1-Yes, I used following text books.
a-Wind Power in Power Systems
Royal Institute of Technology
b-Electric Power System Basics
For the Nonelectrical Professional
Steven W. Blume
2- Fundamentally the wound rotor synchronous generator (WRSG) type can be used in both system but there are many electrical and mechanical characteristics difference between hydro generator and synchronize generator which can be used in mentioned type D configuration. Also induction electrical machine operating in motor/generator conditions can be use in wind power plant and pumped hydro power generation system; because in both them bidirectional power flow is necessary. Conventional pumped hydro uses two water reservoirs, separated vertically. During off peak hours water is pumped from the lower reservoir to the upper reservoir. When required, the water flow is reversed to generate electricity. Some high dam hydro plants have a storage capability and can be dispatched as a pumped hydro. Underground pumped storage, using flooded mine shafts or other cavities, are also technically possible. Wind turbine in 40MW range is not applicable, however it seems using type A, B configuration in pumped hydro generation is possible theoretically.
The WRSG which applied in wind power plant (type D) is the workhorse of the electrical power industry. Both the steady-state performance and the fault performance have been well-documented in a multitude of research papers over the years, (see L. H. Hansen et al., 2001).
The stator windings of WRSGs are connected directly to the grid and hence the rotational speed is strictly fixed by the frequency of the supply grid. The rotor winding is excited with direct current using slip rings and brushes or with a brushless exciter with a rotating rectifier. Unlike the induction generator, the synchronous generator does not need any further reactive power compensation system. The rotor winding, through which direct current flows, generates the exciter field, which rotates with synchronous speed. The speed of the synchronous generator is determined by the frequency of the rotating field and by the number of pole pairs of the rotor.
The wind turbine manufacturers Enercon and Lagerwey use the wind turbine concept Type D with a multipole (low-speed) WRSG and no gearbox. It has the advantage that it does not need a gearbox.
Since waterwheel generators are custom designed to match the hydraulic turbine prime mover, many of the generator characteristics (e.g., short-circuit ratio, reactances) can be varied over a fairly wide range, depending on design limitations, to suit specific plant requirements and power distribution system stability needs. Deviations from the nominal generator design parameters can have a significant effect on cost, so a careful evaluation of special features should be made and only used in the design if their need justifies the increased cost.
The electrical and mechanical design of each generator must conform to the electrical requirements of the power distribution system to which it will be connected, and also to the hydraulic requirements of its specific plant.
The voltage of large, slow speed generators should be as high as the economy of machine design and the availability of switching equipment permits. Generators with voltage ratings in excess of 16.5 kV have been furnished, but except in special cases, manufacturing practices generally dictate an upper voltage limit of 13.8 kV for machines up through 250 MVA rating. Based on required generator reactance, size, and Wk2, a lower generator voltage, such as 6.9 kV, may be necessary or prove to be more economical than higher voltages. If the generators are to serve an established distribution system at generator voltage, then the system voltage will influence the selection of generator voltage, and may dictate the selection and arrangement of generator leads also.
The majority of hydroelectric installations utilize salient pole synchronous generators. Salient pole machines are used because the hydraulic turbine operates at low speeds, requiring a relatively large number of field poles to produce the rated frequency. A rotor with salient poles is mechanically better suited for low-speed operation, compared to round rotor machines, which are applied in horizontal axis high-speed turbo-generators.
Generally, hydroelectric generators are rated on a continuous-duty basis to deliver net kVA output at a rated speed, frequency, voltage, and power factor and under specified service conditions including the temperature of the cooling medium (air or direct water). Industry standards specify the allowable temperature rise of generator components (above the coolant temperature) that are dependent on the voltage rating and class of insulation of the windings (ANSI, C50.12; IEC, 60034-1). The generator capability curve describes the maximum real and reactive power output limits at rated voltage within which the generator rating will not be exceeded with respect to stator and rotor heating and other limits. Standards also provide guidance on short-circuit capabilities and continuous and short-time current unbalance requirements (ANSI, C50.12; IEEE, 492).
Synchronous generators require direct current field excitation to the rotor, provided by the excitation system described in the section entitled ‘‘Excitation System’’. The generator saturation curve describes the relationship of terminal voltage, stator current, and field current.
While the generator may be vertical or horizontal, the majority of new installations are vertical. The basic components of a vertical generator are the stator (frame, magnetic core, and windings), rotor (shaft, thrust block, spider, rim, and field poles with windings), thrust bearing, one or two guide bearings, upper and lower brackets for the support of bearings and other components, and sole plates which are bolted to the foundation. Other components may include a direct connected exciter, speed signal generator, rotor brakes, rotor jacks, and ventilation systems with surface air coolers (IEEE, 1095).
The stator core is composed of stacked steel laminations attached to the stator frame. The stator winding may consist of single turn or multi turn coils or half-turn bars, connected in series to form a three phase circuit. Double layer windings, consisting of two coils per slot, are most common. One or more circuits are connected in parallel to form a complete phase winding. The stator winding is normally connected in wye configuration, with the neutral grounded through one of a number of alternative methods that depend on the amount of phase-to-ground fault current that is permitted to flow (IEEE, C62.92.2, C37.101). Generator output voltages range from approximately 480 VAC to 22 kVAC line-to-line, depending on the MVA rating of the unit. Temperature detectors are installed between coils in a number of stator slots.
The rotor is normally comprised of a spider frame attached to the shaft, a rim constructed of solid steel or laminated rings, and field poles attached to the rim. The rotor construction will vary significantly depending on the shaft and bearing system, unit speed, ventilation type, rotor dimensions, and characteristics of the driving hydraulic turbine. Damper windings or amortisseurs in the form of copper or brass rods are embedded in the pole faces for damping rotor speed oscillations.
The thrust bearing supports the mass of both the generator and turbine plus the hydraulic thrust imposed on the turbine runner and is located either above the rotor (suspended unit) or below the rotor (umbrella unit). Thrust bearings are constructed of oil-lubricated, segmented, babbit-lined shoes. One or two oil-lubricated generator guide bearings are used to restrain the radial movement of the shaft.
Fire protection systems are normally installed to detect combustion products in the generator enclosure, initiate rapid de-energization of the generator, and release extinguishing material. Carbon dioxide and water are commonly used as the fire quenching medium.
Excessive unit vibrations may result from mechanical or magnetic unbalance. Vibration monitoring devices such as proximity probes to detect shaft run out are provided to initiate alarms and unit shutdown.
The choice of generator inertia is an important consideration in the design of a hydroelectric plant.
The speed rise of the turbine-generator unit under load rejection conditions, caused by the instantaneous disconnection of electrical load, is inversely proportional to the combined inertia of the generator and turbine. Turbine inertia is normally about 5% of the generator inertia. During design of the plant, unit inertia, effective wicket gate or nozzle closing and opening times, and penstock dimensions are optimized to control the pressure fluctuations in the penstock and speed variations of the turbine generator during load rejection and load acceptance. Speed variations may be reduced by increasing the generator inertia at added cost. Inertia can be added by increasing the mass of the generator, adjusting the rotor diameter, or by adding a flywheel. The unit inertia also has a significant effect on the transient stability of the electrical system, as this factor influences the rate at which energy can be moved in or out of the generator to control the rotor angle acceleration during system fault conditions.
3- In modern pumped hydro power plant the power generator type opposite in dam hydro power plant is induction generator.Generally Variable-speed motor-generators allow operation of the pump-turbine unit over a wider range of head and flow, making them economically advantageous for a pumped-storage facility.
The 1,060-mw Goldisthal pumped-storage plant on the Schwarza River is the biggest hydroelectric project in Germany and the most modern in Europe. It is an important component of Vattenfall Europe Generation AG & Co. KG’s generation capacity. Construction on the project began in September 1997, and the plant started commercial operation in October 2004.
The Goldisthal project is unique in that two of the four vertical Francis pump-turbine units feature variable-speed (asynchronous) motor-generators. This arrangement provides several benefits for Vattenfall Europe, including: power regulation during pumping operation, improved efficiency at partial load conditions, and high dynamic control of the power delivered, for stabilization of the grid.
The most important innovation at the Goldisthal project is the first-ever application of variable-speed motor-generators of this size in a hydro plant in Europe. In essence, turbines have one optimum operating point in terms of head, flow, unit size, and speed. But when these units are coupled with a variable-speed motor-generator, operating speed can be varied over a certain range of the nominal synchronous speed of the turbine-generating unit. As head and flow vary, the unit is able to increase or decrease its speed to operate closer to peak efficiency for this unique set of conditions.
The difference between synchronous and asynchronous machines is the rotor. While classical synchronous generators have salient poles, variable-speed generators have a three-phase winding on the rotor. And while the synchronous rotor is energized by a direct current (DC) to create a rotating magnetic field, the asynchronous rotor is energized by a low-frequency alternating current (AC). A direct frequency converter in the rotor circuit is used to control the frequency. If the frequency is changed, so too is the speed of the unit.
The rotor can be retarded or accelerated opposite the stator field, from 90 to 104 percent of the synchronous speed. The variable frequency of the asynchronous generators at Goldisthal ranges from 5 Hertz (Hz) opposite the stator field of 333 revolutions per minute (rpm) (which provides 300 rpm) to 0.01 Hz (which is nearly the rated speed of the unit) to 2 Hz additional to the stator field (which provides 340 rpm).
Asynchronous motor-generators provide several advantages, including:
• More flexibility in their operation;
• Higher efficiency over a wide range of operations at partial load conditions;
• A wide range of controllable and optimized power consumption in pump operation;
• Additional and faster features for grid control, such as fast power outlet regulation;
• Better use of the reservoir because higher water level variations can be allowed; and
• Better contribution to grid stability because of the high moment of inertia of the rotating masses.