Tuesday, October 20, 2009

Veolia Chooses Eaton's Arcon For Switchgear Safety

EMS has selected a design based on Eaton's Moeller Modan modular switchboard system for a critical application at the Selchp energy recovery plant owned by Veolia Environmental Services. Additionally, as Veolia Environmental Services is committed to ensuring high safety levels, it was decided that the switchboard should be fitted with an Arcon arc-fault protection system.

This system was developed by Eaton's Moeller business and is approved by VDS Schadenverhutung, an independent international accredited and notified authority for safety technology. Veolia Environmental Services' new switchboard, which replaces an existing board that could no longer meet current operational needs, supplies power for the aero condenser installation that underpins the operation of the cooling towers at the company's Selchp plant in south London.

The plant incinerates 400,000 tonnes of waste per annum and uses the heat produced to generate enough electricity to supply around 48,000 homes. If the cooling towers are out of action, then the plant cannot operate. 'In applications such as this, fully withdrawable switchgear is the best solution,' said Craig Walford, technical sales engineer at EMS. 'This means that if an assembly should fail it can be replaced by a spare in a matter of minutes.

'That made a Modan W board the ideal choice for the project, especially as the system could be fitted with the Arcon arc-fault protection system. 'For Veolia Environmental Services, this was a particularly important point,' he added. Arc faults are a major risk to the reliable supply of electrical energy. Even today, despite all the precautionary measures that are taken, they still occur in electrical distribution systems.

Arc faults occur more frequently than is usually realised and, because of the high energy available from the mains supply in a typical switchboard, their consequences are often devastating. In around 10ms - well before the breaker protecting the board has time to trip - temperatures around the fault can rise to about 13,000K and pressures to two atmospheres or more. These conditions create an extreme risk of fire and explosion, possibly leading to injury or even death for anyone in the vicinity.

They also result in severe damage to the equipment, which will almost always need to be replaced after the fault rather than repaired. Often, this means extended downtime while suitable replacements are sourced, together with the high costs associated with the purchase and fitting of replacement equipment. The Arcon system has been specifically developed to eliminate these problems. It will also minimise the risk of this mission-critical switchboard being out of service for an extended period if an arc fault should occur. Arcon has four major components: a photodetector, a current sensing system, a logic module and a quenching device.

The photodetector comprises a flexible fibre-optic cable that is routed through all the areas of the switchboard where an arc fault might occur. The cable can detect light over its entire length. Under normal conditions, a transmitter at one end of the cable continuously sends light pulses to a receiver at the other end, thereby constantly confirming that the system is operating correctly. If an arc fault occurs, however, the receiver sees the light from the arc instead of the normal pulses and instantly sends a signal to the logic module. The current sensing system is also connected to the logic module.

If the module receives an arc-fault signal from the photodetector at the same time as there is a rapid increase in current, it triggers the operation of the quenching device, which is connected as close as possible to the load side of the incoming circuit breaker. Once triggered, the quenching device short circuits all three phases in less than 2ms. This means that the fault-current energy is diverted away from the arc fault and is safely contained by the quenching module until the incoming circuit breaker trips. Extensive tests have shown that the risks of explosion and fire are eliminated.

This has been confirmed by operational experience in Germany, where more than 250 Arcon installations are currently in service. Arcon users are said to have found that after the system has quenched an arc fault, damage to the switchboard is minimal, allowing it to be returned to service as soon as the source of the arc fault has been eliminated. For the Modan board supplied by EMS to Veolia Environmental Services, the Arcon equipment was incorporated in its own compartment adjacent to the main 1,000A incoming air circuit breaker.

The board also included eight 45kW DOL withdrawable starters, and a six-stage 200kVAr automatic power factor correction system. The modular design of the Modan system allowed the board, which is just 600mm deep, to be split into two 1,200mm-wide sections for ease of transport and installation. Eaton's Moeller Modan switchboards are available in fixed and withdrawable versions to suit almost every power distribution requirement up to 6,300A. All types can be fitted with the Arcon arc-fault protection system during manufacture, and the system can, in some instances, be retrofitted to existing Modan boards. In all cases, Arcon systems can only be fitted by specially trained and approved suppliers.

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