1 Institut für Grundlagen der Elektrotechnik und Messtechnik Prof. Dr.-Ing. Heyno Garbe /...

1Institut für Grundlagen der Elektrotechnik und MesstechnikProf. Dr.-Ing. Heyno Garbe / Dipl.-Ing. Sven Battermann

COST 286

Workshop 'Impact of Communications

Technology to EMC'

PLC - Measurement of Mains Characteristics

Sven Battermann, Heyno Garbe

Institut für Grundlagen der Elektrotechnik und MesstechnikUniversität 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

220 V Netz

Fed with DM-Mode Conversion to CM

Conversion to CM

RJ-45 orUSB to PC

Problems and known effectsObservations:• 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?

Common mode current development

PLCModem

Radiation

power-line

symmetricalfeeding(DM-current)

aymmetricalstructure(CM-current)bad symmetry

changing impedanceresonances...

Fed withdifferential mode

Partially convertedto common mode

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

broadbandtelecommunication

service

Short-wave Service(e.g. broadcast)

What is the interference scenario?

Coupling Line guided interferenceField guided interference Transferfunction?

Interference scenario - victim• What is the impact of a common mode current on a

connected device (receiver)?

Ed Hare: Radio frequency interference

Power Supply – mains network

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 16-4-4Quantification 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

1. Simultaneous use of interference source and victim2. Use of the same frequency3. Use in a distance, that will allow disturbances4. Full use of limits over large frequency ranges

2 2 2 2 2 2Limit w m p z a c β u α w m u z a cU R t t

R R P;P R R

Interference scenario CISPR 16-4-4

Where is the back path for the common mode current?

Worst case: Receiver with indoor antenna!

0 5 10 15 20 25 30-10

70Measurement with dipole antenna (Comb.-Gen. CM)

f / MHz

without mains / without chokewith mains / without choke

0 5 10 15 20 25 30-10

70Measurement with rod antenna (Comb.-Gen. CM)

f / MHz

without mains / without chokewith mains / without choke

Dipole outdoor antenna Indoor rod antenna

Model of the transmission (channel model)

Description with 2- and 4 port devices

Generator with

Feeding

(source)

Mains with

sockets

(channel)

Radio with

powersupply

(victim)

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?

Expansion of the model

Generator withfeeding(source)

Mains network with the used socket

Radio with power supply(victim)

All 3 components have to be described in detail!

Expansion of the model

Differential mode feeding

RX-Chassis

Receiver/Radio-Dummy

Rod-antenna

Coupling-network

MainsGenerator

Common-mode chokeCurrent-Balun

SymmetryVoltage-Balun

Feeding-Network

Isym,in

Iasym,out

sym,insym/asym 10

asym,out

20 logI

Common mode feeding

RX-Chassis

GeneratorCounter-poise

Receiver

Rod-antenna

Feeding-network

Coupling-network

49 W22 nF

Iasym,outIasym,in

asym,inasym/asym 10

asym,out

20 logI

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

Receiver

ICM,Antenna

ICM,Chassis

Receiver

Rod antennaCoupling

network to mains

Feeding with comb-generator

Generator

Counterpoisecurrent-probe

Generator

CM-chokebalun

Common mode feeding Differential mode feeding

Attenuation CM in / CM out

0 5 10 15 20 25 300

100DCM/CM - mit Netzverbindung

f / MHz

dBWald (norm. Wohnung)Stadt (Altbau)Kantstraße (leeres Haus)

Attenuation DM in / CM out

0 5 10 15 20 25 300

100DDM/CM - mit Netzverbindung

f / MHz

dBWald (norm. Wohnung)Stadt (Altbau)Kantstraße (leeres Haus)

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

0,symsym/asym 10

20 logU

0,asymasym/asym 10

20 logU

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

0 5 10 15 20 25 3070

f / MHz

Measurement with Signalgenerator (sym. feeding)

UV-Netw / dBµVIN-VNetw / dBµAIN-Mains / dBµA

0 5 10 15 20 25 3040

f / MHz

Measurement with Signalgenerator (asym. feeding)

UV-Netw / dBµVICM-VNetw / dBµAICM-Mains / dBµA

Differential mode feeding Common mode feeding

STSM - Measurement Setup

Common mode currents on cabling

0 5 10 15 20 25 3015

65PC LAN Side - PLC off

f / MHz

KeyboardMainsMouseLANMonitor

0 5 10 15 20 25 3015

65PC LAN Side - PLC on

f / MHz

KeyboardMainsMouseLANMonitor

Impedance measurement with VNA

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

0 5 10 15 20 25 30-30

40Rauschmessung K

f / MHz

0 5 10 15 20 25 30-30

40Rauschmessung M

f / MHz

Country side City

0 5 10 15 20 25 30-20

10Rauschmessung K

f / MHz

0 5 10 15 20 25 30-20

15Rauschmessung M

f / MHz

Median

0 5 10 15 20 25 300

16Standardabweichung der Rauschmessung K

f / MHz

0 5 10 15 20 25 300

14Standardabweichung der Rauschmessung M

f / MHz

Standard deviation

Long term – Mains – Country side

Long term – Mains – City

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

Source

Connection – the line

victim

Measurements

• First idea was the measurement of LCL and TCL

• Derived from good results with telecommunication cables

Longitudinal Conversion Loss

Feed the voltage EL and Measure VT.

Measurement ?

)log(20T

Measurement adapter

Longitudinal Conversion Loss

Industry area Old house installation

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...

1 Institut für Grundlagen der Elektrotechnik und Messtechnik Prof. Dr.-Ing. Heyno Garbe /...

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