Study On Definitions And Measurments Of Power In Electric Power System Under Nonsinusoidal And Unbalanced Operation

Definitions for active-, reactive-, apparent- power, and power factor are clear in the 1-phase or 3-phase balanced sinusoidal circuit. But concepts for power are rather complicated when currents' or voltages' waveforms in the electric power system are distorted. The conventional power definitions are unable to explain or describe all power phenomena exactly, so it is an important fundamental task to establish power theory which can also describe exactly power phenomena of the distorted waveform and the unbalanced circuit within the scope of electric power system analysis and measurment. In addition, how to control reactive power and voltage is also significant to improve the stability and economical efficiency of electric power system. However, the effective control of reactive power lies on the accurate measurement, so the measurement technique about reactive power has received more and more attentions. Since electric locomotive is a 1-phase rectified load which injects a lots of harmonics into the electric power system and result in negative-sequence current while consuming active power. What' s more, harmonics and negative-sequence current affect greatly the safety of electric power system and lead to the definitions and measurements of power based on 1-phase sinusoidal or 3-phase balanced sinusoidal circuit nonapplication. This thesis studies mainly the theory of reactive power in electric power system, and applies it to measure reactive power and power factor of traction power supply system for electrified railway.First, this thesis explains the concept about electric power quantities, analyses the definitions extensively the sinusoidal or non-sinusoidal, the balanced or unbalanced 3-phase circuits detailedly,and proves it inexact to measure reactive power using Budeanu' s definitions of reactive power. Then, the thesis summarizes the measurement arithmetic, studies the influence of harmonic to measurement arithmetics and power meters.Next, this thesis explains and analyses the IEEE Trial-Use Standard1459-2000, "Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions" .presents the limitations of traditional definitions and the improvements of effective apparent power in the IEEE Trial-Use Standard according to the relation between line loss and apparent power, then defines the nonactive power of 3-phase non-sinusoidal unbalanced system, as can be also called generalized reactive power. Points out the arithmetic apparent power or the vector apparent power which extensively used cannot reflect exactly the line practical loss and bring error for measurement. So this thesis proposes to use the effective apparent power, non-active power and power factor to measure powers in 3-phase nonsinusoidal unbanlaced electric power system.At last, this thesis proposes that power supply system of traction is regarded as an unbalanced 3-phase system while measuring active-, reactive- power and power factor. The simulation is performed using the data provided by Dechang and Lugu substation of traction, which constructs a 3-phase unbalanced system, analyses the error of the results computed from different definitions of power, and proves that the definitions of effective apparent power and generalized reactive power recommended by the IEEE Trial-Use Standard are the most scientific and practical.