Theory Of Operation - GE Grid Solutions Multilin 9450 Instruction Manual

THEORY OF OPERATION

12.2 Theory of Operation
12–2
Flicker can be caused by voltage variations that are in turn caused by variable loads, such
as arc furnaces, laser printers and microwave ovens. In order to model the eye brain
change, which is a complex physiological process, the signal from the power network has
to be processed while conforming with Figure 12.1, shown on page 12-4.
• Block 1 consists of scaling circuitry and an automatic gain control function that
normalizes input voltages to Blocks 2, 3 and 4. For the specified 50 Hz operation,
the voltage standard is 230 V RMS.
• Block 2 recovers the voltage fluctuation by squaring the input voltage scaled to the
reference level. This simulates the behavior of a lamp.
• Block 3 is composed of a cascade of two filters and a measuring range selector. In
this implementation, a log classifier covers the full scale in use so the gain
selection is automatic and not shown here. The first filter eliminates the DC
component and the double mains frequency components of the demodulated
output. The configuration consists of a .05 Hz Low High Pass filter and a 6 Pole
Butterworth Low Pass filter located at 35 Hz. The second filter is a weighting filter
that simulates the response of the human visual system to sinusoidal voltage
fluctuations of a coiled filament, gas-filled lamp (60 W - 230 V). The filter
implementation of this function is as specified in IEC 61000-4-15.
• Block 4 is composed of a squaring multiplier and a Low Pass filter. The Human
Flicker Sensation via lamp, eye and brain is simulated by the combined non-linear
response of Blocks 2, 3 and 4.
• Block 5 performs an online statistical cumulative probability analysis of the Flicker
level. Block 5 allows direct calculation of the evaluation parameters Pst and Plt.
Flicker Evaluation occurs in the following forms: Instantaneous, Short Term or Long Term.
Each form is detailed below:
• Instantaneous Flicker Evaluation: An output of 1.00 from Block 4 corresponds to
the Reference Human Flicker Perceptibility Threshold for 50% of the population.
This value is measured in Perceptibility Units (PU) and is labeled Pinst. This is a real
time value and it is continuously updated.
• Short Term Flicker Evaluation: An output of 1.00 from Block 5 (corresponding to the
Pst value) corresponds to the conventional threshold of irritability per IEC 1000-3-3.
In order to evaluate Flicker severity, two parameters have been defined: one for
the short term called Pst (defined in this section) and one for the long term called
Plt (defined in the next section).
The standard measurement time for Pst is 10 minutes. Pst is derived from the time at level
statistics obtained from the level classifier in Block 5 of the Flicker meter. The following
formula is used:
=
P . 0 0314 P
st
where the percentiles P(0.1), P(1), P(3), P(10), P(50) are the Flicker levels exceeded for 0.1, 1, 2,
20 and 50% of the time during the observation period. The suffix S in the formula indicates
that the smoothed value should be used. The smoothed values are obtained using the
following formulas:
EPM 9450/9650 ADVANCED POWER QUALITY METERING SYSTEM – INSTRUCTION MANUAL
+ +
. 0 0525 P . 0 0657
0 1 . 1 s
CHAPTER 12: FLICKER AND ANALYSIS
+ +
P . 0 28 P . 0 08 P
3 s 10 s 50 s