ISA T1000 PLUS User Manual page 88

DOC. MIE91093 Rev. 1.34 Page 88 of 145
X
Z3
Z2
Z1
R
The first decision for the operator is to select the angle at
which he wants to perform the test. It can be that purpose of
the test is to check a limited number of settings; if so, they
are typically given at the line angle (usually 75° to 85°), and
possibly also at 0° and 90°. Please note that this angle is the
Φ(I-V) angle to be used during the test, but WITH NEGATIVE
SIGN: the reason is that
Z = V / I
As the current is at the denominator, the angle sign is
changed.
Now it must be understood that once the angle is selected, the
phase angle line intercepts the characteristic at the setting
values; this is represented in the Z-t plane by the following
curve.