Sven Battermann, Heyno Garbe

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1 Sven Battermann, Heyno Garbe
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

2 Overview Introduction – Description of the problem
Interference scenario Derivation of limits (CISPR ) Idea and description of new measurement techniques Results of STSM Barcelona/Hannover Conclusions – new interesting work that has to be done

3 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!

4 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

5 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?

6 Common mode current development

7 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!

8 Interference scenario
broadband telecommunication service Short-wave Service (e.g. broadcast) What is the interference scenario? Coupling Line guided interference Field guided interference Transferfunction?

9 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

10 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

11 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.

12 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?

13 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 gives hints for the derivation of limits based on 10 influencing factors even under consideration of broadband services => Rational derivation of limits.

14 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, Rp Protection 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

15 Interference scenario CISPR 16-4-4
Where is the back path for the common mode current?

16 Worst case: Receiver with indoor antenna!
Dipole outdoor antenna Indoor rod antenna

17 Model of the transmission (channel model)
Description with 2- and 4 port devices

18 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?

19 Expansion of the model Generator with feeding (source) Mains network with the used socket Radio with power supply (victim) ? ? ? All 3 components have to be described in detail!

20 Expansion of the model

21 Differential mode feeding

22 Common mode feeding

23 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?

24 Receiver chassis: Flow of current
Rod antenna Coupling network to mains Receiver

25 Feeding with comb-generator
CM-choke balun mains Generator Counterpoise current- probe Common mode feeding Differential mode feeding

26 Attenuation CM in / CM out

27 Attenuation DM in / CM out

28 Mains Decoupling Factor
Measured voltage at the radio dummy for both feedings Normalized to the measurement voltage on the AMN

29 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.

30 Measurement with AMN Differential mode feeding Common mode feeding

31 STSM - Measurement Setup

32 Common mode currents on cabling

33 Impedance measurement with VNA

34 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

35 Long term – Mains – Country side/City

36 Long term – Mains – Country side/City
Median

37 Long term – Mains – Country side/City
Standard deviation

38 Long term – Mains – Country side

39 Long term – Mains – City

40 Measurement with outdoor antenna
Country side City

41 A lot of work has to be done! 
But a real interesting one! 

42 Used frequency ranges - ISDN
VDSL => will even use MHz!

43 Used frequency ranges - PLC
Measured antenna feed-point voltage

44 Source

45 Connection – the line

46 victim

47 Measurements First idea was the measurement of LCL and TCL
Derived from good results with telecommunication cables

48 Longitudinal Conversion Loss
Measurement ? Feed the voltage EL and Measure VT.

49 Measurement adapter

50 Longitudinal Conversion Loss
Industry area Old house installation

51 Is LCL sufficient? A lot of LCL measurements have been performed all over the world. It is the correct quantity to describe the interference scenario? Let us try to model the interference scenario...