An enterprise recently switched to an online UPS system after experiencing regular equipment failures. The company had upped its production, which significantly increased its power consumption. While the company did use line-interactive system for power backup, constant voltage fluctuations and overload hampered operations, resulting in unnecessary delays. Understanding the limitation of line-interactive systems to deal with frequent voltage fluctuations and higher loads, the enterprise switched to online UPS system. Since then, it has been a smooth sail for the company with very few hiccups.
The underlying technology
UPS systems can be divided into three categories—online UPS, offline UPS and line-interactive UPS. While offline UPS are mostly used in households to offset power cuts, line-interactive UPS are used in offices for power backup.
There is technically no hard-and-fast limit of the online UPS power capacity. However, generally, online units have capacities between 1kVA and 500kVA due to high-power requirements of industrial equipment and critical devices. In comparison, line-interactive systems are rated below 1kVA, more commonly within 500VA range. Line-interactive systems can also be scaled to support high-power devices, but the increase in price and size and, more importantly, the lack of effective current-correction provision (something we will discuss later) keep the motive of large-scale backup unattended.
As line-interactive UPS systems cost much less, these are sold more—even at enterprise level. However, large-size companies using expensive and sensitive devices require higher and cleaner power backup, which makes line-interactive UPS unsuitable for them. Industry-level devices usually require at least 5kVA power capacity, with general requirements ranging above 25kVA, which can go much beyond even 100kVA.
Thus online UPS systems are suggested for large enterprises. These systems can again be divided into two categories—online double-conversion and online delta-conversion.
Online double-conversion UPS systems have two paths for power flow: inverter and bypass. The main power path of this topology is inverter, which means backup power is provided to the inverter—wasting no time in switching in the event of a power cut. Bypass route is used in case the inverter fails to switch on for some reason. Waiting time for switching to the bypass power path is negligible. There is an internal two-step current conversion (AC to DC, followed by DC to smooth AC) that helps in the rectification and smoothening of the inconsistent input voltages before powering the connected device—saving the device from power surges, sags, brownouts or any other kind of power fluctuation. This is the greatest benefit of the online UPS topology for consumers. However, this is also associated with extra energy dissipation, and therefore reduced system efficiency.
Online delta-conversion UPS systems have a comparatively new set of architecture that overcomes the shortcomings of double-conversion mode. While bypass remains the secondary power flow path, just as in double-conversion systems, the delta conversion setup has an additional delta transformer and a delta converter (replacing the battery charger) inserted in the power flow path. Hence, this topology makes direct load connectivity and simultaneous load isolation (in case of any harmful power flow) possible.
It also avoids unnecessary power dissipation, increasing the system efficiency. During unavailability of AC mains power, the battery kicks in to run the inverter.
Benefits
Keeps your devices safe. An online UPS system completely isolates the connected devices from the source by placing itself directly in the power path. The main power route being the rectifier-inverter path, disproportionate DC current and voltages are rectified, removing all sorts of voltage inconsistencies, and thus providing a uniform smooth output to the connected device. This saves sensitive high-end equipment from possible damage.
Eliminates waiting time. Since the battery and the inverter are both connected to the main power path of the device, when input current cuts off during power failure, the battery immediately powers up the inverter, keeping the system running without any pause whatsoever. No transfer of power path is required, essentially eliminating the waiting time for the backup to kick in. Mission-critical activities and data centres, where down-time elimination is very essential, stand to benefit greatly from this feature.
Long lifetime and easy installation. Online UPS systems, if used under suitable conditions, can go a long way. Batteries may need to be replaced every three to four years, but rest of the device remains functional for a long time. Also, the device installation is simple, requiring only the connection of power grid and devices to the UPS.
Drawbacks
High price. Online UPS cost more than double the line-interactive UPS, that too at the basic level. While proper usage can avoid unnecessary repair costs, the initial cost of investment is quite high, making many medium-size businesses prefer other UPS systems.
B.N. Mohapatra, purchase manager at DHN Technologies, shares, “Online UPS are most suited for critical applications like healthcare, data centres and any other sector where continuous power supply is most important.” An entry-level 3kVA online UPS can cost anywhere between ` 20,000 and ` 30,000. Higher-rating 60kVA systems cost up to ` 600,000, while mission-critical UPS (such as the ones used in data centres) cost even more.
Loss of efficiency in double-conversion. As stated before, the two-step AC-DC conversion process in online double-conversion systems causes significant loss of energy, lowering the system efficiency down to 89 per cent. Delta-conversion online architecture solves this problem. Unfortunately, there is not much awareness about this benefit of delta-conversion UPS.
Nevertheless, industry players are hopeful that the market for delta-conversion UPS will pick up in the future. Kunwer Sachdev, managing director of Su-Kam, explains, “Delta-conversion online UPS are available in the Indian market. As all motor applications in manufacturing units use delta-conversion online UPS, the market for their application is huge.”
What’s the ROI?
Annual servicing is a major operational cost, accounting for almost 12 to 15 per cent of the original price of the UPS. Therefore it is important to check service centres and after-sales policy of the UPS manufacturer. An online UPS system’s return on investment (ROI) is based on the amount of load used, application and purpose, downtime and efficiency of the UPS.
Rajesh Manocha, owner of Aropower Technologies, says, “An online UPS can start giving ROI after one or two years if there is a considerable use of the UPS with no downtime. It will take longer to realise the ROI if the UPS suffers a large downtime. Since the UPS architecture can be customised to users’ requirements, the chances of downtime can also be controlled likewise. But the cost of the UPS will vary accordingly.”
Any equipment can start giving ROI if the firm is able to utilise its full potential. Mittal explains, “Say, every day there is a cumulative power cut of 30 minutes. The work saved in those 30 minutes, which could have been lost without the UPS, becomes the ROI. For a BPO, for example, saving 30 minutes worth of time and work can save a huge amount of data and finance for the company.”
Solar is the future
In the future, customers can expect higher-efficiency online UPS along with lower maintenance costs. “The UPS technology is gaining steam in the Indian market and solar is the future with respect to power back-up industry. However, there are many places that have a shortage of installation space and hence the people in those areas are bound to purchase normal online UPS,” says Kartik Sachdev, marketing head, Solar, Su-Kam.
