High Frequency Measurements and their Applications in Distribution Network. Contents. Power Line Communication. Background.

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1 1 Contents 2 High Frequency Measurements and their Applications in Distribution Network Bashir Ahmed Siddiqui Tampere University of Technology, bashir.siddiqui@tut.fi 29 March 2012 Background Power Line Communication - PLC Standard - Problems with Power Line Communication Origin of High Frequency Distortion - High Frequency Notches - High Frequency Interference Sources Motivation Measuring Equipments HF Emission by Different Electronic Loads Research Activities at DEEE, TUT Laboratory Measurements Made at DEEE, TUT Interference Caused to End-User Equipment Short Demo Summary References Background 3 Power Line Communication 4 The concept of smart grid is developing rapidly and spreading globally as an enabling technology for efficient and flexible power delivery. The adequate power quality guarantees the necessary compatibility between all equipment connected to the grid. Therefore, it is a considerable issue for the successful and efficient operation of existing as well as future grids. Nowadays, the electrical power grid is a critical infrastructure and the electric power distribution companies are investing to upgrade their distribution networks to smart grids. One of the main communication technologies in the smart grids are the power line communication (PLC). Power line communication (PLC) is a technique that employs the infrastructure of electrical power distributed system as a communication medium. The existing alternating current (AC) power lines serve as a transmission medium by which voice or data is transmitted. The power lines allow a simultaneous bidirectional communication between the devices located on different parts of the power network. The system is attractive because it uses the existing low voltage (LV) distribution network, since no new wiring is required. We are talking about narrow band PLC because it uses low frequencies, which reduce the data signal attenuation. 1

2 5 6 Cont. PLC Standard The use of electric network are not unlimited, of course, because when occupying a frequency band of about 9 khz to 20 MHz, existing services such as long-wave, medium-wave and short-wave radio and amateur radio bands will be over laid. The European PLC regulation is called CENELEC EN : Signaling on low-voltage electrical installations in the frequency range 3kHz to 148.5kHz. Some standards are necessary in order to regulate the use of this lowfrequency band. It defines the allowed frequency ranges of power line communication, maximum signal amplitudes, as well as the limits of the interference to the surrounding frequency bands. The frequency range division is shown in the Table given below. In Europe, the available frequency intervals for communication systems in low voltage and medium voltage (MV) power networks are established by CENELEC EN Cont. 7 Problems with Power Line Communication 8 A maximum signal level of 122 dbµv (= 1.25 V) applies equally to B, C and D bands. The signal level in the A band may be 134 dbµv (= 5 V) at 9 khz and can be lowered to 120 dbµv (= 1 V) up to 95 khz. The primary purpose of power lines is to carry power not data which means reliable communication over power lines are difficult due to noises created by loads and devices connected to the LV network. The characteristics of the channel are dependent of the frequency, location and equipment, which are connected to the channel, and it is very sensitive to the impulsive noise, background noise and fading. Power quality and high frequency interference problems have increased in power networks during the past few years with the introduction of sophisticated devices, whose performance is very sensitive to the quality of power supply. All power electronic devices generate and emit unwanted electrical signals (EMI noise) that can lead to a performance degradation of PLC network. 2

3 Origin of High Frequency Distortion 9 High Frequency Notches 10 Switch mode power supplies (SMPS) use switching technique. Modern fluorescent lamps also use switching technique. Some of the main benefits of using HF ballasts are less flicker, longer life times and better energy efficiency. Active power factor corrector (APFC) bring another switching function to the load. It is also showing up in SMPSs for computers. Converters are, of course, also a source of high-frequency distortion, since they use HF switching technique. Power line communication is another source of high-frequency distortion in distribution network. High voltage levels at the terminals of the enduser equipment due to power line communication can result in high currents through the equipments. Controlled rectifier (right) and high frequency notches (left). HF Interference Sources 11 Motivation 12 The most common high frequency noise sources are compact fluorescent lamps (CFL), switched mode power supplies and frequency converters that can cause significant amount of reduction in signal-to-noise ratio (SNR) in PLC network. Other potential sources of high frequency interference are AC motors (which can be found in vacuum cleaners, electric shavers and many common kitchen appliances) and other loads containing power electronics e.g. Dimmers switches etc. In Finland and many other countries, the power lines are used for remotely reading of the energy meters i.e., AMR. The frequency range used for PLC is the same that is often used for switching in switched mode power supplies, high frequency (HF) ballasts, etc. It is a considerable issue for the successful and efficient operation of AMR meters. The frequency range in the traditional harmonic range up to 2 to 3 khz has been under investigation for several years. However, little or no attention has been paid to the frequency range above the low-frequency harmonic range, or at least between 2 to 150 khz. 3

4 Cont. 14 Measuring Equipments The product standards covering harmonic set limits up to about 2 or 3 khz. Radio disturbances standards mainly sets limits from 150 khz and up. WHY? Probably due to the apparent absence of well documented cases of interference found within this frequency range. Another more fundamental reason is the lack of appropriate measuring equipment to record and analyze high frequency phenomenon in distribution network. 15 Effect of Lamps on LV Network HF Emission by Different Electronic Loads Voltage with and without lamp (top and middle, respectively) and current (bottom) drawn by the lamp. 4

5 Cont. 17 Effect of Computer 18 Spectrum of the background voltage without the lamp being connected (top), the voltage at the lamp terminals (centre) and the current drawn by the lamp (bottom) in the range 2 to 150 khz. The spectrum of the background distortion (upper). The voltage (middle) and current (lower) at the terminals of the computer. Effect of CFL, Laptop and TFT 19 Research DEEE, TUT 20 Measurement Setup Energy Meter The spectrum of the current drawn by a CFL upper, Laptop (middle) and TFT screen (lower) between 2 to 150 khz. Load Setup Front End Monitoring Device 5

6 Monitoring Device Developed at DEEE Interface Board 4MSPS AD Converter 225 MHz Processor Power Supply Laboratory Measurements Made at DEEE, TUT Input Port Real-Time Intelligent Electronic Device for Monitoring HF Interference Problems in Distribution Network. Monitoring of PLC Network Spectrum of the Captured Data 24 Volt (V) Time-Domain Waveform PLC Communication Signal No PLC Communication Signal Time (s) Time-domain waveform (without scaling) of 50 Hz signal captured by monitoring device. U(dB V) Frequency-Domain Spectrum 43 khz Signal 86 khz Signal 129 khz Signal Frequency (Hz) x 10 4 Frequency domain analysis of the load network computed by monitoring device. 6

7 Spectrum of the Captured Data Interference Caused to End-User Equipment - Demo 26 U(dB V) Frequency-Domain Spectrum 12 khz Signal 41 khz Signal 115 khz Signal Frequency (Hz) x 10 4 Another frequency domain analysis of the same load network computed by monitoring device. Summary 27 References 28 This research work focuses on the study of high frequency interference problems in PLC frequency range as well as increasing knowledge on voltage and current distortion in the same frequency range. Monitoring and management of power quality (PQ) in distribution networks are becoming more important because customers are demanding better services and high power quality. Utilities understand that measurements are important in detecting, analyzing and solving HF distortion problems to enable smooth operation of AMR. One of the promises of Smart Grid is improved power quality. Thus, PQ and condition monitoring measurements would enable smarter planning of network refurbishments. 1. EN , Signaling on low-voltage electrical installations in the frequency range 3 khz to khz-part 1: General requirements, frequency bands and electromagnetic disturbances. 2. A. Larsson, High frequency distortion in power grids due to electronic equipment, Licentiate dissertation, Luleå Univ. Technol., Skellefteå, Sweden, S. Rönnberg, Power Line Communication and Customer Equipment, Licentiate dissertation, Luleå Univ. Technol., Skellefteå, Sweden, Phill Sutterlin, Walter Downey. A Power Line Communication Tutorial- Challenges and Technologies. Echelon Corporation 4015 Miranda Ave. Palo Alto, CA USA. 5. Bashir Ahmed Siddiqui, M. Pikkarainen, et al., Development of DSP Based Instrument for Monitoring PLC and Other High Frequency Signals in Distribution Networks, 21 st International Conference and Exhibition on Electricity Distribution, CIRED, Frankfurt, Germany June,

8 Thank you! 8