Electricity + Control August 2019

POWER QUALITY, STANDBY + BACK-UP

apparent. One example for the use of a UPS is the supply of an elevator controller. Here, in the event of mains failure, the operator or even the emergency services must be notified by means of remote signalling. The power consumption of the required uses is a maximum of 4 A, and the required buffer time exceeds five minutes. Furthermore, special normative requirements also apply to these types of applications: the connected energy storage device must be actively monitored, for example. For such applications, Phoenix Contact offers a practical solution in the form of second generation Trio Power uninterruptible power supplies. Combining a power supply unit with wide- range input and integrated UPS, the devices are particularly suitable for applications where space is very limited and all connected loads need to be buffered.

width of around 35 to 50 mm. Factor in the dc UPS for the same performance class, which has an almost identical overall width, and this results in a maximum overall width of almost 100 mm. The energy storage device usually takes up the most space. For example, to buffer 5 A for around 20 minutes, an energy storage device with a nominal capacity of 3.4 Ah for 24 V dc is required. This has an overall width of about 85 mm. This means that, in total, 18.5 cm is already required on the DIN rail. Another aspect that planners need to consider for this common structure of a UPS system for dc loads is the selection of suitable power supply unit and UPS combinations. In the example above, a 5 A power supply unit and 5 A UPS were selected. But what does this actually mean? Both the UPS and the power supply unit can deliver a maximum output current of 5 A under all operating conditions. Does this mean that a 5 A load can be connected and reliably supplied in both mains and battery operation? The short answer for mains operation is no. The charging current has not been taken into consideration thus far. The UPS needs this current in addition to the load current in order to recharge the energy storage device. Assuming an additional charging current of 1.5 A, a correspondingly larger power supply unit must be selected. With some sort of reserve, to compensate for losses in the system, for example, this would require a power supply unit with an output power of 7 A. However, the next most common size is usually 10 A. This means that a power supply unit that is twice as powerful would be selected to ensure a load current of just 5 A. This results in higher initial costs and takes up even more space. However, the modular structure does have advantages. With this option, it is easy to distinguish between critical and non-critical loads. Critical loads must continue to be supplied in the event of mains failure, such as in the case of a controller. Non-critical loads, on the other hand, do not have to be supplied in the event of mains failure. This is why non-critical uses are connected directly to the power supply unit output, while the critical uses are connected to the UPS output first. A practical example In numerous applications, however, a complete structure, such as a control cabinet, needs to be supplied. This is where the problem of working with limited space really becomes

… Trio Power uninterruptible power supplies combine a power supply unit with wide-range input and integrated UPS and are particularly suitable for applications where space is limited and all connected loads need to be buffered.

The new Trio Power dc UPS devices, combining power supply and UPS, are available in three different performance classes.

In the elevator application, an output current of 4 A is required. The ideal solution here is the Trio Power UPS with 5 A nominal output power, which has a 20% reserve to support extension. With an overall width of just 60 mm, the compact device also provides a maximum charging current of 1.5 A internally on a permanent basis, in addition to the load current. The user can therefore be confident that the 5 A device has sufficient reserves to charge the energy storage device. Users can select the device that best suits the load requirements of the particular application. No further consideration needs to be given to the charging current. In order to achieve the required buffer time, an energy storage device with 1.3 Ah simply needs to be connected to the UPS using two cables. The UPS system is then ready for use.

Electricity + Control

AUGUST 2019

21