In lab tests, complex relay protection systems are usually not involved, but there are many instruments and testing devices. Among these, the microcomputer relay protection tester is the most critical tool. One straightforward way to test amplitude-frequency characteristics is by using a dual-channel oscilloscope. In this method, the test device generates harmonic states, applying a power frequency voltage (U1) to one phase and a high-frequency voltage (Un) to another, ensuring both have equal amplitudes. If the amplitude-frequency characteristics are favorable, the waveforms of the two frequencies will appear at the same height on the oscilloscope. When the high frequency is set to 1000Hz, the waveforms maintain equal amplitude, and the high-frequency waveform remains smooth, suggesting the signal source provides ample data points. Devices like the JJC-1H from Jiangxi Huadong Electric Power Instrument Factory, with 180 points per cycle, show excellent amplitude-frequency characteristics at frequencies below 350Hz. Conversely, the Beijing Witt MRT-02B, with only 40 points per cycle, employs a significant resistance-smoothing technique, resulting in poorer amplitude-frequency characteristics. At the fifth harmonic, the amplitude error reaches over 50%.
For linearity and accuracy testing, relay protection primarily ensures consistency and precision at 50Hz, verifiable using standard current and voltmeters. To calibrate current accuracy, the test device should be evaluated across a wide range of currents, from large to small values, preventing overheating in devices with limited heat capacity. Due to the limited number of D/A bits, particular attention must be paid to accuracy at lower voltages, focusing checks between 0.2 to 30A. The OMICRON CMC156 excels in accuracy and linearity thanks to its A/D feedback automatic correction. However, its output capacity is relatively small, leading to greater waveform distortion at lower voltages and currents, affecting the microcomputer's sampling. The domestic equipment generally performs well at power frequency but struggles with accuracy at smaller voltages due to reduced A/D bit counts.
Load capacity testing involves using an oscilloscope and variable load resistance. When the output waveform remains undistorted, it’s essential to note the maximum current and voltage without distortion. Testing load capacity is crucial, requiring a variable load resistance under 1Ω and a current capacity of up to 30A. Finding such resistors is challenging; several reactive transformers in series can serve as alternatives. Results show Jiangxi JJC-1H maintains an undistorted voltage of 10-11V at 30A, while Singapore’s VENUS330 achieves only 3.8V, highlighting the former's superior load capacity.
The ability to superimpose harmonics helps evaluate the test device’s accuracy and amplitude-frequency characteristics. Foreign devices excel here due to their excellent amplitude-frequency characteristics, exemplified by Jiangxi JJC-1H’s effective harmonic synthesis and rapid response to step waves. For non-transformer output devices, observing square and step wave outputs via oscilloscopes assesses performance.
Magnetic susceptibility tests for differential relays offer a simple method to verify a test device’s automated testing capabilities and handling of results. Similarly, impedance relay action zone tests examine whether the device can superimpose harmonics or automatically generate fitting curves.
Seiko relay current tests assess dynamic testing abilities. Poor transient responses lead to larger discrepancies in precise current measurements, particularly at low currents. This analysis considers both the protection device’s transient dispersion and the test device’s transient characteristics, along with evaluating fitted current precision lines, especially amid data fluctuations to prevent unreasonable oscillations.
By expanding on these areas, the testing process becomes more comprehensive, ensuring reliable evaluations of relay protection systems.
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