Wing Kin Lee

On Wireless Sensors Communication for Overhead Transmission Line Monitoring in Power Delivery Systems

The transmission of energy is monitored in the smart grid through deploying sensors in all the components, including the overhead transmission lines. There are many poles/towers supporting a long overhead transmission line. Naturally, sensors are deployed on the location close to the poles/towers on each span. Due to the limited transmission range of the wireless transceiver module of a sensor, researchers generally assume that data generated by a sensor have to be delivered to the substation through a set of sensors in-between. This results in a linear network model. In this paper, we first analyze the performance of this model in handling the traffics extracted from an existing testbed. We realize that the linear network model may not be sufficient to support future smart grid applications which may have diversified requirements on data delivery. We then study a new network model in which sensor/relay nodes can also communicate with other nodes using a wide area network such as the cellular network. In this new model, the network formed can be reconfigured based on the application requirements to deliver information to the substations efficiently and effectively.

Novel Application of Magnetoresistive Sensors for High-Voltage Transmission-Line Monitoring

High-voltage transmission lines are responsible for transmission of electric power. Their sag and electric current are important parameters for transmission-line monitoring. In this paper, a simple and promising method based on magnetoresistive sensors is proposed for transmission-line monitoring. This is a noncontact method and its installation is simple without the need for power cut. The method involves measuring emanated magnetic field from a line conductor at the ground level and, then, calculating the source position and current inversely. A proof-of-concept laboratory setup was constructed and a series of experiments were carried out for demonstration. This method can handle complicated transmission-line configuration by integrating the stochastic optimization approach into the inverse electromagnetic calculation. It was tested with the computational simulation of a 500 kV transmission-line configuration. The result shows the feasibility of using this transmission-line monitoring method in reality.

Operation-State Monitoring and Energization-Status Identification for Underground Power Cables by Magnetic Field Sensing

In this paper, a novel nondestructive method based on magnetic field sensing is proposed for underground power cable operation-state monitoring and energization-status identification. The magnetic field distribution of the cable is studied using finite element method (FEM) for the power cable operating in different states, i.e., current-energized state (the cable is energized and carries load current) and voltage-energized state (the cable is energized but carries no load current). This innovative method can reconstruct all the source parameters of the cable based on a set of measured magnetic field values. Stochastic optimization technique is applied to realize the reconstruction based on the measured magnetic field. The technology is developed with an artificial immune system algorithm that is able to find out the global optimum with high probability even if very little knowledge about objective function is provided. Application of this method is demonstrated on an 11 kV cable with metallic outer sheath. The results highly match with the actual source parameters of the cable. For application in practice, possible limitations introduced by the nonidealistic of magnetoresistive sensor on magnetic field measurement are discussed and corresponding solutions are suggested. An experimental setup is constructed and the test results are used for the demonstration of this method. This paper shows that the proposed method is able to monitor the operation states of an underground power cable with high accuracy. Engineers can also correctly identify the energization status of the target cable during onsite maintenance. This method is adaptable to other kinds of power cables simply by updating the geometrical and material parameters of the cable in the FEM computation. Moreover, this is an entirely passive method and does not need any active signal injection into the cable.

Underground Power Cable Detection and Inspection Technology Based on Magnetic Field Sensing at Ground Surface Level

In this paper, a novel technique based on magnetic field sensing is proposed for underground power cable detection and inspection. In this technique, the current sources of the underground power cables are reconstructed based on a set of measured magnetic field values at the ground surface level emanated by the electric currents carried by the underground power cables. The stochastic optimization technique developed with an artificial immune system algorithm is applied to realize the reconstruction. The principle of this method was proved and verified experimentally by our laboratory setup. Application of this method was demonstrated on the simulation models of 11- and 132-kV underground power cables. The reconstruction results of the electrical and spatial parameters of the cables match accurately with the actual source parameters of the cables in the models. This paper shows that the proposed method is able to remotely detect the horizontal locations and vertical depths of underground power cables with high accuracy at the ground surface level requiring no prior knowledge about the exact locations of the cables. Thus, it can be potentially used to develop a portable locator for providing a map of the underground electrical cables by simultaneous detection of multiple power lines. This method can also enable engineers to correctly inspect the operation states of the target cables during onsite maintenance. This technique is applicable to various laying conditions and cable configurations (three core or single core) of the underground power cables. In addition, this is an entirely passive method and does not need any signal injection into the cables.

Train Detection by Magnetic Field Measurement with Giant Magnetoresistive Sensors for High-Speed Railway

Train detection, as part of the railway signaling system, is important for safe operation of high-speed railway. The recent flourishing development of high-speed railway stimulates the research need of train detection technology to enhance the safety and reliability of train operation. This paper proposes a new technique for train detection through magnetic field measurement by giant magnetoresistive sensors. This technology was studied by the analysis of magnetic field distribution in the high-speed rail system obtained from modeling and simulation. The results verify the feasibility for detection of train presence, number of rolling stocks, speed, and length. It can overcome the limitations of track circuits and provide additional measurement capabilities to the signaling system. This detection system can be built with low cost and minimal maintenance load as well as compacted construction. Therefore, it may serve as a new train detection system to help improve the current systems, enhancing and promoting the safety and reliability of high-speed rail system.

On-Site Non-Invasive Current Monitoring of Multi-Core Underground Power Cables with a Magnetic-Field Sensing Platform at a Substation

Current monitoring can facilitate preemptive action in electrical distribution network, so as to relieve power congestion, improve transmission efficiency, and ensure network reliability. The non-invasive current sensing devices are promising since they do not require contacting hazardous high voltage and their installation is much easier compared with invasive current sensing devices. However, the existing non-invasive current sensing devices, such as current clamps and Rogowski coils are only applicable for measuring single-core underground power cables. In this paper, we established a non-invasive technique, that can monitor the currents of a multi-core underground power cable by measuring the emitted magnetic field around the cable surface. The additional magnetic fields generated by induced and leakage currents on the cables were firstly evaluated. Magnetoresistive (MR) sensors in a circular array were adopted to measure magnetic field around the cable surface, and a triple-layer shielding was designed to reduce the effects of external interference. Regarding intrinsic noise in MR sensors (e.g., 1/f noise and thermal noise), magnetic flux concentrators were supplemented to improve the signal-to-noise ratio. The developed platform was tested in a substation, and the reconstructed results closely matched the real geometrical configuration and current records of the tested cable. Apart from the non-invasive feature, the platform also shows great potential to improve the sensing capability of current amplitude and frequency compared with CTs by adopting MR sensors.

Non-Contact Capacitive-Coupling-Based and Magnetic-Field-Sensing-Assisted Technique for Monitoring Voltage of Overhead Power Transmission Lines

Adopting non-contact capacitive coupling for voltage monitoring is promising as it avoids electrical connection with high-voltage transmission lines. However, coupled voltage transformation matrix to correlate voltage of overhead transmission lines and induction bars has not been achieved mathematically due to the lack of equivalent electric circuit model for analyzing the physical phenomenon. Moreover, exact spatial positions of overhead transmission lines are typically unknown and dynamic in practice. In this paper, a technique based on non-contact capacitive-coupling and assisted by magnetic-field sensing for monitoring voltage of overhead transmission lines was designed and implemented. The technique in this paper is demonstrated on a single-circuit transmission line as an example, while it is also applicable for multi-circuit transmission lines. The capacitive coupling between overhead transmission lines and induction bars were modeled as lumped capacitors, and then, the equivalent electric circuit model was established. The coupled voltage transformation matrix to correlate voltage of overhead transmission lines and induced voltage of induction bars mathematically was formed accordingly. This paper was also carried out to analyze the effect of ground wires, sensitivity of induction bars, the ability of high-frequency transient measurement, and the intrinsic capacitance of a measurement instrument. The exact spatial positions of overhead transmission lines were acquired by integrating magnetic-field sensing with the stochastic optimization algorithm. The methodology was verified by simulation on the 10-kV single-circuit three-phase overhead transmission lines taking non-ideality of signal measurement in account, and wavelet de-noising algorithm was supplemented to filter the interferences. A scaled testbed to experiment the technique was built to monitor 220 V overhead transmission lines in the lab, and also the typical waveform of a high-frequency switching surge (up to 1 kHz), which was generated by a programmable ac source. The reconstructed results match well with the actual values. This technique can largely improve transient-fault identification over traditional potential transformers by the virtue of the increased upper measurement limit and bandwidth through capacitive coupling. Moreover, it can be implemented with low-cost copper induction bars and compact magnetoresistive sensors, enabling large-scale application to realize sectional monitoring in the wide area.

Energization-Status Identification of Three-Phase Three-Core Shielded Distribution Power Cables Based on Non-Destructive Magnetic Field Sensing

Three-phase three-core distribution power cables are widely deployed in power distribution networks and are continually being extended to address the ever-increasing power demand in modern metropolises. Unfortunately, there are high risks for the repair crew to operate on energized distribution power cables, which can cause deadly consequences such as electrocution and explosion. The predominant energization-status identification techniques used today are either destructive or only applicable to un-shielded power cables. Moreover, the background interferences affect the sensing technique reliability. In this paper, we have developed a non-destructive energization-status identification technique to identify energized three-phase three-core distribution power cables by measuring magnetic fields around the cable surface. The analysis shows that the magnetic-field-distribution pattern as a function of azimuth around the cable surface of the energized (current- or voltage-energized) three-phase three-core distribution power cable is distinguishable from the de-energized one. The non-idealities of phase currents and cable geometry were also discussed, and the proposed method still works under these circumstances. The sensing platform for implementing this technique was developed accordingly, consisting of magnetoresistive sensors, a triple-layered magnetic shielding, and a data acquisition system. The technique was demonstrated on a 22-kV three-phase three-core distribution power cable, and the energized status of the cable can be successfully identified. The proposed technique does not damage cable integrity by piercing the cable, or exposing the repair crew to hazardous high-voltage conductors. The platform is easy to operate and it can significantly improve the situational awareness for the repair crew, and enhance the stability of power distribution networks.

Voltage-energized status identification of three-phase underground power cables via non-destructive magnetoresistive sensor

Identification of voltage-energized cables can potentially prevent deadly consequences such as electrocution and explosion. We find that the voltage-energized status can be identified by measuring the distribution pattern of magnetic flux density around the cable surface. The weak magnetic fields emitted from the charging current of the voltage-energized cable are measured by sensitive magnetoresistive sensors in high spatial resolution. The feasibility of this non-destructive platform was verified on a 22 kV three-phase underground power cable. The platform can improve situational awareness of serviceman dramatically.

A Laboratory-Based Smart Grid Sensor Network Testbed

A laboratory-based sensor network testbed for Smart Grid was developed at the Smart Grid and High Power System Laboratory of The University of Hong Kong. The setup is featured by a scaled transmission-line model, visualization of sensor measurement, optical communication network, and integration with global positioning system (GPS). The transmission-line model consists of a power cable and towers in which various types of sensors including magnetic sensors, infrared sensors, strain gauges, and accelerometers are installed to monitor the condition of the transmission line and the transmission towers. Magnetic sensors and infrared sensor are employed as advanced sensors which can provide more accurate and comprehensive information of the transmission line. The sensor data is transferred to the computer for analysis and visualization. Graphical user interface (GUI) was designed in LabVIEW to integrate the data acquisition and display of measurement results including cable position, inclination and vibration of the tower, frequency and waveform of the cable current. The host computer also forms an IP network with five remote computers, via optical fiber and optical interface card, for testing various communication protocols. The topology and connectivity of the network is graphically displayed. The sensor network is integrated with GPS and can perform synchronized measurement with the GPS timing. This sensor network testbed provides a platform for the implementation testing, experimentation, and feasibility evaluation of new sensor applications under test in Smart Grid.