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Reliability Analysis

1. Introduction
Reliability, availability, and maintainability (RAM) are system design features that have substantial effects on the sustainment of a developed machine system. These features influence the machine’s ability to effectively perform the envisioned mission without failures. Reliability, in this case, is the likelihood of a machine to record nil failures over a specified period of time interval (Mitre.org 2012). Availability, on the other hand, is the proportion of time a machine or a particular system is regarded ready for use when commissioned, while maintainability is the level of ease and promptness in which a system or machine can be repaired to its operational status after a failure. Maintainability of a system may also include concepts such as preventive maintenance, essential maintainer expertise level, and availability of support equipment. These skills will help the maintainer understand how to use reliability and availability techniques to support decisions on the maintenance processes (Headquarters Department of the Army 2007). System maintenance is vital to any machine since some repair and restoration activities must be carried out during the life period of a machine to align it to the mission. Some of the logistics strategies to ensure reliability and availability of machine systems include maintainer training, provision of maintenance manuals, and identification of requisite support equipment (Criste et al. 2012).


2. Failure and Repair of Automatic Transfer Generator Switch
This paper focusses on the reliability and availability of hardware and software of an automatic switch industrial generator. The issue is essential because the software performance impacts the entire system performance mission in case of power outage or if the power voltage reduces below the acceptable level as set in the design. Therefore, this paper seeks to perform comprehensive reliability and availability techniques’ assessments and benchmarking; these actions include identification of the probable RAM improvement areas on the generator, analyses of the failure modes and effects on the machine performance, identification of the root causes of the component and outlining the machine modifications that can eradicate the root causes of system failure, as well as comparing the results with best-practice metrics in the industry (Cristea et al. 2012)
The reliability and availability of the automatic generator is dependent on the reliability of the automatic transfer generator switch, which monitors the amount of incoming power voltage that comes from the utility line (GeneratorJoe 2012). In a normal system operation, when utility power is disturbed, the automatic transfer switch (ATS) instantaneously senses the outage and signals the generator to start running. Once running at the appropriate speed, the ATS safely switches off the utility line and concurrently connects the generator power line to the generator to allow flow of power currents. This allows the generator to begin supplying electricity to the emergency circuits of a business facility or within a home.


In the meantime, the transfer switch continues monitoring the utility line power voltage situations, such as when the ATS senses that the voltage at the utility line is back to its steady state, it re-transmits the electrical load of the system back to the utility line and continues monitoring for subsequent loss of the utility voltage. The generator continues running for several minutes to allow the engine cool-down; at the same time, the entire generator system remains ready for the next power outage or voltage reduction (GeneratorJoe 2012). This automatic generator system means that the failure of the automatic transfer switch to sense loss of power voltage from the utility line subsequently leads to the failure in a series of operations and the whole system, since the generator cannot be signaled to start running.


3. System Availability in Series
The generator system is modeled in an interconnected series since the failure of the ATS part results into subsequent failures in its other parts. The generator becomes inoperable unless started manually. This results into damages in the critical emergency areas of the industry (Eventhelix.com 2012).

The above Diagram 1 indicates combined availability of how the two parts of the system, X (ATS) and Y (subsequent generator parts), are considered to be functioning in a series. This shows that the failures of either X or Y parts result into failure of the whole combination, thus leading to no electricity generation. The joint system is functional only if both Part X and Y are available.
The combined availability is expressed as follows:
This equation indicates that that the joined availability of two or more modules in a series is lower than the availability of its singular components.
When collection of failure and repair maintenance data of ABC Company was performed, the following data were obtained.

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The data collected and represented in the chart above indicates the following: out of the 40 registered failures, 95% occurred as a result of failures of the automatic transfer switch with 38 entries. A failure in the generator as a result of inadequate fuel was only recorded twice; in those cases, the fuel indicators failed to warn low fuel load. Therefore, according to the calculations, the reliability and availability of fuel indicator is at 99.45% in a year. On the other hand, the reliability of the ATS is at 89.59% in a year.
4. Reliability Modeling of the System in Parallel
Based on the maintenance carried out according to the data above, a model that ensures enhancement of the generator system’s level of reliability is developed. This involves fixing a parallel connectivity of automatic transfer switch alongside the serial connectivity of the system. The parallel redundancy is to back up the initial single ATS; as a result, if one system fails, the next one picks the signal.

This is conducted by preparing a comprehensive block diagram of the generator system. Such a system comprises an input transducer that senses the signal and transforms it into an appropriate data stream that can be intercepted by the signal processor. The received output is then relayed to a redundant pair of ATS (signal processors). At this point, the active ATS responds to the input by signaling the output transducer for generator to start running, while the standby ATS snubs the data from the input transducer. The outputs from the two ATS are combined and relayed to the output transducer. Only the active signal processor engages the data lines as another remains in a standby state. It should be noted that the input and output transducers are passive elements without microprocessor control (Eventhelix.com 2012).


In this case, the system remains fully functional when at least one ATS (signal processor) – A or B – fulfills its objectives. This, therefore, eliminates the failure of the whole generator system that can arise if one ATS fails to pick the signal. In case a failure of a certain part results into another part taking over the functions of the stalled part, the two components are considered to be functioning in a parallel model.
This parallel reliability model is the most effective since it improves the level of system operation. The maintenance carried out, which involves replacement of the faulty automatic transfer switches, never lasts long, thus increasing the generator reliability. Therefore, this parallel model reduces the chances of complete failure of the system: when one component fails to fulfill its function, another picks the signal. The probability of the two signal processors failing at the same time is minimal.


5. Calculating Availability of Individual Components

Computing of the availability of individual components is performed applying mean time between failure (MTBF) and mean time to repair (MTTR), which are the estimated values for each component. MTBF is the average time of operation the manufacturer of the generator estimates before a failure occurs (Eventhelix.com 2012). The hardware components of the generator system, according to the manufacturer data sheet, are given to be MTBF of 10,000 hours. MTTR, on the other hand, estimates the degree to which the generator system will be observed by operators; it is the amount of time taken to repair a failed hardware module; in this case, this value constitutes 2 hours. MTTR, in this case, includes the time wasted when ATS fails as well as time taken to discover ATS failure. The table below indicates that the average downtime for the signal processor is 1.75 hours in 365 days. The parallel model helps to reduce the downtime; this, in its turn, improves the generator’s efficiency.

From the economic point of view, this parallel model will help reduce the time wasted and the amount of damage that may arise as a result of a power outage. The matter is, manufacturing in the industry that fully depends on electricity supply will stop if a power outage occurs, hence leading to inefficiency in production. This translates to low profits of the firm. One of the consequences will be failing to meet the customers’ orders for the goods and, as a result, loss of market share to other competitors. Similarly, maintenance and repair involves purchase of new parts for replacement. If such incidents become frequent, it will increase the maintenance cost, especially when the maintainer is an outsourced service provider that must be paid. High cost of operation leads to reduced profits.

6. Conclusion
Reliability and availability are system design features that have substantial effects on the sustainment of a developed machine system. These features influence the ability of the machine to effectively perform the envisioned mission without failures (Department of Defense 2009). This paper analyzed the reliability and availability of hardware and software of an automatic switch generator.
The reliability and availability of the automatic generator depend on the reliability of the automatic transfer generator switch that monitors the amount of incoming power voltage that comes from the utility line. According to the data collected, 95% of the generator system failures are caused by the fault in the automatic transfer switch, while only 5% of the failures are caused by the fault of the fuel indicator. The failure is rather severe when one ATS is used. However, the chance of failure can be reduced by introducing a parallel model when another ATS is installed; thus, the failure of one component leads to the second processor taking over the operation. This analysis finds out that parallel reliability model is the most efficient one since it improves the level of system operation. The generators system cannot be stalled when only one of the ATS fails.


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