By Kevin Norris, Solutions Architect at Jasco Power
While load shedding has currently been suspended, the reality is that while you are connected to the utility supply, you are still susceptible to the vagaries of an unstable power system in South Africa. In addition, to possible power outages, you are also exposed to voltage variations, sags, surges, spikes and harmonic problems. Power assurance and power quality solutions are necessary to protect sensitive equipment from these problems.
An Uninterrupted Power Supply (UPS) is essential to provide a failover system between utility power and secondary systems such as a generator. They are also useful for providing sufficient time to safely shut down equipment in the case where secondary power is not available. However, choosing the right UPS technology to suit your application can be challenging.
The right solution for you
Determining what power solution is needed is a science that requires careful consideration of several factors. Things such as the proposed installation environment, the dynamics of the load, and whether the customer is looking for continuity of supply only or complete power conditioning. The outcome of this often not asked question will determine the technology required and therefore the final cost of the solution. If not properly planned, power conditioning solutions can be less than effective and end up costing businesses more than necessary.
It is vital that businesses, particularly those for whom quality of supply is critical, plan their solutions properly. Before purchasing one or more UPSs, or any other power protection equipment, it can be highly beneficial to conduct a power quality survey. This will enable organisations to gain a sound understanding of the precise challenges of their power environment which, in turn, makes it possible for a tailored solution to be designed to achieve the desired results.
Quality of Supply
Quality of supply problems can generally be categorised as follows:
- Surges – These are sustained over voltage conditions, usually as the result of fault conditions on the electrical network. Faulty neutral connections and incorrectly tapped distribution transformers can also result in a sustained over voltage condition, resulting in damage to sensitive electronic equipment.
- Sags – these are generally as the result of poor or aging electrical distribution networks and too large a load being switched in and out of a weak network, resulting in a sustained under voltage condition. Equipment such as electric motors and refrigeration compressors are very sensitive to these kinds of conditions and a continuation of this condition can lead to overheating and permanent failure of the motors. IT based equipment tends to switch on and off under these conditions leading to a disruption in the IT process throughout the environment they are being used in.
- Spikes – These are very common during lightning season and are short duration high voltage conditions. They can also result from network switching and power factor correction compensation. Depending on the frequency of these spikes, they can result in data corruption of process plants and IT networks and permanent damage to sensitive electronic equipment.
- Harmonics – these generally result from the load source and propagate themselves back into the local and distribution networks. Depending on the type and severity of the harmonic, it can result in over heating of the neutral conductors, premature tripping of circuit breakers and possible reversing of electrical motors. The harmonics also influence the power factor of the plant and can be responsible for the failure of the PFC capacitor circuits.
With these quality of supply problems, it’s easy to see that simply having a backup power solution isn’t enough. Businesses who rely on power – and, let’s face it, they virtually all do – can find themselves faced with more than just a power outage. Damage caused by surges, sags, spikes and harmonics can costs businesses hundreds of thousands of in equipment repair and loss of productivity.
UPS – the answer?
UPSs are seen as the “one solution fits all” option to protecting equipment and, while that’s not entirely true, it’s also not quite so simple. There are a lot of factors that influence what type of UPS is required, such as the nature of the equipment being supported, the load, how critical maintaining constant power supply is, and the electrical environment, as indicated above. As can be seen from above, one requires continuity of supply, voltage stabilisation, filtration for the spikes and harmonics and galvanic isolation in order to be called a power conditioner.
There are essentially three types of UPS, starting with the most basic, which is your offline UPS. These, offer just enough time to shut down equipment – usually 3 – 4 minutes and are commonly used to support things like office computers. This type of UPS offers limited protection from surges or voltage instability and are as susceptible to being damaged themselves by poor quality power.
The second type is your line interactive UPS, which have a small amount of power conditioning built in, such as voltage stabilisers to help regulate input power and has an element of line filtering and surge protection to reduce spikes and dips. Very popular in small IT environments, these units are reasonably priced and typically offer about 15 minutes of backup time – just enough to facilitate automatic shutdowns of systems and servers. However, the extent of power conditioning is still limited.
The last type of UPS technology is the true, online double conversion UPS, which is designed to run 24 hours per day, with large battery banks for extended back up during power failures. These UPS’s act as intermediaries between the grid and equipment, offering good power conditioning and can tolerating most surges, sags and fluctuations in supply.
However, experience and the results of many site surveys have shown that UPS’s are not completely effective on their own, and need to be supported by additional power conditioning equipment such as voltage stabilisers for extreme fluctuations in input voltage. The use of isolation transformers, offers very good common mode protection and can help to reduce or increase incorrect supply voltage conditions and are able to contain harmonic conditions in a network. It is also important to understand that a UPS is not a lightning protector and that a lightning protection device should be added to all UPS installations to protect both the load and the UPS from failure due to excessive lightning activity.
Finally, it is very important to refer to the UPS manufacturers electrical and environmental operating specifications, as too often the level of harmonics present and the extreme deviation of the power factor from unity can result in the inability of the UPS to function correctly and results in both the load and UPS being permanently damaged.