Transient thermographic studies of resistive system protection load for wind turbines

The present paper reports findings of the transient thermography studies of three-phase resistive system protection load (RSPL) or diversion dump load used for safeguarding the wind turbines during extreme wind conditions. RSPLs with coil-type and plate-type resistive elements made of Nichrome 80 and SS 304, respectively, were studied. The first set of studies was conducted on the permanent magnet synchronous generator (PMSG) test bench with 24 and 48 V PMSGs as power sources. The second set of studies was conducted on the auto-transformer-based test setup. For both the studies, surface temperature distributions over the resistive elements of the RSPLs were captured under the different test conditions using transient thermography and compared. Quantitative comparison of the variation in maximum temperature of RSPL heating elements and PMSG's rotational speed for a given power rating for both the RSPLs was carried out. Thermographs revealed the presence of localized hotspots in RSPLs with Nichrome 80 based coil-type heating elements. Similar localized hotspots were absent in RSPLs with SS 304 based plate-type heating elements. Maximum surface temperatures of RSPLs with coil-type resistive elements were found to be about 8.25% higher than the other RSPL. Based on these observations, it was inferred that as against the conventional approach of using RSPLs with a coil-type heating element made of Nichrome 80, RSPLs with a plate-type heating element made of SS 304 offered better safety for the wind turbines.