Thursday, January 20, 2011

The Utilization of Digital Fault Recorders in Protection System Analysis on Tenaga Nasional Berhad Transmission System


Abdullah Asuhaimi Mohd Zin, Senior Member, IEEE, and Sazali P. Abdul Karim

Abstract—The protection system is a very critical element in a power system. It is security to the power system for isolating only the faulty plant as fast as possible. A simple fault can lead to a cascade of tripping if it is not isolated accurately and fast enough by the protection system. Furthermore, protection system analysis is a  complicated task for inexperienced engineers. Most of the analysis relied mainly on the relay indications which could lead to incorrect analysis due to the uncertainty of the correct relay operations and  time tagging. Therefore, it is an urgent requirement to explore protection  system analysis to improve system reliability. This paper  describes a method of early detection of protection system failures  in Tenaga Nasional Berhad’s  Transmission Grid using digital fault  recorders. The method has demonstrated to be more accurate, thus
enabling faster decision making and shorter interruption time. Index Terms—Digital fault recorder (DFR), hidden failures, protection  system analysis (PSA).

THE importance of monitoring the performance of power systems has steadily increased over the years. Consequently, evaluation of system disturbances has become more complex and the monitoring of an equipment’s performancehas become essential for power system reliability to ensurecompetitive power supply in the deregulation industry [1].In the electrical industry, the economic factor plays an importantrole to preserve continuous business with the consumers.Domestic and industrial consumers are more sensitive to the
availability of electricity supply being fed to their premises. In this new era of business globalization, whenever wide-area power outage occurs in a country, the power system reliability and security will always be the first to be inspected by the power system regulator.

The main objective of protection system analysis is to assist utility engineers to examine the behavior of secondary equipment in order to improve the reliability of the power systemUnfortunately, only a few engineers can interpret the recorded waveform traces captured during faults and disturbances. The engineer should first have experience in power system operation,network configuration, and power system protection. Forthose who have experience but have not undergone relevant training, they cannot interpret the significance of the recordedwaveform traces. Even the most technically trained engineers will face difficulties in understanding the problems if they do not have experience in fault and disturbance analysis. Protection system analysis using fault records has been use to identify the source of any tripping in a power system. Unfortunately, the digital fault recorder (DFR) has not been extensively applied due to a lack of training. Moreover, with so many DFR models from different manufacturers, the task becomes
more difficult. Failure to understand protection system  operations and the fault’s characteristics can cause a time delay  in power-supply restoration to the consumers

A. Recorder’s Definition
In order to optimize the application of the recorders as a recording device, Tenaga Nasional Berhad (TNB) has defined and categorized two types of recorders, namely the DFR and the digital disturbance recorder (DDR). By adopting these two definitions, TNB is able to decide the strategic locations for installing each recorder in TNB’s Transmission System. The list of fault and disturbance recorders installed in TNB’s Transmission System .

B. Digital Fault Recorder
A DFR is defined as a device to graphically record all of the voltages and currents as well as protective relays’ operations during any fault condition and switching transients using a fast sampling rate. The fast sampling rate shall be at least 2000 Hz and above. The recording time shall be up to 4 s

A DDR is defined as a device to graphically record all of the voltages and currents as well as protective relay operations  during any power system disturbances, including fault condition, power swing, power system frequency deviation, and other information related to dynamic system performance using fast and slow sampling rates. The fast sampling rate must be at least 2000 Hz and above. The slow sampling rate can be as low as 100 Hz. Both fast and slow sampling rates shall be used at the same time. The recording time for the fast sampling rate shall  be up to 4 s and the slow sampling rate shall be up to 60 s

Protection system maloperation is often a contributing factor to most major power outages despite system constraints as discussed in [11]. Although a major blackout is an occasional  event, the impact from a single incident might cost more than  U.S.$ 1 billion. The selection of an appropriate protection scheme must be carefully evaluated in order to prevent any  damage in the power system. In that respect, TNB has implemented  protection schemes to cater to all types of faults, such as  lightning strike and tree encroachment, which are common in  tropical countries such as Malaysia. The fault and disturbance
recorders installed in the TNB transmission grid system have  made significant improvements in the operation of the power  system. With this newly developed tool (PSA), TNB is able to  identify the protection system hidden failures before any major disturbance appears in the power system. In conclusion, PSA  is a valuable tool for decision making, particularly to network  dispatch operators of TNB, Malaysia. Ultimately, reduced
operating costs for every disturbance in the power system will  be achieved. .

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