| Active electronic current transformer is a new type of high-voltage apparatus for current measurement of power system, which is a complete combination of optical electronic technology with fiber optic sensing technology. The main features of the apparatus are focus on small volume, light weight, no iron core, no magnetic saturation and no ferreous resonance, moreover, related advantages such as the large range of transient and frequency response, excellent electrical magnetic compatibility, oil-free configuration, reliable insulation structure, are all the trends of current transformer in the future. Meanwhile, it should agree with the future power gauge and digital, computer, automatic relay protection. It will meet the demand of digital power network.In this paper, the technical problem and new methods of current measurement are fully investigated in the first. Besides, the technical specification, operating principle, crucial problem have been analyzed in detail. The market prospects of this apparatus are forecast at the same time.In this paper, the emphasis is laid on the principle of active electronic current transformer, especially on the sensor head, signal receiver, fiber optic communication, and computer interface. A new method based on laser energizing is used to supply consistent current for the part of high-voltage unit. For the improvement of reliability and stability of the whole apparatus, meanwhile, for eliminating various electric-magnetic disturbance within the power supply and ground, measures such as filter, grounding, shielding are all taken in technique. The special methods are LC filter for power supply, bypass capacitor for suppressing voltage surge in printed circuit board, shielding layer wrapped in sensor head and overall grounded. Reasonable selection of A/D and CPU is very important for sharply shortening the period of sampling and holding, A/D conversion, data transmissions, and final calculation. In data communications, the serial synchronization transmission mode based on the technique of time divided multiplex application is used for detecting multi-channelsof signal only by two channels of fiber optic. The clock and data pulsation signals from upper sensor heads can be received using PIN diode, then, amplified and inverted in logical control unit for the purpose of CPU operation. Hereinafter, the digital signal will be delivered into the central processing unit (CPU) for related calculation, and meanwhile transmitted to a D/A converter for signal recovery after filter and phase-shift circuit.The technical requirements of the active electronic current transformer are described, and total designs on electronic circuit and integrated configuration are finished in this thesis. An experimental apparatus of electronic optic current transformer is manufactured in actual scale with 220 kV of rated voltage and 600 A of rated current. It is shown from the test results that the ratio error and phase error have been integrated to meet class 0.2 of national standard. |
