Recent Entries

  • Automatic supply transfer schemes

      In order to ensure uninterrupted supply to connected loads in thermal power stations or process industries, two types of automatic supply transfer schemes are normally used. One is the automatic bus transfer scheme, used in medium voltage switchgear of thermal power stations, which is requi...
  • Topology of Power Systems

    Early power systems were simple in design but highly unreliable. They consisted mainly of generating units connected to load centers in radial fashion as shown in Figure . The generator is connected to a transformer (xfmg) to raise the voltage to the transmission voltage level. The transmission li...
  • Excel sheet calculator for Power Factor Correction calculations

    Power Factor Improvement If the power factor is low or poor, it is necessary to improve or correct it. It may be improved by injecting a leading current into the circuit so as to neutralize the effect of lagging current. The power factor may be improved ...
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  • Excel calculator for Transformer sizing based on motor starting

    Excel calculator for Transformer sizing based on motor starting currentThis excel sheet calculator will help you to determine the generator size due to large motor starting. download for **** download
  • What is variable frequency (VFD)?

    VFDs are power electronics devices that convert a constant input frequency and voltage into variable frequency and voltage output for the motor. A complete VFD system may consist of all these elements: cabling, an input isolation transformer, power factor correction equipment, harmonic filters, th...
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  • Simple automatic transfer schemes

    Automatic switching equipment may consist of three circuit breakers with suitable control and interlocks, as shown in figure . Circuit breakers are generally used for primary switch-ing where the voltage exceeds 600 V. They are more expensive but safer to operate, and the use of fuses for overcurr...
  • Starting Method for Induction Motors

      Starting Method for Induction Motors   3-phase induction motor is theoretically self starting. The stator of an induction motor consists of 3-phase windings, which when connected to a 3-phase supply creates a rotating magnetic field. This will link and cut the rotor conductors which...
  • CURRENT TRANSFORMERS LOCATION

    CURRENT TRANSFORMERS LOCATION In ideal case, the different discriminating zones should overlap each other as well as the individual circuit protections. The overlap should happen across a circuit breaker, so that the latter lies in both zones. For this configuration it is necessary to put current...
  • RESTRICTED EARTH FAULT PROTECTION (87REF)

      System short circuits may occur across any two or even three lines, or, if the neutral Point is solidly earthed, between any one line and the earthed neutral the effect of a System short circuit is to produce over currents, the magnitude of which is Dependent on the short-circuit level of ...
  • Factors and condition effecting Corona

      Corona   A corona is a partial discharge and takes place at the surface of a transmission line conductor when the electrical stress, that is, the electric field intensity (or surface potential gradient), of a conductor exceeds the breakdown strength of the surrounding air. In such a...