The Design And Research On New Type Electronic Voltage Transformer Applied In High And Medium Voltage Leveled Power Grid

Voltage transformers (VT) are very important equipments in electric power system, which supply secondary voltage signals for energy-meters and relay protective devices. At present, most of voltage transformers under operation are traditional PT&CVT. Because of maturity of electronic and communication technology and traditional VT defeats, some domestic/overseas institutes and related research organization has done researches on the EVT for years,launched several prototypes, and some even were applied in power grid for test. By far, the main types of EVT are EVT based on resistor or capacitor divider and OVT based on Pockels electric-optical effect or other optical effect. However, either EVT or OVT needs processing unit nearby to cope with signals, then transferred to control room by optical fibers, and the transmission system is complicated.A new type of EVT, based on detecting current in resistor or capacitor, was proposed. Through detecting current caused by high voltage between primary side of capacitor or resistor and ground, the high voltage value could be read. The sensor's secondary current was transferred to control room by copper lines, then, changed into a voltage signal by current-voltage unit. By this processing method, there was no voltage drop and current's accuracy was guaranteed; besides, the transmission system was simplified also. The necessity of developing EVT was illustrated by comparing traditional VT with EVT/OVT. The difference, in the aspect of voltage detecting principle between already existing EVT and EVT was proposed in this thesis, was also analyzed. The characteristics of EVT based on detecting current were described. For the medium voltage power grid, an EVT based on detecting current in resistor was proposed. The EVT's structure and principles were analyzed, signal processing unit was discussed, and the equivalent circuit, phase-frequency and amplitude–frequency characteristics were illustrated and presented. A prototype of medium voltage EVT was made and tested in the lab. For the high voltage power grid, an EVT based on detecting current in capacitor was proposed, and the EVT's structure and principles were analyzed. EVTs based on air-core coil and EVTs based on high accuracy TA were described in details respectively; and transient performance about the different types of EVTs was analyzed in theory and tested in lab. At last, an EVT, which could be used as normal voltage transformer, was introduced. High voltage experiments were made, and the test data indicate that the EVT's accuracy has reached the requirements of class 0.2. This thesis also discussed outside interference factors which could affect the metering accuracy of EVT, afterwards, refining measures to eliminate the outside impacts were presented.The EVT, based on detecting current, adopts new sampling method of high voltage, which has a simple signal-processing unit and transmission system, and has high accuracy of measurement. So, this kind of EVT is suitable for being applied in high/medium voltage leveled power grid, and very practical and useful.