Friday, January 24, 2014

Commissioning: Electrical System for Mission Critical Supply (1)

Critical Facilities Engineers should overcome the inherent challenges with functional performance testing for their electrical system.


The overall goal of commissioning must be to ensure that a facility meets the design intent and the owner’s requirements. For critical facilities, this goal is generally achieved by proving to the owner that the reliability, redundancy, and resiliency that he or she paid for is indeed present and operational in the finished facility.

Because there are so many failure scenarios and variables, it is rarely possible or cost efficient to reasonably test each one, but the commissioning authority has an obligation to provide a level of testing that will allow the owner to feel confident that each system is working and capable of maintaining a proper planned operational state during common external events.

As expected, the owner will want to use the commissioning process to be certain that the installation, performance, and operation of new equipment is acceptable before it supports critical load, and he or she will strive to do this as cheaply and as quickly as possible.

In the forthcoming posts, we will explores the best practices for testing several electrical systems, as well as some of the challenges encountered. Implementing these best practices and lessons learned on future projects will improve the quality of the product provided to the owner:


(1) Generator
(2) Automatic transfer switch (ATS)
(3) UPS
(4) Generator paralleling switchgear
(5) Main electrical switchgear
(6) Static transfer switch (STS)
(7) Electrical power monitoring system (EPMS)


Generator

Including the generators in the commissioning scope for a critical facility is imperative because they are the only source of long-term standby power when the utility becomes unavailable.


When testing a generator, it is best practice to ensure that the load for step loading and endurance testing has a power factor rating that matches the nameplate power factor on the generator, as the generator will be tuned and calibrated to operate best at its rated conditions. The manufacturer also will not likely be able to provide documentation on how the generator is expected to perform if the load used for testing deviates from the name plate conditions. The tuning and calibration is especially important when attempting a 0% to 100% step load, and often the system will not respond properly within acceptable tolerance if the power factor of the load does not match the nameplate rating.

Due to new some regulations in several countries, generators are now limited regarding the amount of pollution that they can emit under all running conditions, including when responding to step loads. This has been a challenge for generator manufacturers who in the past simply allowed the system to call for more fuel, which resulted in billows of black smoke entering the environment. In an effort to minimize pollution, manufacturers have had to finely tune the generators, resulting in the increased importance of testing the generators at rated power factor. In addition, because the generators are typically exercised under load for routine maintenance and testing, the owner often buys a permanent resisted load bank (unity power factor) sized for the rated capacity of the generator. It is important to explain to the owner that the permanent load bank that will be used for future load testing may not be appropriate to use during commissioning if it is rated at unity power factor.


Next Post: Commissioning: Electrical System for Mission Critical Supply (2)