Integration of SEL Relays to Provide Motor, Transmission Line, and Transformer Protection

The objective of this project is to familiarize the performers with the principles of operation of the Schweitzer Engineering Laboratories (SEL) protective relays in both normal and fault conditions. The SEL-587, SEL-311L and SEL-710 microprocessor-based relays are used to provide protection for a system composed of transformers, simulated transmission lines and a 3-phase induction motor. Each of these relays provides protection by sending a trip signal to local breakers upon sensing a fault condition. The SEL-587 provides overcurrent and differential protection for a 3-phase transformer, while the SEL-311L provides differential and distance protection for a transmission line, and negative sequence. The SEL-710 protects motors by monitoring the supplied current for locked rotor conditions, overcurrent, unbalanced phases, and undervoltage conditions and situations which would result in the motor overheating. This project involves testing the individual protective relays as well as incorporating all relays into a functional system, with independent regions of protection. That is to say that for fault in a given piece of equipment, the relay responsible for protection should be responsible for tripping the local supply breaker, providing protection in the event of a fault. The benefits of the lab are familiarization with protection schemes, the proper implementation of protection equipment and programming SEL relays and associated logic functions

Design and Implementation of Overcurrent Protection Relays Test Bench

The electrical power simulator in Engineering Sciences Building (ESB) at WVU was dismantled in July 2018. The simulator was used as a teaching tool for EE students to conduct lab experiments. The power simulator employed electromechanical and microprocessor protection relays, manual isolation and industrial circuit breakers, switches, variable autotransformer (VARIAC), voltmeters and ammeters. During the dismantling, a lot of equipment was retrieved for future possible use. This led to the idea of designing and implementing a simple circuit on a test bench that can be used as a lab equipment to demonstrate the operation of overcurrent protection relays. It was decided to design the circuit so that it employs equipment removed from the power simulator including microprocessor-based SEL-751A Feeder Protection Relays, Westinghouse CO-8 electromechanical relays, variable autotransformer (VARIAC), voltmeter, ammeter, isolation circuit breaker, and a tripping circuit breaker. A circuit test bench, available in the lab, was modified for this purpose. The bench provides the advantage of having a setup on a small and movable platform. The circuit of the Overcurrent Protection Relays Test Bench has a variable autotransformer with protection relays, protection breakers and changeover switches installed on the primary and secondary side of the transformer. SEL-751A or three electromechanical CO-8 relays, one on each phase, can be selected as the main protection device on both sides of the transformer. There was only one industrial circuit breaker available in the lab. This has been installed on the secondary side. For the primary side, a breaker circuit has been designed and used which uses general-purpose DPDT and electronic relays, DC power supply, voltage limiting resistors, toggle switch and push-button reset switch. This use of the breaker circuit has saved a lot of costs since most of the components used in the design were already available in the lab. Based on the cost-effective design, it is planned to design a similar circuit that can demonstrate the operation of differential current protection relay based on SEL-387A Current Differential Relay

Design and Implementation of High-Efficiency, Lightweight, System-Friendly Solid-State Circuit Breaker

Direct current (DC) distribution system has shown potential over the alternative current (AC) distribution system in some application scenarios, e.g., electrified transportation, renewable energy, data center, etc. Because of the fast response speed, DC solid-state circuit breaker (SSCB) becomes a promising technology for the future power electronics intensive DC energy system with fault-tolerant capability. First, a thorough literature survey is performed to review the DC-SSCB technology. The key components for DC-SSCB, including power semiconductors, topologies, energy absorption units, and fault detection circuits, are studied. It is observed that the prior studies mainly focus on the basic interruption capability of the DC-SSCB. There are not so many studies on SSCB’s size optimization or system-friendly functions. Second, an insulated gate bipolar transistor (IGBT) based lightweight SSCB is proposed. With the reduced gate voltage, the proposed SSCB can limit the peak fault current without the bulky and heavy fault current limiting the inductor, which exists in the conventional SSCB circuit. Thus, the specific power density of the SSCB is substantially improved compared with the conventional design. Meanwhile, to understand the impact of different design parameters on the performance of SSCB, an analytical model is built to establish the relationship between SSCB dynamic performance and operating conditions considering the key components and circuit parasitics. Simulation and test results demonstrate the accuracy of the proposed model. To limit the fault current with the proposed SSCB without a current limiting inductor, power semiconductors need to operate in the active region temporarily. During this interval, a severe voltage oscillation has been observed experimentally, leading to the DC-SSCB overstress and eventually the failure. A detailed MATLAB/Simulink model is built to understand the mechanism causing the voltage oscillation. Three suppression methods using enhanced gate drive circuitry are proposed and compared. Test results based on a 2kV/1kA SSCB prototype demonstrate the effectiveness of the proposed oscillation mitigation method and the accuracy of the derived model. Meanwhile, when the system fault impedance is close to zero (e.g., high di/dt), the influence of the parasitic inductance contributed by interconnection (e.g., bus bar, module package, etc.) cannot be neglected. To study the influence of the bus bar connections on SSCB with high di/dt, a Q3D extractor is adopted to extract the parasitic parameters of the SSCB and understand the influence of different bus bar connections. A vertical bus bar is proposed to suppress the side effect and verified by the Q3D extractor and experimental results. Finally, a system-friendly SSCB is demonstrated. The proposed gate drive enables the SSCB to operate in the current limitation mode for the overcurrent limitation. The current limitation level and limitation time can be tuned by the gate drive. Then, this dissertation provides an all-in-one solution with integrated circuitries as the fault detector, actuator for the semiconductor’s operating status regulation, and coordinated control. This allows the developed SSCB to limit system fault current not exceeding short-circuit current rating (SCCR) and also take different responses under different fault cases. The feasibility and the effectiveness of the proposed system-friendly SSCB are validated with experimental results based on a 200V/10A SSCB demonstrator

Multi-kw dc power distribution system study program

The first phase of the Multi-kw dc Power Distribution Technology Program is reported and involves the test and evaluation of a technology breadboard in a specifically designed test facility according to design concepts developed in a previous study on space vehicle electrical power processing, distribution, and control. The static and dynamic performance, fault isolation, reliability, electromagnetic interference characterisitics, and operability factors of high distribution systems were studied in order to gain a technology base for the use of high voltage dc systems in future aerospace vehicles. Detailed technical descriptions are presented and include data for the following: (1) dynamic interactions due to operation of solid state and electromechanical switchgear; (2) multiplexed and computer controlled supervision and checkout methods; (3) pulse width modulator design; and (4) cable design factors

Microgrid Protection Student Laboratory

To better prepare students for careers in the electric power industry, specifically in the discipline of power system protection, the Electrical Engineering Department at Cal Poly San Luis Obispo proposed an initiative calling for the creation of new laboratory curriculum that uses microprocessor-based relays to give students hands-on experience in the application of protection theory. This report describes the creation of a system that meets this need by providing a laboratory-scale power system that demonstrates the use of common protective relays and protection schemes. This system provides a platform for laboratory coursework using protective relays for transmission line, transformer, and induction motor protection. Within this laboratory system, one of the primary goals of the project was the integration of the SEL-311L Line Protection Relay and the SEL-710 Motor Protection Relay as part of the overall protection scheme. Development of the project was completed successfully, producing a protection scheme that protects power transmission equipment and the induction motor in both radial and bidirectional systems. The system clears all desired fault types and abnormal operating conditions with primary protection elements for each piece of equipment, as well as time-coordinated backup protection system-wide. The completed protection system is selective, removing only the minimum amount of power equipment necessary to clear fault conditions. It is also secure, in that normal operation does not result in unnecessary trips, and reliable, in that all fault conditions are cleared even when primary protection devices do not operate. The SEL-311L and SEL-710 relays were implemented successfully, and used to demonstrate more complex and advanced protection methods than simple overcurrent elements, such as permissive overreach transfer trips and motor thermal modeling

A NEW SUPERVISORY CONTROL SYSTEM FOR DOMESTIC PROTECTION SYSTEM

Power failure is a common problem when there are electrical faults occurred, which would lead to discontinuity of electrical supply to domestic building. For domestic consumers, power continuity is very important since some of the appliances such as refrigerator, aquarium and alarm system require a continuous electrical supply. However, fault occurred in the system will trip the earth leakage circuit breaker (ELCB) and disrupt the supply to all the appliances. Fault may occur due to short circuit, ground fault or overloading. Thus a New Supervisory control system is being developed to supervise the faults which occur in domestic building using zigbee wireless technology and to automatically control the system via wireless to ensure power continuity and avoid any property lose

Beyond Power over Ethernet : the development of Digital Energy Networks for buildings

Alternating current power distribution using analogue control and safety devices has been the dominant process of power distribution within our buildings since the electricity industry began in the late 19th century. However, with advances in digital technology, the seeds of change have been growing over the last decade. Now, with the simultaneous dramatic fall in power requirements of digital devices and corresponding rise in capability of Power over Ethernet, an entire desktop environment can be powered by a single direct current (dc) Ethernet cable. Going beyond this, it will soon be possible to power entire office buildings using dc networks. This means the logic of “one-size fits all” from the existing ac system is no longer relevant and instead there is an opportunity to redesign the power topology to be appropriate for different applications, devices and end-users throughout the building. This paper proposes a 3-tier classification system for the topology of direct current microgrids in commercial buildings – called a Digital Energy Network or DEN. The first tier is power distribution at a full building level (otherwise known as the microgrid); the second tier is power distribution at a room level (the nanogrid); and the third tier is power distribution at a desktop or appliance level (the picogrid). An important aspect of this classification system is how the design focus changes for each grid. For example; a key driver of the picogrid is the usability of the network – high data rates, and low power requirements; however, in the microgrid, the main driver is high power and efficiency at low cost

Improved transient earth fault clearing on solid and resistance earthed MV netwworks

Includes bibliographical references.The aim of this thesis is to endeavour to develop, through a literature study, a method or methods whereby transient earth faults on neutral earthed MV networks may be cleared without customer supply interruptions, without compromising public safety and without compromising network integrity. In order to propose such a method, or methods, it is important to understand the various earthing practices employed in MV networks in terms of network behaviour under earth fault conditions, as this may influence network component insulation rating requirements, as well as the way in which such a system may function

Development of DC Circuit Breakers for Medium-Voltage Electrified Transportation

Medium-voltage DC (MVDC) distribution is an enabling technology for the electrification of transportation such as aircraft and shipboard. One main obstacle for DC distribution is the lack of adequate circuit fault protection. The challenges are due to the rapidly rising fault currents and absence of zero crossings in DC systems compared to AC counterparts. Existing DC breaker solutions lack comprehensive consideration of energy efficiency, power density, fault interruption speed, reliability, and implementation cost. In this thesis, two circuit topologies of improved DC circuit breakers are developed: the resonant current source based hybrid DC breaker (RCS-HDCB) and the high temperature superconductor fault current limiter based solid state DC breaker (HTS-FCL-SSDCB). The RCS-HDCB utilizes a controllable resonant current source based upon wide bandgap (WBG) switches that enable low loss and fast fault interruption due to the fast switching speed. The voltage applied by the controllable resonant current source is much lower than the rated voltage of the DC breaker, allowing the utilization of significantly lower voltage rated WBG switches. The conduction path\u27s sole component is a fast-actuating ultra-low resistance vacuum interrupter for high efficiency during normal operation. As the second DC breaker concept, the HTS-FCL-SSDCB is subdivided into a fault current limiter (FCL) and solid state DC breaker (SSDCB). The FCL is based upon a high temperature superconductor cable which has natural fault current limiting capabilities while having negligible insertion losses for normal load currents. The SSDCB utilizes WBG switches to decrease conduction losses compared to Silicon-based breakers. The FCL reduces fault current such that the number of semiconductive switches in the SSDCB is minimized. Both breakers feature a metal-oxide varistor device in parallel to clamp overvoltages and dissipate energy after fault interruption. Modeling, simulation, and analysis in electrical and thermal domains are conducted to verify the functionality of the DC circuit breakers. The simulation results confirm the feasibility of these two DC breakers in their proposed applications of 2.4 kV electric aircraft and 20 kV shipboard MVDC distribution systems