Magnetically controlled reactors (MCRs) are usually used as three-phase shunt reactors. They have low harmonic distortion independent of the third harmonic current because most three-phase MCRs are delta connected. However, as arc suppression coils, MCRs are operated in the single-phase mode, and the harmonics can be much higher than those of three-phase MCRs. In this paper, the structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed. There are two stages with different lengths and areas in the iron cores. The stages saturate at different times when the TSMCR outputs reactive current. The current harmonics of the first saturated stage can be compensated for when the second stage begins to saturate, to reduce the total harmonics of the output current. The mathematical model that reveals the distribution characteristics of the current harmonics for the TSMCR is also presented. A study of the mathematical model indicates that there are two key factors that affect the total current harmonics of the TSMCR. One is the parameter k, which represents the area ratio of the second stage to the first stage. The other one is the parameter m, which represents the ratio of the length of the first stage to the total length of the magnetic valve in the iron core. The simulations and experiments show that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current when k and m are chosen according to the theoretical mathematical model.

Modeling and Harmonic Optimization of a Two-Stage Saturable Magnetically Controlled Reactor for an Arc Suppression Coil

In the case of motors and generators, the benefits of using high-temperature superconducting (HTS) coils could be represented by the reduction of 50% in both losses and sizes compared to the conventional machines of the same rating. However, it is hard to establish the quench detection and protection devices for the HTS coils applied to the rotors of motors and generators. Therefore, the stability of the coils is lower than the quiescent coils applied to NMR, MRI, and so on. Therefore, it is important to improve the self-protection ability of HTS coils. We have been developing a novel self-protection method, which removes the insulation turn-turn winding and inserts various metal tapes instead of the insulation. In our previous research, the higher self-protection ability for the thermal disturbances in the HTS coils removed the insulation and inserted Cu tape has been proved. This paper presents the results of an experimental study for the quench current using the insulated, the noninsulated, and the Brass tape inserted HTS coils in liquid nitrogen and background magnetic fields. Also, the measured quench currents of each coil will be discussed.

The Transient Stability of HTS Coils With and Without the Insulation and With the Insulation Being Replaced by Brass Tape

The electrical modulation of magnetization through the magnetoelectric effect provides a great opportunity for developing a new generation of tunable electrical components. Magnetoelectric voltage tunable inductors (VTIs) are designed to maximize the electric field control of permeability. In order to meet the need for power electronics, VTIs operating at high frequency with large tunability and low loss are required. Here we demonstrate magnetoelectric VTIs that exhibit remarkable high inductance tunability of over 750% up to 10 MHz, completely covering the frequency range of state-of-the-art power electronics. This breakthrough is achieved based on a concept of magnetocrystalline anisotropy (MCA) cancellation, predicted in a solid solution of nickel ferrite and cobalt ferrite through first-principles calculations. Phase field model simulations are employed to observe the domain-level strain-mediated coupling between magnetization and polarization. The model reveals small MCA facilitates the magnetic domain rotation, resulting in larger permeability sensitivity and inductance tunability. Voltage tunable inductors (VTIs) with high working frequency and tunability are desired for new design of energy efficient electronics. Here the authors demonstrate magnetoelectric VTIs operating up to 10 MHz with tunability over 750% via strain mediated magnetoelectric effect and magnetocrystalline anisotropy cancellation strategy.

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Colossal tunability in high frequency magnetoelectric voltage tunable inductors

In order to flexibly compensate reactive power, it is necessary to develop a controllable reactor in long distance and ultrahigh voltage system. A leakage flux-controlled reactor (LFCR) is developed in this paper. The operation principles of LFCR are discussed in detail, and a 380 V single-phase LFCR prototype is developed. Relevant experiments have been done to test its performance. The results of the experiments indicate that LFCR has no harmonic and the reactance of LFCR is stable. Also, LFCR with two control windings can realize four kinds of reactance adjustment rates: 1.94%, 75.99%, 90.53%, and 99.05%.

Development of a Leakage Flux-Controlled Reactor

A novel variable reactor based on transformer is proposed in the paper. In the variable reactor, a transformer with air gap is chosen, and the primary voltage is detected and used as the reference signal. A voltage-sourced inverter is applied to track the reference signal in order to yield a controllable voltage, which is applied across the secondary winding of the transformer. When the secondary-controlled voltage and the primary voltage satisfy a proportional condition, the equivalent impedance of primary winding of the transformer will vary continuously. According to the novel variable reactor, a novel shunt power quality controller is proposed and its principle is analyzed in detail. The shunt power quality controller is characterized by parallel topology and single frequency control. The approaches of decreasing the transformer leakage inductance are addressed. The experimental results verify the validity of the shunt power quality controller.

A Novel Variable Reactor and Its Application to Shunt Power Quality Controller

Reactive power compensation is vital for obtaining efficient operation of long transmission power lines or cables. A controllable shunt reactor that controls the transmission of power by continuous reactive power compensation will reduce the transmission losses and increase the transmission capacity of active power. We show that the saturation phenomena of iron and the high current density of a high-temperature superconductor can be utilized to design controllable reactors with large dynamic range, low losses, and limited harmonic distortion. We have designed and constructed a small-scale prototype of a controllable shunt reactor with a high-temperature superconductor control winding. We present a simple model of the magnetic circuit of the controllable reactor and we compare calculations from the model to experimental measurements on the controllable reactor

S. Valdemarsson

Papers

Magnetic circuit for a controllable reactor