Generator Paralleling Switchgear
This is a crucial component to a critical facility in situations where the generator supported load exceeds the capacity of one generator.
Generator paralleling switchgear systems should be tested at the rated power factor of the generator paralleling switchgear system—typically 0.8. This is important to show that each generator properly shares the kW and kVAR loads. Just because paralleled generators evenly share kW while serving a resistive load does not always mean that they will evenly share kVAR when serving a reactive load.
A major challenge with testing generator paralleling switchgear systems is that they are often rated for very heavy loads due to the number of generators that can be connected to them. In some cases, it may not be practical and may also be very expensive to load generator paralleling switchgear systems to rated capacity.
It is recommended that enough load be provided so that it exceeds the capacity of one generator. Ideally, the load banks provided will be sized to the expected operational capacity of the generator paralleling switchgear, but not necessarily to its full design capacity.
Generator paralleling switchgear systems rely heavily on programming within the programmable logic controller (PLC) for operation. Knowledge of how this program operates is often limited to a handful of experts. Changes to PLC programming must be documented in a PLC programming change log. The log should include the date of the change, the reason for the change, a description of the change, and the new version number of the program that includes the change. Older versions of the program should be saved in the event that updates create additional problems and reverting back to an earlier version of the program is required.
Main Electrical Switchgear
It is also an important component to a critical facility because it distributes power to all of the downstream electrical distribution equipment.
Circuit breaker settings must be inputted, coordinated, tested, and verified throughout all main electrical distribution equipment. If there is a fault in the system, it is imperative that selective coordination is implemented so that the fault is isolated as far downstream as possible.
Main circuit breakers must be properly set up to ensure that they will stay closed during fault conditions and wait for downstream equipment to clear the fault. This will be ensured by implementing proper National Electrical Testing Association-recommended circuit breaker testing including instantaneous pickup, short time pickup, short time delay, long time pickup, long time delay, ground fault pickup, ground fault time delay, contact resistance tests, and insulation resistance tests.
While main electrical switchgear is an integral part of the electrical distribution system, the system’s current carrying capacity may increase the arc flash hazard. To avoid injury, main electrical switchgear should be disconnected before it is opened or worked on.
Because the owner will often not own a means of disconnect ahead of this equipment, it usually requires involvement from the utility provider, which can be problematic and difficult to schedule.
Static Transfer Switch (STS)
An STS is an important and useful component for a critical facility because it provides the ability to seamlessly transfer load during both failure and maintenance situations.
STSs behave similarly to ATSs, but because they are designed to transfer within a few msec, there are several settings that must be coordinated. STSs are commonly fed from UPS systems. These UPS systems are present to prevent interruptions to the downstream STSs. During a planned maintenance event or during a utility power failure, the UPSs are designed to perform transfers to bypass or battery within a certain time frame.
Because the STSs are set up to transfer on a loss of the primary source for a certain duration, the time frame must be longer than the allowable interruption seen from the UPS. If not coordinated properly, a routine transfer to bypass at the UPS level can cause the downstream STSs to transfer to their secondary source.
On several occasions, phantom voltage and current readings have been observed at the STS screens with no connected load. Rebooting the system typically corrects this problem. While the manufacturers generally indicate that there are no operational risks, this anomaly is puzzling.
Electrical Power Monitoring System (EPMS)
The EPMS allows all of the electrical systems within the critical facility to be monitored from a single location, giving the operator visibility to ensure that all systems are not generating any alarms and are operating properly and efficiently.
When confirming that the EPMS is monitoring systems correctly, multiple states must be checked for each point. Points must be modified in the field and checked to ensure that the same values or statuses observed in the field are properly reported back to the EPMS.
One difficulty encountered in this area has to do with discrepancies with points. Design engineers typically specify points to be monitored by the EPMS, but they often approve equipment submittals that are unable to provide these points. To avoid this problem, it is best to meet with the design engineer and the equipment manufacturers prior to the acceptance of the submittals to ensure that the points that are important to the design engineer can be provided by the equipment.
Conclusion
The equipment in the electrical distribution system of mission critical facilities must operate dependably. After commissioning challenges have been resolved and best practices have been employed, these systems will meet the original design intent and owner’s requirements, ensuring the owner that the facility embodies reliability, redundancy, and resiliency.
About The Blogger
Strategic Media Asia (SMA, www.stmedia-asia.com) is a leading technical training and event organizer for corporations specialized in data center design & build, E&M facilities, telecom, ICT, finance and colocation. Currently, SMA delivers a series of data center trainings and qualification programs in Hong Kong, Taiwan and Macau.
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