Medium Voltage Research Papers - Academia.edu (original) (raw)

Partial discharge (PD) measurements conducted in the high voltage (HV) laboratory are less affected by electromagnetic disturbances (EMD). However, on the other hand, online/on-site PD measurements are often affected by several EMD... more

Partial discharge (PD) measurements conducted in the high voltage (HV) laboratory are less affected by electromagnetic disturbances (EMD). However, on the other hand, online/on-site PD measurements are often affected by several EMD sources. Extracting low level PD ...

Three-level NPC active-front-end three-phase (3LAFE) converters can be applied to high-power medium voltage applications, with 4-quadrant unity-power-factor operation, allowing a broad range for power conversion systems, such as... more

Three-level NPC active-front-end three-phase (3LAFE) converters can be applied to high-power medium voltage applications, with 4-quadrant unity-power-factor operation, allowing a broad range for power conversion systems, such as decentralized energy distribution and utilization. Switching losses and network interaction limit the operation of 3LAFE high-power converters, especially when GTO-converters are used.

This paper focuses on simulation based dielectric design rules of air insulated medium voltage power equipment. After a brief overview on the classical dielectric designing procedure, we propose possible new concepts and present first... more

This paper focuses on simulation based dielectric design rules of air insulated medium voltage power equipment. After a brief overview on the classical dielectric designing procedure, we propose possible new concepts and present first experimental results on streamer inception and propagation affected by dielectric surfaces. For evaluation of the inception voltage we achieved a good experimental agreement for a path

The present research study is focused on the design, development and validation of a device based on multilevel converter for medium voltage distribution networks. It regulates the reactive power exchanged with the grid (up to 3 MVAR),... more

The present research study is focused on the design, development and validation of a device based on multilevel converter for medium voltage distribution networks. It regulates the reactive power exchanged with the grid (up to 3 MVAR), allowing to achieve the following objectives: Network voltage regulation, reactive power compensation and power factor control. The device is composed by an IGBT based 4 level NPC (neutral point clamped) converter. The adopted modulation strategy is the space vector modulation and it takes into account the bus capacitor voltage balancing. The reactive power regulation will be carried out by a vector control technique. The correct behavior of the electronic system connected to a radial distribution network is validated in simulation. Firstly the behavior of the system is analyzed under normal operation conditions. After that, its robustness is analyzed when sudden network voltage changes occur

Arc flash is an important consideration for personnel safety. This paper shows test results for overhead arc flash scenarios and arc flash in a padmounted switch. Both scenarios result in more incident energy than expected. For overhead... more

Arc flash is an important consideration for personnel safety. This paper shows test results for overhead arc flash scenarios and arc flash in a padmounted switch. Both scenarios result in more incident energy than expected. For overhead arc scenarios, longer arc lengths are considered when analyzing arc flash. For the padmounted switch, an equation is developed to help coordinate protective clothing with minimum approach distances and upstream protective relaying.

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge... more

This paper investigates the repetitive surge-voltage withstand of low-voltage mush-wound machines operated on adjustable-speed drives (ASDs) using insulated gate bipolar transistor (IGBT) semiconductor technology. Historical work on surge testing of motor insulation has focused on one or more of the following aspects: (1) large horsepower motors; (2) medium-voltage form-wound motors; (3) single-shot impulse-type transients; or (4) low-voltage machines with surge risetimes >200 ns. IGBT drives can have risetimes of 50-200 ns. Thus, a new study on electrical stress of insulation systems due to the nonlinear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and risetime of the repetitive ASD surge-voltage transient induced on the machine terminals is reviewed first. Next, surge propagation into the winding was investigated to identify maximum voltage stress points on the conductor insulation. Potential failure mechanisms observed at these points are then discussed. The significance of decreasing surge risetime and increasing cable lengths on internal nonlinear voltage distribution is studied with experimental results from a 7.5-hp motor with a tapped stator winding

In this paper is presented a solution for optimal operation of the Francis turbine, the most used hydro energy converter in small hydro plants. As the efficiency of this turbine is highly dependent from the water flow, which generally has... more

In this paper is presented a solution for optimal operation of the Francis turbine, the most used hydro energy converter in small hydro plants. As the efficiency of this turbine is highly dependent from the water flow, which generally has a large variation, variable speed operation was chosen. Due to the fact that all hydro generators are AC machines, the connection to the 50 Hz power grid can be done only using as interface the AC/DC DC/AC static converters. For higher than 1 MW power generators, front end three level inverters are recommended. In addition, for higher than 1 kV voltage, double three level inverters shall be used, as these are allowing their connection directly to the medium voltage grid, eliminating in this way the need of separation transformers. The converter control is done by a single chip DSP controller TM3202028, which takes care of all system functions.

There has been a considerable amount of discussion concerning partial discharge (PD) measurements on medium voltage motors and generators. If one considers the total plant electrical distribution system and production equipment, motors... more

There has been a considerable amount of discussion concerning partial discharge (PD) measurements on medium voltage motors and generators. If one considers the total plant electrical distribution system and production equipment, motors comprise only a small part of the plant electrical equipment. If a motor should fail, part of production will likely be shut down and there will be lost revenue. However, there is a wide variety of other equipment in a facility besides a motor that can fail and can have a much more devastating effect on the plant's production. Additional items to consider for partial discharge monitoring are the plant incoming transformers (they may be owned by the plant if the plant is purchasing primary power), the incoming switchgear, cables, bus duct, other remote substation switchgear and power center transformers. Methods have been developed for monitoring partial discharges in all types of medium voltage equipment. This paper discusses application of sensors, methods of measurement and data interpretation and presents several case studies

Partial discharge technology has been applied to medium voltage rotating machines for many years. This technology can now be applied to support on-line diagnostics of medium voltage switchgear assemblies. Partial discharge sensors have... more

Partial discharge technology has been applied to medium voltage rotating machines for many years. This technology can now be applied to support on-line diagnostics of medium voltage switchgear assemblies. Partial discharge sensors have been developed, with calibration both in the factory-test floor environment, as well as in the field under normal operating conditions. The application of partial discharge measurement technology to MV switchgear will be presented, with actual examples of pending failures, which were identified by on-line partial discharge measurements. This application of partial discharge technology can greatly aid in the day-to-day reliability and life-extension of the medium voltage electrical power substation assemblies

An ultracapacitor bank control system for an Electric Vehicle has been simulated. The purpose of this device is to allow higher accelerations and decelerations of the vehicle with minimal loss of energy, and minimal degradation of the... more

An ultracapacitor bank control system for an Electric Vehicle has been simulated. The purpose of this device is to allow higher accelerations and decelerations of the vehicle with minimal loss of energy, and minimal degradation of the main battery pack. The system uses an IGBT Buck-Boost converter, which is connected to the ultracapacitor bank at the Boost side, and to the main battery at the Buck side. The control of the system measures the battery voltage, the battery state-of-charge, the car speed, the instantaneous currents in both the terminals (load and ultracapacitor), and the actual voltage of the ultracapacitor. This last indication allows to know the amount of energy stored in the ultracapacitor. A microcomputer control manipulates all the variables and generates the PWM switching pattern of the IGBTs. When the car runs at high speeds, the control keeps the capacitor discharged. If the car is not running, the capacitor bank remains charged at full voltage. Medium speeds ke...

Contact with overhead power lines is regarded worldwide as one of the leading causes of electrical fatalities. The analysis carried out in this paper refers to a real accident that occurred in Greece a few years ago, involving the contact... more

Contact with overhead power lines is regarded worldwide as one of the leading causes of electrical fatalities. The analysis carried out in this paper refers to a real accident that occurred in Greece a few years ago, involving the contact of a heavy vehicle (concrete pump) with the medium voltage lines of the national distribution network. For a better understanding of the incident, a description of how the protection system of medium voltage distribution lines works when a fault occurs is given. Furthermore, emphasis has been laid on possible ways to avoid similar accidents in the future.► A heavy vehicle came into contact with an overhead power line with a fatal outcome. ► The analysis showed that the existing network protection system is anthropocentric. ► Technical and organizational proposals are made to reduce future accidents. ► Safer work ethic and an increased awareness in society should be promoted. ► The electrical community should support a global effort.

Multilevel inverters are in state-of-the-art power conversion systems due to their improved voltage and current waveforms. Cascaded H-bridge (CHB) multilevel inverters have been considered as an alternative in the medium-voltage converter... more

Multilevel inverters are in state-of-the-art power conversion systems due to their improved voltage and current waveforms. Cascaded H-bridge (CHB) multilevel inverters have been considered as an alternative in the medium-voltage converter market and experimental electric vehicles. Their variant, the asymmetrical CHB (ACHB) inverter, optimizes the number of voltage levels by using dc supplies with different voltages. However, the CHB and ACHB inverters require a large number of bidirectional and isolated dc supplies that must be balanced, and as any multilevel inverter, they reduce the power quality with the voltage amplitude. This paper presents a solution to improve the already mentioned drawbacks of ACHB inverters by using a high-frequency link using only one dc power source. This single power source can be selected according to the application (regenerative, nonregenerative, and with variable or permanent voltage amplitude). This paper shows the experimental results of a 27-level ACHB inverter with a variable and single dc source, but the strategy can be applied to any ACHB inverter with any single dc source. As a result, the reduction of active semiconductors, transformers, and total harmonic distortion was achieved using only one dc power source.