Application Cases

Experiment Name: Study of Fundamental Sensor Characteristics

Research Direction:
Designing an optical voltage sensor based on the inverse piezoelectric effect and fiber Bragg grating (FBG) sensing principles to achieve all-fiber transmission and measurement in power grid voltage sensing, thereby enhancing the electromagnetic shielding performance of the voltage sensing unit and maximizing optoelectronic isolation. The primary research focus includes the fundamental design principles of the sensor, the demodulation principles of grating signals within the sensor, and the corresponding energy coupling models, as well as circuit and optical path models. This involves the fabrication of a piezoelectric-grating voltage sensor and the establishment of a voltage sensor calibration and testing platform in the laboratory to study and analyze the sensor's fundamental characteristics.

Test Equipment:
High-voltage amplifier, signal generator, oscilloscope, broadband light source, piezoelectric optical sensor, photodetector, etc.

Figure 1: Schematic Diagram of the Sensor Calibration Testing Platform

Experimental Procedure:
To study the performance of the designed sensor, a calibration and measurement platform for the inverse piezoelectric-grating voltage sensor was established in the laboratory. The equipment used in this testing platform can be categorized into optical and electrical devices. Optical devices primarily include a broadband laser source and a photodetector, which provide broadband optical signals and detect output optical signals, respectively. Electrical devices mainly consist of a function generator, impulse voltage generator, high-voltage amplifier, and oscilloscope, which provide and detect various types of voltage signals.

In the experimental design, the electrical equipment includes an arbitrary function waveform generator, a high-voltage amplifier, an oscilloscope, and an impulse voltage generator. The oscilloscope has a bandwidth of 70 MHz and a sampling rate of 1.0 GS/s. The arbitrary function waveform generator can provide 12 standard waveforms and arbitrary waveform voltage signals, with a minimum adjustment resolution of 1 mV. The high-voltage amplifier has an amplification factor of 2000× and, when used in conjunction with the arbitrary function waveform generator, provides various high-amplitude voltage input signals for the piezoelectric optical sensor.

The sensor calibration testing platform is shown in Figure 1. The signal generator and high-voltage amplifier are used together to provide the sensor with fundamental wide-bandwidth, multi-amplitude signals such as sine waves, square waves, and triangular waves. A broadband light source provides the optical signal for the sensor. The sensor's output optical signal is transmitted via optical fiber to the photodetector, where photoelectric conversion is performed. The converted signal is then transmitted via cable to the oscilloscope for display. Before testing, the integrity of the optical path within the sensor must be verified to ensure reliable signal transmission. Specifically, the connectivity of the three ports of the optical circulator, the connection segments between circulators, and the fiber connecting the sensor output to the photodetector should be checked.

Experimental Results:
The sensor was subjected to fundamental sensing characteristic calibration tests, including power frequency response testing, frequency response testing, three basic waveform tests, and impulse voltage testing.

Figure 2: Sensor Power Frequency Response Test Results

In the power frequency response test, as shown in Figure 2, the sensor's power frequency response is linear, with a linear fitting accuracy exceeding 99.9%. The results indicate that for every 1 kV change in the applied voltage, the sensor's photodetector output voltage amplitude is 217.54 mV. The linearity of the sensor's power frequency response is attributed to its operation within the linear region when the applied voltage signal is in the range of 0.5 kV to 5 kV, as shown in the lower-right corner of Figure 2. Meanwhile, the sensor's signal-to-noise ratio is measured as 11.58:1, and the maximum error is 3.7%, meeting the requirements of Level 3 in the relevant international standards IEC 60044-7 and IEC 61869-5:2011. The testing, analysis, and comparison with international standards of the sensor's power frequency response demonstrate that the sensor can meet the requirements for general power frequency voltage signal testing in power grids, providing a preliminary foundation for application.

Figure 3: Sensor Frequency Response Test Results

In the frequency response test, as shown in Figure 3, the sensor's frequency response is generally flat within the frequency range of 50 Hz to 20 kHz. At frequencies of 7 kHz and 17 kHz, minor fluctuations are observed in the sensor's response, but the maximum fluctuation remains within the ±3 dB range. Overall, the sensor's frequency response is flat within the 50 Hz to 20 kHz range.

Figure 4: Sensor Sine Wave Response Test Results at 50 Hz, 3 kHz, 8 kHz, and 20 kHz

In the three basic waveform response tests, Figure 4 shows the sensor's sine wave response test results at frequencies of 50 Hz, 3 kHz, 8 kHz, and 20 kHz. The results indicate that the sensor responds adequately to sine wave input signals at all tested frequencies. At 20 kHz, due to the frequency limitations of the high-voltage amplifier, the input signal resembles a smoothed triangular wave, and the corresponding output signal amplitude decreases accordingly. Overall, within the 20 kHz bandwidth, the sensor's response to sine wave signals is good, with no significant distortion or delay, further demonstrating the sensor's excellent fundamental voltage measurement characteristics within the 50 Hz to 20 kHz range.

Recommended High-Voltage Amplifier: ATA-7020

Figure: ATA-7020 High-Voltage Amplifier Specifications