electrical power engineering course

Measurements Emissions Conducted emission tests comprise measurements of voltage across a defined network which simulates the RF impedance of a typical mains supply. These Line Impedance Stabilizing Networks (LISNs) also provide filtering of the supply to the Equipment Under Test (EUT) and are also known as artificial mains networks or isolating networks. The EUT is connected to the LISN in a manner which is representative of its installation and use in its intended environment. Figure 14.14 shows the general arrangement. The EUT is configured in a typical manner with peripherals and inputs/outputs attached, and operated in a representative way which maximizes emissions. Radiated emissions are made by measuring the field strength produced by the EUT at a defined distance, usually 3 m or 10 m. The measurements are made on an open area test site which comprises a metallic ground plane, over a flat surface with no reflecting objects and within a defined ellipse. The ground plane ...

Equipment marking Prior to the 100a ATEX Directive, hazardous area equipment was marked with a ‘Certification Coding’, a certificate number and other information. A typical equipment label would contain: ● the manufacturer’s name ● the name or type of the equipment ● the ‘Distinctive Community Mark’ ● a serial number ● the certification code ● the certificate number ● any ‘Special Conditions’ for safe use ● electrical ratings ● any other information required by the standards for the equipment In a typical certification code, say EEx de IIB T3 (Tamb = 50°C), E means certified to European standards, Ex means equipment for a potentially explosive atmosphere, de means methods of protection, IIB means group and subgroup, T3 means tem- perature class and Tamb = 50°C means maximum ambient temperature. If the equipment is marked with a temperature in addition to, or in place of a Temperature Class, then this is used to denote the minimum ignition temperature of the gas or v...

Equipment selection Although further selection criteria may be relevant, such as the possibility of chemical attack, vibration, and high risk of mechanical damage, the four essential criteria for equipment selection are: ● the protection concepts and ATEX category are suitable for the intended zone of use (Table 15.7) ● the Apparatus Grouping is suitable for the intended flammable materials (Table 15.8, which applies only to gases and vapours) ● the Temperature Class or surface temperature is suitable for the ignition temperature of the flammable material (Table 15.6) ● the Ambient Temperature limits for the equipment are suitable for the intended location A combustible dust has two ignition temperatures, one for the dust in the form of a cloud ( T cloud) and the other for the dust as a layer. These temperatures depend on the physical properties of the dust, such as particle size, moisture content, and the layer ignition temperature increases as the layer thickness increases...

Hazardous area equipment Methods of protection Electrical equipment has been used in potentially explosive atmospheres for over one hundred years and several methods of protection have been developed during that time. The probability of the equipment becoming an effective source of ignition determines the zone of use. Equipment with a higher probability of being an effective source of ignition can be used only in the zones of lower hazard. The 94/9/EC Directive and the EPS regulations recognize this in specifying the corresponding category for the equipment. All the methods of protection use one or more of only four basic techniques which are summarized in Table 15.3. Type of Protection n is another method of protection for electrical equipment which uses simplified versions of the methods above and is category 3 only (see Table 15.4). All the above methods of protection were originally developed for use with flammable gases and vapours. There is a further method of protection spec...

Standards The three types of EMC standards in current use in Europe are basic standards, g eneric standards and product-specific standards. Basic standards contain the test methods and test levels at limits but do not specify a product type. Product standards contain comprehensive details on how the product should be configured and operated during the test and what parameters should be observed. Generic standards apply in the absence of a product standard and are relevant to all products which may be operated within a defined environment. Both product standards and generic standards may refer to basic standards for their test methods. The important standards in current use in Europe are listed. Those listed in section 14.3.1 and 14.3.2 which are applicable to a particular product or system may be applied by the manufacturer to demonstrate compliance with the EMC Directive. Generic standards EN 61000-6-3: Emissions: residential, commercial and light industrial environment EN 61000-6...

Electricit y and potentially explosive atmospheres Introduction UK legislation has contained requirements for electrical installations in adverse environments in the Electricity Regulations of the Factories Act since 1908. Over the years these have been given more detail as legislation has been updated. Potentially explo- sive atmospheres, otherwise known as hazardous areas or flammable atmospheres , have been given particular emphasis because of the possible major consequences of inadvertent ignition. The disasters at Flixborough and Abbeystead are examples of the many incidents which have occurred, and continue to occur, worldwide. There have been significant changes to the UK legislation in recent years, largely as a result of EU directives dealing with the safety and health of workers. This chapter concentrates on the specific problem of potentially explosive atmospheres, the legal requirements and the practices for meeting them. EU directives The two EU directives dealing s...

EMC limits and test levels Emissions The radio frequency emission limits quoted in EMC standards are usually based on the level of disturbance that can be generated by an apparatus or system such that radio or TV reception in a co-located receiver is interference-free. Conducted emission limits are set to control the disturbance voltage that can be impressed on the voltage supply shared by the source and receptor where coupling by conduction occurs. Limits currently applied in European emission standards are shown in Fig. 14.7. The Class A limits are appropriate for a commercial environment where coupling between source and receptor is weaker than in the residential environment, where the Class B limits apply. The difference in the limits reflects the difference in attenuation in the respective propagation paths. The limits shown apply when using the ‘average’ detector of the measuring instrument, and are appropriate for measuring discrete frequency harmonic spectral line emissi...