Standby system

Block diagram of a standby system with one operating and n standby units. 

X t) = unit time-dependent failure rate or hazard rate 

For constant unit failure rafe (i.e., Mf) = X), Equation (3.35) yields 

MTTFss = standby system mean time to failure 

Assume that a standby system is composed of two identical and independent units (i.e., one operating, the other on standby). The unit constant failure rate is 0.005 failures per hour. 

X f) is the unit hazard rate or time-dependent failure rate. 

For constant unit failure rate (i.e., X = X t)), Equation 3.36 becomes 

---

This FMEA/FMECA shows failure rates that are both demand and time dependent. Adding the demand failure rates gives a train failure rate of 5. 1 E-3/demand. The sum of the time dependent failure rates is 3Ei-10/hr. A standby system such as this, does not exhibit its operability until it is actuated for which the probability is needed that the train has failed since the last use Val " are considered to be part o ng envelope and... 

It can be concluded that selection of proper material or lining for seawater application is important and depends on the criticality of the system, availability of standby system/equipment and availability of isolation devices for maintenance. For process piping in seawater application the success of proper lining or coating material depends on the suitability for in-situ/field application and the proper corrosion monitoring plan. 

Some companies elect to back up systems against failure by contracting with a service bureau for emergency recovery. Essentially it is an insurance policy whereby the pharmaceutical or healthcare company leases a standby system. User terminals and printers are installed in the client offices with network connection to the service bureau that may be at the service supplier s premises or a mobile facility that is driven onto site. User applications typically have a target time to restoration within 24 h. The problem with commercial mobile facilities is that their service providers often require up to 48 h to guarantee deployment. 

D7.2 Have requirements for automatic standby systems been defined ... 

Contingency Plans (sometimes referred to as Business Continuity Plans) must be in place and tested regularly, including any standby systems. It is estimated that only 15 percent of organizations have a tested and effective plan. Such plans would include details of how the system would be recovered in the event of one of several disaster scenarios. Details of a backup system would be outlined, whether an alternative system or paper data. Companies who have such plans in place run periodic tests to ensure that the plan would aaually work in the event of a disaster. 

Equipment arrangement involves the concepts of series and parallel systems as well as standby systems. Redundancy can just be duplication of the procedure, but it also can be having some information confirm the remainder—an error-checking code. For example, giving a meeting date as Thursday, February 25, lets the Thursday confirm the 25. A ZIP code confirms the names of city and state on a postal address. 

In general the survival probability is of interest if a system has to maintain its function during a certain period of time (e.g. a rocket). If, on the other hand, a system has to function on demand, as for example a trip system, the availability is the adequate parameter. Of course, combinations of both parameters can also be appropriate. A standby system like an emergency power supply needs a high availability (probability to start) and a high survival probability (functioning until the grid supply is restored, i.e. until mission time t). 

To be applied as well to standby systems if these are demanded more frequently than once per year ... 

Logic processing circuit including a CPU and standby system. 

Almeida AT, Souza FMC de. 1993. Decision theory in maintenance strategy for a two-unit redundant standby system. IEEE Transactions on Reliability 42, 401-407. 

If a power-conditioning/standby system does not operate with high reliability, the results can often be disastrous. In addition to threats to health and safety, there is a danger of lost revenue or inventory, and hardware damage. Reliability must be considered from three different viewpoints ... 

A standby system built on the critical load principle can be a cost-effective answer to the power-failure threat. The first step in implementing a critical load bus is to accurately determine the power requirements for the most important equipment. Typical power consumption figures can be found in most equipment instruction manuals. If the data is not listed or available from the manufacturer, it can be measured using a wattmeter. 

Hot standby System equipment that is fully powered but not in service. A hot standby can rapidly replace a primary system in the event of a failure. 

The mistakes may have either immediate or delayed consequences. Latent design or maintenance errors may lie dormant for a long time, even for years, if for example they affect the operation of rarely challenged standby systems or protection systems. 

Legally required standby power systems are intended to provide electric power for control of health hazards and to aid in fire fighting or rescue operations. Upon loss of normal power, legally required standby systems must be connected to the alternate power source wiY/i/w 60 seconds. Standby power shall be provided in Group H, Divisions 1 and 2 Occupancies and in Group H, Division 3 Occupancies in which Class I, II or III organic peroxides are stored (UBC 307.2.7). 

With the aid of Figure 3.9 diagram, for independent and identical units, time-dependent unit failure rate, and perfect switching mechanism and standby units, we write down the following equation for the standby system reliability [25] ... 

Calculate the standby system reliability for a 200-h mission by assuming that the switching mechanism is perfect and the standby unit remains as good as new in its standby mode. 

Thus, the standby system reliability for the specified time period is... 

The sequence of events involved in standby replacement is to prepare the standby system for operation (if necessaiy) change over to the standby system and verify that it is operating properly. 

Change over from the failed system to the standby system... 

This is the time required to prepare a standby system for operation. In maintainability analysis, as with reliability, it is usual to recognise two types of standby system hot and cold. In the case of hot standby, the spare item is operating but not carrying any load and the preparation time is essentially zero. 

Consider Figure 8 where power supply PS2 forms a redundant standby to PSl. If PSl fails, it must be disconnected from the load so that it does not affect the ouq>ut of PS2 as it comes up to voltage this requires the voltage reference to be down-stream of the switching. However, such an arrangement may introduce an additional hazard because PSl and PS2 are permanently connected to their reference points, possibly exposing maintenance personnel to unexpected voltages unless additional precautions are taken. Such conflicts between operational and maintainability requirements are not unusual, especially in the practical implementation of standby systems. 

This is the time taken to change over from the failed system to a standby system which is reatfy to assume a load. There will always be a finite Tcs> even in the case of hot standby (Tp ) with automatic changeover. For safety-critical sterns, the timing and sequence of the changeover should be examined in detail, especially since apparently simple tasks may hide subtle complications, such as in the example of Figure 8. Techniques for analysing maintenance tasks are discussed elsewhere [3,12,13], and are not repeated here. 

This is another reliability network or configuration in which only one unit operates and n units are kept in their standby mode. The total system contains (n -H 1) units, and as soon as the operating unit fails, the switching mechanism detects the failure and turns on one of the standby units. The system fails when all the standby units fail. The block diagram of a standby system with one operating and n standby units is shown in Figure 3.5. Each block in the diagram represents a unit. 

---