Planning for unexpected power outages has become an essential part of any security strategy. While the primary types of equipment available for supplying backup power haven’t change much in the last few years, continual technological advances mean that some equipment becomes more relevant than others, depending on the subtleties of their operation.
The UPS is the main backup power mainstay, and is differentiated between off-line and on-line models, as Eurobyte Technology’s Neal Thomas describes: “With an off-line UPS, as the name suggests, the inverter module is off-line and does not feed any power to the protected device. The batteries are however connected to the mains power so they stay charged at all times in the event that there is a power failure. Because the inverter module is not feeding power to the protected device, it is not protecting it from other power issues such as power spikes. Once the power goes off there is a slight delay for the inverter to respond, usually between 2 to 10 milliseconds which could adversely affect sensitive electronics.
“An on-line UPS is always on-line and acts as a buffer between the main power and the powered devices. This regulates the electrical flow from the mains to the devices, which also protects them in the event of power spikes and brownouts. Because this unit is always on-line it means there is no switchover time from the UPS once the mains go out and your electronic devices are not affected by any form of a switchover.
“Lastly we have the line interactive UPS, which uses bits of the technologies from both the off-line and on-line UPS. This allows it to function in the same way as an off-line UPS with the difference that it incorporates a voltage regulator which helps to protect devices from more than just power failures, but also against power spikes and brownouts which we experience frequently in South Africa.”
Legrand South Africa is another company that supplies UPSes and related backup power equipment, and the company’s Marius Labuschagne summarises the differences between on-line and off-line models by saying that “Generally on-line UPSes, unlike off-line alternatives, are expensive and inefficient as the inverter is continuously in operation, however it provides better quality of power as compared to an off-line UPS.”
Further exploring inverter technology, Labuschagne explains that the role of the inverter is to take the utility’s pure AC sine wave and convert it into DC in order to charge batteries. The DC is then rectified back into AC, and two main types of rectifiers are available for this step. “Firstly, square wave rectifiers are a cost effective solution to achieve AC. However, the voltage is not ramped on a smooth curve but instead is pulsed on and off at a frequency of 50 to 60 Hz, thus producing a square waveform. Though this technology works well for the majority of electrical goods, unfortunately certain electronics depend on a smooth sine wave and may not function correctly with the square wave.
“This brings us to the second type: the true or pure sign wave rectifier. The advanced electronics used in these are more costly, but the stable waveform offers high-end electronics and sensitive equipment a true, smoothly ramped sine wave.”
When it comes to longer-term power outages, a generator is the go-to solution, and should always be specified at a higher power rating than the UPS that is being used, according to Thomas. “The reason for this is that the generator is running to your devices through the UPS, so if you are using a generator that has a lower power rating you will still be running down the UPS battery and this could cause damage to your UPS, and in turn damage the electronic devices you are trying to power. Also keep in mind that the generator should have a built in voltage regulator to ensure that the power coming through is clean, so as not to damage the electronic devices – this is also where your choice of UPS becomes important.”
As Labuschagne explains it, “the UPS operates from charged batteries and, depending on the autonomy available, can offer a full load supply instantaneously as the mains fail. This gives the generator time to start up and ramp to the required load, at which point it will support the UPS by recharging in order to sustain power. The full UPS load on the generator should be around half to a maximum of two thirds of the full load capacity of the genset. The reason for this is that any switching of equipment on a generator running close to full load may cause dipping and ramping of voltages and frequency as the generator tries to compensate with little reserve. In order to avoid this fluctuation manufacturers recommend 50% to 70% operating loads on gensets.”
Petrol and diesel powered generators have long been the main contenders, but the use of gas generators is now becoming more common. Labuschagne summarises the main differences between the three options as follows: “Gas gensets are silent with clean combustion. They provide moderate power levels and are very expensive to buy, but the running costs are lower. Diesel units are more noisy and the combustion is not clean, however they are more powerful and cost effective to run. Petrol generators provide strong power output and versatility in application, but are less cost effective than diesel and a bit noisy.”
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