Power Factor PF and cos ϕ Measurement

Power Factor PF

The MicroLogic trip unit calculates the power factor PF from the total active power Ptot and the total apparent power Stot:

This indicator qualifies:

• The oversizing necessary for the installation power supply when harmonic currents are present

• The presence of harmonic currents by comparison with the value of the cos ϕ.

cos ϕ

The MicroLogic trip unit calculates the cos ϕ from the total active power Pfundtot and the total apparent power Sfundtot of the fundamental (first order):

This indicator qualifies use of the energy supplied.

Power Factor PF and cos ϕ when Harmonic Currents are Present

If the supply voltage is not too distorted, the power factor PF is expressed as a function of the cos ϕ and the THD(I) by:

The following graph specifies the value of PF/cos ϕ as a function of the THD(I):

By comparing the two values, it is possible to estimate the level of harmonic deformation on the supply.

Sign for the Power Factor PF and cos ϕ

Two sign conventions can be applied for these indicators:

• IEC convention: The sign for these indicators complies strictly with the signed calculations of the powers (that is, Ptot, Stot, Pfundtot, and Sfundtot).

• IEEE convention: The indicators are calculated in accordance with the IEC convention but multiplied by the inverse of the sign for the reactive power (Q).

The following figures define the sign for the power factor PF and cos ϕ by quadrant (Q1, Q2, Q3 and Q4) for both conventions:

IEC convention
Operation in all quadrants (Q1, Q2, Q3, Q4)	Values of cos ϕ in receiver operation (Q1, Q4)

IEEE convention
Operation in all quadrants (Q1, Q2, Q3, Q4)	Values of cos ϕ in receiver operation (Q1, Q4)

Managing the Power Factor PF and cos ϕ: Minimum and Maximum Values

Managing the PF and cos ϕ indicators consists of:

• Defining critical situations

• Implementing monitoring of the indicators in accordance with the definition of critical situations

Situations are considered critical when the values of the indicators are around 0. The minimum and maximum values of the indicators are defined for these situations.

The following figure illustrates the variations of the cos ϕ indicator (with the definition of the cos ϕ MIN/MAX) and its value according to IEEE convention for a receiver application:

1 Arrows indicating the cos ϕ variation range for the load in operation

2 Critical zone + 0 for highly capacitive devices (shaded green)

3 Critical zone - 0 for highly inductive devices (shaded red)

4 Minimum position of the load cos ϕ (lagging): red arrow

5 Variation range of the value of the load cos ϕ (lagging): red

6 Maximum position of the load cos ϕ (leading): green arrow

7 Variation range of the value of the load cos ϕ (leading): green

PF MAX (or cos ϕ MAX) is obtained for the smallest positive value of the PF (or cos ϕ) indicator.

PF MIN (or cos ϕ MIN) is obtained for the largest negative value of the PF (or cos ϕ) indicator.

Monitoring the cos ϕ and Power Factor PF Indicators

According to the IEEE convention, critical situations in receiver mode on a capacitive or inductive load are detected and differentiated (two values).

The following table indicates the direction in which the indicators vary and their value in receiver mode.

The quality indicator MAX and MIN indicate both critical situations.

According to the IEC convention, critical situations in receiver mode on a capacitive or inductive load are detected but not differentiated (one value).

The following table indicates the direction in which the indicators vary and their value in receiver mode.

The quality indicator MAX indicates both critical situations.

Selecting the Sign Convention for the cos ϕ and Power Factor PF

Set the sign convention for the cos ϕ and PF indicators:

• With EcoStruxure Power Commission software (password-protected)

• By sending a setting command using the communication network (password-protected)

The IEEE convention is applied by default.