Power Capacitor Voltage Research Articles

Selection of antioxidants for capacitor grade polypropylene film: Insights into electrical performance of the oil-film system.

High voltage power capacitors employ the oil-impregnated polypropylene film as the insulation. The swelling phenomenon might drive the antioxidants and small molecules within the film to migrate into the oil. It is necessary to comprehensively investigate the physical migration mechanism of antioxidants and their impact on the electrical performance of the oil-film combination insulation system and, consequently, formulate the proper selective prescription of antioxidants. Theoretical elucidation of the competitive interaction mechanism between the film and the oil in attracting antioxidant molecules was achieved through the calculation of inter-molecular binding energy, and the migration coefficient ηm was introduced to quantify the migration characteristics of antioxidants. Experimentally, the effects of antioxidants on the space charge distribution of the film, the dielectric properties of the oil, and the breakdown characteristics of both the film and oil were investigated. The experimental conclusions are consistent with theoretical analysis. The lamellar structure antioxidant molecules with ηm > 1 tend to migrate from the film to the oil, which results in increased dielectric loss and decreased breakdown strength of the insulating oil. In addition, the presence of phosphorus atoms in phosphite antioxidants contributes to a reduction in the breakdown strength of the film. For capacitor grade polypropylene film, in addition to the synergistic effect between different types of antioxidants on the thermo-oxidative stability, the structure of the antioxidant molecules and its influence on the electrical performance of the oil-film systems should also be taken into account.

Experimental and Simulation Study of Pulse Current Generator

8/20 µs lightning pulse current generators (LPCG) used in testing surge arresters require a laborious production process that needs a high budget. An easily repairable, portable, and affordable test system with a maximum energy of 2.9 kJ and a voltage level of 24 kV that can alter its parameter values was described in this work. Simulation and experimental studies were carried out to investigate the effects of the resistor and coil elements in the Pulse Current Generator (PCG) circuit on the amplitude, front, and tail time of the pulse current. Most components of the experimental system were created using 3D printing technology with polylactic acid (PLA) material. The production costs were significantly reduced, according to equivalent pulse generators. Tests at different pulse currents and voltage levels were performed with the experimental system. Power capacitors may often fail due to overvoltage, switching, and partial discharge reasons. The high voltage (HV) power capacitors used in the pulse generator introduced in the study were obtained with the help of low voltage capacitor stacks. As a result, a less expensive, high-capacity capacitor system that is easily and quickly repairable in case of failure was achieved.

Comparison of Temperature Rise Test Methods for Series Reactors Connected with High Voltage Power Capacitors

In substation, phase advance capacitors are used to improve the power factor. Series reactors are generally connected with the capacitors to reduce the waveform distortion and suppress the inrush current. The fifth harmonic current usually flows into the series reactors for a high voltage power capacitor. Japanese Industrial Standards provide three types of temperature rise test methods, and manufacturer chooses one of them. However, which test method should be selected has not been examined. In this paper, compare the advantages and disadvantages of the test methods using a prototype reactor.

A Proposal of a New Temperature Rise Test Method for Series Reactors Connected with High Voltage Power Capacitors

In substation, phase advance capacitors are used to improve the power factor. Series reactors are generally connected with the capacitors to reduce the waveform distortion and suppress the inrush current. The fifth harmonic current usually flows into the series reactors for a high voltage power capacitor. Japanese Industrial Standards provide three types of temperature rise test methods. Each test method has its own problems. To alleviate them, we have devised a new test method called “Middle Frequency Test” which uses a meddle frequency between the fundamental and fifth harmonics for excitation. This paper presents an implementation method and demonstrates the usefulness of the proposed test method.

Electrical properties of polypropylene-bonded hindered phenol blends

Polypropylene (PP) film is the most commonly used dielectric film in power capacitor applications, thanks to its high breakdown strength combined with low dielectric losses. Today, antioxidants based on hindered phenol (HP) are mixed into the PP resin during manufacturing to provide thermal-oxidative protection during melt processing, however they increase the dielectric losses. Recently, a new PP-HP copolymer has been synthesized containing a few comonomer units with HP moieties, which are homogeneously distributed along the PP polymer chain. Addition of new PP-HP copolymer to PP dramatically improve the thermal-oxidative stability under elevated temperatures compared to neat PP. In the current study the electrical properties of this novel PP-HP copolymer and PP/PP-HP blends are investigated using dielectric spectroscopy and direct current (DC) breakdown strength. By adding lower amounts (2–5 wt%) of the PP-HP copolymer in PP, the dielectric constant and loss remains similar to that of neat PP. The short-term DC breakdown strength of the PP/PP-HP blends is equal or higher than the neat PP reference, combined with a reduced scatter in breakdown data. As a next step, long-term ageing tests of the PP/PP-HP blends are required. These findings may bring an advanced PP dielectric material into the market which is highly beneficial for high voltage power capacitor applications.

Reactive Current Reshaping With Series Resonance Damping for Three-Phase Buck-Type Dynamic Capacitor

By adding Buck-type AC/AC converter to conventional power capacitor, dynamic capacitor (D-CAP) can be formed to compensate variable rather than fixed reactive power. However, some nonlinear distortion factors, namely grid harmonic voltage, voltage drop of switches and dead-time, would cause harmonics in its compensation current, meanwhile, its capacitance may interact with the grid inductance to cause series resonance. Both nonlinear distortion factors and series resonance would distort the waveform of its compensation current and make the grid current failed to meet the power quality standard IEEE Std.519. This paper focuses on the output current distortion of Buck-type D-CAP in reactive power compensation. For harmonic distortion, through establishing the equivalent circuit of Buck-type D-CAP, the generation of low-order harmonic current is investigated under three nonlinear factors. A current reshaping method to simultaneously diminish the harmonics caused by the three nonlinear distortion factors is thus adopted, which is a feedback control of output current harmonics. Then for series resonance, based on the block diagram of Buck-type D-CAP within the grid, transfer function from grid voltage to the output current is deduced and the corresponding Bode diagram is depicted. An active damping method is therefore suggested to shrink the low-order series resonance peak, by detecting power capacitor's voltage for feedback control. Finally, a combined control, reactive current reshaping with series resonance damping is proposed in this paper for three-phase Buck-type D-CAP. A wide variety of experimental results from a 33kVar/220V laboratory prototype are provided to demonstrate the validity of the combined control.

Studies on the Low-Voltage Dynamic Reactive Power Compensation and Switching Control for Capacitors Device

This paper is for the problems of the 400V low voltage power capacitor reactive power compensation and for the problems existing in the transient process, resuming the principle of low-voltage capacitor intelligent technology and its implementation briefly. Propose a synchronization of reactive compensation capacitor switching on-off control system based on the micro controller and adaptive control. Real-time monitoring system is used to access system active and reactive power changes in order to extract the zero voltage signals; intelligent control algorithm is used to realize the intelligence of capacitor reactive power compensation on-spot and cutting, which greatly reduce the over-voltage and flow phenomenon produced by the capacitor in the cutting process. The result checked by actual measured shows that the device is stable, reliable, and can be effective to on-site system reactive power compensation and realize intelligent cutting.

Simplified method for protecting the power capacitor from over-voltage/over-current

A simplified method for protecting the power capacitor from over-voltage/over-current is proposed. The proposed method retrieves the voltage across the power capacitor to calculate the root mean square (RMS) values of the power capacitor voltage and the power capacitor current. The salient point of the proposed method is this method can protect the power capacitor from over-voltage/over-current caused by harmonic or power resonance only sensing the power capacitor voltage. The control circuit generates a trigger signal to actuate the electromagnetic switch to switch off the power capacitor from the power system or adjust the impedance characteristic of inductor/power capacitor for protecting the power capacitor from over-voltage/over-current if an abnormal voltage or current is detected. The proposed method has the advantages of simplified control circuit, easy installation and low implementation cost. A prototype is implemented to verify its performance. The test results show that the proposed method has the expected performance.

The development of high voltage power capacitor technology in Japan

Unlike other countries, Japan has differed from the normal industrial trend toward using large, tank-type high voltage power capacitors. Recent notable achievements are the development of completely enclosed, compact capacitor banks, which are composed of very large capacitor units. Can-type capacitors have been also manufactured and used in Japan and have been highly developed recently, especially in the field of metallized film capacitors. Described in this report is the development of high voltage capacitor technology, especially of tank-type capacitors. The scale of substations has become larger year by year with the expansion of the Japanese economy. Compact capacitor banks save space but allow unit capacities of main substations to be increased.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A New Impregnant for HV Power Capacitors

The main properties of a newly developed impregnant ant for high voltage power capacitors are given. This new liquid, a mono dibenzyltoluene blend (M/DBT), has a very high degree of aromaticity. The results of many tests carried out both on model and large capacitors are reported. A screening test using a transparent micro-model of an all-film capacitor has been used to study the properties of the fluid when submitted to very high electrical stresses resulting from transient overvoltages at low temperature. re. The correlation between the results obtained with micro-models and with real capacitors are reported. Partial discharge extinction ability of M/DBT is compared to that of liquids being used at present for this application. The authors describe the laboratory test that they have developed to evaluate the performances of the polypropylene filmliquid iquid insulation at high temperature. Using this test, the influence of many parameters is studied. They cast new light on all-film capacitor technology.

Reliability Calculations for Capacitor Banks

The reliability of high voltage power capacitor banks has been analyzed using a statistical model based on the failure intensity of the single capacitor element. The expected lifetime of the bank is obtained by computer simulation of element failure sequences leading to bank failure according to a preselected criterion. The computer program can be applied for practically any bank or unit configuration and protection system. It is well-suited for direct comparisons of the performances of different banks. Simulations of banks equipped with internal and external fuses show that the former in general offer longer lifetime and better availability.

Reliability Calculations For Capacitor Banks

The reliability of high voltage power capacitor banks has been analyzed using a statistical model based on the failure intensity of the single capacitor element. The expected lifetime of the bank is obtained by computer simulation of element failure sequences leading to bank failure according to a preselected criterion. The computer program can be applied for practically any bank or unit configuration and protection system. It is well-suited for direct comparisons of the performances of different banks. Simulations of banks equipped with internal and external fuses show that the former in general offer longer lifetime and better availability.