Commissioning electrical systems in mission critical facilities

12/09/2013


 

UPS

Figure 2: The UPS is a critical component to supporting critical loads, as it is the primary system responsible for maintaining continuity of load during a loss of utility. Courtesy: ESDThe UPS is probably the most important piece of equipment in the critical facility because of its ability to maintain power to critical loads, regardless of the operation of all of the other supporting systems (see Figure 2). 

Monitoring the inputs to the rectifier of the UPS, the static bypass within the UPS, and the UPS output bus is considered best practice during functional performance testing. After each transient, step load, or battery discharge test, the waveforms recorded by the power quality meters set up on the system should be reviewed to confirm that no events were triggered and that the output waveforms stayed within tolerance and recovered within the specified time frame. UPS systems are often placed into service quickly after functional performance testing, so it is best to check the power quality meter results—including waveform captures—during on-site testing rather than waiting for a report from the meter technician. This way, any problem discovered during UPS testing can be quickly rectified as the manufacturer often has to consult the factory on problematic internal UPS operation. 

Full load endurance tests should be conducted on UPS systems after the system has been installed on-site, even if full load testing was conducted in the factory. Many components need to be disconnected for shipping and are then reassembled on-site. Electrical equipment can also be affected by problems that develop during shipping and may not be detected without performing the endurance test on-site. Generally, an 8-hr duration for a full load test is considered adequate to confirm that the system will be capable of functioning at full rated load without problems. 

In some cases, it can be difficult to monitor the logic used by the UPS to handle various operations because the actions are carried out by microprocessors installed on circuit boards. This emphasizes the importance of properly setting up power quality monitoring equipment prior to testing the UPS. If a problem is detected during testing, the manufacturer will have a much easier time solving it if it is provided with significant data generated both by the UPS’s internal monitoring system and the external power monitoring equipment used during testing. When a failure occurs, it can be very difficult to understand what is happening inside the equipment. Captured test data almost always improves the issue resolution process. 

UPS commissioning case study: While setting up the system configuration for a battery discharge test, both battery string breakers opened when load was applied to the batteries. The event that caused this response was retested twice with no anomalies noted. During further testing, the failure could not be recreated. The manufacturer replaced parts within the UPS that could have failed and caused the initial problem. After the replacement, the UPS was tested at a variety of load step changes and was transferred to static bypass, maintenance bypass, and back to inverter. An additional 2-min battery discharge at 65% load was then conducted while UPS screen calibration was performed. The manufacturer indicated that the repairs were successfully executed and that the system was operating properly, but was not able to explain why a crucial function within the UPS dramatically failed.

Generator paralleling switchgear

Figure 3: Generator paralleling switchgear must be tested with resistance/reactive loads to confirm the system’s ability to properly share kVAR. Courtesy: ESDGenerator paralleling switchgear is a crucial component to a critical facility in situations where the generator supported load exceeds the capacity of one generator (see Figure 3). 

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. 

Generator paralleling switchgear commissioning case study: After a generator paralleling switchgear system was tested, programming changes were made in response to issues discovered during the testing. Retesting was conducted, but only a portion of the tests were repeated. Later, during owner training, additional programming problems were discovered as a result of the changes made prior to the previous retesting. The PLC programming was changed again after additional tweaks were required. To be sure that both the PLC programming and the system were working properly, a retesting procedure was conducted including every possible user initiated transfer and automatic transfer in both open and closed transition scenarios. The retesting was video recorded and documented, and the PLC event log was extracted to show the transfers that occurred. The retesting was completed successfully with no additional programming changes required.



EDDIE , GA, United States, 01/03/14 05:10 PM:

The anecdotal information contained in the case study presented in this article is doing a great disservice to the reader as it is technically inaccurate. The fact that the voltage dip caused the load bank controls to drop out on site, but not at the factory has everything to do with how the load bank controls were powered and nothing to do with the power factor of the load bank being used. IF all other factors/variables were identical between the two tests, the engiens would have performed better (less voltage dip) on the resistive only test than they did on the 0.8 pf resistive/reactive test which requires more torque / Hp from the engine to overcome.

The value of testing at a power factor that is similar to the actual building load is completely valid and worthwhile, but the data used to try to support the point are invalid.
Anonymous , 01/03/14 07:20 PM:

Torque is needed for power production, less so for VAR production. With a PF of 0.8, the power production is less than with a unity PF so wouldn't the torque required be less, not more?
BHAVESH , MAHARASTRA, INDIA, 01/03/14 11:13 PM:

nice article .

Pls present same type of article for HVAC System .

Bhavesh Mehta
Reliance Industries Limited
nAVI mUMBAI
INDIA
+91 98 676 13136
Anonymous , 01/06/14 08:36 AM:

Never heard of a diesel engine-generator set being "tuned and calibrated" to operate at its rated conditions. It's supposed to meet its published ratings over the entire range of 0.8>pf>1.0
PHILIP , LA, United States, 01/17/14 12:38 PM:

Interesting and Informative.
Tell Eddie to consider using
Reactors to Rid the Dip.
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