ELECTRICAL DESIGN SOFTWARE FEATURE
GETTING TO GRIPS WITH
DESIGN ISSUES
If you’re still modelling a UPS as two separate components in your design, it’s time to consider a simpler and more accurate approach. Tony Schumacher, senior electrical engineer with Amtech explains
T
he whole point of including an uninterruptible power supply (UPS) in
an electrical system is to improve the dependability of the system and increase the resilience of the equipment it serves. Therefore, it is important to get the design right and the right software can make a significant difference to the ease of the work and its accuracy. UPS systems are now becoming increasingly common in commercial and industrial electrical installations. Organisations are becoming more and more dependent on their data and are taking measures to protect it. This presents a challenge for the
electrical designer, because until recently it has not been easy to carry out the calculations required to integrate a UPS into the system. However, recent advances in electrical design software have tackled this issue to make such calculations easier and more accurate.
TWO SEPARATE COMPONENTS The problem with a UPS is that, depending on its status, it needs to be considered as both a load and a source in the same system. As a result, it would traditionally have been modelled as two separate components in the design in order to calculate the system. Designers had to make shrewd decisions as a wrong choice could mean the difference between a UPS that prevents an interruption and a UPS that becomes an interruption. This whole procedure is further
complicated as a UPS can be installed in three different ways - offline, online or line-interactive. With all these variations it starts to get tricky to know exactly what is happening in the system and to
plan for all scenarios. Using the latest design software, a UPS
can now be modelled in projects, with calculations of what is happening in both load and source situations. The software also handles all three types of UPS. This is a significant advance for
engineers who need to present ‘what-if’ scenarios for clients or, as often happens, changes are required in the middle of the project. In the latter situation the engineer can not only satisfy himself to the integrity of the system, but can also produce reports for his client to back this up.
KEEPING THINGS SIMPLE Adding information to the project can be kept simple, for example in the way that Amtech software uses tabbed dialog boxes. The voltage tab allows settings to be added for input phase connection, output phase connection, identical parallel supplies, input voltage/output voltage, input frequency/output frequency and voltage drop settings. The UPS type can be selected during this procedure. For example, when the UPS type is selected as ‘online’, the inverter supply cable will be sized for both the battery charge current and the load current. When offline, the inverter supply cable will be sized for the load charging current only. The inverter tab also includes a range
of settings that include maximum charging current, bypass switch status and fault capacity parameters. As the nature of the fault capability of a UPS is not constant with time, instantaneous, short term (60 second) and continuous fault level scenarios, all have to be
/ ELECTRICALENGINEERING
Above: once the sole preserve of critical facilities such as data centres and hospitals, UPS systems are now becoming increasingly common in commercial and industrial electrical installations
Below: software that can facilitate the integration of a UPS system into an electrical design will save considerable time and reduce the risk of miscalculations
considered. Although there are a lot of variables, things are kept simple - for instance the UPS output rating can be selected in ‘auto’, based on the calculated diversified load and typical UPS ratings, or a manual rating can also be inputted. Ease of use is also a key feature with earthing settings. The local earth impedance panel contains a calculator to obtain the electrode and its bonding conductor impedances to be determined. Otherwise the impedance values can be entered directly into the data input boxes. Clicking the ‘apply’ button applies the local earth impedance values. The earthing impedance panel shows the total earth impedance at the UPS. Circuit protection can also be set. There
are separate protection panels for the inverter and the bypass. The default setting for the bypass is ‘no protection’, in which case protection will be provided by the supply side protective device. The bypass output protection panel will only be enabled where a separate bypass output cable is connected.
Clearly, software that can facilitate the integration of a UPS system into
an electrical design in these ways will save considerable time and reduce the risk of miscalculations. It’s entirely
possible that the electrical design software you are currently using already incorporates these features. So why not take a look under the bonnet to see if it allows you to model UPS requirements and make your life easier.
Amtech
www.amtech.co.uk T: 0800 028 2828
Enter 210 ELECTRICAL ENGINEERING | APRIL 2014 21
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