Development and research of the circuit for measuring the leakage current when testing the insulation with the higher rectified voltage

OBJECT. When developing DC test voltage sources to assess the insulation quality of high-voltage equipment, the task is to measure the leakage current flowing through the test object. METHODS. When solving the problem the authors proposed a technical solution for measuring the current flowing through the test when testing insulation with rectified voltage, which uses a precision resistor, an isolating amplifier, a 2-channel operational amplifier with a unipolar power supply, zero voltage drift, and an ADC of a microcontroller.RESULTS. The article in the course of the study of the stand of the circuit for measuring the leakage current flowing through the tested object when testing the insulation with rectified voltage, an experimental industrial sample was created, which makes it possible to measure the leakage current value in the range from 10 μA to 1000 μA. The use of the developed circuit for measuring the current flowing through the test object when testing the insulation with rectified voltage makes it possible to calculate the DC component of the voltage signal from the alternating signal and in real time, and, therefore, to quickly monitor the current in high-voltage circuits for continuous monitoring. CONCLUSION. So the introduction of this sample will make it possible, on its basis, to create a number of digital measuring microammeters that make it possible to measure the leak-age current in high-voltage test installations for testing the insulation of objects from 15 nF to 200 nF, in the leakage current measurement range from 10 μA to 1000 μA. The results obtained can be used in high voltage technology to study circuits for measuring the leakage current flowing through the test object when testing insulation with rectified voltage.

Low-Noise Programmable Voltage Source

This paper presents the design and testing of a low-noise programmable voltage source. Such a piece of instrumentation is often required as part of the measurement setup needed to test electronic devices without introducing noise from the power supply (such as photodetectors, resistors or transistors). Although its construction is based on known configurations, here the discussion is focused on the characterization and the minimization of the output noise, especially at very low frequencies. The design relies on a digital-to-analog converter, proper lowpass filters, and a low-noise Junction Field-Effect Transistors (JFET) based voltage follower. Because of the very low level of output noise, in some cases we had to resort to cross-correlation in order to reduce the background noise of the amplifiers used for the characterization of the programmable source. Indeed, when two paralleled IF9030 JFETs are used in the voltage follower, the output noise can be as low as 3 nV/√Hz, 0.6 nV/√Hz and 0.4 nV/√Hz at 1 Hz, 10 Hz and 100 Hz, respectively. The output voltage drift was also characterized and a stability of ±25 µV over 3 h was obtained. In order to better appreciate the performance of the low-noise voltage source that we have designed, its noise performances were compared with those of a set-up based on one of the best low-noise solid-state voltage regulators available on the market. Actual measurements of the current noise in a type-II superlattice photodetector are reported in which the programmable source was used to provide the voltage bias to the device.