Chapter A General rules of electrical installation design

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L8
L - Power factor correction and
harmonic filtering
Compensation can be carried out by a
fixed value of capacitance in favourable
circumstances
Compensation is more-commonly effected by
means of an automatically-controlled stepped
bank of capacitors
3 How to improve the power factor?
Fixed capacitors (see Fig. L10)
This arrangement employs one or more capacitor(s) to form a constant level of
compensation. Control may be:
b Manual: by circuit-breaker or load-break switch
b Semi-automatic: by contactor
b Direct connection to an appliance and switched with it
These capacitors are applied:
b At the terminals of inductive devices (motors and transformers)
b At busbars supplying numerous small motors and inductive appliance for which
individual compensation would be too costly
b In cases where the level of load is reasonably constant
Fig. L10 : Example of fixed-value compensation capacitors
Automatic capacitor banks (see Fig. L11)
This kind of equipment provides automatic control of compensation, maintaining the
power factor within close limits around a selected level. Such equipment is applied at
points in an installation where the active-power and/or reactive-power variations are
relatively large, for example:
b At the busbars of a general power distribution board
b At the terminals of a heavily-loaded feeder cable
Fig. L11 : Example of automatic-compensation-regulating equipment
Schneider Electric - Electrical installation guide 2008