Methods Of Speed Control DC Machines
















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1. ABOUT AUTO TRANSFORMER
2. Concept of Self Inductance

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Electrical symbol

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Resistance code ******************************* Symbol of DC machine ************************** Rotating machinery symbol ************************** More useful post 1.  Buchholz Relay- Transformer Protection   2.  Basic Principle of Auto Transformer
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Basic Principle of Auto Transformer

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A Transformer, in which a part of the winding is  common  to both the Primary and Secondary circuit is called an Auto Transformer. It shall be noted that in Two Winding Transformer, Primary and Secondary windings are electrically isolated but in Auto Transformer, the two windings are not electrically isolated. A simplified diagram of a Step-down Auto Transformer is shown in figure below. As shown in the figure above, N 1  and N 2  are the number of turns between winding AB and AC respectively.  If a voltage V 1 is applied across AB, an exciting current will start flowing through the full winding. Therefore, voltage per turn in winding AB is V 1 /N 1 and hence voltage across CB is (V 1 /N 1 )N 2 . As the load current is I 2 and the current taken from the source is I1, neglecting losses Input Power = Output Power V 1 I 1 CosØ 1 = V 2 I 2 CosØ 2  ………………….(1) Assuming internal impedance drop and losses to be negligible, pow...
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Buchholz Relay- Transformer Protection

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Buchholz relay is a gas actuated protection relay which is generally used in large oil immersed transformers of rating more than 500 kVA. It is used for the protection of a Transformer from the faults occurring inside the transformer. A typical Buchhloz Relay is shown below. The gas actuated protective relay is designed to detect faults as well as to minimize the propagation of any damage, which might occur within oil-filled Transformers. The Buchholz relay is therefore particularly effective in case of: Short-circuited core laminations Broken-down of core bolt insulation Overheating of some part of the windings Bad contacts Short circuits between phases, turns Earth faults-puncture of bushing insulators inside tank Buchholz relay `can prevent the development of conditions leading to a fault in the transformer, such as the falling of the oil level due to leaks, or the penetration of air as a result of defects in the oil circulating system. ...
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