Ahmed A. Hossam-Eldin

Interference between HV transmission line and nearby pipelines

Transmission lines are the major source of electromagnetic field interference (EMFI) with metallic structures such as pipelines, railways and under ground cables laying in the same corridor. It is a serious problem because the (EMFI) produces induced voltages on the metallic structures .These voltages can result in hazard volt to operating personnel especially who operate on pipelines .It can affect the pipeline associated equipment (cathodic protection , damage the coating , affect the pipe itself and furthermore will produce corrosion). This paper discusses the study for inductive interference between pipeline and neighboring electrical transmission line .It is especially used to simplify and to automate the modeling for right-of-way configuration involving transmission line and pipeline .It can calculate the voltage on pipeline and the longitudinal current. A practical case study of inductive interference between a pipeline and electrical power line under steady state condition is illustrated.

An Interline Dynamic Voltage Restoring and Displacement Factor Controlling Device (IVDFC)

An interline dynamic voltage restorer (IDVR) is invariably employed in distribution systems to mitigate voltage sag/swell problems. An IDVR merely consists of several dynamic voltage restorers (DVRs) sharing a common dc link connecting independent feeders to secure electric power to critical loads. While one of the DVRs compensates for the local voltage sag in its feeder, the other DVRs replenish the common dc-link voltage. For normal voltage levels, the DVRs should be bypassed. Instead of bypassing the DVRs in normal conditions, this paper proposes operating the DVRs, if needed, to improve the displacement factor (DF) of one of the involved feeders. DF improvement can be achieved via active and reactive power exchange (PQ sharing) between different feeders. To successfully apply this concept, several constraints are addressed throughout the paper. Simulation and experimental results elucidate and substantiate the proposed concept.

Analysis and simulation of field distribution in micro cavities in solid insulating materials

Internal discharges in cavities in solid dielectric materials lead to the degradation, deterioration and complete failure of insulating materials. This would shorten the life time of the electrical equipments, which affects the reliability of power supply. This research is an investigation and study of the internal discharges, as magnitude and energy, in micro cavities in solid dielectric samples. The field distribution in these cavities was simulated, modeled and calculated for certain applied voltage. Alternating high voltage at power frequency at room temperature was applied with different values of the inception voltage of the sample. The cavity shape, cylindrical and spherical, and its dimensions were changed, with the cavity cross-sectional area much larger than its depth. The size of the cavity was much smaller than the sample thickness. The study was done on low density polyethylene (LDPE), polyvinyl chloride (P.V.C) and ethylene polypropylene rubber (E.P.R) because of their important industrial applications. The location of the cavity w.r.t the h.v. electrode in the dielectric sample was changed, to be in the center, adjacent to the h.v. electrode and near to the ground electrode. The number of cavities was changed from one to three either in horizontal or in vertical formation or at random in the sample. The relation permittivity of the dielectric was changed from 2 to 10. The field distribution and its enhancement within the cavity were calculated by a developed program using the boundary element technique. The field magnitude inside the cavity was significantly increased by increasing the relative permittivity of the dielectric, its magnitude was enlarged for cavities adjacent to h.v. electrode. As the number of cavities was increased the discharge magnitude and energy was increased. Multilayer samples showed very interesting results. The simulated results are in good agreement with the experimental findings. This indicates the effectiveness of the simulation developed method.

Investigation of Inter-Line Dynamic Voltage Restorer with virtual impedance injection

The Inter-Line Dynamic Voltage Restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for voltage sag that appears in its feeder (voltage control mode), the other inverters pump the required power into the dc bus (power control mode). Each inverter will have both voltage and power controllers; only one controller is in use during the abnormal conditions according to its feeder state. The voltage controller uses one of the dynamic voltage restoration techniques. In this paper, the in-phase technique is applied and two types of loads are considered (constant impedance and three phase induction motor). Since the voltage restoration process may need real power injection into the distribution system. The power controller injects this power via voltage injection; this voltage injection is simulated by voltage drop across series virtual impedance. A new scheme is proposed to select the impedance value. The impedance value is selected such that the power consumed by this impedance represents the required power to be transferred without perturbing the load voltage. The performance of this system is also studied during voltage swell. Simulation results substantiate the proposed concept.

New measurement technique for modular multilevel converter with IGBT open-circuit failure detection and tolerance control for three-level submodule

Modular multilevel converter (MMC) served as a promising converter for High Voltage Direct Current (HVDC) transmission. However, reliability is one of the most important challenges. Redundant submodules (SMs) are often used to replace the faulty SMs to ensure continuous operation of the scheme and increase the system reliability. In this paper, a fault detection and clearance is proposed for three level SMs topology without additional voltage sensors or complex algorithms. The fault is detected using a measurement technique that has half the number of voltage sensors compared to conventional half-bridge. The main advantage of the proposed technique is the reduction of the number of voltage sensors with full estimation for the capacitors voltages. Moreover, it provides fault detection and tolerance control. A simulation model has been implemented to validate the proposed technique and to evaluate its performance.

Electric Strength of Polymers Under Vacuum at Cryogenic Temperatures

Abstract The electric strength of solid polymers under high vacuum is investigated at a temperature ranging from 293°K down to that of liquid helium (5°K) under power frequency alternating- and direct-voltages. The electric strength of polymers was found to be very dependent on the pre-breakdown partial discharges when measured in cryogenic medium whether gas or liquid. When helium was used as coolant, discharges may extend very far from the electrodes and thus exerted high electric stresses on large areas of the sample under test. These discharges may produce flash-over and serious troubles. It may also lead to localised breakdown of polymers which may give apparent reduction in dielectric strength. A large increase in the electric strength of polymers was observed when used at cryogenic temperatures under vacuum; the increase was very significant for polyethylene and polyimide specially under direct voltages. The results showed promising properties and it is concluded that the high vacuum will offer the...

Maritime structures and ships lightning protection

This paper investigates and demonstrates a developed technique to use the collection volume method (CVM) for the placement of either conventional or non-conventional lightning protection systems (LPS) for ships. Each lightning eliminator assigned a striking distance, which is calculated as a function of ship height, radius of curvature, ship location, ship dimensions, risk factor, and lightning related parameters. This novel technique was applied to a medium war ship, Cargo, destroyer, as well as an air craft carrier, and showed to be a very efficient mean for lightning protection for these ships. For some design cases, a hybrid system was chosen to be the most efficient and the less expensive system.

The collection volume method for lightning protectors placement on naval ships

This paper investigates and demonstrates a developed technique to use the collection volume method (CVM), for the placement of either conventional or non-conventional lightning protection systems (LPS) for ships. Each lightning eliminator assigned a striking distance, which is calculated as a function of ship height, radius of curvature, ship location, ship dimensions, risk factor, and lightning related parameters. This novel technique was applied to a medium war ship, cargo, destroyer, as well as an air craft carrier, and showed to be a very efficient mean for lightning protection for these ships. For some design cases, a hybrid system was chosen to be the most efficient and the less expensive system.

Study and modeling of water treeing in solid insulation of power cables

A study of the phenomena of water treeing (W.T) in h.v. solid insulation is presented in this paper. Laboratory made specimens were used to grow vented W.Ts under accelerated conditions. The behavior of W.Ts were studied and recorded by specially designed video camera attached to a high magnification microscope. The observations were interfaced to a microcomputer where they were analysed. Experiments revealed that W.Ts can grow in some dielectrics while it can not grow in certain types of epoxy resins under the same varying conditions of frequency, voltage, applied field and electrolytic solutions. Novel computer techniques were developed using the Finite Differences Method (FDM) to calculate the equipotential distribution in the point-plane electrode system which simulates the W.T growth and initiation model. Polymeric materials were investigated using different permittivities for W.Ts. The electric field concentration and some other random factors were used to control the W.Ts initiation and propagation in the model. The mechanism of W.T in h.v. cables insulation is discussed and explained on the light of the experimental and simulation results.

The deterioration and breakdown of solid dielectrics by internal discharges at cryogenic temperatures

An investigation into internal discharges in artificial air-filled cavities in impregnated-paper, polythene and polypropylene ueing a multi-channel, pulse-height analyser is described. On lowering the temperature of test samples from 343 K down to that of liquid nitrogen the discharge repetition rate and discharge magnitude under alternating-and direct-voltages are greatly reduced. The electric strength with power-frequency-alternating-, direct-and lightning surge-voltages with polarity reversal, is appreciably increased when the temperature is lowered, the improvement being particularly marked with direct voltages. Operating the electrical apparatus at cryogenic temperatures increases the working voltage, the electric strength and the life time of the electrical insulation.