C4-106 POWER QUALITY MONITORING OF ELECTRIFIED RAILWAY SYSTEM IN MALAYSIA LEONG WHYE HIN* MOHD HALMI MAD DIAH AMINUDDIN MUSA TNB TNB.

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1 21, rue d'artois, F Paris C4-106 Session 2004 CIGRÉ POWER QUALITY MONITORING OF ELECTRIFIED RAILWAY SYSTEM IN MALAYSIA LEONG WHYE HIN* MOHD HALMI MAD DIAH AMINUDDIN MUSA TNB TNB TNB TAI FONG NG ACEI SYEMS SDN. BHD. STEPHANE DO LEM ELSIS (Belgium) Keretapi Tanah Melayu Berhad (KTMB) as the sole railway operator in Malaysia is embarking on a new railway electrification project that stretches from the town of Rawang to Ipoh City. The railway system is powered by KTMB s in-house 25kV two-phase supply, which primary source of supply is derived from Tenaga Nasional Berhad s (TNB) 132kV three-phase electrical system. Four numbers of 132kV feeder substations are being built by TNB at Rawang, Kalumpang, Sungkai and Pengkalan as the points of common coupling (PCC) with KTMB s 25kV system. This recent development is foreseen to have a considerable impact on TNB s power quality. This has led TNB to undertake a systematic approach in investigating and evaluating the issue such as conducting site surveys and power system study using computer simulations. The results of the study revealed that the simulated power quality disturbances were within the permissible limit except for the harmonic voltage distortion, which value was found to be exceeding the permissible level at all feeder stations aforementioned. Based on the findings also, TNB has taken up the necessary measure to continuously monitor the power quality and disturbances at the PCC. This has brought about the application of integrated disturbance and power quality recorder (IDPQR), which has the economic and technical advantages over the typical stand alone Power Quality Recorder. In this paper, TNB shares its experience on the approaches undertaken to investigate, evaluate and monitor the power quality problems arising from the electrified railway project. Keywords: Railway Two-phase - Power Quality Recorder Voltage Transducer *Tenaga Nasional Berhad (TNB), Engineering & Design, Project Services Department, Transmission Division, 3 rd Floor, MPE Buiding, Petaling Jaya, Selangor, Malaysia; leongwh@tnbe.com.my

2 1. INTRODUCTION KTMB s railway load is essentially a 25kV two-phase load, which is tapped from TNB s 32kV system via a step-down two-phase transformer as shown in Figure 1 below. LAHAT Pengkalan Papan SUNGKAI Kalumpang Sungkai KALUMPANG Slim River Bukit Beruntung Rawang Batang Berjuntai Bukit Badong RAWANG New Rawang Figure 1. KTMB s railway system connection to TNB s electrical system. This unique connection to TNB s system, combined with the railway loads in the form of Electro Motive Units (EMU) can affect TNB s power quality. The potential problems are as follows: - Negative Phase Sequence (NPS) or Voltage Unbalance in TNB system at the PCC due to the 2-phase 132kV supply connection to the single-phase 25kV railway load via 132/25kV step-down transformer Harmonic voltage distortion at the PCC due to harmonic currents generated by the railway load i.e. the EMU Very rapid voltage fluctuation or flicker in TNB system due to varying railway load Voltage perturbation or sudden voltage change in TNB system due to sudden imposition of the railway load In view of this, TNB has pursued a systematic approach to investigate, evaluate and undertake necessary measures to monitor and mitigate the problems. This is elaborated in Section 2 onwards. 1

3 2. SITE SURVEY TNB s initial approach was to conduct site surveys to measure the background harmonics voltages at the existing substations surrounding the PCCs. The task was accomplished by the Operation Planning Department, Transmission Division, TNB in the year The site surveys were significant to TNB as it provided snapshot fingerprints of the background harmonics voltages surrounding the PCCs before commencement of the electrified railway system s operation. It was also crucial to determine whether the background harmonics voltages at those locations were within or exceeded the permissible limits. If it was determined that the limits were exceeded, remedial actions shall be taken to mitigate the problem. During the site surveys, the background harmonics voltages were measured for a period of 24 hours. The measurements were tapped directly from the substations Capacitive Voltage Transformers (CVT). It is important to note that the readings obtained from the CVT were not sufficiently accurate due to the fact that the CVT tends to resonate at certain frequencies thus amplifies certain harmonics. These amplified readings were normalised by multiplying with a correction factor, which was obtained by comparing the first set of the CVT readings with the readings taken by a portable Capacitive Voltage Divider (CVD), connected directly to the power lines. Table I. Measured Background Harmonics Voltages Substation Kepong Slim River Papan THD Phase Harmonics 2 nd 3 rd 5 th 7 th 9 th 11 th 13 th R Y B R Y B R Y B From the readings above, it was observed that the measured background harmonics at all substations were within the acceptable limits. 3. POWER SYSTEM STUDY TNB s subsequent approach was to conduct an extensive power system study using computer simulations. The study was carried out by the Grid System Management Department of TNB in collaboration with Balfour Beatty Rail AB Power Systems, Sweden in the year The primary objective of the study was to investigate the effects of the electrified railway load on TNB s power quality with respect to negative phase sequence, flicker, harmonics and sudden voltage change. 2

4 The study took into consideration various scenarios such as: - Peak and Light Load Conditions The expected worst case scenario is in the early year of railway operation that is year 2004 because the prevailing short circuit level is the lowest compared to the subsequent years. Cumulative Effect Study Since the 132kV network is interconnected, harmonics generated at any one KTMB feeder substations will affect all other PCC in the network. Normal Feeding Condition (NF) When all KTMB s 132/25kV transformers are in service. First Emergency Feeding Condition (EF1) - When one of the two KTMB s transformers is out of service Second Emergency Feeding Condition (EF2) When both transformers are out of service and the load normally carried out by the feeder substation is now transferred to the adjacent feeder substations. The key findings of the power system study can be summarised as follows: - The calculated phase unbalance of the TNB system caused by the imposition of the single-phase railway load was within the permissible levels. The calculated flicker severity level caused by the varying railway load was well within the permissible levels. The calculated sudden voltage change on TNB system caused by the sudden imposition of the railway load was within the permissible levels. The calculated harmonic voltage distortion at the PCC exceeded the permissible levels at KTMB s feeder substations. Table II below shows the calculated harmonic voltage distortions for Year 2004 for cumulative effect study. Table II Calculated Harmonic Voltage Distortion Case PCC Highest Individual Harmonics THD No. Railw. Backg. Total Railw. Backg. Total NF Pengkalan 132kV NF Sungkai 132kV NF Kalumpang 132kV NF Rawang 132kV Lahat EF1 Sungkai 132kV Sungkai EF1 Pengkalan 132kV Kalumpang EF1 Kalumpang 132kV Kalumpang EF2 Sungkai 132kV Rawang EF1 Rawang 132kV Rawang EF2 Kalumpang 132kV Based on the findings above, TNB has recommended the following measures: - TNB shall continuously monitor the power quality particularly the harmonics at the PCC during the electrified railway system operation KTMB shall undertake corrective measure to suppress the harmonics generated by the railway loads by installing harmonic filters at all KTMB s feeder substations. 3

5 4. POWER QUALITY MONITORING (PQM) TNB possesses an existing infrastructure for remote monitoring of faults and disturbances in its transmission system. Since the infrastructure is readily available, TNB is expanding the facility by adding PQM function. This has resulted in the implementation of an integrated disturbance and power quality recorder (IDPQR) which provides both economic and technical advantages to TNB as compared to stand alone Disturbance Recorders (DR) and Power Quality Recorders (PQR). In addition to its main function for monitoring faults and disturbances, it can be equipped and integrated with a dedicated PQM module. It is capable of recording the following events upon occurrence: - Dips/swells/interruptions. This type of event is characterized by its time tag, magnitude and duration PQ parameter threshold exceeded This event is characterized by its time tag and magnitude It also archives the following data daily: - histograms on voltage & current harmonics (from 3s averages) histograms on voltage & current RMS and imbalance (from 3s averages) 3 second min/max values of the day for voltage & current RMS, harmonics, THD, active power, reactive power and power factor 10second time recording of frequency 10min time recording of voltage and current RMS, harmonics, THD, active power reactive power and power factor The data are stored in an internal Flash Cards, which can be interrogated remotely via TNB Wide Area Network. The IDPQR offers the following technical and economic advantages over the standard stand alone DR and PQR :- Readily available infrastructure, thus installation costs are reduced Simplicity and ease of maintenance due to one equipment PQ data and disturbance data can be archived, viewed and analyzed via one common system 5. VOLTAGE TRANSDUCER FOR HARMONICS MEASUREMENT For the purpose of harmonic voltage measurement, one of the important aspects which was taken into account by TNB was the selection of the most suitable voltage transducer for this application. Three types of voltage transducers were being considered during the engineering stage. The first was the use of Capacitive Voltage Transformers (CVT) that have been commonly used in TNB system and other utilities in the world due to their excellent performance and reliability. The second option was to use Inductive Voltage Transformers 4

6 (IVT), which have a capability of measuring up to 50th harmonics. The third and final option was to install Resistive-Capacitive Voltage Transformers, also known as RC-Voltage Divider. Table III. Voltage Transducers Comparison Table [4] No. Performance Criteria CVT IVT RC-Voltage Divider 1. Steady State Accuracy Good Excellent Excellent 2. Transient Performance 45Hz to 55Hz 10Hz to 1kHz (Sufficient) 0Hz to 2MHz (Excellent) It can be seen that the IVT and RC-Voltage Divider provide an excellent steady state performance compared to the CVT. The only significant differences between the IVT and RC-Voltage Divider are the latter is capable of measuring high voltage frequencies and unsusceptible to ferro-resonance as compared to the former. These two criteria are essential for accurate measurement of voltage harmonics, which formed the basis of selecting the latter as the most suitable voltage transducer for harmonic measurement. 6. CONCLUSIONS The development of electrified railway system is foreseen to have an impact on the power quality. TNB as the sole electricity supplier has pursued a systematic approach to investigate, evaluate and undertake necessary measures to monitor and mitigate the problems. These include site survey to measure the background harmonics surrounding the PCC and power system study to simulate the railway operation and its effects on power quality. The study revealed potential high harmonic voltage distortions at all PCCs, which exceeded TNB s permissible limits. As a precaution, TNB has decided to monitor this continuously upon commencement of the electrified railway system operation. This is accomplished by using state of the art integrated disturbance cum power quality recorder and R-C voltage divider. During the monitoring, if it is determined that the maximum permissible levels of power quality were exceeded, TNB shall put into place the corrective measures to be implemented so as to mitigate the effects. 7. BIBLIOGRAPHY [1] Tenaga Nasional Berhad, Guidelines of Power Quality Control For Connection To Grid System, [September 2003, 1-15] [2] Tenaga Nasional Berhad, Report on The Technical Power System studies Associated With The KTMB Rawang-Ipoh Railway Electrification Project, [January 2002, 1-29] [3] Balfour Beatty Rail Power Systems, Rawang-Ipoh Electrification Project (Systems); Final Report 25kV & 132kV Power Systems Study, [August 2002, 1-57] [4] Minkner R., A Universal RC Voltage Transformer For High Voltage Networks, [ETZ, vol. 22/2002, 22-29] 5