DC Voltage Tests Research Articles

Design and testing of a high-precision generating voltmeter for metal-enclosed megavolt level DC voltage source.

An extremely stable megavolt (MV) level DC voltage source is the key foundation for many scientific instruments, and the need for accurate measurement and long-term real-time monitoring of its output voltage is increasingly urgent. The utilization of conventional resistive voltage dividers for measurements introduces leakage currents, resulting in considerable measurement errors. The non-contact generating voltmeter (GVM) sensor based on electric field measurement has a simple structure and a low cost, making it expected to be an effective solution. Currently, most research on GVM sensors focuses on the measurement of weak electric fields at kV/m levels with significant interference. In this paper, an improved high-precision non-contact GVM sensor was designed. A DC voltage test platform was built, and the effects of the sampling resistor and motor rotation speed on the measurement results were discussed. The relative combined uncertainty of the improved GVM sensor reached 0.042%, which satisfied the urgent need for MV level DC voltage source measurement. The improved GVM sensor can provide an effective reference for measuring the output voltage of a metal-enclosed MV level DC voltage source or the potential of a suspended electrode.

Long-term DC voltage test method of HVDC wall bushing with resin impregnated paper capacitor core considering electro-thermal coupling coefficient

HVDC wall bushing connects the valve hall and the DC field in the converter station, which is the core equipment in HVDC transmission system. The resin impregnated paper capacitor core inside the bushing withstands long-term full DC voltage and full load DC current during operation. Thus, 2 hours long-term DC voltage test and temperature rise test are required to verify its insulation and thermal performance. However, internal discharge faults caused by overheating of current carrying structure still occur frequently in recent years, which means the insulation and thermal defects of the bushing under long-term electrothermal coupling stress can not be completely inspected only IEC standard test. In this paper, the influence of temperature on internal partial discharge measurement and electrical field calculation of resin impregnated paper capacitor core of HVDC bushing are carried out, and the electro-thermal coupling coefficient is given. Finally, a new long-term DC voltage test method during manufacturing process is proposed. This new method has important theoretical significance and engineering application value for internal defect evaluation, discharge or thermal fault diagnosis, as well as estimation of the reliability of both insulation and thermal performance in the life cycle of bushing.

Electrical tree initiation in XLPE cable insulation under constant DC, grounded DC, and at elevated temperature

Electrical tree initiation behavior was investigated in XLPE insulation samples made from a HVDC cable by applying constant DC and grounded DC voltages under different temperatures. No trees appeared when a constant DC voltage of −60 kV was applied for 12 days at room temperature or 20 days at 90°C, and the tree initiation time was estimated to be more than 200 days by Bayes statistical processing of zero-failure data. In the grounded DC voltage test, −15 kV prestress could trigger a tree, and under −35 kV, the tree initiation rate reached 100 %. With the increase of DC prestress, both the initiation rate and tree length increased. Grounded DC trees were branch trees with dark-colored channels, and a similar material damage could be caused by the same DC prestress. The connection of a grounding resistor could reduce the damage of sample caused by the grounded DC voltage, and the tree initiation rate declined with the increase of the resistance. According to the experimental results, the tree initiation time under constant DC voltage was not significantly shortened at 90°C, whereas tree initiation under grounded DC voltage was promoted by the increase of temperature. From 25 to 70°C, the tree branches became longer and denser, and extended in more varied directions. The observations are explained by the injection, transfer, trapping and detrapping of space charges, and charge detrapping is believed to be the cause of material damage.

Enhancement of the Insulation Properties of Poly(2-oxazoline)-co-Polyester Networks by the Addition of Nanofillers.

Copoly(2-nonyl-2-oxazoline)-stat-poly(2-dec-9'enyl-2-oxazoline)s can be crosslinked by the thiol-ene reaction with glycol dimercaptoacetate. The copoly(2-oxazoline)-stat-copolyester is tested as dielectric for high-voltage applications, either as unfilled resin or as composite with nanoscaled fillers of silica, alumina, and hexagonal boron nitride. During AC voltage tests, all materials have an average breakdown strength of 45-50 kV mm-1 . For DC voltage tests, samples with SiO2 (hBN) have an average breakdown strength of ≈100 (80) kV mm-1 , while the unfilled copoly(2-oxazoline) has an average breakdown strength of ≈60 kV mm-1 . Permittivity measurements at 20 °C and 50 Hz reveal that all nanocomposites are dielectrics (D = 0.06-0.08), while the unfilled copoly(2-oxazoline)s has a high loss factor of D = 8.43. This phenomenon can be retraced to the phase separation in the crosslinked copolymer, the M-OH functionality of silica and alumina particles, and models of polymer-particle interactions such as the Tanaka model, revealing that the nanofillers reduce the interfacial and dipolar polarizability.

InGaAs/AlAs Resonant Tunneling Diodes for THz Applications: An Experimental Investigation

This paper presents an experimental study of InGaAs/AlAs resonant tunneling diodes designed to improve the diode characteristics using five different device structures. A promising high peak to valley current ratio of 5.2 was obtained for a very low current density device. As expected, the measured results show a significant increase in the current density with thinner barriers and quantum well widths. This is, however, at the expense of an increase in the peak voltages for high peak current density devices. A 36-mV/ $\mu$ m2 voltage deviation was found for a diode with a peak current density of 10.8 mA/ $\mu$ m2 that we attribute to self-heating of the diodes, and which were confirmed using pulsed dc voltage tests. To demonstrate how the self-oscillation at low frequency can be eliminated, a 25 $\Omega$ resistor was integrated in parallel with the diodes. The experimental findings suggest that the partially stabilizing resistor is limited by the absolute value of the negative differential resistance. The equivalent circuit of the diodes was validated using on-wafer S-parameter measurements up to 40 GHz. An estimated high frequency operation limit of 2.7 THz was deduced for RTD sample #327.

Influence of void defects on partial discharge behavior of superconducting busbar insulation

For a magnetic confinement fusion device, the superconducting magnets and busbars need to be insulated with one layer of solid insulation to isolate the high voltage potential from the ground. The insulation layer commonly consists of several interleaved layers of epoxy resin-impregnated glass fiber tapes and polyimide films. The traditional electrical inspection methods for such solidified insulation on the magnet and busbar are a DC voltage test or a Paschen test. These tests measure the quality of the insulation based on the value of leakage currents. However, even if there is a larger quantity of high dielectric strength material implemented, if there are some microcavities or delaminations in the insulation system, the leakage current may be limited to microampere levels under testing levels over dozens of kilovolts. Therefore, it is difficult to judge the insulation quality just by the magnitudes of leakage current. Under long-term operation, such imperceptible defects will worsen and finally completely break down the insulation because of partial discharge (PD) incidents. Therefore, a PD detection test is an important complement to the DC voltage and Paschen tests for magnet and busbar insulations in the field of fusion.It is known that the PD detection test is a mature technique in the electric power industry. In this paper, the PD characteristics of samples containing glass fiber-reinforced composite insulations for use with the superconducting busbar were presented and discussed. Various samples with different void contents were prepared and the PD behaviors were tested.

New electrical shunt with two rectangular holes in a copper plate

A new concept of an electrical shunt with two rectangular holes in a copper plate (ESRP) has been developed to be used for measuring a large current with a short‐duration steep wave in a high‐voltage field. The ratio of the input current to the output current is 106, as obtained from a DC voltage test circuit. The electrical shunt has a special configuration. To verify the shunt current ratio of ESRP in a real application, the shunt current was connected to a sphere‐to‐sphere electrode breakdown test circuit with a 10 mm gap to measure the large damping current (8.4 kA) of a DC breakdown voltage. The voltage signal from the shunt was transmitted to excite two light‐emitting diodes (max. 50 mA, 4 V), which were reverse‐connected in series. The light‐emitting diodes operated properly and were illuminated, which validated the capability of the newly designed electrical shunt. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

ADC Static Characterization Using Nonlinear Ramp Signal

Static characteristics of an analog-to-digital converter (ADC) can be directly determined from the histogram-based quasi-static approach by measuring the ADC output when excited by an ideal ramp/triangular signal of sufficiently low frequency. This approach requires only a fraction of time compared to the conventional dc voltage test, is straightforward, is easy to implement, and, in principle, is an accepted method as per the revised IEEE 1057. However, the only drawback is that ramp signal sources are not ideal. Thus, the nonlinearity present in the ramp signal gets superimposed on the measured ADC characteristics, which renders them, as such, unusable. In recent years, some solutions have been proposed to alleviate this problem by devising means to eliminate the contribution of signal source nonlinearity. Alternatively, a straightforward step would be to get rid of the ramp signal nonlinearity before it is applied to the ADC. Driven by this logic, this paper describes a simple method about using a nonlinear ramp signal, but yet causing little influence on the measured ADC static characteristics. Such a thing is possible because even in a nonideal ramp, there exist regions or segments that are nearly linear. Therefore, the task, essentially, is to identify these near-linear regions in a given source and employ them to test the ADC, with a suitable amplitude to match the ADC full-scale voltage range. Implementation of this method reveals that a significant reduction in the influence of source nonlinearity can be achieved. Simulation and experimental results on 8- and 10-bit ADCs are presented to demonstrate its applicability.

Partial discharge study in transformer oil due to particle movement under DC voltage using the UHF technique

Converter transformers are one of the key components in high voltage DC power networks. The insulation of these transformers is stressed by both AC and DC voltages. Therefore, AC and DC voltage tests are routinely applied during factory tests to verify the performance of the insulation structure. Partial discharges in an insulation system are incipient discharges that can damage materials and may eventually lead to complete failure of the insulation system during operation. Recently it has been shown that monitoring such discharges formed under AC stress is feasible using Ultra High Frequency (UHF) measurement technique and that there is a reasonable correlation between the partial discharge magnitude and the amplitude of the UHF signal generated by partial discharges. However, the partial discharge activity under DC voltages is not fully understood. This paper describes a study using the UHF technique to improve our understanding of particle-induced partial discharge activity under DC voltages in mineral oil insulation. UHF signals generated due to conducting particle contamination in transformer oil under AC and DC voltages are compared and analyzed. A method for distinguishing particle discharges in regions of high or low electric field stress is proposed based on frequency-domain analysis of the measured UHF signal.