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RCDs are an effective means to provide protection against fire hazards because control over the level of leakage current is the only way to manage this risk. For TN-S systems (MEN), the risk of electrical fire hazards is eliminated by a 300 mA RCD. Analysis of the risk • in the 1980s and 1990s, a study carried out by an insurance company in Germany on fires on industrial and commercial premises revealed that: • the cost was extremely high, reaching several hundred million euros PDL’s IP66 Distribution solution will ensure you are in good hands in harsh environments. • The 56CB13 surface mount board will allow an array of MG products such as timers, main switches, RCCB’s and miniature circuit breakers for virtually all of your installation needs. • The transparent flap, incorporating the patented selflocking feature, provides a quick and easy focal point for devices that have operated. The flap can be opened permanently, allowing flexibility whilst performing maintenance. • The unit is available in both chemically resistant orange and white. This will help protect against those chemically challenged installations. • The PDL distribution board encompasses 13 x 18mm ways, supplied with one earth and two neutral busbars. The E6 base has been designed with dedicated conduit entries providing the flexibility for surface or rear cable entries into the 56CB13 distribution board • The 56CB13 fully complies with AS/NZ 3439.3 and supersedes the DBWS13C. Available now at your Electrical Wholesaler. Protection using Vigirex RCDs Protection of property: fire hazards • the cost increased 600 %, i.e. much faster than the increase in the GNP (> 2 times faster over 20 years). It is necessary to become aware of the dangers of fire hazards not only in terms of safety, but also in terms of cost. An analysis of the situation showed that electricity was an important factor (the cause of approximately 40 % of fire accidents). • the analysis showed furthermore that there are two main causes: • the 1st major cause is the creation of electrical arcs and arc tracking due to humidity. These arcs can develop only with impedant fault loops (> 0.6 Ω) and appear only when insulation faults occur or stray currents flow. Very little energy is Tests have shown that a very low insulation-fault current (a few mA) can develop and, starting at 300 mA, cause the start of a fire in an environment of damp dust. Moisture? Dirt? Chemicals? Harsh Environments? No problems for the 56CB13 Origin of fires in buildings. required to launch the phenomenon (a few joules), i.e. an insulation-fault current or a stray current u 300 mA represent a real risk of fire. • the 2nd cause is related to uncontrolled temperature rise caused by incorrectly set protective devices or incorrectly calculated fault-loop impedances (due primarily to age or lack of installation maintenance). Because the thermalprotection devices did not operate correctly, excessive temperature rise due to overcurrents or a shortcircuit resulted in a fire. For more information contact: Bruce Morrison Product Manager Power Distribution Schneider Electric (NZ) Limited PO Box 15 355 Auckland Tel: 09 829 0490 email: bruce.morrison@nz.schneider-electric.com
Slick changeover keeps fish fresh When the mains switchboard at one of the world’s largest tuna-processing plants began feeling its age, Schneider Electric NZ and Napier’s Electrotech Controls Ltd teamed up to design, build and supply a more efficient replacement. The COS Samoa Packing Company in Pago Pago, American Samoa, processes some 300 tonnes of tuna a day and in global terms is second in size only to the neighboring StarKist plant. COS runs a 24-hour operation, and its major electrical demand is for refrigeration, water pumps and generating steam. In recent years power reliability had become an issue as a result of an increasingly fragile mains switchboard. After a tendering process, the plant’s management appointed Electrotech to design, build and supply a replacement, and Schneider Electric supplied much of the hardware. “A major problem with the equipment,” says Electrotech project manager Steve Pardoe, “was the environment in which it operated. There were a few leaks in the roof of the building, and that had caused quite a bit of corrosion. As a result, the local crews were replacing the switchboard’s ACBs on a regular basis – as a kind of preventative maintenance.” Electrotech’s design of the new switchboard was governed by the power feed into the plant – delivered from two 2MVA transformers.That was complemented by three 940kW standby, diesel-generating sets. Designed as standby units, in practice the generating sets ran continuously, in parallel with the electricity supply. “Essentially,” says Pardoe, “we were dealing with three separate switchboards mounted side by side.The generator board – for the three standby generators – and two for the main distribution board.The two main switchboards were linked by power cables. “Because of the potential fault current associated with paralleling two 2MVA transformers, we had to keep our design similar: two switchboards that would be kept totally separate – but interconnected – for the transformers, and one for the generating sets.” DESIGN Optimising and monitoring the performance of the new switchboards was one of the project’s major drivers. “The old control system was fraught with difficulties,” says Pardoe. “It was totally manual and there was no monitoring. Even synchronizing the three generators was a manual operation. Operators had no way of tracking power consumption.” The new <strong>Prisma</strong> switchboards were designed and built at Electrotech’s Napier plant. The design team from Electrotech specified a full distribution and automation system complete with SCADA and power factor correction. Among the challenges the team faced was designing and specifying equipment that complied with US regulations. “We had to take virtually everything we needed with us, because the US system still uses imperial measurements.” In addition, the team had to factor different voltage system into their design – 110 volts, a 240-volt system as well as a 24-volt DC system for all controls. Schneider-Electric’s Bruce Morrison says highly specialised Merlin Gerin breakers were fitted to the <strong>Prisma</strong> switchboards. “As a standard feature, all source breakers were equipped with ammeters to facilitate easier power monitoring.This included full modbus communication with energy management and preventative maintenance monitoring achieved. In addition, all 24 x 800A feeder breakers were supplied with PM500 power monitors.” INSTALLATION The project ran over a five-week period in April and May this year, and installing the two switchboards was by far the most difficult part of the project because of the very tight time limit. “The fish is kept in freezers and the factory can only survive for about 24 hours – tops – without electricity,” says Pardoe. “And that’s what we were given for the changeover.” As it happened, the installation crew only needed 21 hours. “Apart from the success of meeting the time-limit, it was particularly gratifying to witness the improved efficiency of the switchboards. Tests conducted after the installation showed the boards were running at a significantly lower load than the previous equipment. We believe a lot of the ‘excess’ load on the old boards was attributable to heat losses and poor connections.” Control is also much easier. It’s entirely automatic, and operators now monitor the switchboards’ performance on a PC screen. Being able to monitor load in real time, Pardoe points out, “also allows operators to consider strategies such as peak load sharing for the first time – and improve the plant’s overall energy efficiency.” THE HARDWARE Schneider-Electric supplied the majority of the components used in the two switchboards. Below is a selection of the Merlin Gerin items: 2 x 3200A 3P 85kA Masterpact NW ACB Mains Breakers 2 x 3200A 3P ACB Masterpact NW Generator Feeders 3 x 2000A ACB Masterpact NW Generator Breakers 2 x 3200A ACB Masterpact NW Bus Ties 24 x 800A MCCB Compact NS Sub Circuit Feeders 24 x PM 500 Powerlogic power meters 5 x PM 850 Powerlogic power meters For more information contact your local Sales Engineer
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