The latest PowerRod linear motor system from Parker Hannifin is playing a vital role in a series of test machines, for spacer dampers designed for use on overhead power transmission lines.
The test machines use the PowerRod motor and Compax 3 servo drive to replace conventional motor and cam mechanisms, helping to minimise setup time and provide high levels of reliability during tests of 20 million cycles, equivalent to around 5,000km of travel.
The spacer dampers are fitted to high-voltage overhead transmission line conductors, used for long-distance transmission of electricity at 400kV from power stations to substations.
Conductors are normally arranged in bundles of two, three or four lines which have specific separations, maintained and protected from wind-induced sub-conductor oscillation energy by spacer dampers.
Spacer dampers protect the line cables from wear and premature fatigue failures, maintaining electrical and mechanical performance during climatic extremes and system faults.
The quad and triple spacer dampers undergoing test form part of a long-term programme to upgrade the UK power transmission network over the next decade.
The semi-conductive spacer dampers are constructed from aluminium alloy and, in the case of the Quad versions, have four connection arms.
Each of these is linked via a specially designed frame, with the arm arrangement incorporating elastomer damping elements.
These attach to each sub-conductor maintaining, for example, a 500mm separation.
The test rigs are primarily designed to prove the performance and operating life of the elastomer damping elements, effectively moving each pivot arm though a predetermined series of cycles.
These include a deflection test, to ensure that the arm will not deviate beyond specific angular displacements, for example, 12 degrees either side of its neutral position.
Deflection forces are initially 325N, followed by continuous flexing at 260N peak, with a return to the maximum load at intermittent intervals at frequencies between 1 and 5Hz.
These tests are repeated for up to 20 million cycles, which is the equivalent of over 25 years in service.
In the past, test rigs for similar applications tended to use an AC motor, camshaft and various bearings to test each damper.
This arrangement was noisy and consisted of multiple components, so the potential for mechanical wear and failure was high; it was also difficult to change applied forces without lengthy adjustments to the cam settings.
The solution was to use the Parker PowerRod PRA linear motor and Compax 3 servo drive.
This provides a simple, compact and extremely efficient system that is virtually silent and allows easy adjustment to the applied force.
The PowerRod motor is supplied as an integrated system complete with encoder, so that no additional measurement devices are required.
The Compax 3 interfaces with a PC via a standard National Instruments card, allowing simple control of settings on each test rig.
For example, each PowerRod unit can be cycled between 1 and 5Hz, depending on the unit tested, which equates to a test time of 46 days at maximum speed, and can interrupt and restart each test if required.
