Power Analyser Fundamentals Power Analysis and Harmonics

/1 ©Voltech AC power problems and measurement solutions True power and power factor. Fourier transforms. Three-phase systems and harmonic problems. Pulse Width Modulated Motor Drives. IEC Standards. Harmonics & Flicker. Solutions and Measurements.

/1 ©Voltech Historically, only simple measurements required: AC Motor Fixed Speed Lamp Light Heater Heat

/1 ©Voltech Real and apparent power Instantaneous power is the product of instantaneous voltage and current. Resistive load. –instantaneous W is always (+)ve –W = V x A W W Inductive load –current is phase shifted –instantaneous W sometimes (-)ve –W  V x A Apparent Power = V x A Power Factor = Cos 

/1 ©Voltech Modern electronic loads PWM Drive Variable speed More control Greater efficiency HF Ballast Light Compact Greater efficiency Complex waveforms demand sophisticated analysis Drive to better efficiency - more accurate analysis

/1 ©Voltech Rectified and Capacitor Smoothed inputs Current only flows when AC supply voltage is greater than capacitor voltage.

/1 ©Voltech Power factor and cos  The power factor is reduced. Not by phase displacement, but by shape distortion. Why is this important? Power factor of <1 means generation and transmission must be oversized: Power lines and transformers sized to supply VA, not Watts. Power factor <1 due to harmonic distortion: Cannot be corrected by capacitors. (Capacitors may be damaged). Distorts Voltage which increases the losses in motors. Creates electromagnetic interference. EMI. Neutral burn-out in 3 phase 4 wire systems. Distortion is measured and controlled in terms of harmonics.

/1 ©Voltech Fourier transforms Any repetitive waveform may be described by a series of sinewaves….

/1 ©Voltech DFT vs FFT Two methods of performing the calculation. DFT and FFT. D – Discrete F- Fast Fourier Transform Sampling Rate and Synchronisation –FFT must be 2 n, E.g = 1024 samples per cycle Difficult when sampling rate fixed! –Problem corrected by the use of windows (e.g. Hanning) –DFT is synchronised by definition –No problem with DFT, no filters or windows (E.g. ‘Hanning’) to correct errors. FFT also accumulates errors - DFT error the same for each order.

/1 ©Voltech Power factor and cos  Voltage IEC / IEEE Definition Power Factor = Watts Volts x Amps PF = 0.65 Cos  Current Harmonics Fundamental (1st Harmonic) 3rd Harmonic Cos  Angle between fundamental (1st harmonic) voltage and current. Total Current

/1 ©Voltech True Watts computation

/1 ©Voltech Functions derived by computation Watts Volts RMS Amps RMS Volts DC Amps DC Volts Pk Amps Pk Frequency Volt-Amperes Volt-Amperes Reactive Power Factor Volts Crest Factor Amps Crest Factor Harmonics All primary power parameters can be computed from digital samples

/1 ©Voltech Multi-phase measurements Single Phase. 100W 1W 2W lost for every 100W delivered (example) Induction motors require extra winding to start. Three Phase – 120° apart. 100W 1W 100W 1W 100W 1W A B Sum of voltage always = 0 A can be joined to B.

/1 ©Voltech W 1W Multi-phase measurements Three-phase “delta” 1W lost for every 100W delivered (1/2 the copper required for 3 x 2 wire) Induction motors require extra winding to start. 1W “Star” or “Wye” Connection. Centre point, N is called star or Neutral point. N

/1 ©Voltech Multi-phase measurements Power Station 3-phase and 1-phase loads 415V phase to phase 230V phase to neutral Distribution Transformer Industrial, Office and Domestic Loads N For balanced loads (same current in each phase), neutral current = 0 Small neutral conductor

/1 ©Voltech Triplen harmonics Definition: ‘Odd Harmonics divisible by three’. E.g. 3, 9, 15, 21, 27, 33… Why are they so important to the three phase power industry? Third harmonics of each phase IN PHASE with each other.

/1 ©Voltech Triplen harmonics in 3 phase power systems Burnout of neutral conductor or damage to related components Overheating of distribution transformers All harmonics reduce the efficiency of a power system and loads connected to it. Triplen harmonics are significant because the harmonics in each conductor are in Phase. Triplen harmonics can therefore be much more damaging.

/1 ©Voltech Multi-phase measurements 2 Wattmeter vs. 3 Wattmeter connections #1 3 Wattmeter #2 2 Wattmeter V1 V2V3 V1 ph-ph V2 ph-ph 2 wattmeter connection provides all the information required for 3-wire measurements.

/1 ©Voltech Multi-phase measurements Neutral Current Measurements. Kirchoff’s Law: I1 + I2 + I3 = 0 When the sum is not 0, this current must be flowing in the Neutral. This calculation performed on a SAMPLE by SAMPLE basis. All data returned to central processor at ground. Vector computation of inter- phase quantities. Harmonics of ‘neutral”. – Can also be used to calculate ground current for three-wire motor-drive connection. V1 A1 V2 A2 V3 A3 Central Processor Samples Isolation Display

/1 ©Voltech AC motors Input 2 Wattmeter or 3 Wattmeter method. Output Torque and Speed Mechanical Power V I Electrical to Mechanical Efficiency

/1 ©Voltech PWM motor drives Distorted AC Input DC Bus PWM Output Torque & Speed xxx NM & Rev / Min

/1 ©Voltech PWM voltage spectrum Fundamental (E.g. 40 Hz) Switching or carrier (E.g. 10, 000 Hz) Total Power = Fundamental + Harmonics (f) + Carrier + Harmonics(c) + Noise

/1 ©Voltech PWM mode Filters 5Hz to 1kHz Low Frequency Measurements Frequency High Frequency Measurements Sync Fundamental Data Frequency Total W, V, A... Measurements to full 1MHz bandwidth

/1 ©Voltech PWM Mode - Example Fundamental (E.g. 40 Hz) Switching or carrier (E.g. 10, 000 Hz) Fundamental 230 V Filtered 240V Total 255V Total Power = Fundamental + Harmonics (f) + Carrier + Harmonics(c) + Noise What’s required? Total Power (1MHz bandwidth) Fundamental Power Motor efficiency ~ Fund Power x 100% Total Power

/1 ©Voltech Motor Start-Up and Transients Waveform PWM Waveform difficult to synchronize with steady-state. Very difficult when fundamental frequency changing. Unique cycle-by-cycle mode of the PM3000A avoids the need for time- consuming calculations upon raw data points. Gives what is of interest, Total power, PF, V, A etc for every cycle.

/1 ©Voltech Motor Start-Up and Transients Waveform A rms

/1 ©Voltech IEC Standards Harmonics To overcome the problems described with harmonics, the IEC lays down limits that equipment must meet. Standards cover equipment up to 75A. The PM3000A:  DFT measurement of 16 cycles of waveform.  Anti-aliasing filter as specified.  Rectangular window - No gaps  Harmonic accuracy better than 0.2%.  AC source voltage, frequency and harmonics measured during the test.  Single low value shunt ensures compliance throughout dynamic range.  Certified, traceable accuracy.

/1 ©Voltech IEC Standards. Flicker. The IEC aim to limit level of voltage fluctuations that equipment may cause to AC power lines. Standards exist for up to 75A. Change in the load current will cause change in voltage across the load. That change in voltage causes a squared change in lamp output intensity. The perception of ‘flicker’ is dependant on the response of the lamp, our eyes and our brain.

/1 ©Voltech How the PM3000A meets the requirements IEC Flicker Testing Complete IEC flicker meter for IEC dc, dt and dmax testing. Flicker accuracy proved by using both sine and square modulations. Impedance network available for full compliance measurements. Windows TM PC software for presentation, storage, and analysis of results.

/1 ©Voltech Solutions Drives with harmonic correction – Passive or Active. External Filters. Zig-zag transformers. Controlling inrush and transients to meet flicker standards.

/1 ©Voltech PM3000A Measurement Summary All measurements made digitally - No analogue error Stable over time Quick to calibrate Accuracy maintained with wide range of input signal level and frequency: 0.05% Basic - 600V rms, 30A rms, DC to 1MHz Single input shunt technology, accurate with high reliability. Specification maintained with distorted power waveform. DFT (not FFT) harmonic analysis system Sample by sample calculation across 3 phases allows neutral calculation. Useful additional functions like Inrush Current, Distortion and a.c. Impedance Easy to use, all main power parameters available at push of button. Non volatile memory to save any complicated front panel setup configuration. Single phase, three phase and independent channel operation. Fast computation for ‘real time’ feel Many special modes: PWM Motor drive, Ballast, IEC testing etc. Application specific software available, VPAS, (PM3000A) VPAS Lite (PM100), IEC /3 for Windows (PM3000A)

/1 ©Voltech Voltech Measurement Solutions Formed by power electronics engineers to solve everyday power electronics test and measurement problems. World’s first commercial digital power analyser. Patent on automatic transformer testing. PM3000A PM100 Single Phase PM300 Three Phase Low-cost Analysers AT3600 Automatic Transformer Tester ATi LCR Meter / Automatic Tester