FORMATO DE PRESENTACION DE LA OFERTA ECONOMICA

5.6.1 Turbine Control

For the set of tests undertaken as outlined in Section 5.6 it was considered that speed control of the PMSM would be the most suitable control approach. This was considered to be the case as the PMSM was used to undertake rotor torque measurements as well as provide a resistance to the rotor torque developed via the oncoming fluid flow. As outlined in Section 3.4.2 in order to accurately measure the rotor torque via the PMSM minimising the acceleration of the turbine rotor was required. As a result of the above reasoning all of the rotor imbalance test cases undertaken speed control of the PMSM was utilised in order to best measure the rotor transient characteristics.

5.6.2 Test Cases

The purposes of the flume testing campaign undertaken as part of the research activities were two-fold as noted in Section 5.1. In order to test CM approaches at the 1/20th scale and provide data for parametric model development an experimental campaign utilising testing at differing fluid velocities, turbine rotational velocities and with differing rotor conditions

122 was undertaken. Table 5.2 shows the rotor cases and the fluid velocities tested at the University of Liverpool; for each case five turbine rotational velocities were tested leading to λ values of: 1.5, 2.5, 3, 3.5, 4, 4.5 and 5.5. These test cases gave data relating to turbine operation at both differing diameter based Reynolds numbers and at differing kinematic scaling values – this allowed for transient relationships to be developed for turbine model development and to test the performance of monitoring approaches at a variety of turbine operating conditions.

Table 5.2: Outline of the rotor imbalance test cases simulated during the 1/20th _{scale testing along with the} fluid velocities set.

Rotor Condition Fluid Velocity

Optimum:

All blades at 6o _{pitch angle setting} 0.9 ms-1, 1.0 ms-1 and 1.1 ms-1

Offset +3:

Blade 1 at 9o pitch angle, all others at 6o 0.9 ms

-1_{, 1.0 ms}-1 _{and 1.1 ms}-1

Offset +6:

Blade 1 at 12o pitch angle, all others at 6o 0.9 ms

-1_{, 1.0 ms}-1 _{and 1.1 ms}-1

Two Blades Offset:

Blade 1 at 12o, Blade 2 at 9o, Blade 3 at 6o.

0.9 ms-1, 1.0 ms-1 and 1.1 ms-1

In the considerations made for the testing campaign it was noted that the flume and turbine setups may exhibit some inherent imbalance as such the optimal case was included and the processing of condition monitoring approaches were compared with the optimal case. Furthermore considerable effort was made to reduce any unintentional imbalances introduced during the process of setting the blade pitch angles between tests as by necessity the turbine was removed to undertake this process. These provision are outlined in the following sections.

5.6.3 Instrumented Blade Position Setting

In order to set a consistent reference for the turbine rotor position relative to the stanchion, the encoder reference was set to 0o when the instrumented blade was at top dead centre or pointing vertically parallel to the stanchion. This was done by exploiting the flat

123 surface which was created by the blade housing – this can be seen in Figure 5.11a. The flat surface highlighted on the figure was 90o _{± 0.5}o _{to the blade orientation. A digital protractor}

- zeroed relative to the horizontal cross beam to which the turbine was mounted - was then used to confirm the blade housing was at the required angle namely, 0o. This can be seen in Figure 5.11b. Once the position was correct the encoder reference was programmatically set to zero using the Bosch Rexroth IndraWorks software.

a b

Figure 5.11: Blade positioning setup, a) Blade Housing b) Setting the housing position using a digital protractor.

5.6.4 Blade Pitch Angle Setting

The process developed for setting the turbine blade pitch again utilised a digital protractor and the encoder reference set as outlined in the previous section. The turbine rotor was set such the blade undergoing the pitch setting was positioned horizontal relative to the turbine stanchion – in terms of the encoder reference the three angles which set the blades to the horizontal positon required were 90o, 210o and 330o. Once the blade is horizontal, the pitch angle setting relative to the turbine rotational plane can be done relative to the vertical. To achieve this the digital protractor was zeroed relative to the turbine stanchion, which served as a useful vertical reference – see Figure 5.12a.

124 The digital protractor was then positioned across the turbine blade tip and the angle set. Once the angle was set the blade was secured via the grub screws – the angle was then checked and corrected if necessary. The digital protractor used had a resolution of 0.1o, however due to human error the angles set were subjected to an error of ± 1o. This was considered generating the test cases presented in Table 5.2: Outline of the rotor imbalance test cases simulated during the 1/20th scale testing along with the fluid velocities set.

a b

Figure 5.12: The blade pitch setting process, a) Zeroing the digital protractor relative to the vertical stanchion b) setting the blade pitch angel relative to the vertical.

5.6.5 Test Procedure

Testing was undertaken with care to ensure consistent results, specifically in terms of setting the turbine in place and allowing the flume to settle at the next fluid velocity or turbine rotational velocity. Once the 0o zero position of the encoder was set the digital protractor zeroed vertically relative to the turbine stanchion. The process outlined above was then followed to set each blade pitch angle. Once the turbine blades were all set to the required pitch the turbine was moved into position with a crane. The turbine stanchion was

y

125 bolted to a cross beam mounted perpendicular to the flow direction across the recirculating flume – this was checked by measuring the distance of the cross beam from the flume inlet on either side of the flume. The recirculating flume was then set to the required fluid velocity, again, this was checked with ADV. The turbine, generally self-starting was allowed to freewheel for a minimum of 100 seconds. The turbine was then set to the required rotational velocity to achieve the desired λ value, again the turbine was allowed to rotate at this velocity for a minimum of 100s and then the data capture was initiated. Data was collected for 300 seconds and the next rotational velocity set. This process was repeated for each required λ value, as noted in Section 5.6.2. Once all the λ values for the fluid velocity setting were captured the flume was set to the next required flow velocity. This process was repeated for each setting outlined in Section 5.6.2.

126

Scale Turbine Flume-

Testing Results

6.1

Introduction

This chapter presents key results from the flume based test campaign in order to provide an overview of the turbine performance under the differing operating conditions as well as to give an initial insight into the performance of condition monitoring algorithms under flume tank testing.

The chapter presents both mean value characteristics expressed in the usual performance coefficient curves and transient characteristics which were analysed in a variety of ways. Non-dimensional performance curves have been developed to confirm Reynold’s independence during testing. These are used to compare recorded values with the previous values calculated via CFD computations. This is used to compare turbine operation under differing control schemes and rotor conditions. The non-dimensional turbine performance curves are supplemented by drive shaft torque transient results analysis. The transient results have been included in the appropriate sections for comparison of CFD calculated drive shaft torque transients. They also enable the consideration of turbine drive shaft torque transients observed under differing turbine control settings and thus highlight the effect of rotor condition on transient drive shaft torque characteristics. The latter considerations of the effect of rotor condition on drive shaft torque transients culminate in the frequency characterisation of the turbine rotor torque over a range of tip-speed ratios. These characterisations are then used to develop performance surfaces which are then utilised in two ways which are consistent with the goals of the research. Firstly, the surfaces are used

127 to provide ‘parameter surfaces’ for an empirical parametric rotor model presented in Chapter 7. They are further utilised in CM processes outlined in Chapter 3 and applied in Chapter 8.

The chapter ends with the presentation of the application of these CM algorithms the use of the developed surfaces.