The Study On Supervision And Measurement Of Power Quality On Substation Terminal

AbstractFive items, with frequency, harmonics, voltage deviation and voltage fluctuation and flicker respectively, are included in the state standards of energy quality. The main work of this paper is to study a new digital device according to these standards, which is the remote terminal of the supervisory and measuring system of energy quality.FFT is used to get the basic characteristic value, such as the amplitude and phasor of the harmonics. Once the amplitude and phase is attained, three of the five items of state energy quality including harmonics, voltage deviation and three-phase unbalance, is derived. Zero-crossing algorithm is used to get the system frequency. To avoiding the disadvantageous influence of distorting waveform to the zero-crossing point, filter around working frequency is added.The analog system of the IEC flickermeter is simulated. Then the algorithm of digital system is studied and the digital design result is presented subsequently. Simulation result proved that the algorithm and method presented to be correct and acceptable. This makes it possible to continue the supervisory and measuring device.Hardware is designed with a system of industrial controlling structure. Structure of ISA bus and two CPU is adopted. The two CPU's task is allocated as following: the auxiliary CPU only performs the task of flicker-measuring and frequency-measuring, and the main CPU performs the evaluation of harmonics and other tasks such as saving result. Another disadvantage of DFT or FFT is the leakage of frequency spectrum when synchronous sampling is not satisfied. To avoid this, synchronous sampling method is adopted which is composed with a phase-locking ioop and frequency-multiplying circuit.Finally, the software corresponding to the above algorithm is developed, which can implement the design aims such as evaluating displaying and saving.