Siemens 9810 Series, User Manual, Page: 182 / 218

Measurements
A purely resistive load has no reactive components, so its power factor is 1 (PF =
1, or unity power factor). Inductive or capacitive loads introduce a reactive power
(Q) component to the circuit which causes the PF to become closer to zero.
True PF and displacement PF
The meter supports true power factor and displacement power factor values:
• True power factor includes harmonic content.
• Displacement power factor only considers the fundamental frequency.
NOTE: Unless specified, the power factor displayed by the meter is true power
factor.
Apparent, active and reactive power (PQS)
Apparent power (S) is the capacity of your measured power system to provide
active (real power, P) and reactive power (Q).
A typical AC electrical system load has both resistive and reactive (inductive or
capacitive) components. Resistive loads consume real power (P). Reactive power
(Q) is either consumed (inductive loads) or generated (capacitive loads).
+Q
(+kVAR, +kVARh)
-P
(-kW, -kWh)
-Q
(-kVAR, -kVARh)
+P
(+kW, +kWh)
Active power (W)
Exported/received
A
pparent power (VA)
Rea
ct
ive power (VAR)
Imported/de
livered
Quadrant 3
PF lagging
Power factor sign convention:
IEEE = −
IEC = −
Quadrant 4
PF leading
Power factor sign convention:
IEEE = +
IEC = +
Quadrant 1
PF lagging
Power factor sign convention:
IEEE = −
IEC = +
Quadrant 2
PF leading
Power factor sign convention:
IEEE = +
IEC = −
90°
0° 180°
270°
App
arent power (VA)
Rea
ct
ive power (VAR)
Imported/de
livered
Active power (W)
Exported/received
Rea
ct
ive power (VAR)
Exported
/re
ceived
Appar
ent
po
wer
(VA)
Ap
parent power (VA)
Active power (W)
Imported/delivered
Active power (W)
Imported/delivered
Rea
ct
ive power (VAR)
Exported
/re
ceived
The units for power are watts (W or kW) for real power P, vars (VAR or kVAR) for
reactive power Q, and volt-amps (VA or kVA) for apparent power S.
Positive real power P(+) flows from source to load, and negative real power P(-)
flows from the load to the power source.
Current phase shift from voltage
Electrical current can lag, lead, or be in phase with the AC voltage waveform, and
is typically associated with the type of load — inductive, capacitive or resistive.
For purely resistive loads, the current waveform is in phase with the voltage
waveform. For capacitive loads, current leads voltage. For inductive loads, current
lags voltage.
The following diagrams show how voltage and current waveforms shift based on
load type under ideal (laboratory) conditions.
182 7EN05-0390-00