Hot Standby Mode Research Articles

Design of Signal Lamp Filament Monitoring Alarm Instrument

To improve the reliability of the light emitting diode (LED) signal lamp filament current monitoring alarm instrument for metro systems, a new type of hot standby online monitoring apparatus was developed which is based on synchronous transmission data (STD) bus technology. In this system, a double hot standby mode can be achieved by adopting bus arbitration. In addition, to detect the effective value of alternating current which is from 0 to 200 mA in the signal lamp lighting circuit, a precision rectifier signal conditioning circuit and an isolated acquisition circuit were designed. This new type of alarm instrument has high detection accuracy and could meet the functional requirements for metro signal systems after comparing it with some industry products that were applied on the spot.

System design and analysis of thermal power dispatch systems for boiling water reactors

Nuclear power plants are crucial to meeting net zero emission goals and achieving energy sustainability. Integrating these plants with clean energy technologies such as high-temperature steam electrolysis (HTSE) may improve the efficiency and economic competitiveness of these plants. The current study investigates the design and operation of a thermal power dispatch (TPD) system for coupling boiling water reactors (BWRs) to HTSE plants. The TPD system extracts a portion of the steam from the reactor’s main steam line and transfers its thermal energy to an HTSE plant through a power transport loop. A TPD system for 5 % steam extraction has been designed and the system performance during steady and transient operations has been analyzed. The TPD system dispatched a total of 197 MW thermal energy to the HTSE plant under nominal design conditions. Saturated steam at 7.17 MPa from the BWR plant was condensed and subcooled to a temperature of 168 °C, while a mass flow rate of 91.1 kg/s of superheated steam was dispatched to the HTSE plant. Furthermore, the system performance during transient operation showed a continuous transition from the initial hot standby mode to the nominal power dispatch level. The transient simulation results emphasized the importance of investigating component level performance for the TPD system design. The current results will guide future works on the development of integrated energy systems for hydrogen production or process heat applications.

Improvements of Micro-CHP SOFC System Operation by Efficient Dynamic Simulation Methods

Solid Oxide Fuel Cell (SOFC) technology is of high interest for stationary decentralized generation of electricity and heat in combined heat and power systems (CHP) for the residential sector. Application scenarios for SOFC systems in an electricity-regulated mode play an important role, especially in places where an electrical grid connection is not available or rather unstable. The advantages of SOFC systems are the high fuel flexibility and the high efficiencies also under partial load operation compared to other decentralized power generation technologies. Due to the long, energy-consuming system heat-up and the limited partial load capability, SOFC systems do not reach the performance of conventional power generation technologies. Furthermore, stack thermal cycling is associated with power degradation and should be minimized. In this paper, the improvement of these drawbacks are investigated for hotbox-based SOFC systems in the 1 kWel-class for residential applications. Since experimental investigations of the high-temperature systems are limited, modeling tools are established, enabling the visualization of internal system characteristics and providing the opportunity to simulate system operation in critical regions. To achieve this, a methodology for dynamic SOFC system modeling in a process engineering manner is developed based on the modeling language Modelica. A suitable approach is particularly important for modeling and simulation of the strong thermal interaction between the hot system components within the hotbox. The parametrized and validated models are used for the investigation of different dynamic effects, such as the system heat-up and the operation in low partial load points. A second reduced thermal system model aims for annual simulations of the SOFC system together with a battery to investigate the number of thermal cycles and the advantage of a hot standby operation. As a result, it is found that an adequate control of the power input at the start-up device and the cathode air flow has a high improvement potential to increase the stack heating rate and accelerate the heat-up in an energy-saving way. The hotbox-internal thermal management is identified as a crucial issue to reach low partial load points. To avoid the risk of stack cooling, lower heat losses and/or additional heat sources are of importance. Furthermore, the robustness of the tail gas oxidizer is found to be crucial for a higher load flexibility during partial load and the end of life stack operation. The annual simulation results indicate that operating the battery hybrid system with a hot standby mode requires much lower battery capacity for a high grid independence and a complete avoidance of system shutdown and associated power degradation.

Long-Term Experience with a 5/15kW-Class Reversible Solid Oxide Cell System

A 5/15 kW-class reversible Solid Oxide Cell (rSOC) system was developed and experimentally investigated at the Forschungszentrum Jülich GmbH. The main component of this system is the well-established Jülich Integrated Module, which consists of four 10-layer SOC sub-stacks with an active cell area per layer of 320 cm2. The other necessary system components, such as the evaporator, condenser and blowers are compactly arranged in the vicinity of the Integrated Module. The system’s total operation time was more than 9000 h, in detail 2607 h in fuel cells, 6043 h in electrolysis and 448 h in hot standby mode. In fuel cell mode, a power of 5374 WDC at 0.5 A cm−2 at a fuel utilization of 97.3% was delivered, which resulted in a DC electrical system’s efficiency of 62.7% (LHV). Furthermore, in electrolysis mode, a power of −14347 WDC was consumed at 0.89 A cm−2. At this operating point, the system’s DC efficiency reached 70% at a steam utilization of 85%.

Reliability Modeling of Microgrid System Using Hybrid Methods in Hot Standby Mode

The purpose of this paper is to accomplish the reliability assessment of hot standby microgrid system by using few hybrid methods. This paper has shown relative analysis on failure probability and reliability of microgrid system by means of Markov model, fault tree analysis (FTA) using reduced binary decision diagram (RBDD), and reduced sequential binary decision diagram (RSBDD) approaches. Hot standby mode is usually employed for the enrichment of reliability to prolong the system availability during any catastrophic situation. By analysis, microgrid which falls under the hot standby mode indicates that both the redundant as well as active components have similar failure rates. An inverter dominated photovoltaic system integrated to an IEEE 5-bus microgrid system is designed for which comparative overall system availability is calculated and analyzed in terms of failure probability and reliability by using hybrid approaches. Markov-based models mostly suffer from state-space explosion problems and it needs exponential probability distribution function only. Again, FTA-RBDD and FTA-RSBDD approaches have neither any constraint on time-to-failure distributions nor any computational burden issue. Moreover, FTA-RSBDD-based reliability assessment dealings are reusable with different time-to-failure rates.

Using the steam turbines with bypass steam distribution at CCGT for primary frequency control

The system of bypass regulation of the steam turbine for the more effective participation in primary frequency control is examined. Power and relative internal efficiency ratio of turbine with bypass steam distribution for various steam consumptions are calculated. It is shown that the steam turbine with bypass steam distribution in the combined-cycle plant in the hot standby mode with reduced power (to provide power reserve) provides a higher efficiency than when the steam is throttled in the control valve without bypass steam distribution. In addition, power change of the steam turbine with bypass steam distribution provides greater acceleration compared to the operation at the sliding steam pressure and the opportunity of overloading the turbine to the required power level.

Improvement of auxiliary BI-DRUM boiler operation by dynamic simulation

Due to Horizon 2030 objectives, industry is committed to improving traditional auxiliary bi-drum boilers performance in existing plants.In this study, a new operation methodology for auxiliary bi-drum boilers has been developed to reduce the operational cost of the plant.Two new functioning modes have been defined as “hot standby mode” (HSM) and “fast hot startup” (FHS). Both of them will be studied using thermal dynamic calculations. In addition, Power Plant Simulation & Design (PPSD) commercial software has been used for dynamic performance analysis.Results show that auxiliary bi-drum boilers will be able to operate under those conditions only if some additional technological modifications are implemented. For example, automated burners that are adapted to current standards, feed water control valve capable of regulating the flow during HSM, automate superheater valve drains and a continuous blow down valve. This new operation methodology will result in energy savings and reduction in operational cost.

Optimal Periodic Inspections and Activation Sequencing Policy in Standby Systems With Condition-Based Mode Transfer

This paper models a hybrid standby system subject to periodic inspections and condition-based standby mode transfers during a mission. At the beginning of the mission only one element is online and operating. The second element waits in a hot standby mode being ready to replace the failed online element at any time. Other elements wait in less-stressful and less-costly warm standby mode. During the mission periodic inspections are performed for checking conditions of the online and hot standby elements and subsequently triggering necessary mode transfer(s) of available warm standby element(s) to replace the failed hot standby element and/or online element. We suggest an efficient numerical method to assess availability and expected total mission cost (including standby cost, operation cost and mode transfer cost of system elements, inspection cost, system interruption or idle cost) of the considered system. The algorithm is flexible and applicable to arbitrary type of time-to-failure distributions. Then we formulate and solve new optimization problems that identify the optimal combination of inter-inspection interval and element activation sequence to minimize expected total mission cost while satisfying a certain constraint on system availability. As illustrated through examples, the optimization results can facilitate cost-effective and availability-aware planning of system inspection and operation.

Optimal Design of Hybrid Redundant Systems With Delayed Failure-Driven Standby Mode Transfer

Standby redundancy is a design technique that has been widely adopted to enhance system reliability and achieve fault tolerance in many critical applications. In this paper, we consider a 1-out-of- N: G hybrid standby redundant system with unrepairable elements being subject to delayed failure-driven standby mode transfers. Specifically, in the considered system, all the standby elements are initially in a warm standby mode (WSM) but can be transferred to a hot standby mode (HSM) so as to be ready to replace the online operating element when it fails. The WSM to HSM transfer is performed with a fixed time delay after no element resides in HSM either due to the element failure or because the element leaves the HSM to replace the failed online element for operation. A new iterative numerical algorithm is first proposed for evaluating reliability and expected mission cost (relevant to elements’ standby expense, operation expense, as well as mode transfer expense) of the considered hybrid standby system. The algorithm has no restriction on element time-to-failure distribution types. Based on the proposed evaluation algorithm, we further formulate and solve a new optimization problem that finds the optimal delay and optimal sequence of standby elements with the objective to minimize expected mission cost while satisfying a certain level of mission reliability constraint. Examples are presented to demonstrate applications of the proposed methodology.

Reliability and Mission Cost of 1-Out-of-<formula formulatype="inline"><tex Notation="TeX">$N$</tex></formula>:G Systems With State-Dependent Standby Mode Transfers

The paper proposes a new fault tolerant system design model, in particular a 1-out-of- $N$ :G hybrid redundant system with standby elements subject to state-dependent standby mode transfers. Specifically, in such systems, one standby element always resides in the hot standby mode, and thus is ready to replace the failed online element at any time to make the system dependable. If the online operating element or the hot standby element fails, one of the warm standby elements is immediately transferred to the hot standby mode. A numerical algorithm is first suggested for evaluating the reliability and the expected mission cost of the considered system. The algorithm is based on a discrete approximation of element time-to-failure distributions, and can work with any type of distribution. Furthermore, based on the suggested algorithm, the problem of optimal sequencing of standby elements initiation is formulated and solved. The objective of this optimization problem is to minimize the expected mission cost associated with elements' standby and operation expenses, as well as the mode transfer expenses, while meeting a certain system reliability constraint. Illustrative examples are provided.

Optimization of predetermined standby mode transfers in 1-out-of-N: G systems

Warm standby redundancy is an important fault-tolerant design technique for improving the reliability of many systems used in life-critical or mission-critical applications. Traditional warm standby models aim to reduce the operational cost and failure rate of the standby elements by keeping them partially powered and partially exposed to operational stresses. However, depending on the level of readiness of a standby element, significant restoration delays and replacement costs can be incurred when the standby element is needed to replace the failed online element. To achieve a balance between the operation cost of standby elements and the replacement costs, this paper proposes a new warm standby model with scheduled (or time-based) standby mode transfer of standby elements. In particular, each standby element can be transferred from warm standby mode to hot standby mode (a mode in which the standby element is ready to take over at any time) at a fixed/predetermined time instants after the mission starts. To facilitate the optimal design and implementation of the proposed model, this paper first suggests a new algorithm for evaluating the reliability and expected mission cost of 1-out-of-N: G system with standby elements subject to the time-based standby mode transfer. The algorithm is based on a discrete approximation of time-to-failure distributions of the elements and can work with any type of distributions. Based on the suggested algorithm the problem of optimizing transfer times of standby elements to the hot standby mode and optimal sequencing of their transfer to the operation mode is formulated and solved. In this problem the expected mission cost associated with elements’ standby and operation expenses and mode transfer expenses is minimized subject to system reliability constraint. Illustrative examples are provided.

SOFC system and technology

Compact size solid oxide fuel cells (SOFCs), which will be operated at reduced temperature, are becoming a frontier of R and D. These compact size SOFCs will fit well with intermittent loads, of which share in energy system is increasing today, whereas the “conventional SOFCs” will be effectively operated with stationary mode. For such compact size SOFCs, throttle down operation following intermittent loads will be profitable because low current density gives higher efficiency. SOFCs are not suitable for quick start up. It was estimated that the hot standby mode would be more acceptable than cold start mode from the viewpoint of heat loss. The merit of internal reforming will also be lost for the reduced operation temperature. In order to overcome this problem, an electrochemical oxidation of deposited carbon was tested and a new direct internal reforming concept using this carbon deposition was proposed. In order to develop cheap compact size, reduced temperature SOFCs, the feasibility of anode supported SOFCs was investigated on Zr(Sc)O 2, Zr(Y)O 2, Ce(rare earth)O 2, (La,Sr)(Ga,Mg)O 2 electrolytes, examining applicability of wet co-fire process and electrode activity. The feasibility was confirmed with zirconia, not yet with ceria due to its fragility, and pessimistic with (La,Sr)(Ga,Mg)O 2 due to Ni diffusion during co-firing.

Influence of weather conditions on the power of heat removal by the emergency cooling system of a reactor

An analytical and numerical analysis is made of the influence of the slot sizes between gate plates and weather conditions on total heat losses in the hot stand-by mode and emergency operating conditions of the passive safety system of an APS.

Description and mathematical model of a large MSF desalination plant in SCADA configuration

A general block diagram showing the control application functions for the control of production of a very large MSF desalination plant is described. The input data is subdivided in unitary operations, such as signal conditioning, digital filtering, steady state checks, limit value monitoring and logical filtering. The developped mathematical model of the desalination plant forms the heart of the control system. Mathematical algorithms are developped for the optimization of the process. The Fouling Factors and Stage Efficiency evaluations are described. In addition a Heat Balance equation is developped and implemented in the application software. A fail safe dual redundant computer system configuration is hot stand-by mode is adopted and described. All supervisory control functions as applied to Supervisory Control and Data Acquisition (SCADA) systems are implemented. For a large desalination plant preference is given to a reliable and dependable system even at the cost of slow data acquisition. In addition a fully automatic analogue back-up system is available in the case of computer trouble.