Abstract
A method for testing electronic instrument transformers is described, including electronic voltage and current transformers (EVTs, ECTs) with both analog and digital outputs. A testing device prototype is developed. It is based on digital signal processing of the signals that are measured at the secondary outputs of the tested transformer and the reference transformer when the same excitation signal is fed to their primaries. The test that estimates the performance of the prototype has been carried out at the National Centre for High Voltage Measurement and the prototype is approved for testing transformers with precision class up to 0.2 at the industrial frequency (50 Hz or 60 Hz). The device is suitable for on-site testing due to its high accuracy, simple structure and low-cost hardware.
Highlights
Nowadays, there are a variety of types of instrument transformers based on different measurement principles in electric power systems
For digital outputs of EVTs/ECTs, one of the possible approaches is to convert the digital output into an analog one and to take measures by the transformer comparator (TC) method, but the time delay introduced by the repeated conversions will cause a phase displacement that is outside the handling range of the TC
The testing device consists of a precision voltage transformer (PVT), precision current transformer (PCT), data acquisition boards (DAQ1 and DAQ2), synchronous sampling pulse circuit (SPC) and computer (PC)
Summary
There are a variety of types of instrument transformers based on different measurement principles in electric power systems. For digital outputs of EVTs/ECTs, one of the possible approaches is to convert the digital output into an analog one and to take measures by the TC method, but the time delay introduced by the repeated conversions will cause a phase displacement that is outside the handling range of the TC. It is possible to transform the analog output of the standard transformer into digital signal and compare with the digital output of the EVTs/ECTs [15] Each of these testing devices can only test one type of transformer or a few. Since the testing device has a simple structure and uses low-cost hardware, it can be built and is suitable for on-site testing
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