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COST 286. Workshop 'Impact of Communications Technology to EMC' PLC - Measurement of Mains Characteristics Sven Battermann, Heyno Garbe Institut für Grundlagen der Elektrotechnik und Messtechnik Universität Hannover E-mail: battermann@ieee.org. Overview.
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COST 286 Workshop 'Impact of Communications Technology to EMC' PLC - Measurement of Mains Characteristics Sven Battermann, Heyno Garbe Institut für Grundlagen der Elektrotechnik und Messtechnik Universität Hannover E-mail: battermann@ieee.org
Overview • Introduction – Description of the problem • Interference scenario • Derivation of limits (CISPR 16-4-4) • Idea and description of new measurement techniques • Results of STSM Barcelona/Hannover • Conclusions – new interesting work that has to be done
Broadband communication networks • with Primary task => Data transmission • LAN • DSL / ADSL / VDSL • ... • with Secondary task => Data transmission • PLC • ISM-Applications – e.g. configuration of power drives • ... • Totally different electrical characteristics of the used cables / lines!
Mains used for telecommunication network Conversion to CM Fed with DM-Mode 220 V Netz RJ-45 or USB to PC Modem RJ-45 or USB to PC Modem Conversion to CM
Problems and known effects Observations: • For EMC: Radiation • data rate decreases with distance from feed point • Different data rates in different rooms • influence of load condition (used devices) • Operation of “special” devices also decreases data rate Questions: • What are the reasons for this phenomenal experiences? • What is the particular disturbance scenario? • Quantification of mains influence possible?
What is the problem with CM-currents? • Two differential mode signals (DM also symmetric current) with 180° phase shift compensate! => low radiation • The common mode signal (CM also asymmetric current) will be radiated – without compensation! • Problem: The fed DM-signal converts to a CM-Signal, if there are any asymmetries!
Interference scenario Short-wave Service (e.g. broadcast) broadband telecommunication service What is the interference scenario? Coupling Line guided interference Field guided interference Transferfunction?
Interference scenario - victim • What is the impact of a common mode current on a connected device (receiver)? Power Supply – mains network Ed Hare: Radio frequency interference
CM-current in the input circuit The common mode current flows through the input circuit of the receiver -> voltage drop at the input resistor -> interference
Problem • The limits used today have partially been defined in 1930. • At that time narrowband interferers (transmitter) and stochastic broadband interferers (e. g. electric motors) have been known. • Different situation today: • Many telecommunication-services use a broadband spectrum up to the short-wave band. • Different services are always on, therefore they are no stochastic interferers anymore.
Influence on the limits? • The limits (1930) are derived from the old interference scenario. • The interference scenario changed significantly. Questions: • Is it possible to model the situation today (with broadband telecommunication services) with the old interference scenario? • It is reasoned to use the old limits, based on a different scenario for the interference scenario today? • Is it possible to safeguard the radio services?
Derivation of Limits • It has to be expected that the use of the full limits of CISPR 22 cannot safeguard the protection of radio services anymore! What has to be done: • For a valid protection of radio services a detailed analysis of the interference scenario is necessary. • CISPR 16-4-4 gives hints for the derivation of limits based on 10 influencing factors even under consideration of broadband services => Rational derivation of limits.
Influencing factors of CISPR 16-4-4 Quantification of probability • Derivation of limits – just a value with a specified probability of a reception without disturbance. R actual signal-to-interference ratio, RpProtection ratio • Simultaneous use of interference source and victim • Use of the same frequency • Use in a distance, that will allow disturbances • Full use of limits over large frequency ranges
Interference scenario CISPR 16-4-4 Where is the back path for the common mode current?
Worst case: Receiver with indoor antenna! Dipole outdoor antenna Indoor rod antenna
Model of the transmission (channel model) Description with 2- and 4 port devices
Measurements to be performed… • What is a reasonable measurement setup? • It is a „simple“ measurement problem – we just want to know the attenuation of the mains network between source and victim -> Mains Decoupling Factor -> Mains Attenuation Factor Two port network analyser -> that’s it! – Really?
Mains network with the used socket Radio with power supply (victim) Generator with feeding (source) Expansion of the model ? ? ? All 3 components have to be described in detail!
Reasons for these measurements • Why currents – what about well known CDNs with disturbance voltage measurement? • Is the voltage the reason for the disturbance? • What is the influence of the difference between CDN impedance against real mains impedance? • Why don‘t you use a typical balun for telecommunication lines? • Do we have 120 Ohm? • Have you ever checked the characteristics of your balun with other loads than 120 Ohm?
Receiver chassis: Flow of current Rod antenna Coupling network to mains Receiver
mains Generator Generator current- probe balun Counterpoise CM-choke Feeding with comb-generator Common mode feeding Differential mode feeding
Mains Decoupling Factor • Measured voltage at the radio dummy for both feedings • Normalized to the measurement voltage on the AMN
Difference – Mains decoupling factor • The constant impedance of the V-network is an ideal load for the balun. • The measurements of the fed asym. to sym. (ICM‑VNetw) / (IN‑VNetw) current and the measured disturbance voltage at the V-network will show a minor frequency dependence. • When the source will be connected with the mains the asym. (ICM-Mains) and sym. (IN-Mains) currents will change significantly due to the frequency dependent impedance of mains network and the resulting influence on the balun.
Measurement with AMN Differential mode feeding Common mode feeding
Conclusions • Why doing near field measurements? – try to measure the most important quantity for the disturbance -> Current • Measurement Setup was presented during CISPR meeting in South Africa – (-> accepted! - Draft) • What has to be done: • noise floor measurements with radio dummy • more attenuation measurements of mains networks
Long term – Mains – Country side/City Country side City
Long term – Mains – Country side/City Standard deviation
Measurement with outdoor antenna Country side City
A lot of work has to be done! • But a real interesting one!
Used frequency ranges - ISDN VDSL => will even use 20-30 MHz!
Used frequency ranges - PLC Measured antenna feed-point voltage
Measurements • First idea was the measurement of LCL and TCL • Derived from good results with telecommunication cables
Longitudinal Conversion Loss Measurement ? Feed the voltage EL and Measure VT.
Old house installation Industry area Longitudinal Conversion Loss