Electrical Power & Protection


Over-voltage protection: over-voltage suppressors for signal and supply cables

July 2008 Electrical Power & Protection

The prevailing conditions in South Africa make it imperative that operating processes be protected from over-voltage, which is often the cause of systems failures. This can be due either to lightning strikes, prevalent in the summer months, or to voltage spikes in the supply circuit.

Vega supplies a range of suppressors which can be installed to protect measuring instruments in all situations. These include arresters for Profibus PA systems, supply and signal cables and for Ex systems.

Two-wire protection is offered for field devices and control interface units with a suppressor that uses the derivative of the higher current to ground and limit the voltage during the high level pulse.

Also available is a surge protection device that is specially designed to protect process transmitters and devices on Fieldbus systems. The TP32 provides an added level of surge protection for fieldbus transmitters.

The all important earth connection is made via the casing of the transmitter, negating the need for a separate earth connection at the transmitter. In operation, the TP32 ensures that the transmitter electronics are never exposed to damaging transients between the lines and earth. The protection network is a hybrid design consisting of high-power, solid-state electronics and a gas discharge tube, which are capable of diverting surges up to 10 kA.

Installation is simple and the units can be retrofitted at existing installations. The TP32 is screwed into any unused conduit entry on the transmitter case, allowing flying leads to connect the device to the terminal block and the internal earth stud within the transmitter housing. By connecting in parallel to the transmitter circuit, the TP32 does not interfere with the normal operation of the bus. It passes AC or DC signals without adding increased voltage drops across the segment, while consistently diverting surge currents safely to earth and clamping output voltages to safe levels.

For more information contact John Groom, Vega Instruments SA, +27 (0)11 958 1901, [email protected], www.vega.com



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