Did you know that IEC 61508 can be used as a framework to maintain high levels of safety while deploying IEDs on electric networks? This series of blog posts covers three steps utilities can take toward that goal:
- Balance cost and safety
- Apply standards
- Create a maintenance plan
Having discussed step 1 and step 2 in previous posts, today I’ll introduce step 3, which is all about maintenance.
It’s a fact that 35% of the downtime experienced by process control systems is the results of maintenance and modification. That includes not only the work required to detect problems and repair faulty systems, but also the preventive maintenance carried out to avert potential failures.
Building and assessing the safety case of a product according to IEC61508 brings several benefits to maintenance:
- It means that risk has been reduced to an acceptable level before putting the device in operation: a Safety Integrity Level (SIL) 1 safety loop means that without that loop the safety risk is 10 times more than the acceptable level, a SIL2 safety loop 100 times, a SIL3 safety loop 1000 times, and a SIL4 safety loop 10000 times (but do we really need it?).
- It provides failure probabilities per device according to SIL levels. More reliable products require less maintenance.
- Products contain embedded IED software self-tests for sensitive electronic components such as CPUs and memory. When failure occurs, it’s instantly detected and the IED resets to a safe state. Self- test functions help significantly reduce the amount of maintenance.
- It simplifies spare parts logistics. Because failure rate data of each part of the product are available, you can manage a spare parts inventory with more precision, which reduces logistics costs.
IEC 61508 also specifies the following aspects of maintenance plan creation:
- Procedure implementations
- Maintenance scheduling
- Documentation practices
- Functional safety audits
- Documentation of modifications to safety-related systems
Because many IEDs are modular in design, they are often swappable. This means they can be tested off the network, which reduces both maintenance and planned downtime.
For more on this topic, have a look at the free white paper I recently co-authored with my colleagues: Impact of IEC 61508 Standards on Intelligent Electrical Networks and Safety Improvement.
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