Schneider Electric HRB1684301-01 Chapter Power, energy and power factor, Power PQS, Power flow

Chapter 16 Power, energy and power factor

This section describes how the meter interprets and calculates power and power factor.

Power (PQS)

A typical AC electrical system load has both resistive and reactive (inductive or capacitive) components. Resistive loads consume real power (P) and reactive loads consume reactive power (Q).

Apparent power (S) is the vector sum of real power (P) and reactive power (Q):

S = P2 + Q2

Real power is measured in watts (W or kW), reactive power is measured in vars (VAR or kVAR) and apparent power is measured in volt-amps (VA or kVA).

Power and the PQ coordinate system

The meter uses the values of real power (P) and reactive power (Q) on the

PQ coordinate system to calculate apparent power.

PQ coordinate system

+Q

(+kVAR)

Quadrant 2 Quadrant 1

Q (+)

-P

(-kW)

Q (-)

S	S
P (-)	P (+)
P (-)	P (+)
S	S

Q (+)

+P

(+kW)

Q (-)

Quadrant 3 Quadrant 4

-Q

(-kVAR)

Power flow

Positive power flow P(+) and Q(+) means power is flowing from the power source towards the load. Negative power flow P(-) and Q(-) means power is flowing from the load towards the power source.

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