07-09-2016, 09:46 AM
1453376891-nehsCopy.doc (Size: 1.88 MB / Downloads: 6)
ABSTRACT
Day by day the requirement of electrical energy is increasing tremendously for industrialization and domestic use. Hence the transmission and distribution network of electric power is expanding on large scale to fulfill this requirement.
So,The Transformer is very essential for Trasnmission and distribution system of electric power.
In Transmitting the electric power if we transmit the electric power at low voltage level then losses in the transmission of electric power are more. To avoid these losses we have to transmit electric power at high voltage. For these purpose we use the step up transformer.
Again,In distribution system, we require the utilization level voltage so step down transformer is use to decrease the voltage. Hence in the electric transmission and distribution the transformer is very important device. So as an electrical engineer we must have the through about transformer.
INTRODUCTION
Day by day the requirement of electrical energy is increasing tremendously for industrialization and domestic use. So,The Transformer is very essential for transmission and distribution system of electric power
In Transmitting the electric power if we transmit the electric power at low voltage level then losses in the transmission of electric power are more. To avoid these losses we have to transmit electric power at high voltage. For these purpose we use the step up transformer.
Again,in distribution system, we require the utilization level voltage so step down transformer is use to decrease the voltage. Hence in the electric transmission and distribution the transformer is very important device.
WORKING PRINCIPLE OF TRANSFORMER
A transformer is basically electromagnetic static device based on the principle of faraday law of electromagnetic induction. A transformer essentially consist of magnetic core, build up of insulated silicon steel lamination, upon which are wound sets coils suitably located with respect to each other and termed as primary and secondary windings. If one winding is connected to a source of alternating voltage, an alternating flux is set up in the core, most of which is linked with the other winding in which it produce matually induced EMF
1. Core material
Cold rolled grain oriented(CRGO) material used as the core material for transformer. Earlier the transformer manufactures had no other option to use a particular grade of CRGO steel, its availability being restricted to only M-4 grade with 0.27mm thickness. But now a day with advance technology, various material available for core like CRGO-27- M-4, HI-B-0.27,HI-d-0.27.
2. Winding Wire and Strip
Like a CGRO lamination, winding wire and strip are also a vital raw material used in transformer. The basic material available in market are in form of rod having a varying diameter from 8mm to 16mm. the rod is drawn to the required designed size and the insulated with paper or other insulating material. Annealing or heat treatment is also done or drawn material for softening and also stress relieving. The basic material we used for winding is copper or aluminium.
3. Insulating oil.
After core and winding material, oil is also considered to be the most vital raw material affecting the performance of transformer. The oil being used in transformer is from petroleum origin. The oil act in two ways. 1. As an insulating medium 2. As a heat transfer medium. Though it is a petroleum product,it has a very high flash point(about 140 degree celcius) which has permitted to oil in transformer.
WINDING PROCESS
After completion of core assembly, we turn towards the winding process. Before manufacturing the winding, we design the winding properly.
It consist of-
1. no of turns.
2. current calculation.
3. size of conductor.
4. dimension of winding.
After designing the winding, the manufacturing process starts. For manufacturing the winding we used the electric winding machine. Its components are winding drum, driving wheels,foot switch and its work.winding manufacturing is done on rotating assembly and winding form on drum itself only we have to give correct position and direction to conductor. In winding manufacturing, we first manufacture the primary winding.
TRANSFORMER ASSEMBLY
After manufacturing the all component of transformer next we have started the assembly of transformer. Now three limbs were ready to mount the windings. According to designed of transformer we have to mount the secondary winding first while mounting the winding the care should be taken that the core and winding must be isolated from each other for that we used various insulating materials such as cardboard insulation, paper insulation, cotton tape. While mounting the windings the permission gap is placed between core and winding and also in two windings the gap depends upon our design consideration. In view we have mounted the secondary winding first by packing a small sheet of cardboard between core and secondary winding. After mounting the secondary winding now its turned to primary, same careshould taken that the primary and secondary should be isolated from each other for which we kept a permissible gap between both windings and gap is filled by inserting the cardboard sheet between two winding
TESTING OF TRANSFORMER
Necessity of testing :
When transformer are manufacturing in an industry as per a particular design, testing is required whether the performance of transformer is as per the designed data or not.
If not how much variation are there in the actual values and the designed values and whether it is within the permissible limit as specified by ISE or not.
From testing we can also determine the quality of workmanship, quality of material used etc.
Hence, every transformer manufactured in industry is required to undergo certain test.
Different tests carried on transformer:
1) ratio test
2) magnetic balance test
3) insulation resistance test
1) Ratio test:
For conducting the ratio test of transformer there are three methods of testing they are as follows
1. With the help of voltmeter
2. With the help of standard transformer
3. With help of ratio meter
From these three methods we carried the first method. i.e, ratio test with help of voltmeter.
2) Magnetic balance test:
Magnetic balance test is under the category of a special test may be carried out on 10 percent of offered quantities. in case of power transformer we should carry out this test on 100% transformer .
This test not covered under the ISS .but we strongly recommend carrying out this test especially on power transformer, since it gives a clear indication of how the magnetic circuit is built-up.
A single phase voltage of single phase voltage of pre determine value is fed to one of two primary terminals and voltage across each secondary with respect to neutral is measure and recorded.
3)Insulation resistance test:
Insulation resistance test is under category of routine test and carried out on each manufactured transformer. the purpose of carrying this test is to measure, the value of insulation resistance for determining moisture absorbed by the windings, insufficient insulation between windings or effect of atmospheric pollution on windings.
The insulation resistance test is carried out with meggersof a suitable voltage rating. as our transformer is 11000/433 volt we required megger of 1000 voltage rating.
CONCLUSION
After completing the designing and manufacturing of three phase transformer we can conclude following points:
From topic we got throughout knowledge about distribution Transformer. Also we got knowledge about working principle, construction and testing. Also we got the knowledge about dismantling and assembling of transformer.