Mains Supply Research Articles

Electrical hazards: their causes and prevention

Electrical injury is caused by current passing through the body. The source of current is usually the domestic mains supply. The damage and injury to the body are proportional to the amount of current through the body. Electrical hazards and their prevention are discussed.

Detection of Helicobacter pylori by PCR but not culture in water and biofilm samples from drinking water distribution systems in England.

To investigate treated water distribution systems in England as a source of Helicobacter pylori. Water and biofilms were obtained from 11 domestic and seven educational properties and from hydrants, reservoirs and water meters supplied by three water utilities. Samples were cultured on nonselective and antibiotic containing media combined with immunomagnetic separation concentration. Viable helicobacters were not detected in any of the 151 samples but Helicobacter-specific PCR assays detected DNA in 26% of samples from domestic properties, schools and hydrants with the highest frequency in biofilms (42%). Direct sequencing of six selected amplicons confirmed >95% sequence homology to H. pylori. While viable helicobacters were not isolated, evidence was obtained for the presence of Helicobacter DNA, including that of H. pylori. Biofilms on surfaces within water distribution systems may act either as sites for the passive accumulation of helicobacters or as potentially important reservoirs of infection. Our findings strengthen evidence that H. pylori may be transmitted through drinking water. However, there is currently no evidence that viable cells can survive the disinfection levels used in UK mains supplies and the health risk from this source remains unclear.

Children at risk of giardiasis in Auckland: a case-control analysis.

The incidence rate of giardiasis in New Zealand is one of the highest among developed countries, peaking in the 1-4 year age group. A case-control study was undertaken to identify risk factors for giardiasis among Auckland children under 5 years of age. The exposure history of 69 cases and 98 controls were analysed. Ninety-five per cent cases and 86% controls used water from the Auckland Metropolitan mains (AMM) supply for domestic purpose, 44 cases and 42 controls swam and 59 cases and 54 controls wore nappies. Children wearing nappies were at significantly increased risk of the disease (OR = 30, 95% CI = 1.01-8.9), as were those from households which had more than one child wearing a nappy (6.5, 1.8-23.4). The Auckland metropolitan mains water supply was associated with a reduced risk compared to other drinking water sources. Significantly increased risks were also associated with drinking water consumed away from home (4.7, 2.2-10.1), swimming at least once a week (2.4, 1.1-5.3) and travelling domestically (2.5, 1.03-6.0). The study identified vulnerable groups and modifiable risk factors for diarrhoeal diseases, particularly Giardia infection. Nappy wearing was an independent risk factor for infection. Further study is advocated to ensure better protection of public health, especially for children.

A Sinusoidal PWM Series Voltage Regulator

This article presents low cost pulse width modulated (PWM) ac voltage regulator that utilizes series voltage boost technology. The circuit does not require any kind of synchronization with the source mains. The basic component of the PWM ac regulator design is a series boost transformer in which the primary voltage is controlled by a PWM control circuit. The control circuit is composed of a rectifier bridge and one transistor acting as a switch to energize the primary windings at the precise instant of the ac mains half cycle. The transformer secondary is connected in series with the mains supply. The load is connected across both the supply and the transformer. Voltage sags down to 50 percent have been accommodated for a line voltage of 120 volts and load up to 350 watts in an inexpensive laboratory implementation. The load voltage and current are sinusoidal with minimal harmonic as compared to the conventional phase-controlled competitor. The switching of the modulating devices is at high frequency resulting in the use of simple filtering elements. The device complies with ANSI standard C 84.1-1989 for class A secondary distribution voltage regulation.

Risk of giardiasis in Aucklanders: a case—control study

Background: Giardia is one of the leading protozoal causes of human gastrointestinal illnesses. It is prevalent in both developed and developing countries. Currently, giardiasis is the most commonly notified waterborne disease in New Zealand. The aim of the study was to identify potentially modifiable risk factors for Giardia infection in the adult population in Auckland. Methods: This case-control study involved 183 Giardia-positive cases and 336 randomly selected controls, aged between 15 and 64 years. Exposure information was collected retrospectively over the telephone for the 21 days preceding the date of onset of symptoms. Both univariate and multiple logistic regression analyses were carried out. Results: The majority of cases were in the 25–44-year age group and in the New Zealand European ethnic group. Housewives and nursing mothers were at significant risk of the disease (odds ratio (OR)=2.06; 95% CI=1.4–3.74), as were the occupational groups exposed to human wastes (OR=4.04, 95% CI=1.85–8.85). Consumption of drinking water from New Zealand supplies other than metropolitan mains supplies (OR=2.11, 95% CI= 1.36–3.27) or from sources outside New Zealand (OR=7.97, 95 % CI=4.20–15.12) represented a significantly higher risk, as did traveling (OR=7.57, 95% CI=4.03–14.23) and swimming in pools or fresh water at least once a week (OR=2.04, 95% CI= 1.33-3.12). Conclusions: The study identified potentially modifiable risk factors for Giardia infection. These findings should be investigated further in different groups and settings to ensure better protection of the public health.

The role of small-scale independent water providers in urban areas

Most people who live in cities and large towns throughout much of the developing world occupy neighbourhoods and informal settlements that do not have adequate water services. In fact, evidence suggests that more than 75 per cent of the urban poor obtain domestic water from sources other than a direct-piped mains supply. Is it time we looked at the positive alternative role which independent small-scale water providers play in meeting these people's needs?

An overview of harmonic and flicker emission standards and their associated measurements

The limitation of undesirable low-frequency effects generated by electrical appliances connected to the mains supply is considered. If an appliance draws harmonic current from the mains, in general it contributes to the deterioration of the quality of the sinewave supplied by the mains. The article considers these effects and examines the regulatory regime that seeks to limit the increase in mains harmonic distortion.

Some considerations when using a microwave oven as a laboratory research tool

Microwave ovens can be used in laboratories for the rapid heating of material – either to dry them completely or to subject a workpiece to sudden thermal stress or electric field stress. Determinations of the moisture content levels in soil or leaf tissue samples, for example, can be made within tens of seconds rather than hours. It is often assumed that placing a load within a microwave oven will result in it being heated evenly as well as quickly, but this is not always the case. This paper describes how a microwave oven works and illustrates how the heating effect within a workpiece can vary. The size and shape of a sample as well as its physical properties determine the power absorption. Equal volumes of water in different shaped containers attain different final temperatures and a tall, cylindrical water load is shown to have different temperatures at different levels. Most microwave ovens do not have a true, variable power capability, but rely on an on/off timing ratio to vary mean power. If this is not appreciated, then erroneous conclusions might be drawn from a set of experiments involving different power levels. Changes in mains supply voltage can affect the amount of energy dissipated in a load. This may introduce variations in results if experiments are conducted over a period of several hours. Experiments are described which illustrate these effects and some criteria and working practices are suggested to improve the consistency and reliability of results when using a microwave oven as a research tool.

Intelligent standby concept

Modern consumer electronic products like TVs, VCRs, laser disc players, and Hi-Fi equipment offer users the convenience of switching the equipment on and off via a remote control handset. When this type of equipment is switched off, it is said to be in standby mode. In standby mode the equipment still has the power supply operating in order to provide power for the microcontroller and other standby circuitry. This power is typically ten Watts or higher. An intelligent standby circuit is described, whereby a combination of software and hardware interact in order to reduce the standby power. This method allows the power supply to be disconnected from the mains supply.

Exposure of the critically ill patient to extremely low-frequency electromagnetic fields in the intensive care environment

To measure the electromagnetic emission of intensive care medical equipment, in order to assess whether a potentially dangerous magnetic flux is present around the patient, and to evaluate the exposure conditions of the patient to extremely-low-frequency electromagnetic fields (ELF EMF). Descriptive study. Intensive care unit (ICU) at a general hospital. The flux density of alternating (AC) 50-H2, EMF was measured and mapped around electrical devices in a six-beds adult ICU furnished with standard equipment (ventilator, monitor, infusion pumps, heated airbed, humidifier). The overall flux density in the patient area was assessed by measuring the field intensity at the patient's head during the day and at night over 6 days. The magnetic flux density was not uniformly distributed around each device, being higher [up to 40 microTesla (microT)] close to fan motors and mains supply. In 83 % of the patients a field intensity > 0.20 microT (safety limit) was detected. The ICU environment is at risk from electromagnetic pollution, the long-term stay of chronic patients and their "day-long" exposure are additional risk factors. EMFs drop off as the distance from the equipment is increased, according to the inverse-square law, and the exposure risk may be minimized by keeping a safety distance from the EMF source. The actual value of that safety distance may be variable and depends on several factors: (1) type of equipment, (2) orientation of equipment, (3) equipment "overcrowding" and (4) available space in each bed space. The magnetic flux density should be monitored regularly in every ICU for the specific design of each unit.

New class of dual voltage converters for switched reluctance drives

An entirely new class of dual voltage switched reluctance drives is presented. New power converter circuits are introduced, which allow a switched reluctance motor to operate from either an AC mains or a battery supply, with minimal extra power semiconductor components and no extra transformer. Battery charging is achieved without additional components. These converters offer considerable cost savings and flexibility when compared with conventional solutions to the problem of creating a system that can operate from both AC mains supply and battery.

Design and development of a new cryosurgical instrument utilizing the Peltier thermoelectric effect

Warts and some other dermatological conditions may be treated by the application of intense cold. This freezing has to be so severe as to form ice crystals which will rupture the cell membranes. The initial part of this project was to investigate the feasibility of using Peltier thermoelectric coolers (TECs) to cool down a suitable hand-held treatment tip to a temperature of approximately -50°C. The results of these initial experiments showed how this could be accomplished and a prototype cryosurgical instrument, suitable for clinical trials, was designed and constructed. This new design is freestanding, self-contained and is operated from a standard 230 V mains supply. Unlike existing systems it does not use any disposable gases or liquids. A cryoprobe of this new design would allow reliable cryosurgery to be performed in a GP's treatment room where supplies of liquid nitrogen, nitrous oxide or carbon dixoide are not readily available. The design also has a built-in thermometer to measure the treatment tip temperature thus ensuring consistency in treatment. Clinical trials are being conducted at a number of GP practices to evaluate this new design.

Optical Precipitation Gauge

There exists a great need for automatic precipitation gauges for effective road maintenance during the winter period. These gauges should be inexpensive, not require mains supply, need little attendance, give information about presence of precipitation and determine type (snow, rain or sleet) while there is no need for high accuracy of the precipitation intensity. Light attenuation precipitation sensors (optical gauges) fulfil several of these requirements and are used in the Swedish National Road Administration Road Weather System. The optical gauges measure the time it takes for particles of snow etc. to pass (attenuate) a light beam and relate this time to precipitation type and intensity. The rain precipitation mass is approximately proportional to the accumulated attenuation time. To investigate whether or not optical gauges could also be used for solid precipitation, the precipitation mass for snow, rain and sleet was measured with a reference gauge and compared to the attenuation time. The passage time of individual hydrometeorologic particles (snow, rain and sleet) was compared with precipitation type and wind speed. Air temperature could be used as a rough guide to distinguish three precipitation categories for the following temperatures: rain (>+2 °C), sleet (0 to +2 °C) and snow (≤ 0 °C) At low wind speeds (< 3 m/s) the passage time of individual particles could be used to distinguish between rain and snow. The accumulated attenuation time for the same precipitation mass was approximately 25 and 5 times greater for snow and sleet respectively compared to rain. With the attenuation time for the snow-fall corrected for wind influence the quotient between the attenuation time for snow and rain is decreased from approximately 25 to approximately 12 times.

Electric field created by a circumferential sinusoidal charge-density wave on the surface of a cylinder

The paper is concerned with the calculation of the electric field created by a distribution of charge, sinusoidal around the circumference and constant longitudinally, on an infinitely long cylinder. Interest in the detailed analysis of this field was stimulated by the consideration of the field set up by the stator of a dielectric motor which had previously been constructed. Its stator consists of a number of conducting bars fixed longitudinally to a cylindrical surface, and connected in sequence to the lines of a three-phase supply. Such a stator produces a field essentially similar to that set up by the charged cylinder. Analysis shows that the field in space is constant at a given radius and, except in the charged surface itself, is everywhere rotating at an angular velocity determined by the speed of rotation of the cylinder, or in the case of the stator, by the frequency of the mains supply. The field has its maximum magnitude immediately adjacent to the charged surface, and diminishes with distance from it, except for one special case. The cause of the rotating field at every point in space is the rotation of the field patterns resulting from the charges on the cylindrical surface. This pattern is quite complex, and the equations of its field lines are derived analytically.

Fatal nosocomial Legionnaires' disease: relevance of contamination of hospital water supply by temperature-dependent buoyancy-driven flow from spur pipes

The investigation, epidemiology, and effectiveness of control procedures during an outbreak of Legionnaires' disease involving three immunosuppressed patients are described. The source of infection appeared to be a network of fire hydrant spurs connected directly to the incoming hospital mains water supply. Removal of these hydrants considerably reduced, but failed to eliminate, contamination of water storage facilities. As an emergency control procedure the incoming mains water was chlorinated continuously. Additional modifications to improve temperature regulation and reduce stagnation also failed to eliminate the legionellae. A perspex test-rig was constructed to model the pre-existing hospital water supply and storage system. This showed that through the hydraulic mechanism known as 'temperature buoyancy', contaminated water could be efficiently and quickly exchanged between a stagnant spur pipe and its mains supply. Contamination of hospital storage tanks from such sources has not previously been considered a risk factor for Legionnaires' disease. We recommend that hospital water storage tanks are supplied by a dedicated mains pipe without spurs.

Malfunction of medical equipment as a result of mains borne interference

Medical equipment has become more intelligent as the manufacturers have incorporated the latest microprocessor based technology. Equipment malfunction can be caused at any time by inherent errors in the control program but it is particularly important that this is designed to cope with the effects of electrical interference which, in addition, may cause corruption of the software. We have considered interference found in the mains supply in the hospital environment. Using a test protocol with appropriate interference simulators, a wide range of medical equipment was removed temporarily from use and its immunity to electrical mains borne interference tested. Battery operated mains rechargeable devices were unaffected by mains voltage variations including drop-outs and sags whereas mains powered devices were affected to varying degrees of severity. In particular, repetitive drop-outs caused loss of power due to fuse blowing in some life support equipment. Impulses affected 25% and pulse bursts 50% of the equipment tested with some evidence that the more recent designs coped better. The EEC Directive on electro-medical compatibility compliance may cause the design of equipment to be improved but hospitals will have to cope with the above problems in their existing equipment for many years to come.

Quality of electrical mains supplies in hospitals: Implications for microprocessor-controlled medical equipment

Quality of electrical mains supplies in hospitals: Implications for microprocessor-controlled medical equipment

Electromagnetic radiofrequency interference with Doppler equipment

Doppler ultrasound equipments incorporate radiofrequency (RF) receivers operating at the microvolt level and are liable to interference from radiated fields and mains disturbances. The most significant interference routes are: radiation from radio broadcast, paging, communication and diathermy picked up on the transducer and patient acting as an aerial; and mains disturbances from diathermy, X-ray sets, motors and thyristor controls, etc, reaching the equipment interior. Methods for reducing such interference are discussed. Other interference can arise from modulation of a strong RF signal by means frequency power components in the Doppler equipment and from associated computer circuits. Finally, some initial simple acceptance tests for interference susceptibility are proposed, based on the application of 300 mu V of RF signal between transducer body and equipment enclosure and 10 mV to the mains supply.

The influence of rotor design and inverter type on the magnet volume of synchronous machines investigated by numerical field calculation and vector-optimization methods

Numerical field calculation and mathematical vector-optimization methods are applied in order to find the most appropriate design of the rotor of synchronous machines with rare earth magnet excitation. The paper presents an optimization procedure consisting of the formulation of the users preference, the treatment of the nonlinear constraints and different optimization algorithms. To demonstrate the efficiency of the methods different magnet configurations in the rotor of the machine are compared, while considering different supply modes like inverter supply (voltage or current source) or mains supply.

225. 小電源容量で使用できる高出力, 高周波インバータ式 X 線装置の開発(インバータ式装置他)

225. 小電源容量で使用できる高出力, 高周波インバータ式 X 線装置の開発(インバータ式装置他)