The Electrical Engr.

High Voltage Direct Current Transmission or HVDC Transmission is the most efficient method of power transmission over a very long distance. The reason is the various losses associated with the AC transmission over a longer distance (more than 200km). However, HVDC is a complex and costlier than AC transmission. Let us understand how HVDC works exactly and what makes it more efficient than its AC counterpart.

Current Transformer is an important instrument used in power stations and Sub-stations for stepping down the line current to a lower level. These are used mainly for metering or measurement purpose and for protection purpose. Lower current levels allow us to use low range ammeters to safely measure the respective current in the line. On the other hand, there are current transformers used for actuating Relay which in turn activates circuit breakers to separate the faulty line from the system. These type of CTs are called Protection type CT. Now, can we use a protection type CT for metering purpose and vice-versa? If not then why? Let's understand...    

Characteristic Impedance or Surge Impedance is a term defined for a transmission line which tells us about the impedance that will be provided by the line to a surge flowing through it. Surge is a sudden high voltage spike which remains there for a short duration but can make an entire power system unstable. This happens either due to sudden switching or due to a lightning strike on the line.   For an ideal lossless transmission line, the surge impedance is given as the square root of line inductance to the shunt capacitance (capacitance between line and earth) i.e, sqrt(L/C). The ideal lossless line behaves as a pure inductor and hence its capacitance is zero so the surge impedance is sqrt(L/0) i.e, infinite. That's why the surge current can't flow through the line. On the other hand, the shunt capacitance is a pure capacitor and hence the impedance it provides to the surge current is sqrt(0/C) i.e, 0. So, the shunt capacitance provides a short circuit path to the surg

We know, there are various types of three-phase connected transformers like Star-Star, Star-Delta, Delta-star and Delta-Delta. Open-Delta connected transformer is a special case of three-phase Delta connected Transformer where one phase is removed due to some fault linked to it and the transformer we are left with is called an Open-Delta Transformer or V-V Transformer. It might look like the transformer will not be working but that's not true. The transformer is able to supply the loads but at reduced capacity. Let's see, how it works and what is the reduced capacity. I am also going to discuss about the over-loading capacity of the open-delta transformer. The transformer is called V-V connected transformer because the transformer looks like the English letter 'V' after one of the phases has been disconnected.       Download PDF

Variable Voltage Variable Frequency Drive (VVVfD) is one of the best and efficient methods of starting an Induction Motor Drive as well as it provides a smooth and wide range of Torque-Speed control. It saves electrical power and provides good motor starting and running characterstics. VVVfD controls the V/f (Volt/Hz) fraction to let the motor drive achieve good Torque-Speed characterstics as required. Hence it is also called, VSD - Variable Speed Drive or AFD - Adjustable Frequency Drive or Inverter based Drive as it uses Inverter to achieve the set points.  But how VVVfD works and why it is better than various other methods of Starting and Speed Control of Induction Motor based applications. Let's discuss the Theory, Working, Advantages and Applications of a VVVfD in detail.          

 *Note: Not to be confused with Coronavirus or CoVID-19... Corona Discharge is a phenomenon that happens around a High Voltage Transmission Line in which the air surrounding the surface of the conductor glows bluish or greenish and a hissing sound is produced. Mathematically speaking, when the maximum Electric Field Intensity equals the dielectric strength of the medium around the transmission line, the voltage of the transmission line at this point is known as the Critical Disruptive Voltage. Beyond this voltage, the Corona phenomenon is seen on the line. Let's understand each of these things and what exactly is corona discharge, corona power loss and how to control it...