DC operated mini contactors ideal for Rotork

Rotork Controls has simplified the motor control system on its second generation IQ range of intelligent electric valve actuators by switching to a reversing pair of ABB DC operated mini contactors

Rotork Controls has simplified the motor control system on its second generation IQ range of intelligent, non-intrusive 3-phase electric valve actuators by switching to a reversing pair of ABB DC operated mini contactors.

The change, which has enabled Rotork to achieve even greater reliability for the new IQ range by reducing the component count, follows the successful completion of a gruelling series of environmental, vibration and shock tests.

According to Graham Odgen, Rotork's Research and Development Director, the tests simulated "possibly the worst conceivable operating conditions for a contactor." The original Rotork IQ design, launched in 1993, with its innovative non-intrusive, factory sealed actuator enclosure became established as the market leader in remote valve operation for many industries including water and waste treatment, power generation, oil and gas.

The second generation IQ has been restyled and re-engineered to offer a number of extra features such as the integral data logger that stores historical operating information, activity and output torque profiles.

An infra-red commissioning and interrogation system enables configuration and data logger files to be accessed either locally or from anywhere in the world, via a laptop PC or even a mobile phone.

The electronics have also been rationalised for increased reliability with the introduction of a bespoke IQ chip, replacing hundreds of individual components, so that standard actuators now have just one printed circuit board to support all local and remote control functions.

It was as part of the IQ re-engineering process that Rotork decided to review the motor control system, as Graham Ogden explains: "In this application the contactors are required to control 3-phase squirrel cage induction motors utilising an AC3 duty.

The first generation IQ design featured a reversing pair of contactors with 110V coils, but in many cases this set-up also required the inclusion of a pair of relays to complete the control electronics to power switching chain.

So we were keen to explore a change in technology to 24V DC operated contactors.

This would not only enable us to achieve our primary aim of further improving system reliability through increased simplicity and a reduced component count, it would also be more cost-effective as well as saving assembly time.

"Initial discussions with ABB's engineers suggested that, with modification to suit our nominal supply voltage of up to 690V, their DC operated mini contactors would fit the bill.

However changing the contactor design was a major exercise for Rotork, especially as the electrical loads and extreme operating conditions are very different from the normal duty expected from a contactor.

We therefore drew up a very detailed and demanding technical specification and asked ABB to underwrite the performance of the new contactors against it." Key elements in the test specification included: The key test requirement was that the reversing pair of contactors must have an electrical life in excess of 250,000 operations when switching Rotork's specified currents and voltages for both make and break conditions.

They also had to be able to achieve this over the temperature range -30C to +70C.

In addition, they had to be suitable for use over an extended temperature range of -50C to +85C.

Since Rotork valve actuators can be fitted in any position, tests were carried out to ensure that the contactor operation was gravity independent so that they could function in any orientation.

Valve actuators can be fitted in applications where they experience vibrating loads, such as in compressor stations.

The contactors were therefore subjected to both sine-wave and random 10g rms vibration over the 10Hz and 1kHz spectrum, in both energised and de-energised conditions.

Very few contactors are approved for use at this level of vibration, and this is where Rotork believed there could be a major issue in replacing the original AC operated contactors, since conventional DC contactor designs, with their larger moving mass and smaller springs might be more susceptible.

However, the ABB contactors proved to be "fundamentally better." The contactors were also tested to prove that they could withstand accidental impacts of up to 30g in any axis in both energised and de-energised conditions.

Graham Ogden continues: "After successful completion of the test programme we were convinced that ABB's DC operated contactors would operate successfully as an integral part of the reliable switching package we were seeking for the new generation IQ valve actuators.

The actual unit specified is the VBC7 reversing pair of three pole 5.5kW DC operated mini-contactors.

Basically, this is a standard production unit modified for our particular needs, such as the 690V supply voltage together with special Rotork branded tops to provide additional creepage and clearance.

They are supplied pre-wired with links and 'Fast-On' connectors in reusable trays which operate on a flow system between ABB and the Rotork factory in Bath to eliminate the need for packaging." The new generation Rotork IQ range entered volume production at the end of 2000 and ABB is currently supplying around 20,000 of the reversing pairs of contactors per year.

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