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Compatible Units: Building blocks of Utility Design and Estimation

A Compatible Unit (CU) is a design Unit that represents the Material, Labor, External Services, Tools etc. required to perform a Standardized Unit of Work. An Example of this can be installing a Pad Mounted Transformer. To perform this Unit of Work we need the Labor and Materials to perform the required excavation and Install the Pad, Install the Transformer and elbows. The Compatible Units are used as Building blocks to develop Utility design and estimates.

CU Ownership: The compatible Units creation and Maintenance is generally owned by the Standards departments of the Utilities. A Utility Construction / Maintenance standard may be created or modified depending on the technology advancements, changes in national electrical construction changes and the standards department decision to adopt the new technology and standards.  If a Utility decides to use a fiber glass cross arm instead of a wooden cross arm, the relevant construction standard is modified and required modifications are made to the Compatible Units Material and Labor.

Benefits of Compatible Units based Design and Estimation:

  • Enforcement of Construction and Maintenance Standards 
  • Seamless Integration of Design, Estimation, Mapping, Material Management and accounting processes (Discussed in next blog on this topic)
  • Consistency of Design and estimates irrespective of who performs the task
  • Defendability of the estimates. Customers pay the utilities for the new construction depending on the estimates and hence high level of Defendability of estimates is required. CUs are created by performing time studies, technology and cost assessments. As CUs are defendable, the estimates created using the CUs are defendable
  • Reduction in Inventory costs (Biggest advantage of implementing standards)
  • Reduction in wasted field trips due to missing material or tools (CU readily provides the list of all the required tools and Materials)
  • Minimum deviation between estimates and actuals (Huge Deviations can be investigated and required corrections made to the Work Processes or CUs)
  • Scope for continuous improvement (Feedback from Field crews and Periodic Audit helps in identification and rectification of Issues with individual compatible units)

Levels of Compatible Units
Multiple Levels of Compatible Units can be created. The existing Packages support up to nine levels of compatible units. The levels of Compatible Units can be better explained by the following example.

Level 1 CUs: Pole, Cross Arm, Transformer, Arrester
Level 2 CUs: Pole with Cross Arm, Transformer with Arrester
Level 3 CUs: Transformer with an Arrester Mounted on a Pole with a Cross Arm.

As the level of the CUs increases, the number of Possible Combinations increases. How? It is suggested that only the most often used combinations are created as higher level CUs. Otherwise the number of CUs becomes quite unmanageable. 
Note: Transmission and Distribution Utilities generally do not use more than 3 levels of CUs.

What CU Number is the right Number?
The Number of Compatible Units a Transmission and Distribution Utility manages may vary from a few thousands to tens of Thousands. Striking a balance between limiting CU count and supporting requests from designers for new creation of new CUs is a challenge. One way to contain the number of CUs managed by a utility is to create the CU Library afresh during upgrades and new implementations. In this approach, the utility starts with a minimum number of must have CUs and keeps adding newer ones as requested by Designers and Crews only after thorough analysis. Another approach is migrating all the CUs and marking a few as Preferred CUs. Both the approaches have their own pros and cons. Which approach do you prefer?

In my later blogs on Compatible Units, I will be discussing:

  • How the CUs integrate Design, Estimation, Mapping, Material Management and Unitization processes?
  • What should be the system of record for the CUs?  Which Application (Design, Estimation, GIS etc.) has what part of the CU? 
  • Why is "CU based design and estimation" even more relevant for the smart grid implementations?

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