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Ocean Renewable Energy

Temperature Measurements in a Linear Generator and Marine Substation for Wave Power

[+] Author and Article Information
Cecilia Boström

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedencecilia.bostrom@angstrom.uu.se

Magnus Rahm

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedenmagnus.rahm@angstrom.uu.se

Olle Svensson

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedenolle.svensson@angstrom.uu.se

Erland Strömstedt

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedenerland.stromstedt@angstrom.uu.se

Andrej Savin

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedenandrej.savin@angstrom.uu.se

Rafael Waters

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, Swedenrafael.waters@angstrom.uu.se

Mats Leijon

Department Of Engineering Sciences, Division For Electricity,  Uppsala University, Swedish Centre For Renewable Electric Energy Conversion, Box 534, Se-751 21 Uppsala, SwedenMats.leijon@angstrom.uu.se

J. Offshore Mech. Arct. Eng 134(2), 021901 (Dec 05, 2011) (6 pages) doi:10.1115/1.4004629 History: Received June 24, 2010; Revised April 26, 2011; Published December 05, 2011; Online December 05, 2011

This paper analyzes temperature measurements acquired in the offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common dc-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. The first results of temperature measurements on substation components and on the stator of one of the linear generators are presented based on operation in linear and in nonlinear damping. The results indicate that there might be some convective heat transfer in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel in order to avoid heating from neighboring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding polyvinyl chloride cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the wave energy converter could be enhanced. Another suggested alteration is to lower the resistive losses by reducing the linear generator current density.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The WEC with its main components marked

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Figure 2

Overview diagram of the installed system at the Lysekil research site

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Figure 3

(a) The substation casing. (b) Picture taken from the inside of the substation where the sets of dc-link capacitors and the auxiliary batteries can be seen. (c) The transformer with the contactors that are used to switch between different winding taps.

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Figure 4

(a) The three buoys connected to the generators. (b), (c) Photos of L2 and L3, respectively.

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Figure 5

The temperature sensors that are mounted on the stator

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Figure 6

Temperature sensors TS3 and TS5 that are mounted in the substation

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Figure 7

An example of raw data from the sampling of the temperature sensors in the substation

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Figure 8

(a) Stator temperature and ambient temperature of L2. (b) Mean power in the dump load of L2. (c) Maximum power in the dump load of L2. (d) Sea state.

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Figure 9

One-minute mean values of L2 stator temperature as a function of the resistive generator loss

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Figure 10

(a) The one-minute mean WEC power delivered at the substation inputs. (b) The maximum instantaneous WEC power delivered at the substation inputs. The sample frequency was 500 Hz.

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Figure 11

(a) The mean temperatures of the stator of L2 and of various components in the substation. (b) The maximum temperatures of various components in the substation.

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