Xi Xu

LVRT Capability Enhancement of DFIG With Switch-Type Fault Current Limiter

A low-voltage ride-through (LVRT) strategy for a doubly fed induction generator (DFIG) with a switch-type fault current limiter (STFCL) is presented in this paper. The STFCL is composed of fault-current-limiting inductors, isolation transformers, a diode bridge, a semiconductor switch, a snubber capacitor, and a fault energy absorption bypass. The presented STFCL can insert fault-current-limiting inductors in series with the stator branches on occurrence of a grid fault, which can limit the rotor overcurrent and weaken the rotor back electromagnetic force voltage simultaneously. The safety and controllability of the rotor side converter can thus be guaranteed. The STFCL can also absorb the excessive energy stored in the stator during LVRT with the fault energy absorption bypass so as to prevent the semiconductor devices from overvoltage. The feasibility of the proposed approach is validated by simulation studies on a typical 1.5-MW wind-turbine-driven DFIG system. The validity of the proposed approach is further verified by the experimental results on a 2-kW DFIG prototype.

Development of a 630 kVA Three-Phase HTS Transformer With Amorphous Alloy Cores

This paper describes design and operation of a three-phase HTS power transformer with capacity of 630 kVA operated in liquid nitrogen of 77 K for primary/secondary voltages of 10.5 kV/0.4 kV. The windings were wound by hermetic stainless steel-enforced multifilamentary Bi2223/Ag tapes. The structures of primary and secondary windings are solenoid and double-pancake respectively. Cryostat is made from electrical insulating materials with room temperature bore for commercial amorphous alloy core. Fundamental characteristics of the transformer are obtained by standard short-circuit and no-load tests. The ac losses were calculated and measured by method of conventional transformer. The HTS power transformer successfully operated in a live power grid.

Development and Test of 10.5 kV/1.5 kA HTS Fault Current Limiter

Superconducting Fault Current Limiter (SFCL) is an attractive appliance for modern electrical power system. A 10.5kV/1.5 kA three-phase HTS fault current limiter was developed by IEE, CAS. This improved rectifier-type SFCL with HTS coil of 6.25 mH is going on a demonstrated long-term reliable operation in a real 10.5 kV substation located in Hunan, China. In a three-phase-to-ground short circuit test of grid, the prospective fault current of 3.5 kA was limited to 635 A at the pre-setup short-circuit point successfully

Fabrication and Tests of a 1 MJ HTS Magnet for SMES

In this paper, the design, fabrication and tests of a I MJ HTS magnet for SMES was presented. The magnet was fabricated by BSSCO tapes, it consisted of 44 pancakes, the inner diameter of the winding is 400 mm, the outer diameter is 568 mm and the height is 648 mm, the inductance is 6.38 H and the rated operation current is 560 A at 4.2 K. The tests show the magnet could be operated at the design parameters. The magnet will be used for the 1 MJ/500 kVA SMES unit which will be demonstrated at a 10 kV substation in Beijing.

Evaluation of the Performance of BTFCLs for Enhancing LVRT Capability of DFIG

Performance of three kinds of bridge-type fault current limiters (BTFCLs) for enhancing low-voltage-ride-through (LVRT) capability of DFIG is evaluated in this paper. The common BTFCL can effectively enhance the LVRT capability of DFIG. However, the fault-current-limiting inductor (FCLI) is periodically inserted into the stator circuit under normal operation for compensating power losses of the FCLI. The periodically insertion of the FCLI induces stator voltage spikes, which causes significant stator flux and electromagnetic torque oscillations. One feasible way to solve this problem is to use an additional current-regulating circuit (CRC). However, the additional CRC increases hardware cost, reduces reliability of the whole system, and induces more power losses. To solve this problem, a BTFCL with bypass resistor (BTFCL-BR) is presented. The BR absorbs the majority of the current harmonics during normal operation and eliminates the stator voltage spikes. The flux and electromagnetic torque oscillations can thus be significantly reduced. The performance of three kinds of BTFCLs is evaluated by simulation and experimental studies on a typical 1.5 MW wind turbine driven DFIG system and a 2 kW DFIG prototype. By simulation and experimental evaluations, it seems that the BTFCL-BR approach is the most promising solutions among the three kinds of BTFCLs.

Design of a 380 m DC HTS Power Cable

High temperature superconducting (HTS) power cable is an effective power transmission utility with large capacity, high efficiency, and low loss, especially in DC power transmission. This paper describes the design of a 380 m HTS power cable with rated current of 10 kA for an aluminum electrolysis enterprise. The power cable connects the rectifier at a substation at one end with the bus bar of an aluminum electrolysis plant at the other end at Henan Zhongfu Industrial Co. LTD. The power cable will be energized in late of 2010. The design of the cable conductor, cryogenic envelope, termination, refrigeration, and online monitoring system of the 380 m HTS power cable are discussed in this paper.

Development of the World's First HTS Power Substation

With the increasing depletion of fossil fuels and growing environmental pressure, the mankind has got known the need to vigorously develop the renewable energy and the energy-saving technology. The high Tc superconducting (HTS) power technology will be very helpful to enhance the stability, reliability, and efficiency and transmission capacity of the power grid which would be dominated by the renewable energy. In this paper, we will report the installation and operation of a 10 kV HTS power substation which includes a 75 m/1.5 kA HTS power cable, a 10 kV/1.5 kA HTS fault current limiter, a 1 MJ/0.5 MVA high Tc SMES and a 630 kVA/10 kV/0.4 kV HTS power transformer.

Development of a 10 kA HTS DC Power Cable

The new energy revolution which will be dominated by renewable energy will need to develop a corresponding new power grid. Based on the characteristics of renewable energy resources, and the stability problem of AC network, it was proposed that the DC-based transmission grid should be developed in the future. The high Tc Superconducting (HTS) power cable will be a competitive candidate for large-capacity power transmission of renewable energy. In this paper, the progress of the development of a 360 m/10 kA HTS DC power cable is presented, and the prospects of HTS cable is discussed.

Design, Fabrication, and Tests of Three HTS Coils for a Model Fault Current Limiter

The design, fabrication and tests of three high temperature superconductor (HTS) coils for a rectifier-type model fault current limiter (FCL) were presented. The field distributions in the coil were numerically analysed by FEM. Based on the field distributions and the strong anisotropic characteristics of Bi2223/Ag tape, the HTS coils were designed and fabricated. The inner diameter and the height of the coils were 80 mm and 94 mm, respectively. Each of the coils consisted of 8 double pancakes. Every double pancake consisted of 103 turns with 35 meters of Bi-2223/Ag tape. After the characteristics of the coils were tested in liquid nitrogen, three of the coils were assembled in their nonmetallic-material cryostats and works with the model FCL.

Testing and Demonstration of a 10-kA HTS DC Power Cable

A 10-kA/360-m high-temperature superconducting (HTS) dc power cable has been developed and installed in 2012 in central China. The cable is connecting a rectifier at a substation to a bus bar of an aluminum electrolysis plant. Before operating in the power grid, a series of testing on the performance of the cable was conducted. The testing results show that the performance meets the operational requirements and that the critical current of the cable exceeds 12.5 kA. The 10-kA HTS cable was successfully energized at the Henan Zhongfu Industrial Company Ltd., Gongyi, China, on September 26, 2012. Since then, the cable has been stably and reliably supplying power for the companys aluminum electrolyzing plant.