Tuesday, 24 February 2015

Basics of making transformer (part-2)

A transformer transforms voltage and current. But the total electrical input and total energy output is almost same. Some losses are there ( core loss, iron loss etc).
We know that the power is the product of voltage and current(p=v*i).
The relation between primary voltage and secondary voltage is
V1/v2=i2/i1=n1/n2
An actual/theoretical transformer has no loss. But in practical there are several types of losses in transformer. In this page I am dealing with practical transformer making, so we will neglect the loss or take the loss as a predefined constant value.
Basic construction of transformer-
In
General transformers are mainly of two types.
1.Core type
2.shell type
the core of the transformer is mainly made from E and I shape iron plates






Sunday, 22 February 2015

Why transformer rating in KVA or VA?

Why transformer rating in KVA or VA?
Copper loss of a transformer depends on current and iron loss depends on voltage. So, total transformer load depends on voltage-ampere (VA) and not on phase angle between voltage and current.  
It is independent of load power factor.
transformers are used for different types of loads of different power factors. like for lighting purpose it runs almost in unity power factor ,then volt-ampere rating and watt rating is almost same. but for inductive load like motors transformer runs on lagging power factor.here watt rating is less than volt-ampere rating. transformer manufacturers do not know where the transformer will be used. so they give V-A rating, by multiplying it with the corresponding power factor we cal get watt.
This is why rating of transformers is in KVA not in KW.

What should you do when your fan’s capacitor/condenser is not working?

What should you do when your fan’s capacitor/condenser is not working?
We all know that our fan is a single phase AC induction motor. As there is no rotating magnetic field in single phase, single phase motors are not self starting. To solve this problem we temporarily we convert it into a two phase induction motor during starting. For this purpose, the stator of a single phase induction motor is provided with an extra starting winding, called auxiliary winding. The starting winding and the running winding are spaced 90 degree electrically apart from each other. There is a phase difference between starting and running winding current, that is ideally 90 degree. Here capacitor mainly creates that phase difference.
Now suppose your fans capacitor is not working and you don’t have a new one in your lab. Then what should you do?
Method 1- in a split phase motor, running winding has less resistance and more reluctance and starting winding has high resistance and low reluctance. So you put a resistance of high wattage value in series with the starting winding. Then starting winding current lags the voltage with a small angle and running winding current lags with voltage by a large angle. So, a phase difference is created. The motor becomes self starting.
Note- if the wattage value is less the resistor may burnt out.

Make the rotation reversed of your fan

Make the rotation reversed of your fan
Sometimes it happens that we need to change the blades of fans. If the new one is not similar with the original one, it can not draw air. It draws air if it is moved in opposite direction. here we need to reverse the rotation o the fan.
We all know that our fan is a single phase AC induction motor. As there is no rotating magnetic field in single phase, single phase motors are not self starting. To solve this problem we temporarily we convert it into a two phase induction motor during starting. For this purpose, the stator of a single phase induction motor is provided with an extra starting winding, called auxiliary winding. The starting winding and the running winding are spaced 90 degree electrically apart from each other. There is a phase difference between starting and running winding current, that is ideally 90 degree. Here capacitor mainly creates that phase difference.
So for reversing the single phase induction motor we need to reverse the connection of capacitor. 

thank you very much

Basics of stepper motor

Basics of stepper motor
A stepper motor is a widely used device that converts electrical pulses to equivalent mechanical movement with high accuracy.
A stepper motor is widely used in disk drivers ,dot matrix printers , robotics and many other automatic applications.
Construction-
Stepper motor has a permanent magnet rotor that is also called shaft. The most common stepper motor has four stator winding and they are paired with a center-tapped common.
These types of motors are generally called “four phase stepper motor”.  Centre tap needs to change the direction of current flow in each two coils when a winding is grounded. This change in direction in current in stator coil changes the polarity of electromagnetic stator. It helps to control the direction of movement of shaft. 


A conventional motor runs freely, but in stepper motor the shaft moves in a fixed repeatable increment which allows one to move it to a precise position. This repeatable fixed movement is possible by using basic electromagnetic theory. same polarity repel and opposite poles attract. This direction of the rotation is dictated by the stator poles. 

Resolution of a stepper motor- resolution of a stepper motor describes how perfectly the motor can move it’s shaft at a predefined angle. For demonstration purpose we show four stator winding. But practically a good stepper motor has much more number of field winding. Increase in number of field winding increases the resolution of a stepper motor. for example , if a stepper motor having resolution of 5 degree, that means motor shaft moves 5 degree for each pulse. For one full rotati
on of 360 degree 72 pulses needed.
Types of stepper motor
Variable reluctance stepper motor (It has a wound rotor and a stator made of ferromagnetic material. Direction of motor rotation is independent of stator current. Reluctance of the magnetic circuit formed by the stator and rotor varies with the angular position of the rotor. So it is called variable reluctance stepper motor)
Permanent magnet stepper motor(it’s stator is wounded and the rotor is permanent magnet. It has a cylindrical rotor. The direction of the rotor depends on the direction of the stator current)
Hybrid stepper motor ( it has wound stator and permanent magnet rotor. It is best suitable for small step angles like 1.8 degree)
Controlling movement of stepper motor- to control movement of stepper motor microcontroller is mainly used.


 We will use arduino to control the stepper motor in next projects.
Thank you for reading.
Post written by Abhijit Maity

Friday, 20 February 2015

why should we use Three phase electric power system

Three phase electric power system is a very popular and efficient method of electric power generation, transmission, and distribution also. Most of the industries from medium to a larger one is powered by three phase power supply. The most common question that everyone asks that what is the advantages of three phase power supply over single phase power supply? 

Why we need a “Three phase Power supply”?
1.A three phase power system has higher efficiency than a single phase power system.
2. three phase power supply can transmit more power than single phase power .
3.less conductor material is needed for transmission.
4.three phase power transformer is efficient and 15% less in cost.
5.distribution equipment less needed.
6. less cooling needed for three phase power transformer.
7. In three phase system supply never drops to zero, then we can get constant power.
8.calculations shows that 50% increase in transmission cost yields to 200% more power transmission.
9.three phase supply creates a rotating magnetic field in three phase induction motor, that makes the rotor move. three phase motors are easy to manufacture , cost is less and it is efficient too, It makes less vibration than single phase motor.
10.we can get different values of voltages according to our requirement.
These are the common advantages of three phase power supply. More we will discuss later.
Thank you for reading.

Monday, 16 February 2015

basics of making transformer (part-1)

if you ask a child, what is transformer?  most of them will tell about the famous  Hollywood movie, but I think you are not like that. I think all the hobbyists must heard about the transformer.
what is a transformer?
A transformer is an electrical device,which transforms power magnetically with out changing total power and the supply frequency. it is mainly two types 1.step up (transforms lower voltage to a higher level) 2.step down(transforms higher voltage to lower voltage).
why we need a transformer?

the uses of transformer starts from power stations, from where power is transmitted to a longer distance, the extension line has to provide a large amount of power through it, we know that power=voltage*current, and loss is directly proportional to the square of current. as the current through the extension increases the loss also increases,  so for transmitting a fixed amount of power we can make the current less and the voltage higher one to minimise the loss, 
so making this voltage several kilo volt, we need a transformer.
after transmission, at the distribution station we need to make the voltage lower value for household or industrial using,
actually, transformer is everywhere, in every electronic or electrical good.
How a transformer works?
A transformer works according to the principle of mutual inductance,
suppose you have an inductor, and give a ac supply to this inductor,  the there will induce a changing magnetic flux in the coil. if you place another coil near it a counter emf will be generated in that coil. here is air between two coil, for transformer there will be a iron core.
thank you very much. visit again.

Monday, 2 February 2015

what is a piezo?

what is a piezo?
many crystal shows strange properties due to special combination of their inter molecular structure.  A piezo electric material is such a material in which a potential difference appears when it's physical shape is deformed by external mechanical force.
this potential appears due to displacement of charges in the atomic structure of the crystal.
the effect is a reversible process,.  that means if we apply potential difference in the side of the crystal, the shape of the crystal will be deformed. the elements exhibiting piezoelectric effect are called electro-resistive elements.
classification
there is mainly two types of piezoelectric crystal.
one is natural like quartz, Rochelle salt
another type is synthetic like lithium sulphate, ethylene diamine tartrate etc.
mechanical deformation can be made in various way like thickness expansion, transverse expansion, thicknesses shear etc.
mechanical deformation produces charges and this charge appears in form of voltage across two terminals.
voltage=E/C
the polarity of the voltage is very direction sensible, if a tensile force produces a voltage of one polarity and compressing force causes the opposite.

Application of piezo
there are various type of application of piezo mainly in electronics!
1.for its high stability quartz crystal is used in crystal  oscillator
2. it is used as pressure sensor,  a electrical signal is produced due to deformation, and it is analysed by a analyser circuit to know the pressure applied.

3.have you seen what is inside a spark gas lighter? yes you are right,  there is a piezo in speak ignition system,  when we press the button with our thumb the piezo inside is get deformed and instantly produces 350-450 volt, which produces that spark, 

4.one interesting application of piezo is producing electricity, suppose think one such crystal is placed inside your shoes,then for each and every step it will be deformed and the produced charge is harvested in a li-ion battery inside, this charge can be used to recharge your cellular phone. scientists are planning to place thousands of piezos under footpaths.  that can be effective alternative in producing energy from human.
5. speaker or buzzer.