High Response Excitation Research Articles

Analysis of system stability as affected by under-excitation limiter under a brushless high initial response excitation system

This paper presents the mechanism analysis of the dynamic stability about superimposed under-excitation limiter (UEL), used in a brushless high initial response (HIR) excitation system. A single-machine infinite-bus model is derived by using the synchronous machine model with the brushless (HIR) excitation system model (IEEE Type AC2C) and a superimposed multisegment UEL. Based on the linearized model, the relation between the auxiliary damping torque (?MD2) provided by UEL and the pertinent parameters of UEL is extracted. With the damping torque analysis (DTA) technique and superposition principle, it is shown that the dynamic stability of the system can be affected by the value of the slope of the boundary curves (KU) effectively. Additionally, the mechanism analysis shows the influence of the proportional gain (KP) and the integral gain (KI) of UEL on the damping torque of system. Then, results of the frequency-domain and time-domain simulations on a single machine connected to a large system are presented which confirm the conclusions of mechanism analysis.

Two-photon ratiometric fluorescent probe based on NBD-amine functionalized semiconducting polymer nanoparticles for real-time imaging of hydrogen sulfide in living cells and zebrafish

The thiolysis of 7-nitro-1,2,3-benzoxadiazole amine (NBD-A) paves the way for specific sensing of H2S over biothiols and real-time imaging in living organisms. Rational fabrication of NBD-A-based probe with ratiometric mode and two-photon excitation is highly appealing to achieve high quality bioimaging. In this work, the NBD-A molecules are assembled with poly(9,9-dioctylfluorenyl-2,7-diyl) polymer nanoparticles, defined as NBD@PFO, to construct two-photon ratiometric probes for H2S detection through the fluorescence resonance energy transfer (FRET). For the construction of NBD@PFO nanohybrids, polymer nanoparticles are employed as the NBD-A molecular vehicle, energy donor and two-photon absorber, while NBD-A is served as the response unit and energy acceptor. Taking advantages of NBD-A and polymer nanoparticles, the obtained NBD@PFO probes exhibit high selectivity, fast response (<5 s), ratiometric detection and two-photon excitation. Our results indicate that NBD@PFO nanohybrids are successfully applied for monitoring of H2S concentration in living cells and zebrafish, exhibiting great potential of polymer nanoparticles to improve the imaging capability of an organic small molecular probe.

Investigating the Transient Properties of a Superconducting Generator with High-response Excitation Introducing Current Source PWM Converter in an Improved Power System

Recently, power systems are being operated under increasingly stressed conditions, and the ability to maintain the system stability becomes an issue of concern. A Superconducting Generator (SCG) can be one of the ways to obtain higher stabilities, higher power density and higher efficiencies in the near future power systems. In this paper, SCG with high-response excitation is studied, which is identified to have the potential of improving the system stability by its SMES (Superconducting Magnetic Energy Storage) effect. Taking consideration of the facts that the excitation voltage of a SCG is extremely low meanwhile the field current is considerable high in the normal operation, this paper proposed a new type excitation circuit for SCG that is different with the conventional one, which has introduced a current source PWM converter to automatically regulate the field current instead of the conventional automatic excitation voltage regulation. The validity of the proposed method has been examined by digital simulation studies, and the improving effect of the power system stability by the proposed SCG has been verified as well in this study.

A Study of Power Systems Stability Enhancement Effects by Excitation Control of Superconducting Generator with High Response Excitation based on Detailed Excitation Circuit Model

SCG (Superconducting Generator) has a superconducting field winding, which leads to many advantages such as small size, high generation efficiency, low impedance, and so on, and be considered as one of the candidates to meet the needs of high stability and high efficiency in the future power system networks. SCG with high response excitation is especially expected to be able to enhance the transient stability of power system by its SMES (Superconducting Magnetic Energy System) effect. The SMES effect of SCG is recognized that its behaviors are dominated by the structures and controls of its excitation system. For this reason, in order to verify exactly how the SMES effect of SCG influences on the power system stability, the electrical circuits of SCG high response excitation are modeled in detail for conducting digital simulation, and its influence on excitation voltage and active power output of SCG are discussed as well. The simulation results with a typical one machine - infinite bus power system model shows that the SMES effect can be certainly obtained when its exciting power is supplied from SCG terminal bus and may considerably lead to an improvement of power system transient stability.

A Study of SMES Effect by Superconducting Generator with High Response Excitation

A Study of SMES Effect by Superconducting Generator with High Response Excitation

Understanding Power-System Stability

This paper discusses power-system instability and the importance of fast fault-clearing performance to aid in reliable production of power. An explanation regarding small-signal stability, high-impedance transmission lines, line loading, and high-gain fast-acting excitation systems is provided. Transient stability is discussed, including synchronizing and damping torques. The power-angle curve is used to illustrate how fault-clearing time and high initial response excitation systems can affect transient stability. The term ldquopower-system stabilityrdquo has become increasingly popular in generation and transmission. The sudden requirement for power-system stabilizers (PSSs) has created confusion about their applicability, purpose, and benefit to the system. This paper discusses the fundamentals of the PSS and its effectiveness. In today's paper industry, PSSs are being applied on larger machines in the northwest United States and Canada.

Excitation Control System Design of High Response Excitation Type Superconducting Generator for Improving Power System Dynamics

Superconducting generator (SCG) with superconducting field winding has many advantages such as small size, light weight, high generation efficiency. A prominent advantage is to improve power system stability owing to lower synchronous reactance compared with the conventional generator. High response excitation type SCG has a rotor with thermal radiation shield without damping effect; it can enable very rapid change in field current and the magnetic flux due to the change of the field current can reach the armature winding quickly. The excitation power is large and has a rapid change enough to affect the conditions of power system in self-excited operation of the generator. This effect is equivalent to the effect of a superconducting magnetic energy storage (SMES), then so-called “SMES effect, and it is expected to contribuite to transient stabilty improvement. In this paper, excitation control system design for high response excitation type SCG in consideration of SMES effect is proposed for improving power system dynamics by employing eigenvalue sensitivity. The SMES effect is considered to couple with the power system as a nonlinear load. The control performance of the proposed excitation control system is examined in IEEJ East 10-machine and West 10-machine systems. It is made clear that the SMES effect of SCG is utilized effectively and results in both transient and dynamic stability improvement. However, the performance depends on the locations of SCGs and fault contingencies.

Experimental study on system stability evaluation in parallel running of a superconducting generator and a SMES

Parallel running operation of 100 kVA superconducting generator (SCG) with high response excitation and 0.4 MJ SMES (superconducting magnet energy storage) was carried out. The exciter capacity of the high response excitation is rather large compared with that of conventional generators. The exciter controller, that is, AVR (automatic voltage regulator) and PSS (power system stabilizer) are designed taking the exciter power change at the excitation into account to improve the system stability. The SMES can also improve the power system stability. The SMES can give the small active power modulation of sinusoidal wave to the system. The system responses due to the SMES power modulation were observed and analyzed in order to evaluate the designed control functions of AVR, PSS and SMES. Frequency characteristics of the designed control functions were obtained from on-line data of the system. The system stability of parallel running of the SCG and the SMES was evaluated by use of SMES power control.

High response excitation control of superconducting generator for stability of superconducting field winding

Superconducting generators (SCGs) can improve power system stability in steady state and also in transient state with a high response excitation. The authors designed and made an experimental 100 kVA SCG with high response excitation and carried out several experiments for power system stability using an artificial transmission line. In this paper, a high response excitation control of SCG considering stability of the superconducting field winding is discussed and tested. A proposed control system has limiter (over excitation limiter) functions for not only the field current but also for its differential value (voltage). These factors affect a design of the field windings. Transient stability tests were performed by using the test generator and the artificial transmission lines with and without the proposed excitation control. The effects of the proposed control on the transient stability were studied.

Experimental studies on field circuit of superconducting generator

Because of the superconducting field winding of superconducting generators (SCGs), the resistance and voltage drop of the field circuit are extremely low. Therefore, machine constants concerning the field circuit are different from those of conventional machines. In this paper, a method for obtaining these constants is proposed. By the use of this method, the constants are given experimentally. In SCGs with high response excitation, which can improve transient power system stability, the characteristics of high response excitation are discussed both theoretically and experimentally.

Experimental studies on power system stability of a superconducting generator with high response excitation

Superconducting generators (SCGs) have many advantages such as small size, light weight, high efficiency, improvement of steady-state power system stability etc. SCGs with high response excitation have the additional advantage of improvement of power system stability in transient states. By use of the experimental Hesper 1 100 kVA SCG with high response excitation and an artificial transmission line, the authors carried out several experiments on power system stability. Before these experiments, the authors considered a block diagram for the power system stability of SCGs with high response excitation, and designed automatic voltage regulators and a power system stabilizer. This paper describes the above considerations and the experimental results.

速応励磁形超電導発電機の電力系統特性解析シミュレーション法

速応励磁形超電導発電機の電力系統特性解析シミュレーション法

Characteristics of superconducting generator at high response excitation

Superconducting generators have many advantages, one of which is their ability to improve the stability of power systems because of their low synchronous impedances. The advantage may be increased by adoption of high-response excitation. The first 100 kVA high-response excitation superconducting generator has now been built. One of the problems in the design of such generators involves the characteristics of the field circuit, i.e., the field armature winding, losses in the component materials, and loss in the superconducting field winding. In this paper, a 2-dimensional electromagnetic field analysis of field circuit characteristics is presented.

Development and characteristics of superconductor for 70-MW class high-response excitation superconducting generator

The superconducting field winding of the 70-MW classhigh-response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle-shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force. The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low-loss high-current density superconductor will be able to be applied to the field winding of the 70-MW class high-response excitation superconducting generator.

超電導発電機の速応励磁時の特性解析

超電導発電機の速応励磁時の特性解析

超電導発電機用Ｎｉ基合金の強度・物性評価

From the required characteristics of structural material for high response excitation superconducting generators, precipitation hardened Ni base alloys such as Inconel 718, were considered as candidate materials. To improve weldability and make a large size ingot, the chemical composition range of 4.0≤Nb+Ti≤4.5% was determined. Based on the above chemical composition, a thinwalled forged ring, welded at the center, was manufactured. Material strength and physical property tests were conducted systematically from 4K to room temperature for base metal and weld metal of this ring. From the material strength tests, as expected, the material strength rose with falling temperature, but ductility and toughness were almost constant for both of these materials. Also, it was shown that if the sample was re-annealed and aged after welding, original characteristics of the base metal were recovered in this precipitation-hardened material. The physical properties of thermal expansion, electrical resistivity, and magnetization, were also measured. From the comparison of mechanical and physical properties of this material with those of Inconel 718, it was clarified that the differences of characteristics of these materials were closely related with chemical compositions of Nb+Ti and Ni, respectively.

7万kW級超速応励磁形超電導発電機用導体の開発と特性

The superconducting field winding of the 70-MW classhigh-response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle-shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force. The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low-loss high-current density superconductor will be able to be applied to the field winding of the 70-MW class high-response excitation superconducting generator.

Rotor design of a 1000 MW superconducting generator

A conceptual rotor design was developed for a 1000 MW superconducting generator having a high-initial-response excitation system. Field winding design, magnetic field analysis of the field winding, and loss calculations and force and stress analyses for the rotor body were carried out. The results are as follows: (1) the operating point of the field winding at the transient state is 72% of the short sample characteristics; (3) the stress in the rotor teeth at the steady state is 405 Pa; and (4) high initial response excitation can cause quenching of the field winding, so the shaft should have a higher resistivity. The maximum flux density at the field winding end region can be small due to optimum magnetometer force distribution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rotor Design of a 1000MW Superconducting Generator

A conceptual rotor design was developed for a 1000 MW superconducting generator having a high-initial-response excitation system. Field winding design, magnetic field analysis of the field winding, and loss calculations and force and stress analyses for the rotor body were carried out. The results are as follows: (1) the operating point of the field winding at the transient state is 72% of the short sample characteristics; (3) the stress in the rotor teeth at the steady state is 405 Pa; and (4) high initial response excitation can cause quenching of the field winding, so the shaft should have a higher resistivity. The maximum flux density at the field winding end region can be small due to optimum magnetometer force distribution. >

Field Tests and Simulation of a High Initial Response Brushless Excitation System

The extremely long transmission distances associated with the Colstrip mine-mouth power plant called for stability improvement measures in the planning stages which included the application of high initial response excitation systems. The brushless excitation systems on the 819 MVA Colstrip Units 3 and 4 are designed to provide high initial response characteristics. Field tests were conducted during unit operation in which the fast large and small-signal response was successfully demonstrated. Response times are similar to that of static systems, without the use of brushes or collectors. Excitation system model constants were calculated based on hardware characteristics. Simulation results show the ability of the model to accurately reproduce the actual excitation system response.