T.J. Hammons

Effect of Damper Modelling and the Fault Clearing Process on Response Torque and Stressing of Turbine-Generator Shafts

The paper discusses the effect damper circuit modelling and the current interruption process following clearance of grid network disturbances has on machine transient response. Parameters for a 2-direct-axis and 3-quadrature-axis damper circuit model are given, as are those for lower-order damper model equivalents. Torques obtained following clearance of typical L-L-L and L-L non-ground system disturbances at fault current zeros or by simultaneous interruption for detailed and reduced damper models are illustrated. Further, the effect damper circuit modelling has on peak torque response following clearance of supply network disturbances at fault current zeros, sustained L-L-L and L-L stator terminals short-circuits and worst-case malsynchronisation is depicted.

Electrical Damping and Its Effect on Accumulative Fatigue Life Expenditure of Turbine-Generator Shafts Following Worst-Case Supply System Disturbances

The paper examines the effect electrical phenomena has on damping torsional vibrations of turbine-generator shafts resulting from severe disturbances on the system supply. The effect system impedance and power factor has on time constants for decay of predominant shaft torsional vibrations and on fatigue life expenditure of the shaft following worstcase events is investigated. The impact pole slipping resulting from delayed fault clearance has on peak shaft torque and on accumulative fatigue life expenditure of the shaft is also examined.

Effect of Fault Clearing and Damper Modelling on Excitation and Decay of Vibrations in Generator Shafts Following Severe Disturbances on the System Supply

The paper examines the effect damper circuit modelling and the current interruption process has on amplitude and decay of torsional vibrations in turbine-generator shafts following severe supply network disturbances. A phase-variable model of a synchronous-generator with up to 2 direct-axis and 3 quadrature-axis dampers where fault current is cleared at fault current zeros is employed to calculate generator airgap torque which results from a severe disturbance on the electrical supply. Using airgap torque, effective amplitude of torque excitation acting on the generator rotor for each eigenfrequency is determined by Fourier analysis. Amplitude of torsional vibration at each shaft section for each modal frequency is then calculated. Shaft torque at each shaft location for each modal frequency is thereby deduced. These components, together with the steady-state component (and that due to rotor swing), are summed as absolute values for all modal frequencies to yield approximate peak torque at critical locations along the shaft following each disturbance. Approximate peak shaft torque estimated by frequency domain analysis is compared in some instances with peak torque predicted by solution of exact differential equations. Presented results illustrate amplitude of torque excitation and shaft torques as a function of fault clearing time for L-L-L and L-L high-voltage system short-circuits, and effect reactive power and system resistance has on damping predominant torsional vibrations in the shaft.

Accumulative Fatigue Life Expenditure of Turbine/Generator Shafts Following Worst-Case System Disturbances

The paper reviews phenomena which influence accumulative fatigue life expenditure of turbine-generator- exciter shafts following severe disturbances on the electrical supply.

Feasibility of Iceland/United Kingdom HVDC Submarine Cable Link

This paper addresses the viability of a submarine cable connection from Iceland to the North of Scotland extended by HVDC overhead line to the South of England. Hydro development, submarine cables, HVDC overhead transmission lines, rectifier/invertor stations, investment cost attributable to a power sale, availability of the connection, technical considerations and cost comparisons is discussed.

African Electricity Infrastructure, Interconnections, and Changes

A 1996 IEEE PES Summer Meeting panel session focused on African Electricity Infrastructure, Interconnections, and Electricity Exchanges. The session was sponsored by the PES Energy Development and Power Generation Committee and organized/moderated by T.J. Hammons, chair of the International Practices Subcommittee. Panelists discussed energy resources, feasibility studies to interconnect power systems, the present state of the electric power sector, future expansion of African power systems, interconnections and power exchanges, and the impact of the private sector on electricity supply. The presentations were as follows: Prospects of the Evolution of a Unified Interconnection Power System in Africa, Fouad Taher; The World Bank`s Involvement with African Electricity Infrastructure, Alfred Gulstone; Towards the implementation of an Integrated African Grid, Bai K. Blyden, Raymond Johnston; Grand Inga Interconnection Projects, Elese Isekemanga, K. Paluku; The Innovative Southern African Kilowatt Hour, Andries C. Calitz; Report on Burundi, Rwanda, and Zaire, Ngove-Ngulu Simanga.

Measurement of torque in steam turbine-generator shafts following severe disturbances on the electrical supply system-analysis and implementation

Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described. >

Impact of shaft torsionals in steam turbine control

Shaft torsional vibrations are discussed along with their effect on steam turbine-generator control following severe supply-network disturbances and the destabilization of shaft torsional modes through the action of high-speed electrohydraulic controllers. It is shown that shaft flexibility can exert a significant influence on steam turbine-generator response following a severe supply-system disturbance, particularly when the turbine has nonlinear valve stroking and fast valving. The effect can be minimized by the careful location of a speed sensor along the turbine shaft and by filtering speed or acceleration signals to reduce the speed input of troublesome low-frequency torsional vibrations to an insignificant level. The effect of shaft torsionals on control system response to an islanding situation and on the above mentioned destabilization is evaluated. Digital implementation of steam-turbine control systems in relation to quantization, sampling, response time in protection systems, and software integrity is examined. >

Effect of Load and Damper Modelling on Evaluation of Negative Sequence Capability of Large Generators

The paper examines negative sequence losses in solid generator rotors following sustained stator-terminal and HV system L-L short-circuits at full-load and no load with or without a connection to the grid supply. Components of stator current which give rise to rotor heating over the period of the transient are identified and effective intrinsic values ot I22 t for a range of system and machine parameters are discussed. The analysis uses a phase-variable model of a synchronous-generator with detailed and reduced damper representations to compute stator current following rated-voltage line-to-line disturbances on the supply. Simulations from full-load for a variety of system parameters with and without connection of a field discharge resistor on tripping of the generator breaker are performed. From the responses, components of stator current which give rise to rotor heating are isolated by Fourier analysis combined with symmetrical component analysis. These components are integrated over the period of the transient to give effective values of I22 t. Maximum supply-frequency components of stator current taking into account d.c. components have been assumed. Effective values of I22 t using detailed and reduced damper models in simulations with and without voltage regulator action are compared with values predicted by simpler calculations where no allowance is made for generator load or for the connection to the grid supply. A 500 MW, 3600 rpm and a 660 MW, 3000 rpm Machine are analysed.

World Energy Council 16th Congress Review

The sixteenth World Energy Council (WEC) Congress was hosted in Tokyo, Japan, October 8--13, 1995, with a theme of ``Energy for Our Common World: What will the future ask of us?`` Participants in the congress examined several fundamental issues of these times: hot to provide the energy services for an increasing world population, especially in developing countries; hot to meet local, regional, and global environmental and social concerns; how to adapt to changing markets and institutions; how to respond to diversified transportation and other end use patterns reflecting human behavior; how to deal with the emerging interdependence of energy markets; and what action to be pursued individually and collectively. This article summarizes the highlights of the congress, and includes an overview of the World Energy Council (WEC), a synopsis of the events, summaries of the technical program division addresses, and a summary of the congress conclusions.