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Vidhyut S. said:
Hello friends,
I have a confusion about phase shift in a transformer.
When there is a delta/star or star/delta transformer is there,
we say that 30degree phase shift occurs.
What does it mean physically?
thanks for your question and answer. Can u show me with a chat?
Vidhyut S. said:
Absolutely right….
thats ok but iamasking the theoretical basis i.e basedon the polarisation process.
venkat reddy said:
what is meant by inrush current
when the transformer is connected to the line at the instant when the supply voltage in the line is zero the transformer demands a flux which is twice that of rated maximum flux.this is called as doubling effect .in order to satisfy this large magnitude of magnetising current is required.the value of the large magnesing current will be in the order of hundred times of the rated current of the promary.this current is called as the inrush current.this current will last for very short duration only i.e about 20msec so no harm what soever to the transformer due to the inrush current.
Vidhyut S. said:
Hello friends,
I have a confusion about phase shift in a transformer.
When there is a delta/star or star/delta transformer is there,
we say that 30degree phase shift occurs.
What does it mean physically?
yes there is a 30 degrees phase shift in a delta/star or star/delta transformer.the reason is that the phase voltage lags line current by 30degrees.for your understanding consider a delta/star transformer.consider the phase voltages in three phases of both primary and secondaries.you will find that in primary the phase voltage and line voltages are same,let it be Vab(take one phase).but,the corresponding secondary will have the phase voltage only in it's phase winding as it is star connected.the line voltage of star connected secondary and delta connected primary won't have any phase differences between them.so this can be summerised that”the phase shift is associated with the wave forms of the three phase windings.for clear idea refer the phasor diagrams of star and delta connections simultaneously.
well the use of fourrier analysis is the best method to change a square wave into a sum of harmonic sinusoidal waves mathematically.
practically you need to use wave shaping ciruits that employ diodes. the type of filter you want depends on which frequencies do you want to eliminate and which one do you want to preserve.. for instance, if you want to discard the high frequency components of the square wave you can design a low pass filter using its transfer function. the low pass filter will automatically convert the low frequency components of the square wave into sinusoid harmonics and give you low amplitude sinusoidal functions.
more please read the book singals and linear systems by Lathi. you can download this book from the internet through mediafire.com
PK said:
How to calculate the demand in KVA with given KW load for certain area or plant.
You can simply use the formula.
KVA^2 = KW^2 + KVAR^2
OR
KVA/cos(fi) = KW
where fi = phase angle between voltage and current.
Hi,
The formula for the lightning protection, Franklim pole type:
Rp=h*tan A
Where Rp is the radius of protection of a cone defined by the formula, with the height h in meters (h is the top point of the pole) and A is the angle in degrees at the top, that usually is 55º for a class IV degree of protection.
For an electronic protection pole, the formula is rader complicated, and for that you should contact the manufacters because they have tables for each equipment.
Best Regards,
Adriano
I think you need to be a little clearer in what you are asking and trying to achieve.
Are you trying to place lightning dods on the highest points of the building to attract lightning to set locations from which you then provide heavy conductor connections directly to earth so that you control the path of lightning currents rather than allowing them to pass anywhere they like through the building structure. This is lightning protection and is protection for the structure. It is suaually accomplished using air terminals on the highest part of the building with one or more down conductor connections into a buried earth grid. You can get some guidance on the coverage of air terminals from standards such as AS1768 or equivalent other British, intenational or American standards. It may also be worth talking to lightning protection experts such as Erico as there are many types of lightning conductors, other than simple rods, which provide improved areas of coverage.
or
Are you trying to connect lightning devices to electrical systems which may have components outdorrs and subject to lightning strike in order to conduct the high impulse voltage to ground to pretect internal electrical equipment from the excessive voltage spike. This is lightning arresting.
A direct drive generator is one which attaches directly to the shaft of the driving machinery without going through a gearbox. With wind generators this means a very slow turning generator, hense the large number of poles specified. However, the 80 poles specified (assuming 50Hz operation) would mean a synchronous speed of 75rpm which differs significantly from the 9-19prm range also specified so there needs to be some clarification there.
Once you have established the generator you intend to use you then need to design the speed/excitation control equipment which will ensure that the output connection to the grid will always be at grid frequency as the rotational speed of the generator will vary as the wind strength varies.
Smithy
If you are looking for warratie the continous service of the plant, IT Earthing system is the solution, but the main problems are:
– Once your have the first failure, its dificult/expensive to find where is the fault.
– The defect current is low, but the voltage arrise is high, so the life of the components will be longer by the lower temperature stress, but the life of the component will be shorter due the isolating stress. 400V will not have problem, but 690V could be.
– Every electronical component which has a electromagnetic compatability filter (mandatory in Europe) send high frequency current to earth. If the installation has many electronic components you must set your isolating meter at a value that cannot detect a real isolating defect.
