Control Transformer Testing Device With Voltage Recovery
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Solution Overview
Problem
Testing control transformers for permissible instantaneous power is complicated by changing winding resistance during temperature stabilization, high apparent power demands, and unstable mains voltage, making it difficult to set and measure accurate loading conditions within the required short time frame.
Innovation Solution
The device incorporates a measuring circuit with a voltmeter, ammeter, and wattmeter, utilizing a voltage recovery source and adjustable resistors to independently set defined loads, compensating for leakage inductance and allowing for precise power factor control, and uses a three-phase power supply for stable voltage generation, enabling fast and automated testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital measuring instruments are used to measure high apparent power within 50 ms, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The measuring device is divided into separate functional modules: voltage measuring unit, current measuring unit, power factor measuring unit, and control unit. Each module performs a specific measurement function independently, allowing for precise high-power measurements while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
The patent introduces intermediary measurement circuits that can handle the high apparent power conditions (up to 3000 VA) by using appropriate current transformers and voltage dividers. These intermediaries enable accurate measurement of transient power conditions without requiring the entire measuring system to directly withstand the full power load, thus reducing overall device complexity.
2Adaptability or versatility
If variable impedance load is used to set loading apparent power, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent employs adjustable impedance elements that can change their electrical parameters (resistance and reactance) to simulate different loading conditions. By varying the impedance parameters, the device can adapt to test different transformer loading scenarios without requiring multiple physical load configurations, thereby improving adaptability while controlling complexity through parameter adjustment rather than structural changes.
3Productivity
If measurement is performed within 50 ms after attaching load, then productivity is improved, but measurement precision deteriorates due to winding resistance changes
Solution Approach 1:
The patent implements preliminary measurement of winding resistance before applying the full load, and uses this pre-measured value to compensate for resistance changes during the rapid 50 ms measurement window. This preliminary action allows the system to maintain measurement precision despite the short measurement time by having advance knowledge of the resistance state, thus resolving the conflict between speed and accuracy.
Solution Approach 2:
The measuring device incorporates feedback mechanisms that continuously monitor voltage, current, and power factor, and use this feedback to adjust measurements in real-time. During the rapid 50 ms measurement period, the feedback system compensates for winding resistance changes by comparing actual measurements against expected values and applying correction factors, thereby maintaining precision while achieving high productivity.
Data Source
Figure 1~2
AI summary
Device for testing control transformers by the methodology of permissible instantaneous power of transformer, in which the load of the tested transformer (1) is defined by the current flow through the resistance load formed by the first and the second adjustable resistor (4, 12), to which is connected the difference voltage between the output voltage of the tested transformer (1) and the output voltage of the auxiliary power source. For loading by the thermal power serves the first adjustable resistor (4) and the voltage recovery source (2); for loading by the instantaneous apparent power serves the second adjustable resistor (12) and the power source consisting of the voltage recovery source (2) connected in series with an additional voltage source formed by two regulation transformers (9, 10) and the isolating transformer (11). By setting the effective (RMS) value and phase shift of the source output voltage and the resistance of the resistance loads it is possible, based on the information provided by the voltmeter (6), ammeter (7) and wattmeter (8), to set the load of the tested transformer (1) required for a standardized test. Process of the test is controlled by the solid state relay (13) and the output voltage of the tested transformer (1) is measured in defined time sequence by the voltmeter (6). The device allows to recover most of the power, by which the tested transformer (1) is loaded during the test.