ELECTRICAL ENGINEERING

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. ...

BDV test means Breakdown Voltage Test. It is done for checking the dielectric strength of the oil of the Transformer. Dielectric strength means the maximum capacity to withstand voltage of insulating oil. This test shows the dielectric strength of Transformer oil. In transformer oil has mainly two purposes, first for insulation, second as cooling of Transformer core and other winding. So while designing Transformer oil use in transformer depends on voltage rating. So testing of oil is done according to voltage rating. For the purpose of BDV test, oil sample from Transformer is taken in a Sample Bottle. While taking sample of oil from transformer, Sample bottle should be flushed well by Transformer oil and oil in Sample bottle should be vented properly so that atmospheric moisture could not ingress in the sample oil. A typical way of taking oil sample in Sample Bottle is shown in figure below. Breakdown Voltage is measured by observing at what voltage, sparking straits b...

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...

All Day Efficiency  is defined as the ratio of total energy output for 24 hrs i.e. for the whole day to the total energy input for the same day. All Day Efficiency is basically Energy Efficiency of Transformer calculated for a period of 24 hrs. Mathematically we can write, All Day Efficiency = 1 – [Daily Losses in kWh / Daily Input in kWh] What is the need of All Day Efficiency? To understand the need of calculating All Day Efficiency, first we will discuss about the basic difference between Power Transformer and Distribution Transformer. Power Transformers are used at sending and receiving ends of a long, high voltage transmission line to step up or step down the voltage level. These Transformers are manipulated to operate near their rated capacity. Therefore, Power Transformers are disconnected during light load periods. In view of this, a Power Transformer is designed to have maximum efficiency at or near rated capacity. Therefore, the choice of Power Transformer out of...

The weight of conductor for any winding depends upon two parameters: Current carried by the winding Number of turns required in the winding Thus we can say that weight of conductor in a winding is directly proportional to its Ampere Turns i.e. MMF. Now, we will focus our attention on the weight of conductor required for Auto Transformer and a Two Winding Transformer. As discussed in earlier post Basic principle of Auto Transformer, the current carried by winding AC i.e. I AC = I 1  and that of winding BC i.e. I BC  = (I 2 -I 1 ). Also the number of turns for winding AC is (N 1 -N 2 ) and that for winding BC is N 2 . Therefore, The weight of conductor required for Auto Transformer, W CAT ∝ Ampere turns of winding AC + Ampere turns of winding BC ∝  (N 1 -N 2 )xI 1 + N 2 x(I 2 -I 1 ) ∝  N 1 I 1 +N 2 I 2 -2N 2 I 1 But N 2  / N 1 = I 1  / I 2 So, N 2 I 2 = N 1 I 1 Therefore, The weight of conductor...