Development of a 70‐MW‐class quick response excitation superconducting generator

A superconducting generator is expected to be a next‐generation machine due to its many advantages over a conventional generator. Super‐GM has been promoting R&D of 70‐MW‐class superconducting model generators to verify the basic technologies required for the design and manufacture of a 200‐MW‐class superconducting pilot generator. Verification tests of the third model generator, quick response excitation type C generator, were finished in June 1999. The excellent characteristics as a superconducting generator were verified through the series of tests. We report main test results such as “open and short‐circuit test,” “loaded test,” “quick excitation test,” “negative‐phase sequence overcurrent test,” and “sudden short circuit test.” © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 22–29, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10029     

Performance evaluation of 6000‐A‐class superconducting field windings for 600‐MW‐class superconducting generators

Superconducting generators have many advantages such as increasing generator efficiency and improving power system stability. In Japan, a national project has been conducted since 2000 which is aimed at the development of fundamental technologies required for high‐output‐density and large‐capacity superconducting generators. This paper describes the results of this project, focusing on 6000‐A‐class field winding development. Copyright © 2004 Wiley Periodicals, Inc. A superconducting generator with a high output density and a large capacity has inherent factors that decrease superconducting stability. These are: (1) increase in the magnetic field in the winding which is caused by the increase in winding current density and (2) difficulty in fabricating windings which increases as a conductor diameter becomes larger. To secure the stability, we adopted a higher‐copper‐content conductor and a design that increases winding fixing pressure, along with devising a winding method that accommodates larger conductor diameter. These improvements were applied to a partial model of a 600‐MW field winding. Test results of the model showed good stability, indicating that design and fabrication technique for a 6000‐A‐class superconducting field winding has been successfully evaluated. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 7– 18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20332     

Starting method of a superconducting generator in a combined‐cycle power plant

In the combined‐cycle power plant generators are started by using the igniting arrangement up to the ignition rotational speed of the gas turbine. On the other hand, in the case of using the superconducting generator, it is difficult to apply the igniting arrangement used to generate electricity on the combined cycle for the structure as is. We examined the induction motor starting method for the superconducting generator by using the 70‐MW‐class quick‐response excitation superconducting model generator and the VVVF power supply. From the examination, we confirmed the ability to raise the rotational speed from 6 to 360 rpm. Moreover, it was found to be able to start 200‐MW‐class superconducting generators by the induction motor starting method with the analysis. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 30– 38, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20283     

贯流式水轮发电机空载电压波形优化与阻尼条发热抑制

改善空载电压波形、降低阻尼条损耗发热是优化电能质量、保障发电机与电网运行稳定性的重要问题。为此,采用调节阻尼绕组节距与定子斜槽措施相结合的设计方案,对1台30MW的大型贯流式水轮发电机空载电压波形和额定负载工况的阻尼条损耗发热进行了优化设计,并利用多层运动电磁场场路耦合时步有限元模型和三维温度场有限元模型进行了分析与计算。结果表明,在合理增大阻尼绕组节距的基础上,结合斜槽措施,既能明显地优化空载电压波形,又能有效地防止阻尼条过热故障的发生。计算结果与实测数据相符合。该研究结果对提高发电机的设计水平并改善发电机与电网的运行稳定性具有参考价值。     

300MW和600MW汽轮发电机绝缘国产化研究

介绍了３００ＭＷ和６００ＭＷ汽轮发电机采用国内生产制造的绝缘材料和构缘零电部件的性能特性，以及这些材料发电机定，转子绕组上应用性能，这些绝缘材料试验，结构应用试验和机组多年运行实践证明，国产化的绝缘结构和绝缘材料性能已能满足３００ＭＷ和６００ＭＷ汽轮发电机设计的要求，并保证了发电机组安全和可靠地运行。     

Verification of effect of damper windings on the transient condition of synchronous generator

This paper describes the results of an experimental investigation on the effects of the damper winding of a four‐pole synchronous generator at a synchronous generator transient. It is known from simulations that the damper winding acts effectively under synchronous generator transient conditions. However, experimental proof has not been obtained yet. Thus, experiments on damper effects were conducted using a laboratory‐scale power system. The damper winding of the tested generator consisted of five damper bars for each pole; the number of working damper bars could be changed manually. The damper currents at each bar were measured by a Rogowski coil. FFT analysis was applied to both the damper currents and armature currents under different operating conditions. The relationships between damper currents in the rotor and armature currents in the stator were made clearer than before. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(2): 33–42, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21278     

A new variable‐speed,constant‐frequency,stand‐alone power generating system

Variable‐speed and constant‐frequency power generating systems using rotor excitation of the wound‐rotor induction machines have been used for such applications as variable‐speed pump generators and flywheel energy storage systems. However, the stand‐alone generating system of this type has only been reported and has not yet been practically used. On the other hand, the stand‐alone generating systems using diesel engines have been widely used for emergency supplies of plants or isolated islands and so on. However, in these cases, synchronous generators are usually used. If the output frequency is to be kept constant, there is the need to control the speed of the engine using a high‐performance governor. Even then, the output frequency changes in the case of a sudden load change. This paper proposes a new stand‐alone power generating system. In this system, the constant‐frequency output voltage can be obtained even though rotor speed changes by several percent. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 75–85, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10191     

Improvement of Three‐Phase Unbalance Due to Connection of Dispersed Generator by Damper Windings of Synchronous Generator

It is well known in the numerical simulations of a synchronous generator that the damper winding contributes to suppressing three‐phase circuit unbalance in power systems. However, an experimental study has not been performed yet. In this paper, we verify experimentally the suppression of three‐phase unbalance by the damper windings. In order to simulate the three‐phase unbalance, a 470‐W dispersed generator of single‐phase two‐line type was connected to a three‐phase laboratory‐scale power system that included a 6‐kVA synchronous generator. We measured and analyzed line voltages and currents as well as damper bar currents both with and without the dispersed generator. The influence of damper windings on the unbalance of the three‐phase circuit was also investigated. The results show that the damper winding contributes to improving the three‐phase unbalance. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 43–50, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22305     

Magnetic field analysis of a 70‐MW‐class superconducting generator by the 3D finite element method

The three‐dimensional magnetic field and eddy current distribution of the 70‐MW‐class superconducting generator was calculated by a finite element method. The condition for the exciting armature coil was calculated by the jω‐method. In the magnetic flux distribution of the armature winding bore, the value obtained by analysis had good agreement with the measurement. An analysis that let the rotor move by the synchronizing speed was also done. The armature voltage for the nonload condition and the armature current for the three‐phase short‐circuit condition obtained by calculations had good agreement with the measurements. The validity of the analytical model for three‐dimensional magnetic field analysis of superconducting generators was confirmed from these results. In addition, the synchronous reactances were calculated using these results with eddy current in the facing. It was found that the facing had the effect of decreasing synchronous reactance by about 5%. © 2000 Scripta Technica, Electr Eng Jpn, 134(2): 53–60, 2001     

First trial of the electric power transmission of 3.8 kV–460 kVA through the prospective power transmission model system integrated under superconducting environment (PROMISE)

Superconducting technology is regarded as a breakthrough to future electric power transmission because of its highly densified and large transmission capability. This paper proposes a concept of the future power system composed of various superconducting apparatuses. A prototype model system called “PROMISE (PROspective power transmission Model system Integrated under Superconducting Environment)” is constructed to prove the realization of the above concept. PROMISE is composed of a superconducting transformer (60 Hz, 6/3 kV, 1000 kVA class), superconducting fault current limiter (6 kV, 200 A class), and superconducting power cable (5 m, 6 kV, 650 A class). This paper also shows that PROMISE realized the transmission of the electric power of 3.8 kV–460 kVA (50 Hz). This is the first achievement in the world. The voltage-current synthetic test verified that PROMISE can withstand ac voltage of 6 kV while carrying ac current of 170 A (60 Hz). The ac loss of superconducting cables, the heat leak of cryostat and the core loss of the superconducting transformer are measured to estimate the transmission loss of PROMISE. These fundamental performances of PROMISE may indicate the feasibility of the future introduction of superconducting technology for electric power systems.     

Experimental study of squirrel-caged damper structure for superconducting generator

In this paper a double-layer damper is developed which will consist of a squirrelcaged warm damper and a cylindrical cold damper as a part of a 70-MW superconducting generator development project. To evaluate the characteristics of unbalance current capability, magnetic shielding and damping for rotor swing, a one-half scale rotor model is constructed and an experimental study is made. From analysis of the experimental results, design guidelines have been developed and the FEM magnetic field analysis technique is refined. The main results are summarized as follows:

• 1 The squirrel-caged warm damper has sufficient capability against negative sequence current;
• 2 Damping characteristics can be designed to be effective near the rotor swing frequency;
• 3 Flux shielding at low frequencies corresponding to quick response excitation is sufficiently small so as not to prevent field flux change; and
• 4 Magnetic field can be analyzed by the refined FEM field analysis technique which now takes into account the effects of the rotor end region by estimating the end resistance based on the eddy current flow path.

     

A novel voltage clamped snubber circuit topology suitable for a multilevel inverter with lowered power loss performance

This paper presents a novel prototype of lowered loss snubber circuit topology suitable for multilevel voltage source‐inverters and rectifiers for high‐power applications. The reduced power loss characteristics and voltage capability performances of the proposed voltage clamped snubber circuit are evaluated relative to conventional RCD snubber circuits designed for four‐level voltage‐source inverters using IGBTs on the basis of experimental results. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 70–78, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20015     

贯流式水轮发电机空载电压波形畸变与阻尼条损耗发热抑制

为改善水轮发电机电能质量,预防阻尼绕组过热,保证机组与电网运行安全,基于电机电磁场、电路及传热学理论,建立了水轮发电机三维分层非线性时变运动电磁场-电路结合模型与磁极系统三维稳态温度场模型。进而针对一台q=1的36 MW贯流式机组的128种结构设计方案,通过电磁场-温度场综合计算,广泛深入地分析了定转子槽距比、定子斜槽程度以及每极阻尼条根数等结构参数对空载电压波形畸变率和额定工况阻尼绕组损耗发热的影响,在此基础上,讨论了同时抑制空载电压波形畸变率与阻尼绕组损耗发热的设计措施。计算结果与实测数据相吻合。     

Influence of quadrature‐axis reactance of large turbine generator on operation

Two‐pole large generators are extensively used in power utilities. Growing demand for electric power in recent years has led to substantial increases in the capacity of generators. In line with this trend, our company has manufactured two‐pole turbine generators in the 900,000‐kVA to 1,200,000‐kVA classes. As the capacity of generators becomes larger, equivalent circuits are increasingly expected to improve their precision in estimating operation characteristics. The Park model has been widely used as an equivalent circuit model. The Park model with quadrature axis transient reactance $x_{q}^{\prime}$ is claimed to be useful for accurately estimating the load rejection characteristics of turbine generators. However, it is difficult to measure $x_{q}^{\prime}$, few studies based on measured data have appeared. As one of the few examples, we have conducted a measured data on a 500,000‐kVA‐class generator. Recently, the authors obtained test data on $x_{q}^{\prime}$ of a 900,000‐kVA‐class generator. In this study, based on these data, we studied the effect of $x_{q}^{\prime}$ using the finite element method and a transient analysis program (EMTP‐ATP). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(3): 17–27, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21099     

Hybrid configuration of Darrieus and Savonius rotors for stand‐alone wind turbine‐generator systems

The suitable hybrid configuration of Darrieus lift‐type and Savonius drag‐type rotors for stand‐alone wind turbine‐generator systems is discussed using our dynamic simulation model. Two types of hybrid configurations are taken up. Type A installs the Savonius rotor inside the Darrieus rotor and Type B installs the Savonius rotor outside the Darrieus rotor. The computed results of the output characteristics and the dynamic behavior of the system operated at the maximum power coefficient points show that Type A, which has fine operating behavior to wind speed changes and can be compactly designed because of a shorter rotational axis, is an effective way for stand‐alone small‐scale systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 13–22, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20071     

Adaptive control for speed‐sensorless induction motors with uncertain load torque and rotor resistance

The problem of controlling a speed‐sensorless induction motor is addressed. Smooth reference signals for rotor speed and flux modulus are required to be tracked for any unknown constant values of load torque and rotor resistance within known bounds. A fourth order non‐linear adaptive tracking control is presented which is based on a novel rotor speed observer and on two identifiers for the uncertain parameters; it guarantees asymptotic rotor speed tracking and exponential rotor flux modulus tracking with an explicitly computed domain of attraction. The closed‐loop performances are illustrated by simulation. Copyright © 2005 John Wiley & Sons, Ltd.     

New sensorless vector control methods based on a new minimum‐order flux state observer in the “D‐module” for permanent magnet synchronous motors

This paper proposes new sensorless vector control methods that can be applied to both salient‐pole and non‐salient‐pole permanent magnet synchronous motors (PMSM). The proposed method estimates the phase of rotor flux by the “D‐module observer,” which is newly developed for sensorless vector controls of PMSM. The “D‐module observer” has the following attractive features. (1) It is a new state observer requiring no additional approximation to the motor mathematical model. (2) It is a minimum‐order state observer. (3) Observer gain guaranteeing proper estimation in a wide operating range except for singular zero‐speed can be a simple constant, and can be easily designed. (4) It utilizes motor parameters in the simplest manner. (5) Its structure is very simple and is realized at the minimum computing cost. (6) It can be applied to both salient‐pole and non‐salient‐pole PMSM. (7) It can be realized in both rotor and stator reference frames. Detailed designs and analyses for the “D‐module observer” and “D‐module observer”‐based sensorless vector control systems in both rotor and stator reference frames are given. Their validity and usefulness are examined and confirmed through extensive experiments. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 46–62, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20046     

Interconnected power systems with superconducting magnetic energy storage

The objective of this work is to discuss the concept of back‐to‐back interconnection systems with energy storage, especially with a Superconducting Magnetic Energy Storage (SMES) incorporated into a back‐to‐back DC link. In this case, each converter of the back‐to‐back system is used as a power conditioning system for the SMES coils. Since the AC–DC converter can be designed independently of the frequency of the power system, a two‐way switch is connected to the AC side of each converter. This two‐way switch can select the interconnected power systems. By using the two‐way switches, this system can provide the stored energy in the SMES system to each interconnected power system through two AC–DC converters. For instance, lower‐cost power of each power network can be stored through two converters during the off‐peak hours and made available for dispatch to each power network during periods of demand peak. Then this system increases the reliability of electric power networks and enables the economical operations depending on the power demand. This paper describes the unique operations of the back‐to‐back interconnection with SMES and discuses the optimal SMES configuration for a 300‐MW‐class back‐to‐back interconnection. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 37–43, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20482     

灯泡贯流式水轮发电机组常见故障和防治措施

为了系统地了解灯泡贯流式水轮发电机组的故障类型和特点,通过对此类机组典型的故障例子进行分类和分析,总结出定子铁心松动、转子阻尼条断裂以及转子扫膛等故障是此类机组的主要危害因素,并提出了相应的防治措施。     

A dynamic mathematical model and vector block diagrams for class of hybrid‐field synchronous motors

This paper proposes a new dynamic mathematical model and new block diagrams for a newly emerging class of salient‐pole hybrid‐field synchronous motors (HFSM) that have rotor field by both permanent magnet and winding. The proposed mathematical model has the following completeness and generality. (1) It consists of three consistent basic equations such as circuit, torque, and energy‐transmission equations. (2) It deals with pole saliency and contains nonsaliency as a special case. (3) It is a dynamic model and contains a static one as a special case. (4) It is established in the general reference frame including stator and rotor reference frames as special cases. The proposed new block diagrams using vector signals for salient‐pole HFSM are established based on the model. It has the following attractive features. (1) It succeeds in realizing clear configurations with physically meaningful vector signals, which are helpful for understanding motor electromagnetic mechanisms and useful for designing controllers for the salient‐pole HFSM. (2) Vector signals utilized as transfer signals between blocks are defined in the general reference frame. Consequently, the vector‐signal block diagrams in the frame can be directly and easily reduced to the ones in such a specific frame as stator and rotor frames. (3) It is compact. Two typical and compact but sufficiently general vector‐signal block diagrams are newly presented. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 47–57, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20112