SERI/STR-211-2086 November 1983 DE84000030 Television Interference Measurements Near the MOD-2 WT Array at Goodnoe Hills, Washington A Subcontract Report D. L. Sengupta T. A. Senior B. E. Ferris J. Radiation Laboratory University of Michigan Ann Arbor, Mich. Prepared under Subcontract No. DE-AC02-76ET20234 ----------------------------------�·�------------------------------------------------------ Printed in the United States of America Available from: National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 Price: Microfiche A01 Printed Copy A04 NOTICE This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. SERI/STR-211-2086 UC Category: 60 DE84000030 Television Interference Measurements Near the MOD-2 WT Array at Goodnoe Hills, Washington A Subcontract Report D. L. Sengupta T. B. A. Senior J. E. Ferris Radiation Laboratory University of Michigan Ann Arbor, Mich November 1983 Prepared under Subcontract No. DE-AC02-76ET20234 SERI Technical Monitor: Neil D. Kelley Solar Energy Research Institute A Division of Midwest Research Institute 1617 Cole Boulevard Golden, Colorado 80401 Prepared for the U.S. Department of Energy Contract No. DE-AC02-83CH10093 STR-2086 PREFACE The authors gratefully acknowledge the assistance of various indi­ vi duals in the completion of the me asurement program. They are particularly grateful to K. Cavcey and L. Lee of the Bonneville Power Administration (BPA) , and R. Schwemmer, J. Peetz , and G. Soranaka of the Boeing Engineering & Construction Comp any for provi ding us with the necessary help at the test sites. Success­ ful completion of the program would not have been possible without the coordinating efforts of N. Ke lley of SERI and M. Reynolds and P. Renner of BPA . The authors also wish to thank Wanita Rasey for her help in preparing the draft. Neil D � Kelley, Te chnical Man or ·' Approved for SOLAR ENERGY RESEARCH INSTITUTE . � - ;} / >'"'._)�,___.,�Vv. /c�·2-7· tJ Donald Ri tchie , Manager So lar El ectric Conversion Research Divi sion iii STR-2086 SUMMARY El ectromagnetic in terference to televis ion reception caused by the MOD-2 wind turbine (WT) array at Goodnoe Hills , Wash., has been studied by carrying out detailed measurements at a number of test locations or sites in the vicinity of the WT array . The commercial televis ion (TV) signals available in the area were used as the radio frequency (rf) sources during the measurements. Tests were performed at the top of the WT No . 2 tower and at the bases of the three WT towers , and at three other sites chosen to represent the region around the WT array . For some TV channels , all of the sites were in the backward inter­ ference region of the WTs , but for other channels, some of the sites were also in the forward interference region. At each location, some or all of the following types of measurement we re per­ formed on all of the available TV channels: (i) Received field strength. With the WTs stat ionary , the strength of the received signal was measured by rotating the main beam of the receiving antenna until the output was maximum. This provided informat ion about the expected quality of TV reception in the area, and also the field strengths of various TV channels at the WT No. 2 relative to those at a test site, wh ich play an important role in the televi­ sion in terference ( TVI) effects produced by the WTs . (ii) Static or blade scattering . With the blades of WT No . 2 locked in a desired (usually horizon­ tal) posit ion and their pitch set for maximum power, the WT was yawed in azi­ mu th through 360° . Me asuring the TV signals received with the antenna pointed at the WT helped to determine the maximum blade-scattered signals. From these results , the equivalent scattering area (A ) and length (L ) of the blades we re determined . These me asurements were mportant because 1the interference caused by the WT depends crit ically on theseI parameters . (iii) In some cases, as the antenna was rotated the output of the receiver was recorded as a func­ tion of time , with and without the WT blades rotating . These measurements served to determine (a) the horizontal plane pattern of the antenna in an actual te st environment , (b) the effect of the WTs on the received signal , and (c) the amount of signal modulation caused by the operat ing turbines . (iv) Dy namic or televis ion in terference (TVI) . These tests we re performed with the WT(s ) operating and by recording the received signal versus time with the antenna directed at the desired transmitter or at the WT array , wh ile the re ceived picture was observed on the TV screen for any video distortion. Dynamic measurements we re performed at first with one WT operat ing , then two , and finally all three WTs operating together. The equipment setup and the measurement procedures we re similar to those employed in our previous studies. Directional receiving antennas we re used at all test sites. The amb ie nt field strength me asurements in dicated that in the region surround­ ing the WT array , all of the TV signals are extremely weak , and the quality of TV reception in the area is generally very poor to unacceptable. The field strengths on top of the WTs we re generally of the same order as those at the remo te test sites . v STR"'-2086 The equivalent scattering area of the HOD-2 blade, determi ned from static tests using two different channels at one site and one channel at a second site, was very close to the 184 m2 predicted on the basis of laboratory mea­ surements of scale-model MOD-2 blades. Th e dynami c measurements indicated that (a) varying amounts of TVI were pro­ duced at all sites and on some or all of the available channels; (b) with TV the directional antenna in use, most of the backward region interference pro­ duced video distortion that was judged to be acceptable; (c) at one test loca­ tion about 1-1/2 miles from the WT array site, forward region interference was observed on Channel 12; (d) when the blades of the WTs rotate in synchronism, they tend to increase the amplitude of the interference pulses, thereby pro­ ducing more TVI effects; and (e) when the blades do not rotate in synchronism, each WT produces interference effects individually. vi STR-2086 TABLE OF CONTENTS 1.0 Introduction •••••••••••••••••••••••••••••••••••••••••••••••••••• • • •. 1 2.0 Background Information •••••••••••••••••••••••••••••••••••••••••••••• 3 2.1 Physical Environment ••••••••••••••••••••••••••••••••••••••••••• 3 2.2 The MOD-2 'WT••• •••••••••••••••••••••••••••••••••••••••••••• • • •• 3 2.3 Test Sites •••••••••••••••••••••••••••••••••• ••••••••••••••••••• 6 2.4 The.Interference Phenomenon •••••••••••••••••••••••••••••••••••• 9 2.5 Available TV Signals ••••••••••••••••••••••••••••••••••••••••••• 13 3.0 Te st Eq uipment and Procedures ••••••••••••••••••••••••••••••••••••••• 15 3.1 Equipment •••••••••••••••••••••••••••••••••••••••••••••••••••••• 15 3.2 The Receiving An tennas ••••••••••••••••••••••••••••••••••••••••• 17 3.3 Types of Measurement ••••••••••••••••••••••••••••••••••••••••••• 17 4 .0 Measured Amb ient Signal Strengths ••••••••••••••••••••••••••••••••••• 19 4 .1 Received Signal Strength and Qu ality of Reception •••••••••••••• 19 4 .2 Signal Strengths at the WT Ar ray Site •••••••••••••••••••••••••• 20 4 .3 Signal Strengths at Sites A, B, and c •••.. .••••.•.••••.•••. ..•. 21 4 . 4 Conclusions •••••••••••••••••••••••••••••••••••••••••••••••••••• 22 5.0 Blade Scattering (Static Tests ) ••••••••••••••••••••••• .............. 23 5.1 Comme nts on the Blade Scattering Parameters •••••••••••••••••••• 23 5.2 Procedure ••••••••••••••••••••••.• • •••••••••••••••••••••••••••••• 24 5.3 Results •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 24 4 5. Theoretical Exp ressions •••••••••••••••••••••••••••••••••••••••• 28 5.5 Da ta .Analysis •••••••••••••••••••••••••••••••••••••••••••••••••• 30 5.6 Dis cussion ••••••••••••••••••••••••••••••••••••••••••••••••••••• 33 6.0 Television In terference Measurements (Dynami c Tests) •••••••••••••••• 35 6.1 Site A ••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 35 6.2 Si te B ••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 39 6.3 Site C •••••••••••.• ••••••••••••••••••••••••••••••••••••••••••••• 39 4 6. Di scussion ••••••••••••••••••••••••••••• ,. •••••••••••••• ••••••••• 42 7.0 Conclusions ••••••••••••••••••••••••••••••••••••••••••• 45 8.0 Re ferences •••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 47 Ap pendix: Theoretical Considerations •••••••••••••••••••••••••••••••••••• 49 A.l Scattering by a Re ctangular Me tal Plate •••••••••••••••••• 49 A.2 Received Fi eld During Static Measurements •••••••••••••••• 53 vii STR-2086 LI ST OF FIGURES 2-1 A General Roadmap of the Region Surrounding the WT Ar ray Site••••. •••••••••••••.••• . •••. •••••• .-. ....................... 4 2-2 A Sketch of the Immediate Area Indicating the Approximate Locations of the Three MOD-2 Machines . .............................. 5 2- 3 Detailed Sketch of the WT Cluster Site•••••••••••••••••••••••••••••• 6 2-4 Topographical