Circuit breaker ratings The rating of the circuit breaker is given on the duties performed by it.The rating of the circuit breaker should be specified in terms of the number of poles (the number of poles per phase of a breaker is a function of the operating voltage) rated voltage rated current rated frequency and … Read more
Substation Introduction Substation receives the energy transmitted at high voltage from the generating stations and reduces the voltage to a value appropriate for local distribution and also provides facilities for switching. Substation are mainly of switching and converting.In switching substation different connections between various transmission lines are made.Whereas in converting substations converts ac into dc … Read more
Three-Wire DC Distribution System When the voltage is increased the efficiency of the transmission line increases and the cost of conductor material in feeder cables gets reduced but in case of dc system it is not possible to change the voltage between feeders and distributors without using rotating machinery which is undesirable,so the feeders and … Read more
Skin Effect The distribution of current over the cross section of the conductor is uniform for dc only.An alternating current flowing through a conductor does not distribute uniformly but tends to concentrate near the surface of the conductor.In case of an ac system no current flows through the core and the entire current is concentrated … Read more
Bundled conductors Transmission of large amounts of power over long distances,can be accomplished most economically by using extra high voltage(EHV).An increase in transmission voltage results in reduction of electrical losses,increase in transmission efficiency,improvement of voltage regulation and reduction in conductor material requirement.At the high voltage above 300Kv ,a round single conductor per phase is used,corona … Read more
Temperature Rise in Electrical Machine Heat is developed in all electrical machine due to the losses in the various parts, copper loss(I^2R loss) in conductor, Hysteresis losses and eddy current losses in iron and mechanical losses (in rotating machine only) due to friction of the bearing,air friction or windage causing the temperature of that part to … Read more
Choice of Transformer connections 1.Star-star(Yy0 or Yy6) connections:This type of Transformer is most economical for small current and high voltage transformers. Advantages: The number of turns per phase and the amount of insulation is minimum because phase voltage =1/√3 of line voltage. There is no phase displacement between the primary and secondary voltages. It is possible … Read more
Open-circuit Test(or No -Load Test) Open-circuit test is used to determine the : core(or iron excitation) loss,Pi No-load current ,Io shunt branch parameters Ro and Xo of equivalent circuit. Open circuit Test on transformer In open circuit test usually high-voltage winding is kept open circuited and the rated voltage at rated frequency is applied to … Read more
Transformer Efficiency Definition: The efficiency of Transformer(η) is defined as the ratio of useful power output to the input power,the two being measured in same units(either in watts or kilowatts). i.e Transformer efficiency, Now power output=V2I2cosΦ where, V2=secondary terminal voltage on load I2=secondary current at load and cosΦ=power factor of the load. Iron loss,Pi=Hysteresis loss+eddy … Read more
Voltage regulation Definition: Voltage regulation of a Transformer is defined as the change in magnitude of terminal voltage or secondary voltage,when full load(rated load) of specified power factor supplied at rated voltage is thrown off(reduced to no load) with primary voltage and frequency held constant,as percentage of the rated terminal voltage. Explanation of voltage regulation … Read more