Application Note

30 Fluke Corporation Power Quality Troubleshooting
Lighting loads are a major load
for many large facilities. Evalu-
ating these circuits is important
for both energy conservation
and power quality. Keep in
mind that commercial lighting
loads are wired single phase,
with the loads connected from
phase to neutral. Typically, the
phase-to-phase voltage is
480V, with the phase-to-neu-
tral voltage at 277V. Measure-
ments must be taken at the
lighting panel, one phase at a
time, since power consumption
and Power Factor could vary on
each phase.
Table 8.1 Measurements on commercial lighting loads.
Measurement Look for Instrument
1. Power Balance among three phases. 43, 41B
consumption (kW)
2. Power Factor Magnetic ballast will have low DPF. Electronic 43, 41B
(DPF and PF) ballast may have low total PF, although new
generations of ballast often have harmonic
mitigation built-in.
3. Total Harmonic Current %THD <20% is desirable. 43, 41B
Distortion (%THD)
4. Voltage Stability Unstable voltage can cause lights to flicker. 43
Section 8
Troubleshooting Commercial Lighting Loads
1. Power consumption
Excessive phase unbalance can
cause voltage unbalance, which
in turn can affect three-phase
motor loads.
2. Power Factor
Ballast with low PF might have
lower cost-of-purchase but
higher cost-of-operation.
3. Total Harmonic Distortion
Current THD should be consid-
ered when selecting ballast, es-
pecially if there is a possibility
of transformer overloading.
4. Voltage stability
The sags and swells mode of
the Fluke 43 is especially useful
for recording repetitive voltage
sags which can show up as
flickering lights. Both current
and voltage are monitored si-
multaneously. This helps us to
tell if sags are downstream of
the measuring point (load-
related) or upstream (source-
related). For example, if voltage
sags while current swells, a
downstream current inrush
likely caused the sag. If both
voltage and current sag, some
event upstream caused
the sags.
It could be an upstream
load like a motor on a parallel
branch circuit which drew
down the feeder voltage. Or
it could be source voltage-
related, for example, a lightning
strike or breaker trip/reclosure
on the utility distribution
system.
Ø1
Ø2
Ø3
N
Lighting Panel
277V Phase-to-Neutral
480V Phase-to-Phase
Figure 8.1
Figure 8.2 Fluke 43 trends voltage (top) and
current (bottom) simultaneously. Current
swells/inrush caused voltage sags, indicating
that a load downstream from the measure-
ment point is the cause of the disturbance.