Influence of DC & Phase Shift On Power Measurement of WHM - PowerPoint PPT Presentation

Influence of DC & Phase Shift On Power Measurement of WHM Presentation in (Korea Electric Power Corporation)

Consumption of domestic application ∫ ∫ Current load profjles for : Hair dryer Vacuum cleaner and mixer (power regulator using rectifying diode) (motor controller using phase cutting inverters) [ T ] [ T ] mains voltage mains voltage current current Ch1 500mV Ch2 100mV M2.00ms Ch2 0V Ch1 500mV Ch2 100mV M2.00ms Ch2 0V The current wave form has a 50Hz in-phase contribution 50Hz component in current wave form has strong phase (cos φ =1), a large DC-component is present also (I DC ≠0) shift (cos φ =0.7)

Single Core CTs ‒ The DC Problem (1) l prim DC-tolerance is required for residential energy meters according to IEC 62053-21 and-23: Operation with completely half t rectifjed current, limited accuracy R ~ I prim ΔB 1 ~ * ω·A Fe ·N 2 sec 2 t 2 ΔB = B 0 (1-e r ) 1 some seconds for L τ = a good transformer R B t The core can’t get rid of it’s fmux!

Single Core CTs ‒ The DC Problem (1) Half wave rectifjed primary current Flux density B in the transformer core Secondary current of the transformer Primary current 0 0.1 0.2 0.3 0.4 0.5 sec

Meter performance with domestic appliances Realistic meter test (parallel running loads of domestic appliances) Composition of drawn current Results for meter A and B Reference meter 50Hz-current 7.4 A Meter A (linear core) -0.1% cos φ 0.85 i Meter B (combined core) +4.5% Module DC Event Leakage Seg Swell MAX MIN DMD TIME AVG 100 V L-N OUT x 1000 50 L-L ABA LEAD kΩ Over THD ABCA LAG kW Ar% 0 I FUND AVG x 1000 100 OUT 50 RMS BCB mA Over LEAD ABCA LAG THD kW Ar% 0 PF TOT 100 OUT x 1000 DC-current 2 A 50 CAC LEAD mV AΩ Over QS Clear deviation from 2% ABCA LAG kW Ar% 0 x 1000 AVG 100 E P msCH Z Q LEAD 50 kVARh Over S LAG TOT kW Ah% 0 DISPLAY V• I• P• E V• FREQ I P• PF DEMAND ENERGY MODULE INFO ETC SETUP METER EVENT COMM NETWORK RESET DISPLAY MODULE INFO ETC target of IEC standard!!! Meter under test A/B kWh L N I, φ

Test procedure according to IEC standards I max 60A rms I = I ref = 60A 0P 42.42A rms 2 I ref = = = 2 2 Standard Watthour Meter Test Balancing +I Watthour Impedance Meter -I I max 60A rms 30A rms I test = = = 2 2 I balance = 30A rms R b R b I = 2I test = 2·30A rms = 60A 0P

Combined and single core current transformers Strip-wound core solutios on the market: Single core type One core material needs to fulfjll requirements Demands for various, highly advanced core materials (Linearity, DC capability, temperature dependency...) Good opportunities for VAC amorphous and nano-crystalline cores with tailored hysteresis loops Combined core type Two different cores assembled in a core box : Competitors attempt to exploit the advantages of high-permeability Low error in true AC operation Low cost product low-permeability cores DC capability from e.g. China Does it work?

Properties of combined cores Performance characteristics “Combined Core” : Hysteresis loop of combined core (part 1, 2 and combined) 1.5 Extremely non-linear hysteresis loop, i.e. permeability. 1 Part1 0.5 CT performance should be Part2 dependent on : B [T] 0 - signal level - wave form (esp. DC contributions) -0.5 -1 -1.5 1.5 -5 -4 -3 -2 -1 0 1 2 3 4 5 H [A/cm] 1 0.5 B [T] 0 -0.5 cores provide for comparison : -1 VAC cores provide highly linear loops -1.5 -4 -3 -2 -1 0 1 2 3 4 H [A/cm]

Meter performance with domestic appliances Generalized tests and worst case scenarios : Meter A (linear Current Transformer) 20.00 15.00 0.5 10.00 0.5 0.5 5.00 Test conditions : 0.00 1 Meter with linear core CT: Rectifjed current with -5.00 0.5 IEC req. fulfjlled well -10.00 variable “phase shift” ( Δ t) -15.00 (within ± 0.5%) -20.000 5 10 15 20 25 A true measurement half rectifjed current in A Meter B (Current Transformer with combined cores) 20.00 Δ t 15.00 0.5 10.00 0.5 5.00 0.5 1 Meter with combined core CT: 0.00 -5.00 0.5 ~ Up to + 20% (!) error ~ -10.00 in meter reading -15.00 -20.000 5 10 15 20 25 A possible rip-off !!! half rectifjed current in A

Summary and conclusions Present status : IEC tests do not cover “real life“ current mix Meter insuffjciencies due to combined cores are not revealed Substantial meter mismeasurements can occur with combined cores. Publications on this issue Frank Herrmann in Energie Wirtschaft, p. 33, vol. 16, 2007 (German) Frank Herrmann in Metering International, p. 121, issue 3, 2007 (Eng) Proposal for norm amendment well received by German IEC council International IEC council will discuss and probably revise norm accordingly (Oct 2007)

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