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This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material. Index Terms--Generator ground fault protection, generator grounding, ground fault protection, grounding, stator iron damage.

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1--4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material. Index Terms--Generator ground fault protection, generator grounding, ground fault protection, grounding, stator iron damage.

Reliable emergency power supply is essential to fire services installations. However, the extent of reliability and availability of standby generators in Hong Kong buildings are a query so far. This paper presents a generator reliability survey in Hong Kong. The results regarding fault events, reliability, and availability of standby generators are shown by means of analysis of their fault/failure records. Recommendations on reliable operation of standby generators are also provided in the paper. Index Terms--Generator, reliability.

The use of PTFE-faced pads in large vertical axis hydro-generators was pioneered in Russia in the 1970s, prompted by a series of failures of conventional babbitt-faced bearings. Some advantages claimed include higher specific loading, lower power loss and the omission of oil-lift facilities. There is strong interest in the Industry concerning this material, but limited data are available on actual performance. Some results from extensive testing of PTFE-faced pads are given, for two sizes of pad. These are compared directly size-for-size with results for babbitt bearings of nominally the same area. The power losses for the two types of bearing were found to be almost identical. Some of the effects observed during testing are described and discussed, including the effect of creep. The test results are compared with predictions using the GENMAT analysis software. A method of allowing for creep in numerical modeling is discussed. [DOI: 10.1115/1.1576427]

An electric power system with a superconducting generator is described and discussed.

Research involving the application of high temperature superconductor (HTS) technology to generator design is discussed.

Design and development of a high temperature superconducting (HTS) mini power plant (MPP) is described. The system consists of a superconducting generator, transformer, fault current limiter, motor and energy storage device.

We present a single time period decentralized electricity market clearing model that includes reactive power and demand responsiveness in addition to the more common framework of generation-side competition for the real power commodity. The approach allows self-interested agents, namely producers and consumers, independently to maximize their individual surpluses subject to prices. This is consistent with the very notion of a competitive market as defined in equilibrium theory. An auctioneer computes equilibrium prices that achieve power balance at every network node as required by Kirchhoff's laws. The overall scheme is justified by duality theory for which there is a rich theoretical support, and convergence is achieved using a Newton price-updating algorithm. Index Terms--Auction, market coordination, market equilibrium, mathematical programming, optimization methods, power generation dispatch, power generation economics, power generation scheduling, power system economics.

This paper presents a Monte Carlo based approach to evaluate the maximum torsional torques induced in turbine-generator shafts during faults on a HVac/dc power system. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of various factors associated with the practical operation of a power system. The results of these investigations are presented in the form of probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections. A risk index that reflects the likelihood that the torque induced in a turbine-generator shaft exceeds its design value is also presented. Moreover, the paper presents a method for calculating the expected life expenditure ratio and the expected lifetime of turbine-generator shafts. Index Terms--High voltage direct current transmission, stochastic techniques, synchronous machines, turbine-generator shaft torsional torques.

This paper proposes a technique for online determination of the model parameters of synchronous generators, using pseudorandom binary sequence (PRBS) perturbations applied to the reference input of the automatic voltage regulator (AVR). First-order circuit models and the associated mathematical relationships are given for d-axis and q-axis representations of the generator, and the parameter estimation algorithm and implementation thereof are discussed. Experimental results are given for a 5-kVA round rotor synchronous generator. The estimated parameter values are compared with manufacturer's data and are also validated by comparing measured and simulated time-domain responses for the d-axis and q-axis currents and the field current. The technique yields good results, particularly for the magnetizing inductances, winding resistances and the field to stator transformation ratio. Index Terms--Parameter estimation, sequences, synchronous generators.

In this paper, the nonlinear phenomenon known as Hopf bifurcation, chaos, and asynchronous operation of a simple power system are explored. Firstly, taking into account the nonlinearity of the generator shaft and the interaction of mechanics and electrics in the generator sets, we get a transient model by combining Park equations and mechanics equations. Then the Hopf bifurcation, period-doubling bifurcation, and chaos caused by too large a line resistance are investigated with nonlinear mode and Floquet theory. The bifurcation figure of the system is also given. Further study shows that the chaos attractor breaks up into asynchronous operation when the resistance becomes larger. This way of loss-of-stability is different from that caused by loss-of-excitation. Index Terms--Bifurcation, chaos, generator sets, vibrations.

Recent years have seen an increasing development of small generations of electric power. These generators of relatively low power, equal or less than 100 MVA, are protected in an economic way by generator circuit breakers which are located between the generator and the step-up transformer. In 1997 the IEEE Switchgear Committee has issued a new edition of its standard C37-013 for generator circuit breakers, which covers mainly the applications with power transformers rated 100 MVA and above [1]. A revision of this standard is currently prepared by the IEEE Switchgear Committee in order to broaden its scope to all generator circuit breakers. The purpose of this paper is to contribute to the definition of TRV requirements for system-source faults in the case of small generator circuit breakers connected to the step-up transformer by cables. Index Terms--AC high voltage generator, generator circuit breakers.

This paper discusses how the switched reluctance generator (SRG) converts energy as directed by a controller. Beginning with a review of the electromechanics of generation, the paper identifies the implications of the energy conversion process on how the SRG is controlled. The structure of the SRG controller for speed-control and power-control applications is discussed. Practical implementation details for commutation of the SRG are reviewed. Concepts are illustrated with a 6-kW SRG designed to serve as a starter/alternator in automotive applications. Index Terms--Generator control, switched reluctance, synchronous generators.

Special protection systems (SPS) have been widely used to increase the transfer capability of the network by assisting system operators in administering fast corrective actions. Compared with constructing new transmission facilities, SPS can be placed in service relatively quickly and inexpensively. However, increased reliance on SPS results in additional risks to system security. In this paper, based on existing reliability evaluation methods, a generic procedure for risk-based assessment of SPS is proposed. The procedure can help the system operator to identify the risk brought by SPS and to make SPS-related decisions. An illustrative example which uses a generator rejection scheme (GRS) for transient instability is provided. Index Terms--Generator rejection scheme, impact, probability, reliability, risk, special protection systems.

The effect of generator subtransient reactance, rotor saliency, the number of generators in the Group Connection configuration and adjustable speed operation on the commutation reactance and harmonic levels of direct connected units are examined. Restriction limits for firing angles imposed by the commutation angle, generator terminal power factor, equivalent continuous negative-sequence harmonic loading are derived that permit the use of normal generators in direct connected units without the need for extra harmonic loading capacity. The generator harmonic ratings can be taken at the nominal speed and rated power output. Keywords: Unit Connection, Group Connection, HVdc, Converter, Harmonics.

This paper concerns an application of a three-phase cage induction machine (IM) as a self-excited generator connected to the ac side of a voltage-source pulsewidth modulation bidirectional inverter. The generator is supposed to be driven by a low-head unregulated shaft hydraulic turbine. The proposed system is intended to be applied in rural plants as a low-cost source of high-quality ac sinusoidal regulated voltage with constant frequency. Simulation results are obtained based on the [Alpha][Beta][Gamma] stationary reference frame model of the IM. The experimental results demonstrated that the system presents satisfactory behavior when feeding ac loads and during the startup of induction motors. Index Terms - Induction generator, pulsewidth modulation inverter, renewable energy resources.

Permanent-magnet (PM) generators have been used for wind turbines for many years. Many small wind-turbine manufacturers use direct-drive PM generators. For wind-turbine generators, the design philosophy must cover the following characteristics: low cost, light weight, low speed, high torque, and variable-speed generation. The generator is easy to manufacture and the design can be scaled up for a larger size without major retooling. A modular PM generator with axial flux direction was chosen. The permanent magnet used is NdFeB or ferrite magnet with flux guide to focus flux density in the air gap. Each unit module of the generator may consist of one, two, or more phases. Each generator can be expanded to two or more unit modules. Each unit module is built from simple modular poles. The stator winding is formed like a torus. Thus, the assembly process is simplified and the winding insertion in the slot is less tedious. We built a prototype of one unit module and performed preliminary tests in our laboratory. Follow-up tests will be conducted in our laboratory to improve the design. Index Terms - Axial flux, modular generator, permanent magnet, wind energy.

This paper studies operation of the multipole single-phase switched reluctance generator (SRG) under faults, in particular an 8/8-pole switched reluctance machine. A new converter topology which connects coils two banks in parallel is proposed. The combination of multiple coils per phase and the converter circuit suggests improved operation under faults compared with conventional topologies. Output power per coil current under faults is studied by finite-element analysis and static torque measurement. Circuit equations under faults are derived and operation under faults is evaluated by simulation. An SRG controller is constructed and experiments are performed. The experimental results support the equations and simulation results. It is concluded that the SRG can continue generating operation, even when open- or short-circuited coil faults occur, with the proposed converter and proper fault detection circuits. Index Terms - Faults, single-phase multipole machine, split-winding converter, switched reluctance generator.

The paper discuses the development of an axial-flux permanent-magnet generator for a gearless wind energy system which aims to demonstrate the feasibility of integrating wind and photovoltaic energy converters for the generation of electricity and to achieve optimum exploitation of the two energy sources. The merits of an axial-flux generator topology are discussed with reference to the particular requirements of an electrical generator for a direct-coupled wind turbine application. The design, construction and test results of a 5 kW, 200 rev/min permanent-magnet generator, to form a 10 kW pilot power plant with a 5 kW photovoltaic array, are presented.

In this paper we describe the parallelisation of an existing FE code for modeling rotating machines. A geometric mesh partitioning approach is applied within the Bulk Synchronous Programming (BSP) framework for the assembly and solution phases of the finite element computation. This is combined with a nongeometric, data driven parallel procedure for the evaluation of right hand side terms associated with the coils. Index terms - parallel, transient, eddy current

A new algorithm for the computation of steady-state conditions of electric machines is presented. It is based on a large time increment method used in mechanics. It is applied to the electromagnetic field computation in a generator. Compared with the step by step algorithm, the CPU time is strongly reduced. Index terms - Nonlinear algorithms, Maxwell equations, eddy currents, nonlinear magnetics, generators.

This paper proposes a newly developed cooperative control scheme between an HVDC transmission system and a radially connected thermal power plant. The proposed control scheme aims at stable control of the generator frequency during and after the transition from at/de parallel connected operation to radially connected operation of the HVDC system and the thermal power plant due to loss of ac transmission. The advantage of the proposed control scheme is to minimize the loss of generation in the transition state by the high-speed cooperative control where control quantities, calculated based on the necessary data acquired prior to the occurrence of the loss of ac transmission, are applied. A prototype of the control equipment was manufactured and subjected to performance evaluation tests by means of a large-scale analog simulator. Keywords: HVDC, generator-HVDC radial system, PLU relay

This paper presents dynamic performances of an isolated self-excited induction generator (SEIG) under different power-factor loading conditions. Both simulated results based on computer simulations and experimental tests based on a laboratory 1.1 kW induction motor driven by a dc motor are clearly compared. Characteristics of both terminal voltage and magnetizing reactance of the studied SEIG subject to sudden connection and disconnection of various power-factor loads are investigated. Key words: induction generator, self excitation, loading conditions, dynamic analyses.

A high-power transit-time oscillator operating at 4.0 GHz in the cylindrical-cavity T[M.sub.010] mode is proposed. Without requiring an externally applied magnetic field, the oscillator comprises a diode electron gun and a cylindrical cavity that are combined into a single unit that makes for a compact, lightweight device. The transit-time effect, which underlies the operation principle of the oscillator, is examined through a small-signal analysis from which a relation embodying the cavity length, resonant frequency, and cathode voltage is derived. Proper de voltages of 18 kV are applied to the diode gun which runs in the space-charge-limited regime and produces a 27A-current hollow electron beam. Output power is extracted axially from the system by aperture coupling the cavity to an external waveguide where outgoing traveling waves with 60 kW peak power are observed by means of 2.5D particle-in-cell computer simulations. Index Terms - Electron bunching, microwave generation, transit-time oscillator.

Three-dimensional nonuniform plasmas and boundary layers have been studied numerically under an MHD interaction. The nonuniform plasma of 'streamer' owing to weak ionization of seed material has a spiral structure in r-[Theta] plane, and the plasma becomes almost uniform between the walls in r-z plane. This structure is almost the same as that in our previous paper, where the gas (heavy particle) properties are assumed to be invariant and steady. In addition to the streamer, the nonuniform plasma of 'domain' owing to weak ionization of noble gas is revealed. The domain has the structure perpendicular to the streamer. In a strong MHD interaction case, the static pressure considerably increases in the upstream region of a generation channel, and the pseudo-shock waves appear in the generator, but the plasma is almost uniform along [Theta] direction. The boundary layer in the strong MHD interaction is considerably thick, and in the broad region near the wall the Hall current flows reversely. In the weak MHD interaction case, the plasma forms a nonuniform structure along the [Theta] direction, and the Hall current does not always flow in the opposite direction even on the insulator wall since the azimuthal electric field is not zero. Index Terms - Boundary layer, MHD generation, MHD interaction, nonequilibrium plasma, three-dimensional simulation.

Pulse power systems delivering in excess of 100 MJ represent one of the next major challenges to the community. While laboratory pulse power systems in this energy range are feasible, they represent very substantial investments of both time and resources. Prudence requires that fundamental proof of principle for the contemplated application be established before such massive resources are committed. Explosive pulse power systems using magnetic flux compression provide a direct path to such demonstrations. Furthermore, as energy requirements grow, they may represent the only affordable source of ultra-high energy environments. In this paper we report the results of an experimental test of a first generation disk generator system. Individual disk segments have been tested with framing camera diagnostics to evaluate overall performance dynamics and material, and fabrication failure points. In general no bulk failures were observed in several shots and the critical weld joints were seen to maintain integrity for at least 4 [[micro]seconds] after arrival of the detonation front. Single module pulse power experiments have been conducted at reduced initial current (1.5-2.0 MA) with a fixed inductance load of 0.22 nH. Index Terms - Disk explosive flux compressor, flux compression generators, high explosive pulsed power, imploding liners, solid liners.

An universal tabu search algorithm for the optimization of functions with continuous variables is presented based on the tabu method so far used. Essentially, the improvements include the transition criterion for different states, the determination of the step vector, the cancellation of tabu list, the stop criteria, and the restart from the optimum etc.. The numerical performances of the present algorithm are investigated using a benchmark problem and the geometry optimization of the multisection arc pole shoe in large salient pole synchronous generators. Index terms - Inverse problem, Global optimization, Stochastic algorithm, SA algorithm, Tabu search technique.

Pole slipping of synchronous generators operating in parallel with a utility supply system is a complex phenomenon. This paper provides an overview of a new solution for pole slipping protection, together with a review of conventional techniques. Immediate advantages of the new approach are that it simplifies relay settings and avoids the need for extensive simulation studies. Results from simulation studies and field tests are used to demonstrate the performance of these systems. The new technique is shown to offer a significant improvement in performance over conventional schemes. Keywords: Power system protection, Pole slipping protection, Out-of-step protection, Digital protection, Numeric protection.

This paper describes a set of results of detecting nonlinear phenomena appearing in a turbine generator power system with series-capacitor compensation. The analysis was based on the Floquet theory as well as the Hopf Bifurcation theorem. After the first Hopf bifurcation, the stable limit cycle bifurcates to a stable torus and an unstable limit cycle which connects to a stable limit cycle by a supercritical torus bifurcation. The stable limit cycle joins with an unstable limit cycle at a cyclic fold bifurcation. This unstable limit cycle is connected to the second Hopf. It has been also numerically demonstrated that such a strange sequence of periodic orbits is created by a q-axis damper winding. Keywords - Bifurcation, Floquet multiplier, Nonlinear analysis, Subsynchronous resonance, Series capacitor compensation, Power system dynamics

This paper describes a new method of solving the dynamic dispatch problem. Boiler-turbine generators are characterised by variable operating costs and ramp rate constraints and costs. All system costs are piecewise linear. The method employs concepts from dynamic programming and linear programming. Dispatch decisions that minimise system variable cost and marginal costs are determined. Generator outputs are not discretised. Efficiency gains over dynamic programming are achieved by exploiting the underlying convex geometry of the problem and avoiding discretisation of the state space. Keywords: dynamic programming, linear programming, constructive dynamic programming, dynamic dispatch, economic dispatch, ramp rates

A method is proposed to detect shaft torsional vibrations in AC motors and generators from their stator currents. This is achieved by extracting current components at specific frequencies which are the modulation products of the power system frequency and the vibrating frequency. A general closed form proof of this principle is given for both induction and synchronous machines, and the principle is verified quantitatively by digital simulation and experimental results. The effect of the machine operating point is also investigated. The method is applicable to torsional vibrations induced by different causes. When the oscillating torque is developing and the measured stator current is nonstationary, the Wavelet Transform can be used to extend the application of the proposed method to transient conditions.

This paper explores the use of an interior permanent-magnet synchronous machine (IPM) as a source of controlled DC power. A three-phase diode rectifier converts the generated AC power into DC, which is further processed by a buck or boost DC-DC converter with a pulse-width modulation voltage controller for load voltage and output power regulation. The modeling and analysis of the generator system set forth are confirmed to accurately predict the generator characteristics by experimental results derived from a 2 hp interior permanent-magnet generator controlled separately by a buck and a boost DC-DC converter.

Various aspects of system analysis are presently conducted by using an explicit scenario for each perturbation relative to a preestablished base case scenario. Observations presented in this study demonstrate that many single scenarios are often closely similar when distribution factors on interutility transmission ties are used to guide a scenario reduction technique. This process facilitates a reduction in the total number of scenarios needed to characterize a particular network configuration, while preserving their associated parallel path characteristics. This paper applies the technique to energy transactions and generator siting options using generator shift factors and suggests it can be used as an initial screening method for broad area assessment. Keywords - Power systems operations, Transmission open access, Parallel paths, Distribution factors, Data reduction