kV Capacitor Research Articles

Harmonic resonances due to transmission-system cables

This paper gives some examples of harmonic issues that can occur when long ac cables are connected in the transmission grid. The main impact is that resonances can occur at much lower frequencies than when only overhead lines are present. Two illustrative case studies are presented: one for a 275-kV cable, one for a 400-kV cable in combination with a 132 kV capacitor bank. A simple rule-of-thumb is given, to decide if a detailed harmonic study is needed. Some guidelines for such a study are given as well.

Конденсаторная установка для сельской распределительной сети 0,4 кВ: особенности построения

Reactive power compensation based on a capacitor plant connected to a rural 0.4 kV distribution network, when using non-specialized contactors, is accompanied by the occurrence of large starting currents of capacitors. In addition, the installation of a conductor connection with load current transformers requires structural modification of the capacitor plant. In order to eliminate these disadvantages, it is proposed to use a capacitor bank controlled by a time relay and protected from inrush currents by three RL circuits. In this case, the “on-off” mode of the capacitor bank must be switched to by an internal signal of the capacitor bank setting the time interval “on-off”. Using a mathematical model, as well as a three-phase physical model with a power of 1.2 kV, the authors studied the behavior of transient and steady-state currents at various values of the parameters of RL circuits.The initial invariant parameters of the model were the reactive resistances of capacitors and inductors. The nominal value of the phase current of the capacitor bank was 2.14 A. The variable parameters were the values of the active resistances of the RL circuits, which took the values of 0, 10, 20, 30 and ∞. The oscillogram of stationary and transient current was studied. As a result, it was found that in order to match the capacitor bank to the criterion of using circuit breakers and contactors of the 0.4 kV network, the resistance value of the RL circuit resistor of each phase of a three-phase capacitor bank should be tenfold higher than the reactance of the current-limiting coil of the RL circuit and be five times less than the reactance value of the power capacitor of the capacitor bank phase. In rural 0.4 kV electric networks, a single 25 kV capacitor plant with simple autonomous control can be installed to compensate for reactive power. Several capacitor plants can compensate for reactive loads of 50 and 75 kVAr.

A method for tracing impulse voltage peak value using weighted frequency components

This paper studies a method for synthesizing impulse voltage peak error based on frequency energy weight. The research designed three capacitive voltage dividers with a voltage rating of 1 kV, 10 kV, and 200 kV, respectively, and measured their response characteristics using the step wave response test. The scale factor and linearity of the 1 kV capacitor divider were measured at different frequencies and impulse voltages to verify the equivalence of voltage coefficients under power frequency and impulse. Using boundary conditions obtained from AC voltage standard sources and impulse voltage standard generators, the equivalence of 200 kV power frequency voltage coefficient and impulse voltage coefficient was derived.

Modular electromagnetic railgun accelerator for high velocity impact studies.

A modular electromagnetic railgun accelerator facility named "RAFTAR" (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000m/s for an 8g solid aluminum-7075 armature projectile. The current fed was 220kA, having a muzzle time of about 1.75ms. It is a single pulse breech-fed rectangular bore (14 × 13mm2) railgun, and its 1.15m long barrel assembly consists of two parallel copper bars with an inter-gap of 13mm that are encased within 50mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.

Failure Analysis of the 100 T Pulsed Magnet at the WHMFC

A triple-coil pulsed magnet aiming at 100 T (Tesla) was designed and tested at the Wuhan National High Magnetic Field Center. The magnet was powered by a 100 MJ pulse generator, a battery bank, and 25 kV capacitor banks in combination. The magnet failed at 83 T, while the whole structure remained intact. The failure process was analyzed by using the recorded waveforms of the voltage and the current, as well as disassembling and dismantling the failed magnet. It shows that the inner coil broke down first, and then the electrical breakdown occurred between the middle and outer coils. The possible reasons were also discussed. The buckling analysis results show that the inner and middle coils would buckle at 71 T and 83 T, respectively, which were consistent with the experimental results. The cross-ply reinforcement method is proposed to enhance the structural stability of high field magnets.

ABOUT PHYSICS AND MATHEMATICS OF POWER SUPPLIES INDUSTRIAL AND SIMILAR TO THEM POWER CONSUMERS

Based on modern quantum physics, an original approach is proposed to the principle of mod- eling the transmission of electrical energy to industrial and equated consumers with a design power of up to 1000 kVA, which is performed using transformers of the TM-6 (10) / 0.4 kV type, provided that that their secondary voltage is a potential form of the SES electromagnetic energy supplied to such consumers. At the same time, the normal mode of the maximum load of the transformer is considered when its active and reac- tive loads are equal, at which the reactive load factor of the consumer's power supply system has the highest permissible value (the phase angle of the sinusoidal voltage current is zero). A static vector-quantum model of a transformer power transmission has been developed, which simplifies the understanding of the process of compensating for the reactive load of a transformer and makes it possible to refine the operating power of a capacitor bank with 0.4 kV capacitors. At the same time, the idea is confirmed that the value of the reactive load factor of a transformer is not only the main criterion for the electromagnetic compatibility of the SES of a particular electricity consumer, but also a criterion for its economic efficiency. Using the numerical value of such a coefficient, it is possible to determine the value of the economic equivalent of the reactive load of a particular SES.

STATIC VECTOR-QUANTUM TRANSFORMER MODEL ELECTRIC TRANSMISSIONS INDUSTRIAL AND SIMILAR TO THEM ELECTRICITY CONSUMERS UNDER 0.4 KV

Based on modern quantum physics, an original approach is proposed to the principle of mod- eling the transmission of electrical energy to industrial and equated consumers with a design power of up to 1000 kVA, which is performed using transformers of the ТМ-6(10)/0,4 kV type, provided that their secondary voltage is a potential form of SES electromagnetic energy supplied to such consumers. At the same time, thenormal mode of the maximum load of the transformer is considered when its active and reactive loads are equal, at which the reactive load factor of the consumer's power supply system has the highest permissible value (the phase angle of the sinusoidal voltage current is zero). A static vector-quantum model of a trans- former power transmission has been developed, which simplifies the understanding of the process of com- pensating for the reactive load of a transformer and makes it possible to refine the operating power of a ca- pacitor bank with 0.4 kV capacitors. At the same time, the idea is confirmed that the value of the reactive load factor of a transformer is not only the main criterion for the electromagnetic compatibility of the SES of a particular electricity consumer, but also a criterion for its economic efficiency. Using the numerical value of such a coefficient, it is possible to determine the value of the economic equivalent of the reactive load of a particular SES. At the same time, such a coefficient should be normalized to each specific consumer at the point of division of the balance sheet belonging to the electrical network of such a consumer.

Seismic analysis and retrofitting countermeasure for 1315 kV capacitor with multi-column posts

A number of power substations and converter stations are inevitably built in high earthquake intensity regions. There are many types of electrical equipment with multi-column posts in power substations and converter stations. The PLC/RI capacitor with high seismic vulnerability is a typical electrical equipment with multi-column posts. A 1315 kV PLC/RI capacitor was modeled and analyzed using finite element technique. The modal analysis results show that the primary frequency of the capacitor is close to the earthquake dominant frequency. Additionally, the 2nd, 3rd and 4th order frequencies are within the range of the flat segment of the seismic response spectrum. After performing seismic analysis, the most fragile location was identified, that is the porcelain insulator at the bottom of the capacitor. The stress safety factor of the porcelain insulator is 0.71, which indicates the capacitor does not meet the seismic requirement for peak ground acceleration (PGA) = 0.3 g. To improve the seismic performance of capacitor with multi-column posts, enhancing connection stiffness of the structure is proposed. Based on this countermeasure, the thickness of the connecting plate between the upper hollow composite insulators and the porcelain insulators at the bottom of capacitor was increased from 20 mm to 50 mm. After the optimization, the 1315kV PLC/RI capacitor satisfies the seismic requirement for PGA value of 0.3 g.

ТЕПЛОВИЗИОННЫЙ КОНТРОЛЬ КОНДЕНСАТОРОВ И ВЫСОКОЧАСТОТНЫХ ЗАГРАДИТЕЛЕЙ

The article considers the features of the occurrence of violations in the high-voltage electrical network, as well as the thermal imaging control of capacitors and high-frequency traps, the number of monitored points of this electrical equipment, the diagnostics of 35 kV capacitors of the “ladle furnace” installation of converter shops with a description of the transient process in the event of a defect, battery elements, as well as design features of capacitors and high-frequency traps with voltage 110...220 kV, the tangent of dielectric loss angle tgδ, the values of active current and steady-state voltage were calculated, the results are summarized in the table. Based on the calculations, a method of thermal imaging control was formed with the considered terms for eliminating these defects; a conclusion about the need to control the elements of the power supply system was made.

Seismic risk mitigation of cylindrical electrical equipment with a novel isolation device

Cylindrical electrical equipment is common in substations and vulnerable in earthquakes. Isolation technique, as an important method to mitigate seismic demand, has attracted less attention in electrical substation. This study aims at filling the knowledge gap by introducing a novel isolation device for cylindrical electrical equipment. The device is a combination of circularly arranged lead alloy isolator units installed at the bottom of equipment. A 1000 kV capacitor voltage transformer is adopted as specimen, and both non-linear time history analysis and shaking table test are incorporated in examining seismic mitigation effect. Probabilistic seismic demand analysis is carried out with two set of ground motions: recorded ground motions with spectral acceleration's corner periods around 0.85 s and scaled ground motions with corner periods around 1.7 s. Results show that for recorded ground motions, the failure probabilities on both flexural moment and displacement demand are lowered significantly; for scaled ground motions, the mitigation on flexural moment demand is significant but the effect on displacement demand is negligible, revealing that mitigation effect on displacement demand is promising but more conditional on properties of input. In shaking table test, a code spectrum compatible wave is adopted as excitation, and results show that the device is successful to reduce the acceleration, displacement and stress responses by more than 50% under a 1.4 × 0.5 g PGA input. Besides mitigation effects on earthquake induced flexural moment and displacement, the isolation device also avoids residual deformation after shaking and does not increase vibration amplitudes under wind. Numerical model of the isolation device is proposed with a validation by shaking table test result, providing a useful tool for parameter design of the device. The isolation technique and device in this paper offer an important option for seismic enhancement of cylindrical equipment in substations.

Design, simulation and construction of the Taban tokamak

This paper describes the design and construction of the Taban tokamak, which is located in Amirkabir University of Technology, Tehran, Iran. The Taban tokamak was designed for plasma investigation. The design, simulation and construction of essential parts of the Taban tokamak such as the toroidal field (TF) system, ohmic heating (OH) system and equilibrium field system and their power supplies are presented. For the Taban tokamak, the toroidal magnetic coil was designed to produce a maximum field of 0.7 T at R = 0.45 m. The power supply of the TF was a 130 kJ, 0–10 kV capacitor bank. Ripples of toroidal magnetic field at the plasma edge and plasma center are 0.2% and 0.014%, respectively. For the OH system with 3 kA current, the stray field in the plasma region is less than 40 G over 80% of the plasma volume. The power supply of the OH system consists of two stages, as follows. The fast bank stage is a 120 μF, 0–5 kV capacitor that produces 2.5 kA in 400 μs and the slow bank stage is 93 mF, 600 V that can produce a maximum of 3 kA. The equilibrium system can produce uniform magnetic field at plasma volume. This system’s power supply, like the OH system, consists of two stages, so that the fast bank stage is 500 μF, 800 V and the slow bank stage is 110 mF, 200 V.

Investigation of Transformer Winding Architectures for High-Voltage (2.5 kV) Capacitor Charging and Discharging Applications

Transformer parasitics such as leakage inductance and self-capacitance are rarely calculated in advance during the design phase, because of the complexity and huge analytical error margins caused by practical winding implementation issues. Thus, choosing one transformer architecture over another for a given design is usually based on experience or a trial and error approach. This paper presents analytical expressions for calculating leakage inductance, self-capacitance, and ac resistance in transformer winding architectures (TWAs), ranging from the common noninterleaved primary/secondary winding architecture, to an interleaved, sectionalized, and bank winded architecture. The calculated results are evaluated experimentally, and through finite-element simulations, for an RM8 transformer with a turns ratio of 10. The four TWAs such as, noninterleaved and nonsectioned, noninterleaved and sectioned, interleaved and nonsectioned, and interleaved and sectioned, for an EF25 transformer with a turns ratio of 20, are investigated and practically implemented. The best TWA for an RM8 transformer in a high-voltage bidirectional flyback converter, used to drive an electro active polymer based incremental actuator, is identified based on the losses caused by the transformer parasitics. For an EF25 transformer, the best TWA is chosen according to whether electromagnetic interference due to the transformer interwinding capacitance, is a major problem or not.

Development of a compact generator for gigawatt, nanosecond high-voltage pulses.

A compact generator producing 2.2-ns 1.5 GW high-voltage pulses was developed. The generator employed a 27.6 Ω, 0.9 ns pulse-forming-line (PFL), which was charged by an iron core transformer with a turn ratio of 2:33.5 and a coefficient of 0.94. A 1.2 μF, 20 kV capacitor and a hydrogen thyratron were used in the primary circuit. When the thyratron closed at 14.5 kV, 3.4% of the energy stored in the capacitor was delivered to the PFL in 850 ns, producing a peak voltage of up to ∼500 kV. In addition, the principle of triple resonance transformation was employed by adding a 50 pF tuning capacitor and a 1.15 mH inductor between the transformer and the PFL, which led to a significant reduction of the duration and peak value of the transformer voltage without reducing that in the PFL. Meanwhile, an adjustable self-break oil switch was applied. By using transmission lines with impedance overmatched to that of the PFL, the generator delivered a 512 kV pulse across an electron beam diode, generating radiation with a dose of 20 mR/pulse at 20 cm ahead of the diode. The generator provides an excellent ultra-short radiation pulse source for the studies on radiation physics.

Conducted noise analysis and protection of 45 kJ/s, ±50 kV capacitor charging power supply when interfaced with repetitive Marx based pulse power system.

Pulse power systems with highly dynamic loads like klystron, backward wave oscillator (BWO), and magnetron generate highly dynamic noise. This noise leads to frequent failure of controlled switches in the inverter stage of charging power supply. Designing a reliable and compatible power supply for pulse power applications is always a tricky job when charging rate is in multiples of 10 kJ/s. A ±50 kV and 45 kJ/s capacitor charging power supply based on 4th order LCLC resonant topology has been developed for a 10 Hz repetitive Marx based system. Conditions for load independent constant current and zero current switching (ZCS) are derived mathematically. Noise generated at load end due to dynamic load is tackled effectively and reduction in magnitude noise voltage is achieved by providing shielding between primary and secondary of high voltage high frequency transformer and with LCLC low pass filter. Shielding scales down the ratio between coupling capacitance (Cc) and the collector-emitter capacitance of insulated gate bi-polar transistor switch, which in turn reduces the common mode noise voltage magnitude. The proposed 4th order LCLC resonant network acts as a low pass filter for differential mode noise in the reverse direction (from load to source). Power supply has been tested repeatedly with 5 Hz repetition rate with repetitive Marx based system connected with BWO load working fine without failure of single switch in the inverter stage.

Design of Capacitor Blocks with Multi-Channel Switches for Linear Transformer Driver Stages

In the linear transformer driver technology, the low inductance energy storage components and switches are directly incorporated into the individual cavities (named stages) to generate a fast output voltage pulse, which is added along a vacuum coaxial line like in an inductive voltage adder. In this paper, we outline the detailed design concept and the basic parameters of four capacitor blocks with four different types of multi-channel gas switches. The 100 kV capacitor block #1 and #2 incorporate two parallel capacitors (40 nF, 100 kV) and multi-gap multi-channel gas switches with triggering plate or triggering cable. The 200 kV capacitor block #3 and #4 incorporate two capacitors (40 nF, 100 kV) in series and rail-gap gas switches with one triggering rail or two triggering rails. Operating principles of four multi-channel gas switches are illustrated by using the equivalent electrical scheme of each switch. The basic characteristics of four capacitor blocks are given. The effect of stray capacitances on the trigger pulses is also discussed.

Design and test of a flat-top magnetic field system driven by capacitor banks.

An innovative method for generating a flat-top pulsed magnetic field by means of capacitor banks is developed at the Wuhan National High Magnetic Field Center (WHMFC). The system consists of two capacitor banks as they are normally used to generate a pulsed field. The two discharge circuits (the magnet circuit and the auxiliary circuit) are coupled by a pulse transformer such that the electromotive force (EMF) induced via the transformer in the magnet circuit containing the magnet coil is opposed to the EMF of the capacitor bank. At a certain point before the current pulse in the coil reaches its peak, the auxiliary circuit is triggered. With optimized parameters for charging voltage and trigger delay, the current in the magnet circuit can be approximately kept constant to obtain a flat-top. A prototype was developed at the WHMFC; the magnet circuit was energized by seven 1 MJ (3.2 mF/25 kV) capacitor modules and the auxiliary circuit by four 1 MJ modules. Fields up to 41 T with 6 ms flat-top have been obtained with a conventional user magnet used at the WHMFC.

Analysis of the Charging Characteristics of High Voltage Capacitor Chargers Considering the Transformer Stray Capacitance

In this paper, the charging characteristics of series resonant type high voltage capacitor chargers considering the transformer stray capacitance have been studied. The principles of operation for the four operational modes and the mode changes for the four different switching frequency sections are explained and analyzed in the range of switching frequency below the resonant frequency. It is confirmed that the average charging currents derived from the above analysis results have non-linear characteristics in each of the four modes. The resonant current, resonant voltage, charging current, and charging time of this capacitor charger as variations of the switching frequency, series parallel capacitance ratio (<TEX>$k=C_p/C_s$</TEX>), and output voltage are calculated. From the calculation results, the advantages and disadvantages arising from the parallel connection of this stray capacitance are described. Some methods to minimize charging time of this capacitor charger are suggested. In addition, the results of a comparative test using two transformers whose stray capacitances are different are described. A 1.8 kJ/s prototype capacitor charger is assembled with a TI28335 DSP controller and a 40 kJ, 7 kV capacitor. The analysis results are verified by the experiment.

3상 직렬공진형 고전압 커패시터 충전기의 해석 및 설계

This paper suggests a 3-phase series-resonant type high voltage capacitor charger for an EML pulsed power system. The operating principle on the charger is explained by an equivalent circuit. Additionally, we analyze the charging characteristic in one discontinuous conduction mode and three continuous conduction modes. The analysis shows that the resonant current per phase is two thirds of the 3-phase charger’s average charging current and one third of the single-phase charger’s average charging current with the same capacity. We suggest a design method of the 3-phase capacitor charger in each operational mode and present an example of 3.5 kW capacitor charger at ω<SUB>s</SUB>=0.33ω<SUB>r</SUB>. The 3.5 kW 3-phase capacitor charger prototype is assembled with a TI28335 controller and a 40 kJ, 7 kV capacitor. The design rules based on the analysis are verified by experiment.

A Study on the Conducted Interference of Capacitor Charging Power Supply

In this paper, a mathematical analysis of the EMI (Electromagnetic Interference) for a 20 kHz/10 kV capacitor charging power supply in frequency-domain is presented, and a related circuit model considering the transient switching interference is proposed. Due to the high working frequency and the device-switching transitions, the conducted EMI caused by the charging circuit which includes the harmonics of grid frequency, working frequency and device-switching transition frequencies. Thus under certain working situations or loads parallel power supply, the interference may cause charging failure. To solve this problem, a high frequency transformer modeled with stray capacitances and an approximation of the device-switching transition is applied in the Spice-based simulation model, and a mathematical analysis in frequency-domain is presented.

Developments of Multi-extreme High Field ESR in Kobe

Recent developments of “multi-extreme” high magnetic field electron spin resonance (ESR) in Kobe will be reviewed. Our high magnetic field ESR covers the frequency region between 0.03 and 7 THz and the temperature region between 1.8 and 300 K. With this high magnetic field ESR system we can apply the magnetic field up to 55 T using a Cu-Ag pulsed magnet and a 300 kJ (10 kV) capacitor bank. Under this high magnetic field we can also apply the high pressure up to 1.4 GPa. As we can make the measurement under low temperature, high magnetic field and high pressure simultaneously, we name it as “multi-extreme” ESR. Moreover, in order to gain the sensitivity of our high magnetic field ESR, we have developed a micro-cantilever ESR system using a torque method, which enables the ESR measurement of micrometer size single crystal at low temperature. At the moment we are in the process of extending the magnetic field region of micro-cantilever ESR. Recently we have succeeded in making the measurement up to 369 GHz and the achieved sensitivity is about 1010 spins/G, which is much higher than that using the conventional transmission method. Finally our development of magnetization detected ESR using SQUID magnetometer (SQUID ESR) will be also presented.