Cement plants are large installations, with big motors and lots of equipment. And like most industrial manufacturing, cement production is under pressure to reduce costs and increase production while governments add regulations.
A cement plant should always have a current* power system analysis report. If you don’t, I am going to give you three reasons why you should get one started, and how it will help increase the production at your plant.
Electrical Safety Program
You may ask yourself how an electrical safety program can help you with production and reducing costs, the simple answer is by preventing electrical incidents. Every electrical incident at your facility will cost money in lost time, wages, fines, etc, NFPA figures that the average accident costs around $80k (6 Reasons to have an electrical safety program), meaning that a single accident will likely pay for a power system analysis and report.
Protection coordination is a critical part of a complete power system analysis study, and with this tool we will work with you to determine what areas of the plant must be kept online and what areas can be tripped during an incident. You don’t need to necessarily sacrifice selective coordination to reduce arc flash hazards, a great paper outlining these that was presented at the 2010 IEEE-IAS/PCA Conference was titled Methods for limiting arc flash hazards while maintaining system selectivity. The 3 traditional methods include:
- Applying lower short time delays
- Selective Instantaneous trips and ZSI
- Reduced Energy Let-Through (RELT) Mode
A couple of non-traditional methods, that don’t sacrifice selective coordination, but reduce the risk to being exposed to a high energy arc flash event include:
- Maintenance Switches
- Arc Flash Detection
With these newer technologies, I would recommended updating the existing power system analysis report to get an accurate baseline, and with the electrical safety program select areas that are high risk, and would benefit with the newer methods.
Large Motor Loads
Motor load, especially those that are not controlled by a VFD or soft-starter without a bypass, can have a large impact on the fault energy being fed into a arc flash. With VFDs getting cheaper, more motors are being retrofitted for the energy savings they represent. However, that means there is a change in the fault current available for an arc flash, and a reduction of rotating inertia of the system in the case of a three phase fault.
In the case of the arc flash energy, this may mean that the electrical worker is wearing too much PPE for the task at hand. The removal of the motor contribution means that the amount of current available to feed into the fault has lessened.
For the rotating inertia, in the case of a large three phase fault, the rotating motors transiently help support the voltage of the system. If the fault is large enough, and the voltage drops low enough, a fault in one part of the system may cause a cascading trip that will affect a larger portion of the system than needed.
A power system analysis report is a powerful tool to help increase the reliability and safety of the power system at your cement plant. By reviewing the installed system to ensure you have an accurate baseline, and that the system coordination is optimized for reliability and reduction of arc flash incident energy, you will reduce the year-over-year operation costs of the power system.
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