Description of Testrig

The VHM mounted on the testrig is shown in Figure 4.36 and labelled in Figure 4.37.

Figure 4.36: The VHM testrig
Figure 4.37: Aspects of VHM testrig

The role of the testrig is to excite the prototype in a manner analogous to that encountered in wave energy converters: linear, reciprocating and slow peak velocities.

To achieve this a conventional induction machine was coupled to a 0.1 m radius crank though a 14:1 step down gearbox. Peak speeds of less than 0.5 m/s are easily achievable.

To allow for the future expansion of the testrig and accommodate spring elements, hence simulating more closely the conditions of a wave energy converter, there is a system of steel cables and pulleys transferring the crank force to the rotor. This results in slight play between the relative position of the exciting crank and the prototype translator. In order to account for this, a displacement transducer has been mounted to the translator, allowing the exact time displacement data of the testrig to be fed into the electrical models and their performance evaluated.

Experience at the University of Durham dictates that the task of maintaining a small airgap in the presence of high magnetic forces should not be underestimated. Section 4.3.1.2, the normal force based on FEA calculation of Maxwell stress, was used to design the framework structure within which the stator cores were mounted. This framework means that the cores are essentially supported in air and are hence magnetically independent from each other and any other influence. Provision has been given, by way of in-house made screw thread adapters, for the alteration and accurate setting of the airgap.

Figure 4.38: Position of load cell

The translator is supported on each side by solid steel square bars, which also act as the runners for the stud bearings mounted to the stator frame. It is thus a rigid structure which is free to move axially within the airgap.

Both the translator and the stator are made from 1 mm thick laser cut mild steel laminations, held together in compression by a series of steel bolts.

In order to measure the static force reacted by the prototype, the cables used to drive the translator were removed and replaced by a screw thread mounted load cell, Figure 4.38. The position of the rotor was selected and subsequently held in place by the cell. The cell deforms less than 0.4 mm at full load, 1000kg [82], the rotor can therefore be assumed stationary as current is altered within the coils.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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