Cement plants have a cyclical profile where they are producing product before the building cycle, and full out throughout the building cycle (spring to winter) to keep with demand, then annual maintenance in the winter until it is time to get started again.
With leaner engineering groups in all of industry, we recommend a hybrid approach with you using internal electrician and engineering resources to gather the data needed for the complete power system analysis. If there aren't any power quality concerns at the plant, or your power system study isn't current we recommend getting started with:
- Short Circuit,
- Protection Coordination, and
- Incident Energy (Arc Flash)
Recommended Scope of the Power System Analysis
The cement plant power system is large and complex, with a range of voltage levels from 100kV to 120/208V. If you are starting from scratch at the plant, or if you (or the person running the project) don't have a lot of experience with power system studies, it is best to chunk out the system in bit sized chunks. But make sure that how you break out the system is done in such a way that you will have a useable product at each stage.
How much of the Cement Plant Power System
For example, we recommend that you model the entire MV system, from the incomming from the utility down to any 5kV that is on the plant. This will allow you to address all the large motors, generation and utilities on the site that will account for the majority of the fault availability. Depending on the size of the system and budget, this may be all that you get done in the first round.
The next step is to pick one of the feeders in your system, or a single area of the plant and complete the model (and report) to the 600 V (or 480V in the US) system and include all motors 25hp and over, and to the secondary of any 120/208 distribution panels. Motors less than 25hp will likely not affect the available back feed into a fault, and therefore can be neglected.
The 120/208V distribution panels may be contentious and not needed at your facility. I have typically neglected them in the past, however there are still a lot of electricians that will work on a panel at this voltage energized without a second thought, I have started recommending labeling these panels with full Arc Flash/Shock Warning labels with the intent of raising the awareness that the hazard is still present, and PPE is required.
Electrical Safety Program
In the 2015 revision of NFPA 70E mining was removed from the exceptions, and MSHA has endorsed NFPA 70E as the standard for PPE selection with regards to arc flash. What this means to you is that NFPA 70E is the de-facto workplace electrical safety standard for cement plants.
Having a current (every 5 years) arc flash analysis, which includes a power system study, is a requirement for any successful electrical safety program.
Getting Started today
If you aren't in a position to get started with a power system analysis at your cement plant today.'
If you are ready, to go NOW, give us a call and we can provide a free quote and execution plan to ensure that the report meets all operational needs of your engineering and safety groups.
As always, if you have any comments or questions, don't hesitate to give me a call.