Tuesday, March 30, 2010

Moeller Arc Flash Protection

Arc faults still occur in conventional electrical energy distribution systems – regardless of all the considerations and preliminary protective measures which have been implemented. An event of this type is seldom, but the damage caused and its effects are extremely serious. They range from injury to persons to massive damage to the switchgear systems and can result in standstills which can last for weeks and may even necessitate a complete replacement of the switchgear system. The factor of "availability" may not be ignored. An advantage should not be underestimated in today's competitive environment. Suitable protective measures must be undertaken to ensure it.

The most common causes of arc faults are:

  • Human error when working on the switchgear system
  • Bridging between conductor with conductive foreign bodies such as tools, parts or rodents
  • Dirt or condensation
  • Overvoltages
  • Incorrectly dimensioned switching devices.

The ARCON® arc fault protection system from Moeller has been successfully employed in low-voltage switchgear systems for more than a decade. The system has impressively proven its capabilities not just in the laboratory, but also at customers in the field.

The ARCON® arc fault protection system is used whenever enhanced demands in terms of personnel protection or an interruption free energy supply are required, for example in:

  • Computing centres
  • Power supplies in tunnels
  • Glassworks
  • Paper industry
  • Energy supplies for continuous manufacturing processes.

Extremely fast, extremely reliable:
ARCON® – The arc fault protection system from Moeller

The onset of an arc fault must be detected immediately – a lightning fast reaction is required. Moeller solves this with the arc fault protection system ARCON®.

The light sensors (ARC-SL) use optical fibre technology to monitor the main busbars and dropper bars, as well as all busbar assemblies and connection systems along their entire length. The radiation emitted by the arc fault is detected via the sleeving surface of the sensor. Only one line sensor is required for each switchgear section and main busbar system.

Alternatively available with current transformers with secondary currents of either 1 A or 5 A, the arc fault current is detected by measurement transducers positioned upstream of each feeder circuit-breaker. In the event of an arc fault, the light emitted by the fault and the arc fault current are detected by the sensors and evaluated in the master unit (ARC-EM). The central processing unit gives the disconnection signal to the quenching device (ARC-AT). The quenching device creates a bolted short-circuit on three poles parallel to the location of the fault. The voltage required for the arc fault is reduced on account of the short-circuit at the busbars and the arc fault is quenched in less than 2 ms after initiation, which is well before the maximum destructive force is achieved.

This is therefore achieved before the destructive maximum values of the arc fault are reached. The 3-phase short-circuit created by the quenching device is disconnected by the feeder circuit-breaker. This also receives the disconnection signal from the central processing unit as a back-up to the shunt release. Slave units are used to monitor and evaluate sensor signals, and in the event of an arc fault pass on signals to the central processing (master) unit via the bus. In its maximum configuration, the central processing unit can monitor two separate busbar sections and independently switch the individual quenching devices assigned to the busbar sections accordingly. Several central processing units can be used in one system if necessary. They are interconnected via a communication line and exchange overcurrent information with each other in the event of an arc-fault.

The ARCON® arc fault protection system offers personnel protection over and above that which is required by relevant standards. The implementation of system function protection sets new standards in the construction of power distribution systems, offering constantly high quality during operation and ensuring the continuity of the production process.

System function protection

System function protection means that the switchgear system can be immediately re-operated after it has shutdown due to an arc-fault after the cause of the arc-fault has been eliminated, and the insulation resistance has been measured and verified. Exchange of distribution system parts, components and equipment in the switchgear power section resulting from an effect of an arc-fault is not necessary. Complete functional endurance of all system parts and equipment is achieved. The criteria for system and personnel protection (compliant to EN 60439-1, supplement 2) are automatically assumed into the system protection function.


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