Fault Tree-Based Root Cause Analysis Used to Study Mal-Operation of a Protective Relay in a Smart Grid

This chapter presents how root cause analysis based on fault tree technique can be used to study mal-operation of protective relay in a smart power grid. This approach is used to identify disturbances first and root cause of mal operation of protective relays which may lead to unnecessary tripping and hence to blackout. Once the critical root causes are identified, mitigation measures first such as blocking protection functions and digital filters may be used in view of increasing the reliability of the considered protection system. The proposed approach has many advantages as it allows obtaining an important quantitative figure (security). These permits to strongly strengthen the elements of the protecting system which are most likely appropriate to failure and hence the impact on the overall system's cost is significant. Another main advantage is that it takes into account the reliability of the software part of the system which is considered to have a significant contribution in the overall reliability of the protecting system.

INFLUENCE OF THE REMNANT MAGNETIZATION OF THE CURRENT TRANSFORMER CORES UPON THE COMPLIANCE OF THEIR TECHNICAL CHARACTERISTICS WITH THE REQUIREMENTS FOR MICROPROCESSOR TYPE PROTECTIVE RELAYS

Work objective is finding rational technical and economic solutions for examining current transformers for techspecs compliance satisfying the requirements of reinstalled microprocessor type protective relays and automation devices manufactured by NP EKRA LLC, taking into account DC component. Research methods: analytical methods for calculating the time of remnant magnetization in the core of a current transformer. Research results and novelty: it is understood that the saturation time of current transformers of the basic and backup protections, according to the results of the analytical method, was more than 25 ms, and for current transformers of differential bus bar protection was more than 5 ms. The obtained saturation time values for all types of current transformers built into oil circuit-breaker bushings (HV line) of 110 kV and bus bar coupling connector (BCC) of 110 kV (main protection, backup protection, differential bus protection), both in the absence and in the presence of remanent induction magnetic in CT cores with three-phase and single-phase short circuits, satisfy completely technical requirements either of microprocessor type protective relays or CT differential bus bar protection. Conclusion: built into CT BCC circuit-breaker bushings of 110 kV and oil circuit-breaker bushings (HV line) of 110 kV Foundry substations do not necessitate a mandatory replacement in case of non-complex redesign of microprocessor type protective relays and automation devices. When replacing oil circuit breakers with gas-insulated ones, it is recommended to use CT with similar characteristics.

Design and Implementation of Multifunction Relay Based on Microcontroller

The power systems are exposed to many abnormal conditions, so an advanced protection system must be provided to stand up to these challenges. Protection devices evolved continuously with the development of power systems. The accuracy, high response, reliability, and speed of fault detection are required in the operating mode of multi-function protective relays. A Multifunction Relay has been designed and implemented, which consists of three types of relays: over current relay OCR, over/under voltage relay OVR/UVR, and differential relay DFR. The relays OCR, OVR/UVR, and DFR are designed according to the standards IEC 60255, IEEE 1159, and IEEE C37.91, respectively, based on Arduino MEGA. The multi-function relay was implemented to work on a single phase. The setting of the multi-function relay configuration done using a new design based on the MATLAB GUI environment. Furthermore, the results obtained after each test appear on it and LCD screen. The multi-function relay which is designed can work as (OCR, OVR/UVR, DFR) in the case of a single-phase source. The experiential results show that the proposed multi-function relay is accurate, fast response, reliable, selective, good performance, low cost, and sensitivity when used to protect the power system equipment under different operating conditions.

IEC 61850-Based Communication Networks of Distribution System against Cyber and Physical Failures

This paper proposes a decentralized control approach using a co-simulation platform to monitor protective elements and provide complete protection scheme for distribution systems. Real time measurements are obtained by interfacing the system model in RSCAD/RTDS with SEL 421 protective relays and publish/subscribe the voltage and current signals of the buses and transmission lines based on IEC 61850 communication protocol to isolate the fault correctly. The proposed technique helps to identify the location of the fault and introduces primary and buck protection for the system. The communication networks assists in facing cyber and physical threats and finding a new path for healthy relays to remove faults from the system. This technique is investigated on an IEEE 14 bus system for all possible fault locations. The proposed scheme can clear the fault by isolating the minimum part of the system and improving the endurance of the power in it. The system shows the smooth information flow between the cyber and physical parts to isolate faults in it in different cases.