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Appendix E: Power and Power Factor
Sign Conventions
There are is an option to select one of three sign conventions
to be used by the trip unit to display Watts, VARs, and Power
Factor.
IEC Power Engineering Sign Convention
This setting will use the power engineering convention where P
= VI*. Where power is the complex product of volts times the
conjugate of current. Positive Watts & VARs are delivered to an
inductive load:
•
Watts are positive when the phase angle of current relative
to voltage is -90 < theta < +90
•
VARs are positive when the phase angle of current relative
to voltage is 180 < theta < 360. Under these conditions,
current lags the voltage.
•
The sign of power factor follows the sign of watts.
The
definition is PF = P / VA
IEEE Power Engineering Sign Convention
This setting uses the power engineering convention where P
= VI*. Where power is the complex product of volts times the
conjugate of current. Positive watts & VARs are delivered to an
inductive load:
•
Watts are positive when the phase angle of current relative
to voltage is -90 < theta < +90
•
VARs are positive when the phase angle of current relative
to voltage is 180 < theta < 360. Under these conditions,
current lags the voltage.
•
The sign of power factor is positive if the signs of Watts
and VARs are the same. For those conditions where real
power is flowing into the load, a lagging (inductive) PF is
positive.
Alternate IEEE (Direct Mathematical) Sign Convention
This setting uses the direct mathematical convention where P =
VI. Where power is the complex product of volts times current.
Positive Watts and negative VARs are delivered to an inductive
load.
•
Watts are positive when the phase angle of current relative
to voltage is -90 < theta < +90
•
VARs are positive when the phase angle of current relative
to voltage is 0 < theta < 180. Under these conditions,
current leads the voltage.
•
The sign of power factor is positive if the signs of Watts
and VARs are the same. For those conditions where real
power is flowing into the load, a lagging (inductive) PF is
negative.
Figure 26. IEC Sign Convention Phasor Diagram
92
EATON
www.eaton.com
Operating Manual for Series NRX
Digitrip Trip Units 1150 / 1150i
Effective September 2013
Instructional Leaflet IL01301064E