812-4 Use of the wattmeter NP=I‖I|cos(v.-v:) If a positive current is flowing into the(+)end of the current coil while the (+ terminal of the voltage coil is positive with respect to the unmarked end, an upscale reading is obtained
§12-4 Use of the wattmeter W • I − + • V N If a positive current is flowing into the (+) end of the current coil while the (+) terminal of the voltage coil is positive with respect to the unmarked end, an upscale reading is obtained. =| || | cos( • − • ) • • V I P V I
10 10 v1=10020V V2=100∠00V 10I1+j5(11-)=j00 10+j5(1-1)=-100 1118∠153.4°4 P=V2Icos(0-1534°)=100×118×c0s153.4°=-1000( downscale) Reverse a coil(the voltage coil)
+ − = − + − = • • • • • • 10 5( ) 100 10 5( ) 100 1 1 1 I j I I I j I I j I A = 11.18153.4 • cos(0 153.4 ) 100 11.18 cos153.4 1000 ( ) 2 P =V I − = = − W downscale [Reverse a coil(the voltage coil)] I 1 • V2 100 0 V = • V1 100 90 V = • − + 10 10 j5 • I − + W • I