Example Using SCT for Standby Rotation
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This example also appears in the System analysis reference.
This example illustrates the use of state change triggers in BlockSim (Version 8 and above) by using a simple standby configuration. Note that this example could also be done using the standby container functionality in BlockSim.
More specifically, the following settings are illustrated:
- State Upon Repair: Default OFF unless SCT overridden
- Activate a block if any item from these associated maintenance group(s) goes down
Problem Statement
Assume three devices A, B and C in a standby redundancy (or only one unit is needed for system operation). The system begins with device A working. When device A fails, B is turned on and repair actions are initiated on A. When B fails, C is turned on and so forth.
BlockSim Solution
The BlockSim model of this system is shown in the figure below.
- The failure distributions of all three blocks follow a Weibull distribution with Beta = 1.5 and Eta = 1,000 hours.
- The repair distributions of the three blocks follow a Weibull distribution with Beta = 1.5 and Eta = 100 hours.
- After repair, the blocks are "as good as new."
There are three maintenance groups, 2_A, 2_B and 2_C, set as follows:
- Block A belongs to maintenance group 2_A.
- It has a state change trigger.
- The initial state is ON and the state upon repair is "Default OFF unless SCT overridden."
- If any item from maintenance group 2_C goes down, then activate this block.
- It has a state change trigger.
- Block B belongs to maintenance group 2_B.
- It has a state change trigger.
- The initial state is OFF and the state upon repair is "Default OFF unless SCT overridden."
- If any item from maintenance group 2_A goes down, then activate this block.
- It has a state change trigger.
- Block C belongs to maintenance group 2_C.
- It has a state change trigger.
- The initial state is OFF and the state upon repair is "Default OFF unless SCT overridden."
- If any item from maintenance group 2_B goes down, then activate this block.
- It has a state change trigger.
- All blocks A, B and C are as good as new after repair.
System Events
The system event log for a single run through the simulation algorithm is shown in the Block Up/Down plot below, and is as follows:
- At 73 hours, Block A fails and activates Block B.
- At 183 hours, Block B fails and activates Block C.
- At 215 hours, Block B is done with repair. At this time, Block C is operating, so according to the settings, Block B is standby.
- At 238 hours, Block A is done with repair. At this time, Block C is operating. Thus Block A is standby.
- At 349 hours, Block C fails and activates Block A.
- At 396 hours, Block A fails and activates Block B.
- At 398 hours, Block C is done with repair. At this time, Block B is operating. Thus Block C is standby.
- At 432 hours, Block A is done with repair. At this time, Block B is operating. Thus Block A is standby.
- At 506 hours, Block B fails and activates Block C.
- At 515 hours, Block B is done with repair and stays standby because Block C is operating.
- At 536 hours, Block C fails and activates Block A.
- At 560 hours, Block A fails and activates Block B.
- At 575 hours, Block B fails and makes a request to activate Block C. However, Block C is under repair at the time. Thus when Block C is done with repair at 606 hours, the OFF setting is overridden and it is operating immediately.
- At 661 hours, Block C fails and makes a request to activate Block A. However, Block A is under repair at the time. Thus when Block A is done with repair at 699 hours, the OFF setting is overridden and it is operating immediately.
- Block B and Block C are done with repair at 682 hours and at 746 hours respectively. However, at these two time points, Block A is operating. Thus they are both standby upon repair according to the settings.