Thomas Bretterklieber

A Feasibility Study on Autonomous Online Condition Monitoring of High-Voltage Overhead Power Lines

For electric power transmission, high-voltage overhead power lines play an important role, as the costs for power transmission are comparatively low. However, the sag of the conductors (e.g., due to temperature variations, aging, or icing of conductors as a result of extreme weather conditions) may increase safety margins and limit the operability of these power lines. Furthermore, heavy loads due to icing or vibrations excited by wind streams increase the risk of line breakage. With online condition monitoring of power lines, critical states can be detected early, and appropriate countermeasures can be applied. In this paper, we investigate possibilities for monitoring devices that are directly mounted onto a conductor. The feasibility of powering the device from the electric field, protection of electronic circuitry from strong electric fields, and data transmission by means of a wireless link is demonstrated, as well as its operability during the presence of strong magnetic fields due to high currents and transient signals due to partial and spark discharge events.

A Combined Inductive–Capacitive Proximity Sensor for Seat Occupancy Detection

This paper presents a simple and efficient seat occupancy detector. A seat occupancy detector is an integral part of the airbag safety system and, in its simplest form, provides the (occupied or vacant) status of the seat to the airbag control unit. Although the occupancy sensing methods based on a capacitive principle are efficient, they typically require electrodes to be placed in the surface layer of the sitting and backrest areas of the seat. The proposed sensor uses a simple electrode structure, and it is placed below the seat foam in the sitting area of the seat. These features promise a less-expensive sensor as it can be easily manufactured and installed in a seat. The new sensor combines inductive and capacitive proximity sensing principles. The sensor detects the presence of an occupant exploiting the shielding effect of the electric field while its inductive proximity feature senses the presence of conductive objects (e.g., laptop) that may be placed in the seat and helps to achieve reliable occupancy sensing. The measurement system uses a signal conditioning unit based on a carrier frequency principle. A prototype sensing system has been built, and its application as a seat occupancy sensing system in a vehicle has been verified. The developed system successfully senses human proximity and distinguishes it from other conductive objects.

Seat Occupancy Detection Based on Capacitive Sensing

This paper presents a simple yet efficient seat occupancy detection scheme based on a capacitive sensing principle. Parameters such as the presence, position, and type of the occupant of the seat are essential for successful air-bag control in vehicles. Without this information, during a collision, the air bag may be inflated to an empty seat (ES), wasting it and, hence, leading to allied repair and reinstallation. Also, if deployed, it can cause fatal injuries to infants in rear-facing infant seats. The proposed capacitive sensor system detects the presence of an occupant and provides information about the occupants position. A prototype occupancy detection system has been developed, and the feasibility of the new method has been validated through practical tests. The developed system takes 200 mus to complete a measurement and, hence, promises real-time operation of the air-bag system. The presented method employs a carrier-frequency method and lock-in-amplifier technique to measure the capacitances. Thus, the influence of external electromagnetic fields on the final result is kept low.

Energy Harvesting for Online Condition Monitoring of High Voltage Overhead Power Lines

For electric power transmission, high voltage overhead power lines play an important role as the costs for power transmission are comparatively low. However, the environmental conditions in many geographical regions can change over a wide range. Due to the high voltages, adequate distances between the conductors and objects in the environment have to be ensured for safety reasons. However, sag of the conductors (e.g. due to temperature variations or aging, icing of conductors as a result of extreme weather conditions) may increase safety margins and limit the operability of these power lines. Heavy loads due to icing or vibrations excited by winds increase the risk of line breakage. With online condition monitoring of power lines, critical states or states with increased wear for the conductor may be detected early and appropriate counter measures can be applied. In this paper we investigate possibilities for monitoring devices that are directly mounted onto a conductor. It is demonstrated that such a device can be powered from the electric field around the conductor and that electronic equipment can be protected from the strong electric and magnetic fields as well as transient signals due to partial discharge events.

Versatile Sensor Front End for Low-Depth Modulation Capacitive Sensors

Low-depth modulation capacitive sensors, i.e. sensors where the capacitance variations caused by a measurand are only a small fraction of the total capacitance, are frequently encountered in measurement problems. Furthermore, also a conductance (e.g. due to parasitic conductive staining) between the sensor electrodes may affect the capacitance evaluation. We have implemented a capacitive sensor interface in a 0.25 mum CMOS process capable of measuring both conductive and capacitive coupling. The sensor interface provides an offset capacitance compensation and an offset conductance compensation such that a low-depth capacitance modulation can be mapped onto the full scale range of an analog to digital converter. Experimental results for a prototype sensor interface with a capacitive slider array are presented.

Strong and Weak Electric Field Interfering: Capacitive Icing Detection and Capacitive Energy Harvesting on a 220-kV High-Voltage Overhead Power Line

This paper focuses on problems which arise when both a power-harvesting system based on a capacitive principle and a capacitive measurement device [i.e., a capacitance-to-digital converter (CDC)] are used in one electronic system to build up an autonomous measurement device for icing detection on a high-voltage overhead power line. The overall capacitance of the measurement circuitry between the conductor and the energy harvester shell must remain within a well-defined range to keep the energy-harvesting circuitry operational and to operate the CDC within its specifications. A decoupling solution for both the data path and the power supply unit has been implemented and verified experimentally in a high-voltage laboratory and a field test.

Wireless Communication and Power Supply Strategy for Sensor Applications Within Closed Metal Walls

Passive or semiactive wireless sensors, i.e., sensors that require neither wires nor external power supply/batteries, are attractive for many measurement problems. Standard approaches based on Radio Frequency Identification technology usually have difficulties when a fairly conductive matter such as steel or a large amount of water is in the vicinity of the devices. This paper investigates methods for power and data transmission, even through the metal walls, e.g., of a tank or a pipe using super low frequency carrier signals. The feasibility is demonstrated by means of finite-element analysis and laboratory experiments and validated with a prototype setup for both a steel pipe and a tin container. Experimental results for capacitive fill-level measurement inside a metallic container are reported.

A combined inductive-capacitive proximity sensor and its application to seat occupancy sensing

This paper presents a simple yet efficient proximity sensor obtained by combining inductive and capacitive sensing principles. Capacitive proximity sensors based on shielding of electric field are known for detecting presence of humans in its vicinity. Such systems may fail to distinguish the proximity of a human from grounded conductive objects. A novel, cost effective, sensing scheme that uses a single sensor, which performs both the inductive and capacitive proximity mode of operation is proposed in this paper. The measurement system uses a signal conditioning unit based on a carrier frequency principle. A prototype sensing system has been built and its application as a seat occupancy sensing system in a vehicle has been verified. The developed system successfully senses human proximity and distinguishes it from other conductive objects.

A Novel Seat Occupancy Detection System based on Capacitive Sensing

This paper presents a simple and efficient seat occupancy detection scheme based on a capacitive sensing principle. Parameters such as presence, position and type of seat occupant are essential for successful air bag control in vehicles. In the absence of such information, on an accident, the air bag may be inflated to a vacant seat leading to its wastage and hence the associated repair and reinstallation. Also, if deployed, it can cause fatal injuries to infants in rear-facing infant seats. The proposed capacitive sensor system detects presence of an occupant and provides information about the occupant position. The developed system takes 200 mus to complete a full set of measurements hence promises dynamic operation of the air bag system. The presented method employs a carrier frequency method and lock-in- amplifier technique to measure the capacitances. Thus, the influence of external electromagnetic fields on the final result is minimal.

A warning system for chainsaw personal safety based on capacitive sensing

This paper presents a capacitive proximity sensor that helps to improve the personal safety features of a chainsaw. Even though chainsaws are equipped with safety features such as kickback protection and chain brakes, related accidents reported each year are huge in number. Safety can be enhanced to a high degree, by integrating human proximity sensing features to the chainsaw and hence activating its brake and turn-off the chainsaw automatically in the occurrence of an accident. This paper proposes a capacitive sensor to detect human proximity near the guide bar and chain of a chainsaw. A prototype sensing system has been developed and tested, validating the usefulness of the proposed scheme. The sensor capacitances are measured using a carrier frequency method with synchronous detection technique. The developed system provides information about human proximity at least for every 200 mus and hence enables the control unit to react in realtime. The system successfully distinguishes between proximity of human and wood. The developed system senses human proximity up to 15 cm from the chainsaw.