Template:Rotation

Standby Rotation Example

Purpose

This example illustrates the use of state change triggers SCT in BlockSim Version 8 by using a simple stanfby configuration. Note that this example could also be done using the standby container functionality in BlockSim.

Statement

Assume three devices A, B and C in a standby redundancy. Basically only one unit is needed for system operation. The system begins with devise A working. When device fails B is turned on and repair actions initated on A. When B fails C is turned on and so forth.

are in parallel and rotate to perform the task. A is ON initially, B and C are standby. When A fails, Turn B On; when B fails, turn C ON and when C fails, Turn A ON. The desired situation is that, at every moment, one and only one device is operating. This means that, when a device is done with repair, it should be standby if there is already one device operating; or it should be operating when there is not device operating.

BlockSim Solution

The Blocksim modeling of this system is shown in Figure below.

State Upon Repair: Default OFF unless SCT overridden

Activate a block if any item from these associated maintenance group(s) goes down

The failures of all three blocks follow Weibull distribution with Beta = 1.5 and Eta = 1000. The repair durations of three blocks follow Weibull distribution with Beta = 1.5 and Eta = 100. After repair, they are as good as new.

Block A belongs to maintenance group 2_A. It has state change trigger. The initial state is ON and the state upon repair is "Default Off Unless overridden". If any item from maintenance group 2_C goes down, then activate this block.

Block B belongs to maintenance group 2_B. It has state change trigger. The initial state is OFF and the state upon repair is "Default Off Unless overridden". If any item from maintenance group 2_A goes down, then activate this block.

Block C belongs to maintenance group 2_C. It has state change trigger. The initial state is OFF and the state upon repair is "Default Off Unless overridden". If any item from maintenance group 2_B goes down, then activate this block.

All blocks A, B and C are as good as new after repair.

Block Up/Down plot

The system event log is shown in Figure below and is as follows:

1. At 73, Block A fails and activates Block B.
2. At 183, Block B fails and activates Block C.
3. At 215, Block B is done with repair. At this time, Block C is operating, according to setting, Block B is standby. 
4. At 238, Block A is done with repair. At this time, Block C is operating. Thus Block A is standby.
   
5. At 349, Block C fails and activates Block A.
6. At 396, Block A fails and activates Block B.
7. At 398, Block C is done with repair. At this time, Block B is operating. Thus Block C is standby.
8. At 432, Block A is done with repair. At this time, Block B is operating. Thus Block A is standby.
9. At 506, Block B fails and activates Block C.
10. At 515, Block B is done with repair and keep standby because Block C is operating.
11. At 536, Block C fails and active Block A.
12. At 560, Block A fails and active Block B.
13. At 575, Block B fails and put a requset to active Block C. However, Block C is under repiar at the time. Thus when Block C is done with repair at 606, the OFF setting is overwritten and it is operating immdediatly. 
14. At 661, Block C fails and put a request to active Block A. However, Block A is under repair at the time. Thus when Block A is done with repair at 699, the OFF setting is overwritten and it is operating immdediatly.
    
15. Block B and Block C are done with repair at 682 and at 746 respectively. However, at these two time point, Block A is operating. Thus they are both standby upon repair according to settings.