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IM 2041-01
(5) 二電力法による三相電力の測定
三相回路の電力は，2 台の単相電力計 2 台を Fig. 2-6 のように結線
して測定できます。電力値は両電力計測定値の代数和で表されます。
測定回路の力率が 50% 以上のときは，Fig. 2-6 の結線であれば両電
力計とも正に振れますから，求める三相電力は両者の指示の和となり
ます。力率が 50% 未満の場合には，いずれか一方の電力計は逆振れ
します。そのときは逆振れした電力計の電圧端子の二線をいれかえて
正方向に振らせます。その指示を他方の正方向を示した計器の指示よ
り引きます。
5. Three-phase AC power measurement (by two sets of wattmeters)
Three-phase power measurement is made by connecting two sets of single-
phase wattmeters as shown in Fig. 2-6. The power is indicated by the
algebraic sum of the indications of the two wattmeters.
When the power factor of the circuit to be measured id greater than 50%,
both of the wattmeters connected as shown in Fig. 2-6 indicate “positive”
values.
The measured three-phase power is the algebraic sum of the indications
on these two meters. When the power factor of the circuit to be measured
is less than 50%, the pointer on one of the two wattmeters will deflect
backward off the scale. In this case, reverse the voltage connections of
the meter whose pointer deflects backward, so that the meter indicates a
“positive” value on the scale. Subtract this value from the positive value
on the other meter.
±
±
±
±
Fig. 2-6
電源
Power Source
R
T
S
CT
負荷
Load
L
K
k
CT
L
K
k
U
V
v
VT
u
U
V
v
VT
u
Summary of Contents for 2041
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