A current transformer includes first and second transformer assemblies that each respectively comprise first and second groups of stacked iron core components. A first interface and a second interface are defined at an end of the first transformer assembly. A third interface and a fourth interface are defined at an end of the second transformer assembly. At least one of the first interface and the second interface is detachably connected with at least one of the third interface and the fourth interface. When the first and second transformer assemblies are connected with each other, the first and second groups of iron core components are combined to form a plurality of closed ring-shaped iron cores, and coils are respectively wound on at least two closed ring-shaped iron cores. An enclosed area defined between the first and second transformer assemblies causes induced current to be generated in at least one coil.

The invention discloses an error detection wiring circuit and switching device for instrument transformers in distribution power grid, wherein the wiring circuit integrates a three-phase three-wire metering circuit and a three-phase four-wire metering circuit, and the switching device comprises a linear push rod and a driving motor. Through the control of the driving motor, the movement of the linear push rod to the through terminal ports, which consist of the BN terminal, the CN terminal, and the P1B terminal, is realized. With this, the conversion of the two methods can be realized by simply switching the short circuit wiring of the P1B terminal or the BN terminal to the CN terminal and the AN terminal. Using certain measurement method, each phase of the transformer to be tested can be measured simultaneously, which improves the accuracy of the detected data. Meanwhile, the prior art of wiring conduction structure is changed into a rod-shaped jack-type conduction structure, such that the two-step wiring procedure is reduced to one step during measurement, which can be realized by simply controlling the forward and reverse rotation of the driving motor. No manual wiring operation is required, which is safer and more convenient, and greatly improves the efficiency of wiring conversion during measurement.

An arrangement includes an A/D converter and a processing circuit. The A/D converter is configured to generate digital samples of voltage and current waveforms in a polyphase electrical system. The processing circuit is operably coupled to receive the digital samples from the A/D converter. The processing circuit configured is to obtain contemporaneous phase current and voltage samples I.sub.A, I.sub.B, I.sub.C and/or I.sub.N, and V.sub.A, V.sub.B, V.sub.C. The processing circuit is further configured to determine source leg current sample values based on three of the current samples of I.sub.A, I.sub.B, I.sub.C, and I.sub.N, and also based on a ratio of the impedance on one leg of a center-tapped source transformer secondary winding to another secondary winding of a source transformer. The processing circuit is further configured to determine a VA value based at least in part on the source leg current samples. The processing circuit is further configured to provide information representative of the VA calculation to one of a group consisting of a display, a communication circuit, a memory and a billing calculation unit.

A device for harvesting energy from a power line carrying AC current including: a transformer having a core with separate first and second sections, the core being formed of ceramic material or layered nickel alloy tape; a first secondary winding wound around the first section of the core; a second secondary winding wound around the second section of the core; a first DC core-flux control winding wound around the first section of the core; and a second DC core-flux control winding wound around the second section of the core; wherein the core is configured to be in operative communication with a magnetic field radiated from the power line, such that an AC voltage is generated in the first and second secondary windings, and the maximum AC voltage produced by the first and second secondary windings is limited by the first and second DC core-flux control windings.

A device for harvesting energy from a power line carrying AC current including: a transformer having a core with separate first and second sections, the core being formed of ceramic material or layered nickel alloy tape; a first secondary winding wound around the first section of the core; a second secondary winding wound around the second section of the core; a first DC core-flux control winding wound around the first section of the core; and a second DC core-flux control winding wound around the second section of the core; wherein the core is configured to be in operative communication with a magnetic field radiated from the power line, such that an AC voltage is generated in the first and second secondary windings, and the maximum AC voltage produced by the first and second secondary windings is limited by the first and second DC core-flux control windings.