Renewable energy turns to electric valve control

Paul Boughton

The combination of intelligent electric valve actuation and digital two-wire monitoring and control is proving to be an attractive formula for the operators of renewable energy installations. Aitor Laso reports.

In one of the latest solar power plant projects, Olivenza Thermosolar in Spain, more than 100 Rotork IQ actuators and two Pakscan P3 hot-standby master stations have been supplied for the heat transfer and generating plant.

Rotork's intelligent IQ actuator technology is widely recognised as industry-standard for isolating and modulating valve duties in the field of power generation. The use of solid-state electronics as an alternative to switch mechanisms and counter limiting devices, combined with programmable micro-processor based control and instrumentation functionality, offers many proven benefits.

These include 'non-intrusive' configuration and data transfer by means of a hand held instrument via a secure, bi-directional link. This system is used to perform all the switch setting and commissioning functions that were traditionally only achieved by removing electrical covers. Using the multi-lingual menu on the actuator display screen, it is quick and easy to commission the valve, with or without mains power connected.

The inclusion of a data logger enables an event-by-event history of valve activity to be generated, including the torque profiles produced during each opening and closing. Using Rotork's IQ-Insight software, these can be compared with the valve torque signature profile logged during the commissioning process to identify the trend of valve operating wear or isolate tight spots and other problems. Analysis of this data improves asset management through fault diagnostics and preventative maintenance.

Digital two-wire control is provided by Rotork's Pakscan P3 system, the third generation of a market-leading product, capable of monitoring and controlling up to 240 field units without repeaters on a single highway with a length of up to 20 kilometres. Designed specifically for the valve actuation environment, Pakscan combines high reliability and efficiency with low maintenance costs. In providing the vital link between the actuators in the field and the centralised supervisory control room, Pakscan incorporates secure field communications with inbuilt network redundancy to maintain control even in the event of equipment or cable failure.

A similar valve actuation package is utilised in the wind farm industry, as illustrated by the DanTysk offshore farm in the North Sea. Here Rotork is supplying electric valve actuators with two-wire digital control for isolating, regulating and modulating duties. Almost 100 Rotork quarter-turn electric actuators will control butterfly valves on the transformer platform, situated 70 kilometres west of the German island of Sylt.

Approximately half the actuators are IQ intelligent isolating and regulating duty units, the balance comprising CVA fully modulating control valve actuators. The CVA units share the IQ's advanced and user friendly non-intrusive programming and commissioning technologies, combined with comprehensive integral data logging, diagnostic and asset management capabilities.

Rotork CVA electric actuators deliver continuous, repeatable modulating control with a programmable fail to position option. Resolution, repeatability and hysteresis performance is quoted at less than 0.1 per cent of full scale, offering suitability for the most demanding control valve applications.

Aitor Laso is with Rotork Controls Ltd, Bath, UK.