Uninterrupted power supply

Dirk Schneider, Wilhelm Sölter

Although the European power grid is of an extremely high standard with an availability of 99.98%, there are ap-proximately 150 short-term power failures annually in any one local network. There are also surge voltage peaks, voltage and frequency fluctuations, distorted voltage curves and even total power cuts. In process control systems, this leads to loss of data, system failures, permanent damage to hardware and software as well as other disturbances. In general, the results are financial losses and sometimes even environmental damage or injury to persons.

In the chemical industry, EMC resistance plays an important role, since the devices and plants that are used have to be particularly robust, due to the very nature of the external conditions. This is particularly true of safety-relevant parts, such as process control. The chemical industry therefore acted as a pioneer by developing the NAMUR recommendation in the eighties. For the first time ever, specific interference immunity levels were defined for Germany. These are now manifested in today’s European standard, EN 50082-2.

Immunity to external interference (environmental phenomena) is a crucial equipment characteristic for determining the availability of a UPS system. External influences can be interference from the electricity supply network, such as fast overvoltages (bursts) and powerful overvoltages (surges), or environmental interference such as electrostatic discharge (ESD) and high-frequency electromagnetic fields (radio frequencies). These environmental phenomena are taken into account in European and international standards (EN/IEC). Furthermore, different immunity levels have been laid down in the European standards for different environmental conditions and applications. In generic standards (EN 50082-1/-2), a distinction is made between domestic, office and commercial buildings as well as small-scale businesses supplied via the public grid on the one hand, and industrial premises supplied by their own transformers on the other. In EN 50091 Part 2, the UPS product standard, the EMC requirements are defined by laying down particular levels. These immunity levels are designed for domestic and small-scale business use. They are not intended for applications under the „special conditions of an industrial environment“.

The devices in the Protect 5 family generate a synthetic sinusoidal voltage within a narrow tolerance band, thus guaranteeing the supply of power in an emergency. This series was developed specially for the oil, gas and chemical industries, and covers capacities between 5 and 240 kVA (3/1 or 3/3-phase).

The compact supply units are ready to connect and consist of a rectifier section, an inverter section and a static bypass switch (EUE). The manual environment and the control and monitoring electronics are located in the cabinet. There is also a battery housed in a separate cabinet or frame. All the major components are accessible from the front after opening the door and removing the corresponding covers. The degree of protection is IP 20. The design of the fans used for cooling is redundant, with air intake from below and air outflow from above. The noise level of the UPS itself is between 55 and 70 dB(A), depending on the type. All the de-vices have a supply voltage of 3 x 380 V, 3 x 400 V or 3 x 415 V/50 Hz, and an output of 1 x 230 V for the single-phase devices and 3 x 400 V or 3 x 415 V/50 Hz for the three-phase devices.

AEG SVS

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Further information cpp-227