The Japanese cable-maker Oki has developed a compact, water-resistant surge suppressor which can be used outdoors. A 15kW eco Surge U suppressor is one-fifth of the weight and a quarter the size of a conventional filter of a similar rating. The suppressors are suitable for motors from 0.2–75kW.

Using a similar transmission line technology to the recent eco Surge µ, the new device has a patent-pending sealed enclosure (developed jointly with Fuji Electric) with a high heat dissipation efficiency, making it suitable for outdoor use – unlike most conventional filters.

As inverter switching speeds get faster and higher voltages are being used to improve efficiency, micro-surges induced by impedance mismatches between motor and their cables, are also increasing. This can cause problems such as a deterioration in motor coil insulation. 
 
The conventional remedy is to insert LC filter circuits between the inverter and motor to slow down the surge rise on the drive waveforms and to dissipate the surge energy as heat. However, as motor powers increase, this requires large and costly high-power capacitors and coils.
 
Unlike the conventional approach of inserting the filter between the inverter and the motor, the new suppressor is connected directly to the motor terminals. It can be used in new installations or retrofitted to existing systems, and is suitable for use with drive cables up to 50m long.

The surge suppressor is due to go on sale in September, and Oki expects it to generate sales worth £3.3m in the year ending March 2011.