WHAT IS HYSTERESIS LOOP ( B-H CURVE ) ?
WHAT IS HYSTERESIS LOOP ( B-H CURVE ) ?
Welcome again to our site www.bossonlearning.com . Today we are going to discuss about Hysteresis loop
The B-H curve is indicated the curve way where Flux density (B) varies with the Magnetising force (H) .For material which are use in electro magnet , the B-H curve is very important , In electro magnet material ,The condition on applied current and after a loop is created which is known as HYSTERESIS LOOP . This curve is made with B-H variation .So today we are learning about the hysteresis loop in this blog , So let's learn .
When we present a B- H curve of any magnetic material in a four quadrant , then the B- H curve known as Hysteresis loop . We can present this loop in some step in below . Just follow the diagram with instructions.To Start this presentation , you should family with some term ,
We know , H = (Ni )/l ------------------------(a)
Other one is , H = B / (µ) -----------------------(b)
At point (0,0) , before applied current supply , then I = 0 , so H=0 , then B= 0 , This situation mentioned the (0,0) Pointer .
Now we applied current . So current is applied on the magnetic circuit . Due to increase of I , The H will also high according to the increase of I , for this the B will also increase so this condition are denoted the path 0 -1. A technical term is used for the point of 1 , named , " Magnetic saturation " .
In situation of magnetic saturation , the magnetic material is perfectly saturated with the applied current , there is no change after the magnetic saturation , if we increase the current .
In last we know that the last point is 1 , so now we are decreasing the current supply . Due to the current fall , according to equation 'a' the H becomes 0 and follow the path 1- 2 . But in this situation , according H=0 , the B will not be zero . That means when i decrease the current after magnetic saturation , the H will come into ultimate zero position but that time this magnetic material have a finite value B men's magnetic flux density . So it have flux when H=0 . This lagging of B behind of H is called Hysteresis . Please follow the curve , you can see , when I comes in to I =0 , then H also come into zero but B not . In this graph the path 0- 2 is represented the residual flux density. The degree to which a magnetic material retains its magnetism after the Magnetising force is reduced to zero is called retentivity.
When we use electro magnet, we don't want that after disconnected from supply , the electro magnet still have their power , so this situation we should apply current in opposite directions . Due to the opposite of direction of current , the H will also be reversed . The B-H curve follows the path 2-3 . To decrease the value of B to zero the H have nagetive value. This value called coercive force . To reduce the B , we applied an extra force . This value is varying for different magnetic material . This loss of power is usually said Hysteresis loss .
You can see on this graph , that to turn down the B at zero , the H becomes nagetive and increasing the current the the B also reverse and nagetive .In this situation the H become large value in nagative and it comes in magnetic saturation point 4 same as in positive quadrant poin 1 . The 4 point is the mirror point of 1 . The magnitude are same but in reverse condition .
If H is now reduced , the B also decrease and follow the path 4-5 . Here 0- 5 is called residual flux density which is same as 0-2 in positive quadrant .
If the direction of H reversed , then it came again in positive quadrant . For lagging condition the B also situated in negative then it comes in zero position until the H comes in a actual value in positive and this path is 6- 1 when B=0
In this step we covered a complete path of 1-2-3-4-5-6-1. This complete path is called in Electrical engineering is Hysteresis loop.
Thanks for reading , hope you understand
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