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Whenever a dead short-circuit fault occurs in the transformer circuit, the transformer delivers a very large current. Under this condition, the apparent power delivered by the transformer becomes very high. The maximum MVA that the transformer can deliver during this fault condition is the fault MVA of the transformer. Calculation of Fault Current of a … Read more
1. A transformer works on the principle of: A) Self inductionB) Mutual inductionC) Eddy currentD) Hysteresis Answer: BExplanation: A transformer has a core on which the primary and secondary windings are wound. When the primary winding is energized, it draws a magnetizing current and produces magnetic flux in the core. This flux links with both … Read more
A power substation requires the earthing system for three main purposes. The purpose of earthing is to keep any voltage on metal frameworks below dangerous levels during normal or fault conditions. In directly earthed neutral system, it is not always possible to keep metal parts exactly at true earth potential when fault current flows. Therefore, … Read more
A Controlled switching device facilitates the close – open operation of the CB contacts at a pre-determined point of the electrical reference signal waveform to minimize switching surges. Controlled Closing with CSD The controlled closing triggers closing mechanism of a single phase pole contacts of CB at a desired voltage point-on-wave angle of that phase. … Read more
Surge impedance loading, or SIL, is the quantity of power in MVA that a transmission line can carry most efficiently. For understanding the basic concept of surge impedance loading, first, we have to understand the effect of reactive power in a transmission line. How does it reduce the efficiency of the transmission system? The expression … Read more
Tariff-Based Competitive Bidding (TBCB) is a procurement method in the power sector. Here, government bodies or distribution utilities invite bids from power supplier agencies. The power supplier has to feed the specified quantity of power to the grid. The project offering the lowest tariff (price per kWh) is selected through tender. This mechanism was introduced … Read more
Why are stress cones used in cable termination? When a high-voltage cable is cut for termination, the metallic sheath or screen of the cable is also cut. As a result, a sharp edge is created at the cut end of the sheath. At this sharp edge, the electric field becomes highly concentrated, which produces high … Read more
What is a VRLA Battery Bank? The full form of VRLA is “Valve Regulated Lead Acid”. Therefore, a VRLA battery means a Valve-Regulated Lead-Acid battery. It is essentially a modified version of a conventional low-maintenance lead-acid battery. Overchargings form oxygen and hydrogen gases due to electrolysis of water. These gases escape through vents provided on … Read more
Lead-acid batteries are the most commonly used battery bank systems in substations. This is a popular and robust rechargeable battery system. Before diving into the details of a lead-acid battery, we should first understand its basic charging and discharging cycles. Discharging Reaction of Lead Acid Battery During Discharging at Negative Pb Plates Diluted sulfuric acid … Read more
Normally, two kinds of overvoltage may appear in an electrical system. Power Frequency Withstanding Voltage One type is power-frequency overvoltage. In a three-phase system, a fault in one phase can increase the voltage in the healthy phases to an elevated value. This condition can continue until the clearance of the fault. Also, due to sudden … Read more