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New circuit breakers / power switches made of Ultramid – a reliable plastic at work |
Working with the customers – benefits for the customers
New circuit breakers / power switches made of Ultramid®
– a reliable plastic at work
News Release to the Report of Ralf Hartkamp, Head of Materials Testing Division,
Institute for International Product Safety GmbH (I 2PS),
Testing laboratory of MOELLER GmbH, Bonn, Germany
Trade Press Conference K 2004, June 23, 2004, Ludwigshafen, Germany
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Most of us at some time have had to reset the trip switch on our home's electricity distribution board following a short circuit in some or other faulty electrical appliance. A system that ensures safety at the relatively small currents found in the home, must do the same at the far higher power levels used by industry. Such devices are known as power circuit-breakers. Moeller, the market leader in Germany for compact power circuit-breakers, has recently launched its new NZM series of breakers moulded from Ultramid® A3X, a nylon 6.6 from BASF (figure 3).
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New Moeller circuit-breaker range NZM
Moeller’s new NZM series of circuit-breakers comprises four devices for protecting transformers, motors and other industrial equipment with load currents between 20 and 1600 amps. The smallest NZM member, the NZM1, has a short-circuit breaking capacity of up to 100 kA and is intended for small sub-distribution and small industrial applications. NZM1’s bigger brothers – NZM2, NZM3 and NZM4 – are used in applications requiring breaking capacities of up to 150 kA. The NZM4, which can weigh up to 30 kg and carry up to 1600 amps, with a breaking capacity of 120 kA at 415 V, is used to protect transformers in large buildings or industrial plants for example. It can also act as a residual current device to protect against the risk of electrocution in confined workspace environments such as onboard ships. For special tasks, the NZM4 can also be set to carry short circuits of 25 kA for up to one second. This allows selective tripping of subordinate circuit-breakers, preventing nuisance tripping, that would result in plant and machinery being shut down unnecessarily (figure 7).
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Compact and modular design
The four members of the NZM range are designed for compactness and modularity. Accessories too have been matched to all four devices for easier installation, handling and inventory control. Using the withdrawable or plug-in unit circuit-breakers can be easily replaced or plugged into existing installations – important for example in the case of time-critical chemical processes, smelting furnaces or nuclear research reactors, where speedy resumption of operation is essential. The circuit-breakers can even be interfaced – either locally or remotely via a fieldbus – to a diagnostics system. Another feature is their ability to communicate with Moeller's innovative “LSE Titan”, an electronic position switch, first shown at the Hanover industry fair in 2003. For devices that undergo 10 million switching operations at up to 6000 times per hour during their service life, arcing resistance of the plastic components is a must. All NZM circuit-breakers are approved for worldwide use.
“Our new NZM circuit-breakers were designed with modularity in mind and cover the entire spectrum of requirements”, says Andreas Gindorf, product manager at Moeller in Bonn. “Safety requirements may well stay the same, but as devices become smaller, their power densities increase, which in turn places greater demands on the dielectric strength of the materials used.”
The choice of suitable materials for Moeller was undertaken by the Institute for International Product Safety GmbH (I²PS). I²PS's materials experts recommend Ultramid® A3X resins whenever particularly high performance is required, including at high sustained service temperatures (figure 10).
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Requirements on the plastic
Ultramid® A3X is a glass-fibre reinforced nylon 6.6 containing a red phosphorus flame retardant. A3X is what BASF markets as a global grade – a standard resin, available to a constant specification throughout the world. Its stiffness/toughness balance is very good. Ultramid A3X is a low-density, flame-retardant resin. And its high dielectric strength is of course particularly important in electrical applications. Materials used for the housings of high-current devices must exhibit excellent mechanical and thermal properties. They must not distort as a result of current flow, magnetic field, mechanical load or temperature variation, and must be stable to moisture, grease and acids. The arc produced when a transient short-circuit current is broken can generate temperatures of up to 5000°C and a pressure of several bars; the highest currents can exert loads of up to one tonne on the components (figure 14).
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What is a circuit-breaker exactly?
A circuit-breaker is a switching device used to protect people and equipment from impacts resulting from a short circuit or overload in the power supply. Whether the equipment is a domestic household appliance or a heavy-duty motor operating an industrial valve, the circuit breakers used to protect them work on the same principle. The only real difference is the voltage levels involved: 230V in the home compared with anything up to 1000V for industrial plant, which may draw load currents of up to 1.6 kA and where current surges of up to 150 kA might occur in the case of a fault.
So what happens during a short circuit? A short circuit will result in a momentary surge of current through the circuit-breaker. On conventional breakers this current activates a thermal-magnetic mechanism to cause a physical break in the circuit. On more advanced devices, the fault situation is detected electronically with a current sensor. The electrical arc produced when the contact opens is directed into an arc-chute, containing metal grid plates, where it is extinguished within milliseconds.
Moeller (Bonn, Germany) has been the leading manufacturer of circuit breakers and motor protection devices in Germany for 50 years and has a market share of about 28%. The holding company – Moeller Holding GmbH & Co KG – comprises three business divisions, covering industrial automation, building automation and systems. The company employs 10,900 people worldwide and generated sales of €1.05 billion (2003) (figure 15).
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