Constant power supply is fundamental to the operation of a mission-critical facility. Yet, according to Eben Owen, Enterprise and Solutions manager for South Africa at Schneider Electric, as power outages are not uncommon, certain electrical design considerations need to be put in place to help minimise the risk posed by such outages. 
“The first line of defence would be a generator to provide backup power when electrical utilities fail. Generator solutions range from a simple single generator and Automatic Transfer Switch (ATS) up to a complex multi-generator plant.
“However, a generator is only of use if it is ready to come online and power a full equipment load when asked, making the testing, care and maintenance of your generator fundamental to the survival of your facility,” he says.
Testing an emergency generator on a weekly basis with no load will reassure users that the generator is operational. However, these tests may also lead to “wet stacking”.
Owen explains that wet stacking occurs when a generator is operated for extended periods with little or no loads applied. Then, when the generator is asked to come online to power a full load, the “wet” fuel deposits that have built up during no-load tests prevent it from operating at the peak efficiency needed to full power the proper load.
Wet stacking does not usually cause any permanent damage and can be remedied by applying additional load to relieve the condition, effectively blowing out these deposits from the system. Whenever possible, the generator should be tested under loaded conditions in order to prevent this build up as it can take several hours to burn off the accumulated unburned fuel.
“It is best to consult your generator manufacturer or infrastructure specialist for their recommendations on the frequency and length of load testing,” he advises.
“Also, generators deplete crankcase oil during extended runs. To prevent your generator engine from grinding to a screeching halt, you must know your generator’s crankcase oil consumption rate and add sufficient oil well in advance. Your generator manufacturer or service provider will be able to calculate your lube oil consumption rate,” he says.
Aside from keeping the oil topped-up, it is important to also keep an eye on coolant levels since most generators have low-coolant alarms and shutdowns that prevent the generator from running when the coolant is low.
“The number of outages caused by low coolant levels is surprisingly high, this is unacceptable when dealing with mission-critical facilities. Periodic maintenance is key to avoiding major problems caused by minor oversights. Try to have enough coolant and oil available to get your facility through a minimum of one week of constant duty,” adds Owen.
Engine block heaters allow standby generators to start and take up load quickly in an emergency, but the constantly heated water and generator vibration causes wear-and-tear on the hoses and fittings. By installing isolation valves between the engine block and block heaters the hoses and heaters can be replaced without taking the generator out of service.
ATSes take care of moving electric power supply to/from the generator during a power outage. As soon as the ATS senses that the utility power is interrupted, it signals the generator to start.
Once the generator is running at the proper load, the ATS safely shuts off the utility power line and simultaneously opens the generator power line from the generator.
This switching system also works in reverse once utility power is restored, with most transfer switches waiting a prudent amount of time before automatically switching back. These transfer switches contain parts and connections that can and will fail, therefore continual maintenance is essential.
“When possible, wraparound feeders, or the use of isolation bypass, will allow you to maintain power to your facility when your ATS is out of service,” says Owen.
Uninterruptible power supplies (UPSes) are essential equipment at mission-critical facilities. From a small UPS plugged into an outlet at a personal computer, to large parallel systems that power large data centres, UPSes all have one thing in common – batteries.
A UPS differs from standby generator in that it will provide almost instantaneous protection from power interruptions, by supplying energy stored in these batteries; however, UPS batteries have a limited life span and must be tested regularly. There are many different types of UPS systems and configurations, each with its own strengths and weaknesses, but it always comes down to the batteries.
“There are two basic types of UPS batteries: electrolytic (flooded wet cell) and vented (VRLA). Flooded batteries have a higher initial cost, but are more reliable and will last longer than VRLAs. The typical life of a flooded battery will be 15 to 20 years, whilst a VRLA only lasts three to five years,” he says.
“If your facility opts for VRLAs, have your UPS manufacturer configure your batteries into separate battery strings with their own DC breakers and cabinets. This will allow for one string to be isolated from the UPS system, keeping it online during maintenance and replacement,” he continues.
“The battery is the heart of the UPS system, and using battery monitors will help extend the life of batteries and increase the reliability of the battery plant. The maintenance of all your facility’s batteries cannot be neglected; from generator-starting batteries, program logic controllers (PLCs), monitoring and control systems, to breakers and trip units.”
He adds that even UPS systems are not immune to failure. Companies must build in appropriate measures to ensure that their critical load remains operational in the event of a UPS failure, with even some maintenance tasks entailing taking the UPS system offline.
With a system-plus-system design or external wrap around maintenance bypass, maintenance tasks can be performed without affecting the critical load.
“Once you have determined the proper UPS configuration you need to now distribute that power to the facility. This is done through power distribution units (PDUs), remote power panels (RPPs), distribution panels and an assortment of power cables and strips,” he says.
Many facilities are designed with state-of-the-art technology, however, all that technology is wasted if the final connection hinges on inadequate cabling, breakers and distribution methods. The 32-amp breaker should be a tested bolt-in breaker rather than a snap-in version, which tends to be used in residential applications.
Although the snap-ins are cheaper and easier to use and install, they are also less secure, untested, and far less reliable; attracting a failure rate of 20%to 50%.
“A cheap breaker can negate all the built-in measures preceding it. Don’t leave millions of rands in infrastructure at the mercy of a cheap powerstrip with an even cheaper push-out circuit breaker and switch,” says Owen.
Lastly, a load bank is an essential tool in the maintenance of a mission-critical facility. Load banks are devices designed to provide electrical loads for testing power sources such as generators and UPS, to ensure they can handle the necessary load during an emergency.
Load banks are also used to reduce “wet stacking” problems in generators. Users can install permanent load banks or have a service provider bring temporary units in for maintenance.
“Either way, be sure you make the provisions in your switchgear to connect the load bank to the UPS system and generators. This extra load bank breaker will save you a great deal of grief later,” Owen concludes.