Power Quality &
Synchronisation
Ben Kemink
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Power Quality
What is the Quality of the Power Measurement?
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Subjects Covered
1. Definition of Electrical Power
2. The meaning of “T”
3. Should we select the Voltage or the Current input channel for Synchronization?
4. Is an Observation Time an alternative for “T”?
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Power Quality
Before discussing quality of power, lets have a look at how do we
define
the measurement of electrical power?
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Traditional
CONSTANT AVERAGE=0
Applied Voltage : u(t) = Upk.sin(t)
Resulting Current : i(t) = pk.sin(t+)
Amplitude=UrmsxIrms
p(t) = u(t) . i(t) =
= ½ . Upk . Ipk . cos( ) - ½ . Upk . Ipk . cos(2t+ )
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Definition of Average Power
dt ) .
t 1
T(
average 0
p
P T
The most difficult task for the power meter is to find the period time T
correctly!
Especially with distorted signals this can be very difficult.
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Traditional 50Hz
Amplitude=Urms x Irms Vpk
Ipk
Pavg
Tp Ti
Tu
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Zero Crossing?
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The zero crossing lasts at least for one acquisition interval. An uncertainty caused by time resolution.
Δt = resolution of Tperiod
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Current input channel is used for synchronization.
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What if the period is longer than the acquisition memory of the power meter?
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A too low Display Update Rate will not detect changes of short duration despite a high acquisition speed.
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Power Quality is first of all related to an accurate Power Measurement
Factors that influence the total error for power are:
Amplitude
Frequency of the fundamental of the input signal
Crest Factor of the input signal (BW)
Crest Factor setting of the Power Meter
Power Factor
Temperature
Use of filters
Acquisition interval
Acquisition Clock Stability
Correct Detection of Period Time “T”
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There is enough energy. The challenge is how to control it!
For Example:
If of 1 gram uranium all atoms split, the heat developed (energy) can make a water basin, 6 x 6 x 5 meter filled with water of 0 degrees Celsius, boil.
Source: Van Barnsteen naar Kernchemie, Dr. K.K. Darrow
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Three ways to control Electrical Power
1. The current is manipulated.
Example:
Switched Power Supplies, Resistors.
2. The voltage is manipulated.
Example:
Pulse Width Modulated Power Inverters, Frequency Converters, Soft-starters, Thyristor Controlled Power Supplies,
Inductive Cooking.
3. Both the voltage and the current are manipulated.
Example:
Electronic Ballasts for Lighting
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1. Current Manipulation
Voltage
Current
Example: Switching Power Supply
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1. Current Manipulation
Voltage
Current
Power
example: Switching Power Supply, Voltage, Current & Power Harmonics
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2. Voltage Manipulation
example: Inductive Cooking
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2. Voltage Manipulation
example: 3-Phase Frequency Inverter Output
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2. Voltage Manipulation example: Soft starter
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3. Voltage & Current Manipulation
WT1600 example: Lighting Industry, electronic ballast
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3. Voltage & Current Manipulation
example: 50kHz Electronic Ballast for TL
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Design engineers are very creative.
Summary
Today electric power consumption is controlled by high speed (switching) electronics.
To limit the negative side effects for others, new regulations are issued frequently to set new guidelines for design.
The definition of the average electric power has not
changed, but the selection of the true repetition time T (period) requires special attention.
The power meter should allow the user to select the
appropriate synchronisation source for the measurement calculations.
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The power meter should allow the user to select the synchronisation source for the measurement calculations.
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