It is becoming increasingly clear that the decline in popularity in the field of electrical engineering is undergoing rapidly due to the fact that more young people are moving away from the science. The primary goal of this paper is to recognize the importance of educational new effort and, second, suggest social-provided education support needed to meet this challenge.
Functions and performances of digital relays have improved with progress of various digital technologies, such as high-speed data sampling. On the other hand, it has been becoming difficult to keep service parts such as CPU and memory whose improvement or elimination cycle is considerably shorter than replacement cycle of protection systems. In such situation, a technical committee was established in ETRA in order to research future images of protection relays and so on. This paper summarizes a future vision of protection systems based on the investigation carried out by the committee.
The opportunity for distributed generators to be connected to the power system has been increasing since the introduction of electricity deregulation. Moreover, a power system which has a new concept such as a micro-grid or a smart-grid is going to appear. The increase in the uncertainty of power flow and the power system operation under an irregular system configuration is supposed in such new power systems. And the sensitivity of a protection relay may decrease or a protection relay may miscoordinate with other protection relays. Under the above conditions, to prevent the fault expansion is required of the electric power utilities. From the background, the development of a program that can check the relay setting and the coordination between protection relay systems is desired. The development of “Support System for Setting and Coordination between protection relays” called SSSC was initiated in 2006, and it will be completed in 2011. SSSC has the following features; ·It enables us to check whether the protection relay is set as operate correctly against all of assumed system faults. ·It enables us to check automatically whether the coordination between the protection relays is proper as prevent the fault extension even if an unexpected condition occurs. ·It enables us to analyze the response of the protection relays in the power system where some apparatus with nonlinear characteristic is installed. This paper describes the prototype of the SSSC based on the dynamic analysis like Y-method. Furthermore, in this paper, the checking method of coordination between protection relays for short circuit fault, and the verification results of the prototype in the 6.6kV model distribution system are described.
A severe fault may cause a loss of synchronism between two groups of generators. And this may lead to a separation of power system network. If the imbalance between total power output of the generators in a group and the total load in the separated network is large, the deviation of frequency will increase or decrease and a further loss of synchronism will occur and result in a wide-area blackout To prevent a loss of synchronism from expanding, we propose a new method for selecting a set of power lines to be opened. The method comprises three steps. The first step is to collect lines that predict or detect out-of-step. The second step is to find the separated networks. The third step is to switch lines so that the imbalance is minimized. In the second step, a fast method of computing an inverse admittance matrix is developed and a new approach is developed to find the group of nodes that are connected and the group of nodes that are not connected. In the third step, a procedure to select lines that will be opened is developed in order to minimize the imbalance between total generator output and total load. The validity of this method is shown by simulations using several models including a East10-model and a large-scale model composed of 799 nodes.
This paper verifies the mechanism of occurring over voltage phenomena in the distributed power system on energizing the transformer. This over-voltage, which is observed at the actual distributed power system, with heavy inrush current is found to occur at about 0.1-0.2sec after the energizing and continue for a duration of more than 0.1[sec]. There is a concern that this over-voltage may operate the protection relay and deteriorate the insulation of apparatus. It is basically caused by the resonance between the shunt capacitors and saturated/unsaturated magnetizing inductance of transformer, system inductance. By using analytical formulation of a simple equivalent circuit, its mechanism has been verified through simulations carried out by using EMTP. Moreover, the sympathetic interaction between transformers is prolonged the duration of the over-voltage by the field test data is discussed in this paper.
In the past, a current transformation ratio of a current transformer (CT) has been different for each facility corresponding with a rated current of a primary circuit in high voltage (6kV) equipments. By unifying specifications of a CT, there is no need to prepare a CT with various ratings corresponding with a capacity of a load facility, it becomes easier for consumers to modify facilities, and for manufacturers, it enables to standardize of a design and shorten a production period. Recently, it has been popular composition of a secondary circuit of a CT being connected with a digital protection relay bundled with protection and measurement functions not being connected with relays, meters and transducers separately. Because the composition enables to reduce a burden of a secondary circuit of a CT, reduction in size and weight of a CT is achieved and it also contributes to reduce a size of a cubicle and improve a mounting efficiency of a panel. We have developed a CT corresponding with a multi range input (a multi-range CT) and a digital protection relay utilizing its advantages which enable to standardize of a facility design and reduce a size of a cubicle, and report them in this paper.
The microgrid is an energy system which aims to improve the environmental performance by using renewable energy generations, and it aims to enhance the degree of autonomy without depending on the adjustment capability of electric utility system by maintaining own energy balance of the demand and supplies which uses plural distributed generations with various characteristics. Therefore, it is required that the demand and supply controller (DSC) is applied for the microgrid, and DSC is usually composed by computer system because flexible and intelligent management technology is necessary. On the occasion of developing the DSC, it is important that dynamic characteristics and behavior of the electric power grid are considered sufficiently, and it is difficult to develop the software of DSC without controllable actual facilities. Accordingly, we developed the real-time simulator (RTS) which can simulate behavior of the microgrid on the desk of software developer for aiming to develop the DSC efficiently. Developed RTS has a feature that enabled to simulate continuously both grid connecting operation and islanding operation by using a new proposing method. This paper presents the outline of RTS functions, calculating method, and modeling method of DG, and then it shows verification results of accuracy in RTS and evaluated result of real-time performance.
A fault detection system is applied to power lines consisting of both overhead power line and underground power cable in order to detect a fault on the underground power cable section and prevent the automatic reclosing. The fault detection system using optical fiber current sensor has two subjects. The fist subject is that we have to use wound-type current transformer together, when applying the fault detection system to single-core underground power cable. The second subject is that we are not able to detect three-phase short-circuit fault in using the fault detection system. This paper describes that we developed a new fault detection system using optical fiber current sensor by applying the multiplex transmission technology of optical fiber current sensor signal in order to solve these subjects.
The task of setting a protective relay requires various analytical calculations and coordination studies, and is thus complex and takes much time to complete. We, Tohoku Electric Power Co., have introduced Integrated Support System for Protectiv Relay Setting that helps relay engineers' business concerning decision of relay setting and examination of relay operations when fault occurred. The purpose of introducing the system is to improve the certainty of these businesses and engineers' workforce optimization.
We have developed the Reliability Analysis System for Protection Relays (RASPR) in which equipment data and failure data of Electric Power utilities in Japan except the Okinawa Electric Power Company have been stored since 1997. By using the data, we have proposed the extension of the periodic testing interval of digital relays and reduction of the testing items in a periodic testing, based upon the statistics and the reliability analysis result, and we have estimated quantitatively the effect of the automatic supervision of a digital relay. On the other hand, the second generation digital relays have been widely used from the background of the progress of hardware and soft ware technology, but the analysis based on the features of failures is not clear. Actual conditions of equipment and the failure for digital relays and the analysis result of reliability by using the data for 11 years that have been stored in RASPR, are described in this paper. So, in this paper, analyzing the data for 11 year stored in RASPR, the features of the failure are clarified from the analysis of the failure found by the incentives of finding failure except automatic supervision, and we list up the items on which should be concentrated in maintenance. And we show the decrease of the reliability for the first generation digital relays from the reliability analysis.
JEC-2501, a future JEC standard for protective relays' EMC environment is now under creation in conformance with related IEC's EMC standards and existing Japanese EMC standards. This paper describes history of EMC related standards for protective relays in Japan, Structure and meanings of IEC's EMC standards referred by JEC-2501, relation between EMC standards of IEC and those of Japan, and finally desirable way of creating future EMC standard in Japan.
The Recently, electronics and IT technologies have been rapidly innovated and have been introduced to power system protection & control system to achieve high reliability, maintainability and more functionality. Concerning the distribution substation application, digital relays have been applied for more than 10 years. Because of a number of electronic devices used for it, product cost becomes higher. Also, products installed during the past high-growth period will be at the end of lifetime and will be replaced. Therefore, replacing market is expected to grow and the reduction of cost is demanded. Considering above mentioned background, second generation digital protection and control unit as a successor is designed to have following concepts. Functional integration based on advanced digital technologies, Ethernet LAN based indoor communication network, cost reduction and downsizing. Pondering above concepts, integration of protection and control function is adopted in contrary to the functional segregation applied to the previous system in order to achieve one-unit concept. Also the adoption of Ethernet LAN for inter-unit communication is objective. This report shows the development of second-generation digital relay for distribution substation, which is equipped with control function and Ethernet LAN by reducing the size of auxiliary transformer unit and the same size as previous product is realized.
Recently digital control panels have been installed for various controls adjacent to GIS. As the distance between the digital control panels and GIS is short, switching surge is transmitted without attenuation. Therefore we developed the digital control panel that implemented surge countermeasure. We verified that the digital control panel adjacent to 500kV GIS did not malfunction for switching surge. Moreover we measured the switching surge at the digital control panel and analyzed the intrusion route of switching surge by EMTP. As a result, we observed that the maximum voltages at a secondary circuit of CT and the maximum voltages at a secondary circuit of VT were 2.4kVp-p and 2.8kVp-p, respectively. The major frequencies of those voltage waveform were distributed almost more than 10MHz. In the EMTP, the intrusion route from the GIS to the secondary circuit of VT was calculated. The voltage waveforms at VT terminal calculated by EMTP agree with measured results in the view point of amplitude, frequency and damping time.
This is the development report for our new type relay systems, Islanded System Automatic Synchronizer (ISAS) and the predictive step out prevention relay system using power flow parameters. ISAS is a kind of device for self-healing. It performs emergency system re-synchronize operation automatically when the islanded system is separated from the main grid. TEPCO applied some ISAS devices in Tokyo metropolitan area and resulted that reliability in the area was much improved. The predictive step out prevention relay system mentioned above is a kind of special protection scheme, which predicts generator step out and calculates how much amount of generator should be tripped to stabilize the power system when the fault on the transmission lines is detected. A New predicteve step out calculation algorithm using power flow parameters was developped so that it can be applied for the complex power system. TEPCO applied the new relay system to the area where TEPCO's criteria was not satisfied due to transient instability problem and resulted that the stability was improved enough to meet TEPCO's criteria.
This paper proposes a new computation method for Total Transfer Capability (TTC) with respect to thermal and voltage magnitude limits. TTC is formulated as an optimization problem and solved by The Primal-Dual Interior Point Method (PDIPM). In stressed power system, mho relays are possible factors for causing cascading failures because of their unnecessary operations caused by decrease in voltages in heavy load conditions. Therefore, in order to consider mho relay characteristics, the relay operating conditions are taken into account in the optimization problem as constraints to compute TTC. The effectiveness of the proposed method is demonstrated through IEEE 57 bus system model.
Open access and deregulation have been introduced into Japan and some independent power producers (IPP) and power producer and suppliers (PPS) are participating in the power generation business, which is possible to makes power system dynamics more complex. To maintain power system condition under various situations, it is essential that a real time measurement system over wide area is available. Therefore we started a project to construct an original measurement system by the use of phasor measurement units (PMU) in Japan. This paper describes the estimation method of a center of inertia frequency by applying actual measurement data. The application of this method enables us to extract power system oscillations from measurement data appropriately. Moreover, the analysis of power system dynamics for power system oscillations occurring in western Japan 60Hz system is shown. These results will lead to the clarification of power system dynamics and may make it possible to realize the monitoring of power system oscillations associated with power system stability.
Economic load dispatch among thermal units has been one of the most important problems in the field of power systems operation. Usually so called equal marginal cost criterion is adopted to this calculation. Recently global trend of utilizing more and more renewable energy makes this problem more important than ever. In case of large penetration of fluctuating power sources such as PV or wind, thermal units are more often required to change their prescheduled operation pattern because the outputs from PV and wind power generators are affected by uncertain change of weather condition. In a sense the large scale utilization of natural energy depends on the flexible and adaptive operation of the thermal units. In such a situation it is easily imagined that thermal units would be required to change their output faster than before sometimes violating the limitation due to the physical constraints of the plant including boilers. We will need a load dispatch calculation method which maximally utilizes their output change capability within the upper limits of the ramp rate. Dynamic economic load dispatch has been studied for a long time to give appropriate load dispatch among generators considering the above stated constraints. However the existing methods are not enough in case of the scenario of very steep demand change. Some more sophisticated calculation scheme is highly needed today which gives us feasible solution in severer situations. This paper proposes a new calculation scheme for the above stated dynamic economic load dispatch problem based on functional optimization which numerically solves Euler's differential equation in the field of calculus of variations. The constraints related to units output and output ramp rate are readily considered by the logarithmic penalty function terms in the objective function together with the equality constraint regarding the total demand balance. Numerical examples show that the proposed method can solve the above stated severe situation which has been difficult to treat by the existing methods. Convergence performance is also discussed.
SMES of the10,000kW for the power control in power system has been manufactured, and connected to a real power grid. In addition, innovative basic researches, for example, low cost converter, maintenance-free cryo-coolers, inter-locks system and so on, have also been developed. The SMES was installed in the metal rolling factory with hydro power plant. Field test has been carried out for load fluctuation compensation. SMES was able to compensate for the active power according to the fluctuating load, and confirm the situation with a smooth load change of 11kV bus of hydro power stations. In this paper, field test results are presented.