As the main electrical component for the reactive power compensation, the power capacitors are widely applied in many fields. And since the insulation condition of power capacitor could be identified accurately by using the on-line monitoring system, it attracts more and more attentions in recent years.
In this paper, a novel on-line monitoring equipment for power capacitor based on wireless sensor network is presented. The operation data which includes the current and voltage of every capacitor is collected at first, and then the FFT is utilized to calculate the amplitude and phase of every signal, thus the insulation condition and the fault symptom could all be diagnosed accurately by analyzing the FFT results. In order to realize the effective isolation and the reliable communication between the sensing part and the merging unit, the wireless sensor network is adopted. The high reliability and transmission rate could be realized by using 2.4GHz UHF and 5GHz ISM radio bands. Thus the on-line monitoring system could be manufactured, and the lab test is carried at last. The testing results illustrate that this system could satisfy the requirement of on-site real-time measurement.
The power transformer is the key equipment of the power system; its insulation condition will directly influence the security and reliability of the power system. Thus, the on-line monitoring of power transformer is urgently required in order to guarantee the normal operation of the power system. Moreover, the dielectric loss factor is a significant parameter reflecting the condition of transformer bushing, so the on-line measurement of dielectric loss factor is really important. In this paper, the phase-to-phase comparison method is selected as the on-line monitoring method based on the overall analysis and discussion of the existing on-line monitoring methods. At first, the harmonic analysis method is utilized to calculate the dielectric loss of each phase of the three-phase transformer bushing, and then the differences of dielectric loss between every two phases are calculated and analyzed. So the insulation condition of each bushing could be achieved based on the careful analysis of different phase-to-phase dielectric loss. The simulation results of phase-to-phase comparison method are carried out in this paper, and the validity is verified. At last, this method is utilized in an actual equipment of on-line monitoring.
The hidden danger exists in the power capacitor of power system due to long-time operation under the environment of high voltage. Thus, it is possible to induce serious fault, and the on-line detection system is urgently required. In this paper, two methods of the on-line detection system are compared in order to realize the better real-time condition detection. The first method is based on the STM microprocessor with an internal 12 bit A/D converter, which converts analog signals which is arrived from the sample circuit into digital signals, and then the FFT algorithm is used to accomplish the measurement of the voltage and current values of the capacitor. The second method is based on the special electric energy metering IC, which can obtain RMS (Root Mean Square) of voltage and current by processing the sampled data of the voltage and current, and store RMS of voltage and current in its certain registers. The operating condition of the capacitor can be obtained after getting the values of voltage and current. By comparing the measuring results of two methods, the second method could achieve a higher measurement accuracy and more simple construction.