Voltage Sag Source Location: A New Method Based on Current Information

Voltage sag is one of the major power quality (PQ) problems, and has been the focus of PQ studies due to the impact on sensitive industrial loads and costs led by the damages and maintenance. Voltage sag source location is significant for the customers and suppliers to solve the issue between them, as well as for possible mitigation. Five main methods (the disturbance power and energy method, the slope of system trajectory method, the real current component method, the resistance sign–based method, and the distance relay method) are reviewed first. However, these methods used single criteria, and their effect is limited as the literature shows. This paper presents a pattern recognition way to locate the source of voltage sag. In the proposed method, features for pattern recognition are extracted first, based on these five methods. Then, the thought of source location by pattern classification is discussed with three steps in detail, and support vector machine (SVM) is applied in the case. The nonl...

Enhanced real time coordination of distance and user defined over current relays

This paper analyses the different voltage sag phenomenon of the different voltage sag sources and summarizes the characteristics of the different voltage sag sources, including the amplitude of the voltage sag, the swell happening at the same time of the sag, the characteristics of the voltage changes during the sag and the three phases voltage balance or not. Most of the existing voltage sag source recognition methods and their disadvantages and application have been analyzed in this paper. Considering that in actual power quality monitoring network, many monitoring equipments only can provide parts of the voltage sag data, so a simple and practical method is proposed in this paper. Only the RMS voltages are calculated in this method. Based on the different voltage sag amplitudes, the voltage jump happening at the end of the sag(or the voltage changes in trends during the sag), the different deviations of the three-phase voltages and some other characters according to different sources, the characteristic value corresponding can be extracted, and then the classification of voltage sag caused by the short-faults, transformers energizing and large-capacity induction motor starting can be realized. The correctness of the method is proved by simulations.

The precise location of voltage sag sources plays an important role in formulating a voltage sag governance plan and clarifying the responsibility for the accident. The traditional location method of voltage sag sources is difficult to establish a precise mathematical model and locate the complex voltage sag sources accurately in the complex distribution network. In order to solve these problems, a location method for complex voltage sag sources based on random matrix theory is proposed in this paper. Firstly, the augmented matrix is constructed based on the influence factor data and the operation state data of the distribution network as the data source matrix, and the statistical characteristics of each data are analyzed by using the random matrix theory to determine the suspicious area of voltage sag source. Then, the disturbance signal of each node in the suspicious area of voltage sag source is analyzed by using the atomic algorithm and disturbance active power method, and it can determine the location of each disturbance source in the complex voltage sag event and the cause of voltage sag at each node. Compared with the existing model-based methods, the proposed method in this paper is a data-driven approach, which does not need the physical model and topology information. Furthermore, it can reduce the amount of data and improve the analysis efficiency on the basis of determining the suspicious area of the voltage sag source. Finally, the examples are given to show that the proposed method can accurately locate the disturbance sources in complex voltage sag events.

Directional overcurrent and earth-fault protections for a biomass microgrid system in Malaysia

A pilot-based distance protection scheme for meshed distribution systems with distributed generation

Overcurrent relays are widely used for power systems protection. Transmission side uses more directional type relays, while distribution systems, e.g., radial and ring-main subtransmission systems use nondirectional types. The fault direction may be forward (between relay and grid), or reverse (between relay and source), the normal power flow being from source to the grid. Traditional directional overcurrent relays utilize the reference voltage phasor for estimating the direction of the fault. This requires measurement of both current and voltage using respective sensors. This makes the directional overcurrent relays more costly than the nondirectional type. In this paper, a novel current-only directional detection possibility is highlighted along with theoretical, test signal analysis, challenges and associated solutions. Possible utilizations of the current-only directional relay in the distribution side protection are described, which is a key focus area for enabling the smart grid.

This study proposes a multi‐function power system protective relay hardware design built with various functional hardware processing cores on the field programmable gate array (FPGA). This practical and systematic method lends itself to a paralleled and pipelined hardware emulation of individual signal processing and protection components. Detailed emulation designs are presented for the following protective relays: distance, directional overcurrent, voltage, and frequency protection. The necessary signal processing functions required to operate these relays are also emulated, allowing the protection system to be stand‐alone and fed with instantaneous fault data. Real‐time experimental results are presented to verify the functions of the target hardware relay on the Xilinx® Virtex‐7 FPGA. Case studies provide the efficacy of the multi‐function relay design in terms of accuracy, latency, and resource consumption.

Let-through energy (LTE) refers to the I 2 t or Joule energy that a conductor is exposed to during a fault on the feeder. This energy is influenced by the magnitude of the fault current and time it takes for the protection system to clear the fault. If the LTE exceeds the conductor thermal energy limit, the conductor will get damaged. This concept of LTE evaluation is applied to the inverse definite minimum time (IDMT) current based back-up protection elements on a multisource high-voltage feeder in a hypothetical and actual network. Another method to calculate the relay operating time for IDMT relays was developed based on an average disk speed of electromechanical over-current relay and the proportionality of its speed to the magnitude of the fault current. This method was incorporated into a software application to generate results. These results allow the user to evaluate the conductor LTE exposure, total fault time exposure, the effect of instantaneous fault clearing and the application of auto-reclose cycles. An energy-area evaluation was applied to quantify and evaluate small protection settings changes. The conclusion is that LTE analysis on back-up protection should be considered for high-voltage feeders to ensure that the conductors are protected.

Due to the concerns for reduction of system losses, providing back-up power during loss of the grid, mitigation of energy security risks and conspicuous perturbation of power outages triggered by severe environmental constraints; the modernized distribution grids elicited grid resiliency and reliability enhancement through pragmatic enforcement of the Microgrid (MG) concept with distributed generation. With the proliferating power ultimatum, several intricate factors prone to MG operation modes, bidirectional power flow complexities, management and control of power transfer, varying fault current contribution, and high impedance faults (HIF) customized the network configuration and imperiled the protection system operation and system stability. The propitious utility framework persuaded the prerequisites to embrace the integration of state-of-the-art affiliated Distributed Energy Resources (DERs), which requires assimilated and coordinated studies to emphasize the outcomes of an efficient, reliable, and fast protection scheme for both the grid-connected and islanded modes of operation. Operating modes of distributed generation (DG) will affect the magnitude and direction of fault currents resulting in failure of protection coordination between directional overcurrent relays (DOCRs). In this paper, the negative-sequence based adaptive directional overcurrent relay (NSADOCR) stratagem is proposed. Protection coordination is accomplished by a new adaptive approach, which alters time dial setting (TDS) of negative-sequence overcurrent relay based on the ratio of the normal mode to operating mode of plug setting multiplier function. Furthermore, the direction of fault is attained using phase change in between the pre-fault and superimposed negative-sequence current components. Performance of the NSADOCR is evaluated on the dSPACE controller board, which is interfaced with Real- Time Digital Simulator (RTDSTM) to perform the hardware-in-the-loop (HIL) tests. Extensive simulation studies and hardware results on DG systems exemplify and indicate that the new adaptive technique results in effective protection coordination over the conventional approach, considering various distribution network (DN) modes of operation.

The common form of bus differential protection is to use either a high impedance differential relay or a biased low impedance differential relay. Bus protection using a feeder overcurrent blocking scheme is also widely used in the sub-transmission and distribution levels due to the high cost of the complete bus differential protection solution. IEEE Working Group C-14 of the Power System Relaying Committee published a report on Use of Synchrophasor Measurements in Protective Relaying Application on April 8, 2013. In this report, it was pointed out that the synchrophasor measurements could be used for bus differential relaying in the near future and provided some guidelines on how to realize the bus differential protection using phasor measurements. This paper studies this novel bus differential technology of using synchrophasor data to realize fast, reliable bus differential protection. Together with other bus differential protection, it can satisfy the requirement for bus protection and provide an option for a low-cost complete bus protection system.

Technological developments in protective devices have established the basis for appearance of numerical overcurrent relays (OCRs), which enable the users to apply their desired time‐current characteristics (TCCs). This study propounds novel stepwise and combined stepwise–piece‐wise linear TCCs and presents clear procedure to utilise them for coordinating OCRs in large meshed power systems. The TCCs keep constant time interval between the main/backup relay pairs within entire fault current range. They are examined first by coordinating the OCRs in a 4‐bus power system and by coordinating the ground fault OCRs in a practical 60 kV looped power system. Then, the OCRs of the IEEE 14‐bus test system, which is a rather large meshed power system with 39 OCRs and 102 main/backup pairs, are coordinated by using the novel TCCs. The same relays in the aforesaid power systems are coordinated using some non‐standard TCCs recently introduced in the literature. The comparison verifies that the lowest operating times are achieved by using the novel TCCs. The devised TCCs are simply formed as look‐up tables to be exactly set on the existing industrial relays. This fact is verified by setting them on an industrial OCR, and then, by testing the relay through the current injection method.

Summary form only given. We have discussed a mobile multi-agent based framework to address the aspect of topology discovery in ad hoc wireless network environment. In other words, we have designed a multi-agent based protocol to make the nodes in the network topology aware. Our primary aim is to collect all topology-related information from each node in the network and distribute them periodically (as updates) to other nodes through mobile agents. The notion of stigmergic communication has been used through the implementation of a shared information cache in each node. Moreover, we have used a concept of link stability and information aging based on which a predictive algorithm running on each node can predict the current network topology based on the current network information stored at that node. We have demonstrated through performance evaluation of a simulated system that the use of mobile multi-agent framework would be able to make each node in the network topology aware without consuming large portion of network capacity. This would eventually help us to implement a proactive routing protocol without much overhead. Moreover, as a direct outcome of infiltrating topology information into the nodes, the foundations for designing distributed network management and implementing communication awareness get automatically laid.

Multi-function multi-phase static overcurrent relays, using digital technology available today, provide basic time, (51) (51G) (51N) and instantaneous (50) (50G) (50N) three phase and ground overcurrent protection, and may offer some or all of the following additional functions: undervoltage (27); overvoltage (59); reverse phase sequence (47); negative phase sequence voltage (47N); directional overcurrent (67) (67N); frequency (81O/U); reverse interlocking trip coil monitoring; and battery monitoring. This article describes two applications that use some of the additional functions in such a relay: reverse interlocking, also using the directional overcurrent (67) function; and ground fault detection for systems utilizing high resistance grounding. The first application was installed on a 4160 volt power system which was supplied by two 5000 kVA transformers.

As one of the most prominent power quality problems in the power system, voltage transients threaten the use of many electrical and electronic devices. The rapid and accurate location of voltage drop sources can better define the responsibility between the power supply and the customer. It can also provide a reliable basis for future grid development planning. In this paper, a random forest model is set up to extract data from several electrical characteristics of voltage transients according to the classical voltage transient location method, which is used as training and test samples to input into the random forest model to achieve the upstream and downstream location of voltage transient sources. The random forest model is more accurate than the single decision tree model and the traditional upstream and downstream voltage drop location method. It is possible to determine which of the traditional judgments is more important under this model.