Top-down and bottom-up are two different approaches to systems engineering which both offer distinct advantages and disadvantages. This chapter contains a short explanation of each approach, and outlines how Helinks STS can be leveraged with it to increase productivity.
Bottom Up
Basic Explanation
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Specification consists of informal documents (Excel, Vision, etc.)
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System Integrator or Vendor generates all design and tests to meet the specification
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IEDs are engineered directly with all Datasets, Reports, Goose and signal flows using the IED Configuration Tool (ICT) provided by the vendor
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CIDs are exchanged multiple times between IEDs to set up subscriptions
Advantages
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Allows for a faster learning experience to build up basic competency in IEC61850
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Higher initial flexibility, allows for easier changes (good for brownfield, or ‘one-off’ cases)
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Higher immediate practical application
Disadvantages
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Design changes require significant re-engineering
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Change management for engineering standards is significantly more difficult
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Low reusability of engineering for subsequent projects
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Scales poorly with the complexity of a project due to high number CID exchanges
Top Down
Basic Explanation
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Create a formal specification in the form of a Substation Specification Description (SSD) file
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IEDs are imported as IED Capability Descriptions (ICDs) and engineered in the System Configuration Tool (SCT)
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SCT creates a Substation Configuration Description (SCD) which is used with the ICT to configure the IEDs
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IED Instance Descriptions (IIDs) and the SCD may be exchanged multiple times to complete the process
Advantages
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High reusability
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Design iterations are simple
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Reduced whole of life costs
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Results can be simulated and tested early to match requirements
Disadvantages
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Higher initial costs
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Higher initial design time
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More difficult to apply to brownfield sites