Differential protection method for EHV transmission line based on current traveling wave prediction

Lightning stroke is the main cause of trip-outs of EHV and UHV transmission lines in China Southern Power Grid (CSG). In order to improving the lightning performance of overhead transmission lines, the lightning activities of CSG in 2006 to 2014 was analyzed. It indicates that the coastal Guangdong and Guangxi province are suffered more ground flashes, where the average ground flash density is over 7.98 flashes/km2/year. 306 lightning flashover incidents of 500kV AC, ± 500kV HVDC and ± 800kV UHVDC transmission lines were investigated. It is inferred that about 84% lightning flashover incidents was caused by lightning shielding failure. The corresponding ground wire protection angle for 81% incidents is larger than 5°, and with protection angle decreases, lightning trip-out failures are significantly reduced. Based on the guidelines proposed by IEEE and CIGRE working group, CSG has developed their own lightning risk estimation tool named LPTL. The predication result of six 500kV AC transmission lines was compared to field experience which validates the IEEE recommended method for 500kV AC transmission lines. Further works should be done to revisit the validity of existing risk estimation method for HVDC transmission lines.

Non-unit transient based boundary protection for UHV transmission lines

A transmission line is the most important & integral part of a power system. Due to occurrence of more than 80% of disturbances or short circuit faults in an overhead line, this section has become the most vulnerable part of the electrical system. The differential protection one of the main protection of the transmission line which trip immediately under fault condition. This paper recommends a detail theory about working principle of differential protection & differential relay design for a 400kv transmission line. The simulation results of MATLAB show that the design relay can be used as a main protection scheme for the 400 kv transmission line. This paper presents improved phase comparison technique & cosine function which is notable form of differential protection which compares the phase angle of end currents of transmission line & are able to discriminate the faulty phase accurately using equivalent π model of transmission line. The new technique can successfully differentiate between internal & external faults.

Since China entered the era of high-voltage AC and DC hybrid power grids, many high-voltage transmission lines have been successfully constructed. Due to the high voltage and long transmission distance of high-voltage transmission lines, once a fault occurs, it will cause serious losses. The research on the relay protection method of high-voltage transmission lines based on time-frequency analysis is proposed, which has important contribution value to ensure the stable development of the power grid. The fault signal of the high-voltage transmission line is extracted based on time-frequency analysis. The fault transient component of a high-voltage transmission line is detected by decomposing the fault signal characteristics. The phase correlation protection based on the fault transient component is realized to realize the relay protection of the high voltage power transmission line. The simulation results show that the accuracy of the proposed method is 100%, which verifies the reliability of this method.

This paper presents a real-time wide-area disturbance monitoring and protection (RWADMP) methodology for the backup protection of EHV transmission lines in smart grids (SG). The proposed methodology employs harmonic phasors (1st, 2nd, and 3rd order) of 3-Φ current signals estimated using multi-phasor measurement unit (MPMU) for fault detection, classification, and discrimination of faulty line accurately. Further, the stressed condition such as load encroachment is discriminated from fault. The phasors which were estimated at MPMU are communicated to phasor data concentrator (PDC) at system protection center. MPMU is realized in hardware using NI cRIO, current sensor and GPS module in conjunction with LabVIEW software. Performance of the proposed methodology has been validated on the scale down laboratory models of 400 kV EHV transmission systems such as two-generator two-bus and two-generator three-bus systems. The experimental results show the efficacy of the proposed methodology in improving the overall reliability of the protection system. Also, the proposed methodology is less sensitive to the different fault conditions like fault resistance (FR) and fault distance (FD). Further, the user-friendly LabVIEW monitoring system enhances the visualization of the power system state in PDC. Also, it helps the grid operator to take appropriate action in case of system stressed condition and avoids the mal-operation of the protective devices.

TEQC is a tool which can be commonly used in GNSS data translation, editing, and quality checking, it's widely used in GNSS data preprocessing. This paper has introduced the common syntax and instruction of TEQC when it used in GNSS data processing, also introduced the testing examples of GNSS receiver under three environments: 220KV UHV transmission line environment, 500KV UHV transmission line environment and standard GNSS calibration field, then using TEQC to preprocess and analysis the data. The results showed that: a)The GNSS observation data Efficiency is not effected from radio interference generated by EHV transmission lines; b)Within 25 meters ranges GNSS observation data under EHV transmission line, the multi-path effects (mp1 and mp2 value) significantly exceeded the normal range, and the voltage higher, the multi-path value larger. c)Apart from 50 meters outside EHV transmission line, there is almost no effect about multi-path affects in the high-precision GNSS observation data.

Fault location and distance protection in transmission lines are essential smart grid technologies ensuring reliability of the power system and achieve the continuity of service. The objective of this chapter is to presents an accurate algorithm for estimating fault location in Extra High Voltage (EHV) transmission lines using Artificial Neural Networks (ANNs) for high speed protection. The development of this algorithm is based on disturbed transmission line models. The proposed fault protection (fault detection/classification and location) uses only the three phase currents signals at the one end of the line. The proposed technique uses five ANNs networks and consists of two steps, including fault detection/classification and fault location. For fault detection/classification, one ANN network is used in order to identify the fault type; the fault detection/classification procedure uses the fundamental components of pre-fault and post-fault sequence samples of three phase currents and zero sequence current. For fault location, four ANNs networks are used in order to estimate the exact fault location in transmission line. Magnitudes of pre-fault and post-fault of three phase currents are used. The ANNs are trained with data under a wide variety of fault conditions and used for the fault classification and fault location on the transmission line. The proposed fault detection/classification and location approaches are tested under different fault conditions such as different fault locations, different fault resistances and different fault inception angles via digital simulation using MATLAB software in order to verify the performances of the proposed methods. The ANN-based fault classifier and locator gives high accuracy for all tests under different fault conditions. The simulations results show that the proposed scheme based on ANNs can be used for on-line fault protection in transmission line.

Using sampled values in line differential protection – Analyzing the scheme feasibility and protection performance under communication stress scenarios

Application of Haar functions for transmission line and transformer differential protection

Until the invention of the transistor in 1948, power system control and protective relays were almost exclusively electro-mechanical. There were a few special applications, such as automatic synchronizing of ac generators, that used vacuum tubes - but these were clearly the exceptions. The physical structures of these electro-mechanical relays were robust, with current and potential coils designed to pass one minute power frequency production tests at 2000 volts. In addition, they were required to pass design (type) impulse tests at 5 kV. Insulation failures were rare. The most common failure modes in the field were dirty contacts, worn or dirty bearings (on induction cup or induction disc relays), or incorrect settings. Routine preventive maintenance was scheduled to address these problems. A few years after the invention of the transistor in 1948, some transistors designs became available that could withstand the typical extreme temperatures in electric utility substations. Their capability as solid state amplifiers was very attractive to the designers of protective relays, as the search was always on for more sensitive and faster, yet secure, products for transmission line relaying. These products -“solid state relays” (or sometimes called “static terminals”) - were often applied for EHV (345, 500 and 765 kV) transmission line protection to reduce fault clearing times. Relays for other functions such as transformer differential protection and automatic synchronizing also used transistors.

A novel algorithm for improving the differential protection of power transmission system

This paper presents an improved current differential protective principle. Marti model of the transmission line is applied in this principle, which place emphasis on solving frequency-dependent line parameters. The operating current expressions for an internal fault are also deduced in frequency domain. Finally, simulating comparison have been carried out between the proposed protective principle and Bergeron model based protection for Chinese 1000kV UHVAC test demonstration project. Simulation results show that this improved principle has high reliability for both internal and external faults. The 1000kV UHVAC transmission lines which are being constructed in China, in hybrid with HVDC links, will form the backbone of the future Chinese grid to cope with the requirement of increased power transmission over longer distances. It is important for relay protection to secure normal operation of UHV grid. The split-phase current differential protection is first applied owing to its rapidity and absolute selection. But due to the negative impact of large distributed capacitive currents, the reliability and sensitivity of traditional current differential relay decay seriously (1). Therefore, some scientists proposed the novel protective principles, which can not be affected by capacitive current (2), (3), (4). Reference (2) put forward a principle of pilot differential protection based on Bergeron model. It describes that currents at both sides of a line could be calculated by means of Bergeron model formula firstly, and then compared with the measured currents at the same side. This comparative result is just operating current in this protective scheme. Here the calculated currents and the measured currents at the same side are taken for comparison, by contrast in a traditional current differential relay a current value at one side is subtracted from that at the opposite side. The advantage lies in the Bergeron model-based principle is independent on the capacitive current, and it is unnecessary to calculate the compensating current. It must be noted that a transmission line is assumed to have constant parameters in the Bergeron model. However it has long been recognized that line parameters vary with frequency in actual electromagnetic transient process. Therefore if Bergeron model formulas are used, there exits calculating errors which would cause the accuracy and sensibility of relays reduce obviously. In order to solve this problem, an improved current differential protective principle is presented in this paper. The principle applied Marti model of the transmission line, which is based on traveling wave propagation. The frequency-dependent characteristics of line parameters are taken into account. By using of this approach, we will get a more accurate result. In addition, a new criterion adapting to this principle are presented. Finally, by making use of EMTPE and MATLAB software, the improved current differential protective principle, and the protection based on Bergeron model are both simulated on the first 1000kV UHVAC transmission line in China, also called as the 1000kV UHVAC test demonstration project. Simulating comparison shows that this improved principle is correct and reliable.

Longitudinal current differential protection is often used as the main protection of ultra-high voltage (UHV)/extra-high voltage (EHV) transmission lines. It's sensitivity and selectivity will be severely influenced by the considerably increased distributed capacitive current with the increase of voltage level and transmission distance. In this study, a novel UHV/EHV transmission line protection is proposed based on longitudinal tapped impedance. For sound transmission line or transmission line with external faults, the calculated impedance is approximately equal to the capacitive reactance of the line. If internal faults occur on the line, the computed impedance of the faulty phase is approximately equal to the parallel value of the line capacitive reactance and the fault resistance. The proposed protection does not require the compensation of capacitive current and is not affected by load current and system impedance. This new protection principle has an improved selectivity and natural phase selection ability, and very high sensibility for high resistance faults. The correctness and effectiveness of the proposed protection have been verified by simulation tests.

An electric power system is often faced with disturbance problems. The 150 kV transmission line from GI Ngimbang to GI Babat 1 experienced several disturbances due to a single-phase short circuit to the ground. The approach to determining the value of the impedance is by considering the value of the capacitance using the Phi Nominal Method with the center of the capacitance value located at the ends of the line which is divided equally in size. The main protection system used on the transmission line is the Distance relay, but the Distance relay is still not reliable and responsive. So with these shortcomings, it can be overcome by using a Line Current Differential transmission line protection system, it is proven that the Differential Line Current performance can work well. The research was conducted to analyze the performance of the Line Current Differential protection relay on the 150 kV Ngimbang-Babat 1 transmission line by calculating the impedance and capacitance values. The calculation is simulated in modeling the system against short circuit faults in determining the protection relay settings. From the results of the study, it was found that the accuracy of the Line Current Differential setting value can work by providing a disturbance signal to the power breaker (PMT) to perform tripping when a disturbance occurs in an area that is secured by a protection relay (internal fault), while the protection relay cannot work when an external disturbance occurs. secured area protection relay(external fault).

The shunt large capacitor, on both sides of voltage source converter based HVDC (VSC-HVDC) transmission lines, will rapidly discharge to the fault point when a fault occurs. The system side can be equivalent to the shunt large capacitance in the fault component model. According to this characteristic of the VSC-HVDC system, a novel pilot protection scheme for VSC-HVDC transmission lines based on parameter identification is proposed in this paper. The protection principle can distinguish internal faults from external faults by identifying the capacitance on two terminals with the time-domain algorithm. The capacitance on two terminals can be accurately identified simultaneously when an internal fault occurs, while the capacitance at both ends cannot be accurately identified simultaneously when an external fault occurs. Therefore, a pilot protection criterion is constructed. The simulation results show that the protection scheme can distinguish internal faults from external faults reliably and quickly, and it is not affected by transition resistance, distributed capacitance of lines, and the control mode. In addition, the method can be implemented easily with simple computation and has certain practical value.