Transcript Electricity theory

Energy Meter
in the Age of the
Photovoltaic
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
Converts DC to AC, the result is not a pure Sine wave and therefore contains Harmonics
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Energy Meter in the Age of the Photovoltaic
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Displacement of Power Factor (PF)
Current in the Neutral wire (for 4 wire system)
DC-Component in the Current flow
Impact on Current & Voltage Sensors
Impact on Power Supply
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Energy Meter in the Age of the Photovoltaic
Blondel's theorem (named after André Blondel), states that:
In a system of N wires, needs (N-1) wattmeter to measure the electrical Power.
For example: 3 phase meter , 3 wire needs 2 wattmeters, but a 3 phase meter, 4 wire (with a neutral)
needs 3 wattmeters.
Wattmeter
Power (P) = Voltage (V) * Current (I)
Single Phase Meter needs
1 Element
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Energy Meter in the Age of the Photovoltaic
Current in the Neutral wire, we need to add Current-Meter
1.5 Element
Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
in this case Pave is Maximum
MAX
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
(1)
(2)
Reactive Energy
 (1) ø = 00 , only Active Power
 (2) ø ≠ 00 , phase shift between Voltage and Current, portion
of the Power curve going negative  Reactive Energy
 (2) Pav is decreased
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Energy Meter in the Age of the Photovoltaic
 Active Power (W) produces real work
 Reactive Power (var) is the power required to produce
the magnetic fields to enable the real work to be done
 Apparent Power (VA) is considered the Total Power that
the Electric company supplies to produce the required
amount of Active Power
Active Power
√
Reactive Power
?
Apparent Power
??
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
for pure Sine wave PF calculated as follows
 PF = Ratio of Active Power to Apparent Power (W/VA)
Power Space Vectors
 PF depends on the phase angle between Voltage and Current
waves
 A low PF indicates a low energy efficiency (losses)
Energy Meter in the Age of the Photovoltaic
Harmonics from large number of Photovoltaic converters cause
Displacement of Power Factor (PF) hence increase
Reactive Energy
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Energy Meter in the Age of the Photovoltaic
3rd Harmonic
anti-phase 3rd Harmonic
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Energy Meter in the Age of the Photovoltaic
PAV1 = VRMS1 * IRMS1
>
PAV2 = VRMS2 * IRMS12
P(W)
S(VA)
Q(var)
S(VA)
Displacement of PF
PF
produces Reactive Energy
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Energy Meter in the Age of the Photovoltaic
Fourier Transform
for distorted Sine wave PF calculated as follows
Energy of the harmonics is mainly Reactive energy
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
Harmonics can cause current on the Neutral Wire
in 3 Phase 4 wire system
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Energy Meter in the Age of the Photovoltaic
 Toroid for CT meters up to 15A (no DC-Tolerance)
 Toroid for Direct Connection up to 200A
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No DC tolerance (needs strong shielding), problem with DCComponent
DC-Tolerance (large Core, needs strong shielding – Expensive)
 Shunt current up to 120A
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No problem with DC component
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Energy Meter in the Age of the Photovoltaic
 Distorted wave: “Fourier Transform” shows DC component
 DC Component impact on the Energy measurement
Shunt
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Energy Meter in the Age of the Photovoltaic
Magnetic Hysteresis
DC component impact on CT Linearity
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Energy Meter in the Age of the Photovoltaic
 "Linear-Power-Supply" and “Switched-Mode-Power
Supply”, using a step-down transformer. Usually when
correctly designed using high quality capacitors, these types
do not “suffer” much from harmonic distortion
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Energy Meter in the Age of the Photovoltaic
 “Capacitor-Power-Supply” using a Voltage Dropping
Capacitor. The capacitor can be damaged significantly by
harmonics
 The problem is more difficult when the Meter is installed
outside under a burning sun
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Energy Meter in the Age of the Photovoltaic
 Meter cannot resolve the problems caused to the Voltage and
Current waveforms, the meter will use those waves to
measure energy quantities (P, Q, S)
 Voltage and mainly Current Sensors are affected by Harmonic
distortion
 Photovoltaic Energy supplier’s billing should be based on
three electrical quantities: Active power (P), Reactive
power (Q) and Apparent power (S)
 Meter should be with measurement of P, Q and S. The
difference in kVA meter measurement can be as large as 30%
when the waveform is distorted
 For PF displacement, it is necessary to install “PF-Correction Capacitors”
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Energy Meter in the Age of the Photovoltaic
 Energy of the harmonics is mainly Reactive energy, even
though there are no requirements in the IEC standards for
testing Reactive Energy under the effects of harmonics??
 3 phase 4-wire system, Meter should be of type “1.5 Element”,
(measurement of the Neutral wire current)
 CT current sensor cannot detect DC-Component, and also
affected by DC-Component. So it is a question if a meter uses CT
as a current sensor can be used?
 Shunt current sensor can detect DC component . Can be used,
provided that the Meter can measure DC-Component (“AllPass”)
 Capacitor-Power-Supply: only with high quality capacitors,
that can withstand harmonic distortion
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Energy Meter in the Age of the Photovoltaic
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Energy Meter in the Age of the Photovoltaic
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