Bi-Directional Power Flow in Switchgear with Static Transfer Switch Applied at Various Renewable Energies

In this study, we describe the development of a plug-in type of switchgear that can control bidirectional power flow. This switchgear system can connect distributed generations such as photovoltaic and wind turbine generation, and AC and DC loads. The proposed switchgear system consists of an inverter for connecting distributed generations and DC load, a static transfer switch (STS) that can control and interrupt the bidirectional power flow, and an intelligent electronic device (IED) that can control each facility using a communication system. Since the topology inside the switchgear is composed of DC bus, it can be operated as a plug-in type of system that can be used by simply connecting the converters of various distributed generations to the inverter in the developed switchgear system. In this study, we describe the overall structure of the proposed switchgear system and the operation of the components. In addition, prototypes of each facility are developed and the results of building a small testbed are presented. Finally, we verify the operation of the inverter by performing an experiment on the testbed and show that throughout a test sequence the proposed switchgear system works normally. The contributions of this study are the development of a plug-in type of switchgear for AC/DC and the actual test results presented through prototype development and testbed configuration.

IEC 61850-Based Centralized Protection against Single Line-To-Ground Faults in Ungrounded Distribution Systems

We developed an International Electrotechnical Commission (IEC) 61850-based centralized protection scheme to prevent single line-to-ground (SLG) faults in the feeders and busbars of ungrounded distribution systems. Each feeder intelligent electronic device (IED) measures its zero-sequence current and voltage signals and periodically transmits zero-sequence phasors to a central IED via a Generic Oriented Object Substation Event message. Using the zero-sequence phasors, the central IED detects SLG faults in feeders and busbars. To achieve centralized protection, angle differences between the zero-sequence currents and voltage phasors are exploited, and their calculation compensates for data desynchronization. The feeder IEDs were implemented using the MMS-EASE Lite library, while the transmitted zero-sequence phasors were calculated based on fault signals simulated by Power System Computer Aided Design / Electro-Magnetic Transient Design and Control (PSCAD/EMTDC). The central IED determined if the SLG fault was in a feeder or busbar by aggregating and analyzing the zero-sequence phasors received from the feeder IEDs. The results confirmed the validity and efficiency of our centralized protection scheme.

Applying the permissive overreaching transfer Trip of SEL 311L distance relay to protect the transmission line

Vietnam\'s electricity system has been increasingly invested in development, meeting the growth rate of energy consumption demand in all socio-economic aspects. In particular, the energization and commission of solar and wind power plants greatly affect the stability and safety of the Vietnam power system. To improve the system\'s stability when incidents occur, one of the current solutions is to coordinate relay calibration settings which have a rapid reaction time at all voltage levels. To meet the above requirements, an option is to use Intelligent Electronic Device (IED) with fast processing speed, reduced latency, and multiple functions with intelligent algorithms. In addition, the solution to coordinate the protection areas between IEDs is being concerned. This paper presents the coordination of Permissive Over-Reaching Transfer Trip (POTT) interlock function of SEL 311L relay for power transmission lines to reduce the fault clearing time compared to the traditional calculation method.

A Novel Methodology to Sense CT Saturation Using Numerical Protection Relays

The necessity for dependability and safety in power system is rising at an alarming rate as the power system designs are getting more & more complex. In order to ensure maximum reliability, the numerical protection relays must receive accurate measurements. One of the most important input measurements desired by the relay is current. Nevertheless, the current measurements expected from current transformers (CTs) can be inaccurate due to occurrence of a phenomenon called as CT saturation. CT saturation causes distortion in the secondary current, which is not linearly proportional to the primary current, leading to mal-operation of protection devices. Therefore it becomes extremely vital that the numerical protection relay, also known as intelligent electronic device (IED) senses the CT saturation condition and blocks its operation so as to avoid mal-operation of the IED which may lead to supply interruption, further resulting in production losses and undesirable switching of the sensitive equipments affecting system reliability and customer satisfaction. This paper includes a review of the background about CTs & proposes a novel methodology to exclusively sense the CT saturation using the numerical protection relays reliably and cost effectively.

Augmentation of situational awareness by fault passage indicators in distribution network incorporating network reconfiguration

Power distribution systems are profoundly inclined to disturbances like untimely switching of breakers & relays, sympathetic tripping, and uncertainties regarding fault location. Thus, system stability and reliability are greatly affected. In this way, situational awareness and system integrity are the crucial factors in developing power system security, as it empowers successful decision making & timely reaction by the operators to any disturbance and also maintaining continuity of power supply. This paper focuses on the enhancement of situational awareness by fault location through fault passage indicators (FPI) to improve nominal impedance-based methods in distribution networks. Also, the proposed method is validated by comparing it with Intelligent Electronic Device (IED) based fault location method. Further, simultaneous reconfiguration of the system is incorporated to maintain the continuity of supply. The analysis has been tested on IEEE 33 bus distribution system.