RESISTORS 37
The South American climate and resistors
Stewart Wittering, marketing director for South America at resistor manufacturer, Cressall Resistors, explains how the South-American geography and climate affects the resistor market.
T
he power needs of communities and remote locations can have a number
of indirect effects on the resistor market. Geographical constraints on electrical distribution have resulted in a de facto reliance on localised generation and battery technology in some places. Localised generation systems, which often consist of several generators, are usually isolated from the grid network. In the event of an earth fault,
resistors can be used to limit the flow of current and thereby the risk of damage to generators and other equipment, however, where multiple generators are connected in parallel to avoid circulating earth currents, only one generator should be earthed. One way of ensuring this is to use a single earthing resistor with multiple vacuum contactors. It is essential that backup battery systems work
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“Because Cressall’s load units were originally developed for use in the field by telecoms, rail and offshore companies, they are easy to handle and can be operated by one person.
properly when called into action. Portable Load Units can be used to test the capacity of standby batteries and the output of generators by simu- lating the working load. As standby systems are often installed at remote locations, test equipment must be easily transportable. Because Cressall’s load units were originally developed for use in the field by telecoms, rail and offshore companies, they are easy to handle and can be operated by one person. Because of the challenging
environments found in South America, it’s important that
equipment is designed appropriately, with respect to mechanical, electrical and environmental positions. Equipment needs to be resilient to earthquake tremors. Enclosures must be used to
protect contents from external elements, including wind, rain and sea mist, yet allow sufficient ventilation to dissipate the heat generated during operation. In order to achieve
trouble-free operation, engineers must ensure enclosures are designed to avoid high levels of humidity and contamination as these can reduce insulation resistance. Using non-hygroscopic
materials and correct insulation design mitigate against the build-up of pollution, which will ensure the long and safe working life of equipment. Originally developed for use
in rail traction and onboard ships, Cressall’s resistors are
robust and can be designed to withstand high levels of shock and vibration. Where specific seismic criteria need to be met, finite element analysis tools are used to ensure suitability. With Latin America
expected to commission more than 47 GW of new wind power capability between 2017 and 2026, this particular renewable source is a popular choice. Multiple types of resistor are used in wind power generation, including pre-insertion resistors (PIRs), dynamic braking resistors (DBRs) and crowbar resistors. PIRs limit the in-rush current
into transformers when the system is switched on. DBRs control the over-speeding of turbines from gusting winds and crowbar resistors can prevent damage to the power electronics of the turbine by short-circuting the rotor windings in the event of a grid disturbance.
www.cressall.com Worldwide Independent Power January - February 2018
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