in Europe, and is located in Norway and Switzerland. ECOHZ endeavors to play an active role in the current energy transition through its vision of “changing energy behavior”.

For more information see: http://www.ecohz.com

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