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Capacitors 135
TECHNICAL
Power factor in Fluorescent and
HID Circuits
For a pure resistive load in an electrical circuit,
the voltage (V) and current (I) are in phase with
each other and the overall power factor (cosΦ)
has a value of unity. It can also be said that
the average power (P) of the resistive circuit is
equal to the apparent power (S), ie. P = V x I.
However, in a pure reactive electrical circuit,
there is no resistive component; the voltage
and current are 90° out of phase, ie. cosΦ = 0.
Electrical circuits containing a combination of
both resistive and reactive elements display
both average power and apparent power
components.
Power factor is therefore the ratio by which
the apparent power is multiplied, in order
to obtain the average power actually being
consumed in the circuit, ie. P = V x I x cosΦ.
For example, a power factor of 0.5 indicates
that the circuit has a reactive component
having a phase angle of +60° or -60°.
In common practice most loads are inductive
and therefore the current lags the voltage
(lagging power factor), whereas a typical
capacitive load has a leading power factor.
Fluorescent and HID lamp circuits have an
inherent low power factor (around 0.4 to
0.5), due to the control gear inductance.
The inductance is in the circuit to limit the
current through the lamp, however, in lighting
installations where many lamps are used,
high input current increases the cost of mains
reticulation.
Raising the power factor by means of the
inclusion of a capacitor (opposite effect to an
inductor) substantially reduces the current
drawn from the mains, giving improvement
in the reticulation efficiency, which in turn
enables a reduction in copper wire size and
transformer sizes (the generating equipment).
Most power distribution authorities have a
requirement of high power factor (HPF) for
lighting installations of generally 0.85 to 0.95
minimum.
Figure 1 Figure 2
A typical discharge lighting circuit without
power factor correction, eg. 400W high
pressure sodium, has a power factor of
approximately 0.4. Figure 1 shows the
relationship of current and voltage in this
application.
This power factor characteristic can be
corrected to approximately 0.9 by adding
a capacitor (leading) to the lagging line
current, to cancel the phase shift. Figure 2
illustrates this.
In common application therefore, by
connecting a capacitor into the lighting circuit,
the power factor can be improved to the
values normally prescribed by the regulatory
authorities so that practically inductance free
operation results.
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N
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Ballast
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Lamp
Capacitor Quality
Assured quality of capacitors is first and
foremost and cannot be compromised. Hella
uses accepted IEC and BSI Standards as the
minimum measure of quality.
Production is integrated with an audited
Quality System that is accredited to AS/NZS
ISO9002 and supported by a technical team
and fully equipped laboratory facilities.
Hella power factor correction lighting
capacitors have been certified by British
Standards Institute to BSEN 61048, and
BSEN 61049 and has ENEC approval (License
no. KM 30180).
These standards provide, thorough quality
checks of materials and capacitance
characteristics, a capacitor that retains its
integrity under the required conditions of
operation.
Quality Test Program
• materials / component inspection
• end spray thickness test
• voltage test
• capacitance tolerance check
• dissipation factor
• physical inspection
• end product batch test
• endurance test
• Assured Quality Systems (ISO9002 series)
• BSI certification
• ENEC approval
• testing of the dielectric materials
• in-line 100% capacitance testing
• new automatic ‘AC’ tester
• stud mounting or alternative clip spring
accessories.