* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electricity theory
Survey
Document related concepts
Transcript
Energy Meter in the Age of the Photovoltaic 1 Energy Meter in the Age of the Photovoltaic 2 Energy Meter in the Age of the Photovoltaic Converts DC to AC, the result is not a pure Sine wave and therefore contains Harmonics 3 4 Energy Meter in the Age of the Photovoltaic 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 5 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 6 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 8 Energy Meter in the Age of the Photovoltaic 9 10 Energy Meter in the Age of the Photovoltaic in this case Pave is Maximum MAX 11 Energy Meter in the Age of the Photovoltaic 12 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 13 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 ?? 14 Energy Meter in the Age of the Photovoltaic 15 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 17 Energy Meter in the Age of the Photovoltaic 3rd Harmonic anti-phase 3rd Harmonic 18 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 19 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 20 Energy Meter in the Age of the Photovoltaic 21 Energy Meter in the Age of the Photovoltaic Harmonics can cause current on the Neutral Wire in 3 Phase 4 wire system 22 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 No DC tolerance (needs strong shielding), problem with DCComponent DC-Tolerance (large Core, needs strong shielding – Expensive) Shunt current up to 120A No problem with DC component 23 Energy Meter in the Age of the Photovoltaic Distorted wave: “Fourier Transform” shows DC component DC Component impact on the Energy measurement Shunt 24 Energy Meter in the Age of the Photovoltaic Magnetic Hysteresis DC component impact on CT Linearity 25 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 26 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 27 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” 28 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 29 Energy Meter in the Age of the Photovoltaic 30 Energy Meter in the Age of the Photovoltaic 31