Standby redundancy

Forced Circulation System—Using foreed eireulation in a waste heat reeovery system allows the use of smaller tube sizes with inherent inereased heat transfer eoeffieients. Flow stability eonsiderations must be addressed. The reeireulating pump is a eritieal eomponent from a reliability standpoint and standby (redundant) pumps must be eonsidered. In any event, great eare must go into preparing speeifieations for this pump. 

For example, consider tlie case of a standby redundancy system consisting of one operating pump and two on standby so that tlie system can survive two failures. Assume tlutt tlie pumps are independent with respect to failure and tliat each lias a probability of failure of 0.1. Thus, n = 3, r = 2, 1 - p = 0.9, and tlie reliability of the system is found from Eq. (20.5.3)... 

In addition to tlie applications cited above, tlie Poisson distribution can be used to obtain tlie reliability of a standby redundancy system, in which one unit is in tlie operating mode and n identical units are in standby mode. Unlike a... 

Tliis is tlie probability if n or fewer failures in the time period specified by t. For example, consider tlie case of a standby redundancy system with one operating unit and one on standby (i.e., a system tliat can survive one failure). If the failure rate is 2 units per year, then tlie 6-nionth reliability of the system is... 

Redundancy. The existence of more than one means for accomplishing a given task, where all means must fail before there is an overall failure to the system. Parallel redundancy applies to systems where both means are working at the same time to accomplish the task, and either of the systems is capable of handling the job itself in case of failure of the other system. Standby redundancy applies to a system where there is an alternate means of accomplishing the task that is switched in by a malfunction-sensing device when the primary system fails Ref Anon, OrdTechTerm (1962), 251—52... 

It is common practice to have two inverters available to supply a common distribution board or switchboard. How they are conflgured and controlled depends upon the performance required when one unit fails. If a short duration interruption can be tolerated then a simple electromagnetic changeover switch can be used to switch the load over to a live standby unit. This is called a standby redundant UPS system. 

A better method, also called standby redundant, is to incorporate a static switch in each of the inverter output circuits. Static switches can function rapidly, with an almost imperceptible disturbance at the load terminals. One static switch is kept open whilst the other is closed . 

Failure rates of complex equipment can often be greatly reduced through redundant arrangements. Redundancy provides multiple means of warning and shut down systems to ensure personnel and equipment are safe from failures that could result in a hazardous situation. Redundancy is based upon how critical an event is to worker safety or process continuation. Two separate switches or two separate alarms provide redundancy. In addition, there is standby redundancy. In this case, a piece of equipment operates until a failure is indicated, at which time another duplicate piece of equipment is turned on either automatically or manually. An excellent example of redundancy is fire water pumps. There are always at least two or more. A unit does not want to experience a fire, the site has only one pump, and that is the day the pump fails. 

However, implementation of cold-standby strategies is more sophisticated because of the meeting the requirements to detect failures as they occur and activate the redundant component. This is not necessary for active redundancy because all components will be never idle. In addition to its complex implementation due to diagnostic inspection and cost of such system, deploying of standby redundancy have been a poor choice in the vehicle context so far. However deploying active redundancy is very popular, a system design is required synchronistically implement active and stand-by redundancy in various parts of new mechatronic system in order to achieve certain level of reliability. 

Some efforts are made successfully for standby redundancy (Coit 2003). 

The calculation of reliability and PFD for the structure with Cold-standby redundancy... 

For cold-standby redundancy a detection and switching mechanism is required to sense the presence of a failed component and to activate a standby component. The reliability of a series and parallel system with... 

Figure 5. Standby redundancy versus active redundancy in association with number of component.

The best failure rates are determined using GA and generalized pattern search in the presence of active or standby redundancies. On the other hand, ASIL indicator shows that implementation cold redundancy is more complex and leads to more safety requirements... 

Coit, D. 2003. Cold-Standby Redundancy Optimization for Nonrepairable Systems, IIE Transactions, vol. 33, no. 6, June 2001, pp. 471 78. 

However the ratio is not known and we wfll consider the worst case to design of the Markov model. It means the case of standby redundancy with fully loaded reserve (with fail-safe switch). We can calculate from the formula above that mean time to failure for main filament is 400 hours and for reserve filament 400 hours as well MTTFp = 400 hours). 

Standby redundancy— When an operating component fails, a standby component is put into operation, and the system continues to function. 

A standby redundancy system may consist of the two components A and B, together with a switch, SW. In the case of A failing, the switch SW activates B, which has been idle. Supposing, now, the reliability of SW and B was not affected by A being in operation (which would be doubtful, since factors like temperature and vibration should affect the reliability of idle components, anyway) then the reliability of the standby system would be... 

Redundancy, standby Redundancy wherein the alternative means of performing the function is not operating until it is activated upon failure of the primary means of performing the function (Reference 7- 3). 

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