Impulse electric field measurement should satisfy some special requirements such as intensive signal amplitude, appropriate insulation, broadband response, and small size. Three types of integrated electro-optic sensors, designed and fabricated for measuring intensive impulse electric field, was implemented in this paper. The theoretical concerns and specific characteristics of these integrated electro-optic sensors were illustrated in terms of their structures and key parameters. The time domain input/output characteristic and frequency response of the sensors were examined too. Comparison of the time domain characteristics of these sensors revealed that the mono-shield sensor was more efficient than those with antennas in measurable amplitudes, which is critical for high electric field measurement in gas breakdown research. In addition, the application of the sensor in the lightning impulse experiment upon air gap not only verify the existence of streamer charge but also ensured that this sensor is expected to be widely used in transient measurement investigations such as the measurement of lightning electric field, air breakdown procedure, and maybe surface discharge.

Design and application of an integrated electro-optic sensor for intensive electric field measurement

In order to meet the demands for the electric field measurement along the composite insulators simultaneously, such as intensive signal, fine insulation, passive and small size, a novel measurement system based on the core device, the integrated electro-optic sensor, was developed. First, the theory of the system and the sensor were introduced. Second, after fabrication, the input/output character was obtained and the calibration was implemented between two parallel square metal planes under power frequency. By optimum design, this kind of novel sensor was suitable for insulated, intensive (> 250 kV/m), small size (55 mm x 2 mm x 1 mm) electric field measurement. Third, the axial and radial electric field distribution of the insulators were measured carefully in laboratory, and by combining the BEM and CSM method, the electric field of the same insulators was numerically calculated. Finally, the measurement and calculated results of electric field distribution were compared and the relationship between them were analyzed. This comparison verified the suitability and importance of the measurement system.

Measurement of electric field distribution along composite insulators by integrated optical electric field sensor

Electric field sensing schemes, using Lithium Niobate (LiNbO3) electro-optical retarders, are being studied since several years. A birefringent LiNbO3 electro-optic waveguide (BEOW) has been used as an optical retarder and simultaneously as electric field sensor. The optical delay acts as the carrier of the sensed electric field. The modulated optical delay is transmitted to a measurement receiver, which is based on a second optical retarder acting as demodulator. The sensed electric field can be detected only when the sensor and demodulator are optically matched. An important issue when using BEOW's is their inherent sensitivity to temperature, which manifests as dc-drift at the output of the sensing-detection process and limits practical applications. A novel electric field sensing scheme, using LiNbO3 unbalanced Mach–Zehnder interferometers instead of BEOW's is described in this paper. This new scheme contributes to three main aspects related to electro-optic sensing: sensing-detection of electric fields using matched optical delays; proposes a simple technique for linearizing the sensing-detection process and demonstrates a strongly reduction of the dc-drift phenomena. The contributing aspects are novel and are described in this paper. Such features become very attractive for implementing practical electric field sensing schemes using LiNbO3 integrated optics devices.

Novel Electric Field Sensing Scheme Using Integrated Optics LiNbO3 Unbalanced Mach–Zehnder Interferometers and Optical Delay-Modulation

This thesis presents a method of detecting electrical islan d i low voltage distributed generator networks by measuring negative sequence impedance difference s between islanded and utility connections. Extensive testing was conducted on a commercial building an d 25 kV distributed generator fed network by measuring naturally occurring and artificially injected negative sequence components. Similarly, this technique was tested using the IEEE 399-1990 bus test case us ing the EMTP software. The practical measurements have been matched to simulations where furthe r syst m performance characteristics of detecting power system islands has been successfully demon strated. Measured results indicate that unbalanced load conditions are naturally occurring and readi ly measurable while deliberately unbalanced loads can increase the accuracy of negative sequence impeda nce islanding detection. The typically low negative sequence impedance of induction motors was found t o have only a small effect in low voltage busses, though large machines can effect the threshold sett ing . Careful placement of the island detector is required in these situations. The negative sequence impe danc measurement method is an improvement on previous impedance measurement techniques for isla nding detection due to its accuracy, and distinctly large threshold window which have challenged pr evious impedance based islanding detection techniques.

Negative sequence impedance measurement for distributed generator islanding detection

We have measured the temporal duration of 45 MeV picosecond electron beam bunches using a noninvasive electro-optical (EO) technique. The amplitude of the EO modulation was found to increase linearly with electron beam charge and decrease inversely with distance from the electron beam. The rise time of the temporal signal was limited by our detection system to ∼70 ps. The EO signal due to ionization caused by the electrons traversing the EO crystal was also observed. It has a distinctively long decay time constant and signal polarity opposite to that due to the field induced by the electron beam. The electro-optical technique may be ideal for the measurement of bunch length of femtosecond, relativistic, high energy, charged, particle beams.

Electro-optical measurements of picosecond bunch length of a 45 MeV electron beam

A new optical high voltage sensor using a Pockels microsingle crystal in a longitudinal modulation arrangement is presented. A prototype of the sensor is assembled and shows an advantage of directly measuring voltage levels up to 50 kV without any potential divider in a wide frequency bandwidth of direct current to 116 MHz. In conventional Pockels sensors, acoustic resonance driven by piezoelectric effect introduces oscillatory components to signals obtained from measurements of lightning impulse voltages. In the new sensor, the measured signal is free from the oscillatory components. An accuracy of 1.9% in good agreement with predicted values is obtained from the lightning impulse voltage measurement.

Muslum Cengiz Taplamacioglu

Papers

Optical high voltage measurement using pockels microsingle crystal