The authors company has had extensive experience providing steam turbines including auxiliary systems as a turn key contractor for more than 40 years. Bypass systems are an integrated part of modern Combined Cycle Power Plants (CCPP) [1]. Bypass systems contribute a major part for operational flexibility. They allow the shortest start-up times by minimising mismatches between boiler/HRSG and turbine. Bypass systems also lead to predictable and repeatable start-up times, as well as reducing solid particle erosion of component, to a great extent. The functional requirements for bypass valves are: • Control mode for an accurate control of the IP and LP bypass steam flow during the unit start-up and shut-down, as well as during normal operating transients. • Fast closing mode for bypass-trip (supported by spring force) when required for condenser protection. • Combined mode for fast reaction on pressure increase to a define set point and further action in control mode. In the past, a combined stop and control valve design, each with a separate stem, was common. The challenging objective for the bypass valve design was to integrate the control function and the trip function with a single stem design. The authors company has developed this advanced steam turbine bypass valve that incorporates hydraulic actuator with a single stem design. The valve bodies have noise reduction fittings and are equipped with large extensions on the outlet side to reduce vibration throughout the bypass system. The bypass valve body has an integrated steam strainer which protects both valve parts and the condenser from external debris. The bypass design is prepared for Power Plants with elevated temperatures which allow for the highest plant efficiencies [2]. Surface coating protect moving components against oxidation and reduce friction by means of a surface coating. Steam at high temperature passes through the bypass to the condenser. An incorporated water attemporating flow control system reduces the steam temperatures before entering the condenser. Condensate water is injected through an orifice in the bypass system. The orifice is located down stream in the pipe between the bypass valve and condenser. Electro-hydraulic supply units deliver the control fluid to the bypass valves. An optimized bypass system has to provide: • Long service life with low maintenance costs; • High stroke speed; • Pressure control by unit set point; • High actuation forces; • Accurate positioning; • Very short trip time into closed position. By means of bypass station, one can get highest flexibility of power plants use of the new valve one will get highest control performance and shortest reaction time.

The output capacity of combined cycle power plants is reduced in many cases, and sometimes forced to outages, when its main components are affected by faults, i.e., when the rotating equipment such as turbines, generators, compressors, pumps and fans suffer a failure. Normally, the overall reduction of the efficiency, and sometimes the component efficiencies, is monitored but it is difficult to identify the primary causes of the fault of the specific equipment that causes the reduction of plant efficiency. Therefore, to reduce the time of faulty operation, a precise diagnostic tool is needed. One such tool is an expert system approach, which is presented in this work. It consists of several expert systems for the identification of the faults caused by deterioration of the inner parts of the equipment, Fig. 1. Such faults not only reduce the plant efficiency but in many cases also increase the vibrations of the rotor-bearing system. Based on knowledge, the various expert systems have been constructed and their algorithms (efficiency reduction) developed for the following equipment: steam turbines, gas turbines and compressors, condenser, pumps and water cooling system. An expert system for detecting faults that increase the vibration of the rotor–bearing system is also presented. As far as the turbo compressor expert system is concerned the fault hybrid patterns previously developed were implemented and described elsewhere [1].

This paper presents an application of a non-contacting blade tip timing measurement system using two-sensor method (so-called BSSM) at a low-pressure model steam turbine to investigate dynamic blade stress in extended operation conditions (so-called windage). An analysis method to identify the vibration frequencies and to determine the response amplitudes for the first few excited vibration mode shapes is described in detail. Objective of this paper is to discuss the performance and inherent limitations of the non-contacting measurement system. For that the BSSM results were compared with the blade vibration data obtained from strain gauges. Some experiences and suggestions are also made to improve the reliability and accuracy of this measurement system.

The fossil fuel depletion and the CO 2 warming due to the combustion are becoming serious environmental issues. Therefore, alternative energy systems minimumizing fossil fuels dependence are now required to be developted. Hydrogen is a best candidate for alternative energy sources friendly to the environment, but the essential point is how we produce hydrogen, independently of fossil fuel with a minimum energy input. This work aims first at proposing an alternative hydrogen gasifier from acid water by immersing ionicity metals, and second at applying the gasifier to a hydrogen ultra micro gas turbine electric generator charger system to construct hydrogen self supply energy system. First, D 2 SO 4 as acid aqueous solutions and (Zn+Cu) and Zn plates as ionicity metals electrodes are selected here for H 2 gasifier. The hydrogen production rate is experimentally characterized by changing the pH and temperature of the solution and the metal surface area. The gasifier has a good performance of hydrogen production of about 18 l/min at 60°C per unit electrode area under the pH = ∼1.0. This flow rate increases almost linearly to the acid temperature. In addition, the zinc resolved into the acid water, ZnSO 4 in the case of D2SO4 for example, is able to be easily recrystalized on the electrode by reasonable electricity input of ∼2.5V. Second, the produced hydrogen is applied to ultra micro turbo electric generator / charger as hydrogen self supply system. This smart system is well applicable to hydrogen electric car, because of an ideal power source having small size, lightweight, low vibration, early start, no NO X and CO 2 emissions, very low fuel consumption, long trip, etc. In the experiment a car turbo charger is converted into a compressorturbine system, and a high revolution electricity generator is connected to the turbo system. A combustor is designed for very low hydrogen consumption by ultra lean burning which causes almost no NO X emission due to low temperature < 1000°C. The turbo system is tested, resulting in a high efficiency, in spite of its small size, enough to generate electricity for charging a battery of electric car. By using these two elements, we aim to construct HSSES (Hydrogen Self Supply Energy System) which is found to be attractive especially for small electric cars and home cogenerations.

Entergy’s Willow Glen Unit 4 main boiler feed pumps experienced high vibration levels and short run times since installation in the 1970’s. The two 14,000 horsepower units have been rebuilt many times, with operating life averaging 18 months before vibration levels became excessive. To operate the unit until the next outage, operators had to reduce the running speed of the turbine drivers to control pump vibration and generate less electricity. Vibration and modal analysis testing coupled with lateral rotor dynamic computer models indicated that changing the stiffness of the bearing housing supports and rotor could significantly improve the pump. It was decided to proceed with design changes and as an interim solution fit the pumps with dynamic absorbers to reduce bearing housing vibrations. After the design changes were incorporated the pump operates with vibration levels in the .15 ip/s range.

The mechanism of disk cracking was investigated and an evaluation method for its failure occurrence rate was developed. It was found that the disk cracking was caused by the corrosion pit growth, the superposition of the multiple vibration modes, and the increase in the scatter of the natural frequency due to the interface condition change after long-term operation. The effects of several uncertainties on the failure occurrence rate were examined and the values of the uncertainties were obtained by solving the inverse problem according to the failure analysis; the examined uncertainties were the standard deviation of the natural frequency and the stimulus ratio. It is recommended to perform the replica inspection by removing the blades and to take the proper maintenance actions based on the remaining life evaluations because relatively small corrosion pits can cause crack initiation. It was found that a continuous cover blade is superior to the conventional tenon-shroud-type grouped blade because the former reduces resonance points in the interference diagram and eliminates any tangential modes which are main contributors for the disk cracking.

Vibration related outages due to an unbalance in rotating equipment have been a historic problem in the power generation industry and have resulted in increased plant operating costs. Until recently, the only means for solving these vibration problems was to perform manual balancing on the rotating equipment. Active balancing systems have been used in other industrial processing applications, on ID/FD fans, compressors, and turbines, for many years. Further developments in active balancing capabilities have positioned these systems to cover the broad range of applications in the power generation industry today.

Large turbine generators have torsional modes of vibration that can be excited from the electrical grid by torques applied through the generator. The most significant of these torques has a frequency at twice the grid frequency and is due to the negative sequence current in the generator caused by operation at unbalanced load or during grid transients. When the twisting modes of the low pressure turbine rotors combine with the vibratory modes of the last few stages of blade rows, and the frequency of the combined torsional mode is close to the frequency of the exciting torques, significant vibratory response of the shaft and blades can occur. The accumulated fatigue damage caused by such vibration over time can result in failure of the blades. Since this low damped torsional vibration can not be seen on any of the plant instrumentation, it can result in the loss of low pressure blades with little or no warning. To ensure that the turbine generator is not susceptible to damage from the torsional vibratory response of these modes, it is necessary to confirm that the torsional frequencies are sufficiently removed from the frequency of the exciting torques when the turbine generator is operating. For a large turbine generator, the torsional modes of concern are often between the 15th to 25th mode of vibration. Analysis techniques may not be able to determine the frequency of these modes within the accuracy required to ensure that they are not excited. The only reliable way to determine the natural frequencies of such modes with sufficient accuracy is to measure them directly while the turbine generator is operating. On-line monitoring is often the preferred approach for such measurements since it does not impact the operation of the plant and it determines the torsional natural frequencies at the plant operating conditions. Torsional natural frequencies tend to change as a function of turbine generator speed while the turbine generator is off-line and as a function of power while the turbine generator is on-line. On-line monitoring uses sensitive instrumentation and time averaging techniques to determine the torsional natural frequencies of a turbine generator from random vibration of the shaft while the turbine generator is operating. Identifying the torsional mode that is associated with each measured frequency requires the combination of a good analytic model of the turbine generator and an understanding of how the torsional frequencies react to specific changes in operating parameters. The analytic and measurement techniques that have been developed through experience and implemented during numerous on-line measurements are described in this paper. These techniques have also been used to determine blade stress response levels to torsional excitation in order to evaluate the susceptibility of a specific turbine generator to damage from torsional vibration. In this regard, there is some evidence that the torsional response of the turbine generator can be amplified by the steam flow through the blade path. Finally, these techniques can be used to evaluate any specific transient that occurs during operation of the plant with respect to its impact on fatigue usage of the turbine blades and shaft. If necessary, modifications can be designed to shift the torsional natural frequencies away from the problem torques once the complete response of the turbine generator to torsional excitation is understood.

Machine degradation has become a key issue with respect to the operational and maintenance costs associated with industrial and power generation facilities. Current online techniques for monitoring rotor integrity are largely based on lateral overall vibration levels that may provide only a very short notice of impending failure. As an alternative, shifts in rotor torsional natural frequencies could be used as early indicators. Torsional vibration spectra have been gathered on numerous horizontal hydro turbine generator shafts at two Southern Company owned hydro plants. The data was trended for approximately 2 years and changes were compared against findings from visual and nondestructive testing. It was determined that in the very early stages of failure the torsional frequency shifts are minute and may be masked by or be indistinguishable from other phenomena but are detectable. As the degradation progresses, the frequencies shifts may increase greatly with the crack size and are easily discerned. While the degree of early warning capability based on this technique will more than likely vary with each failure occurrence, it should generally outperform existing lateral vibration based techniques.