UPS (Uninterruptible Power Supply is an electronic device that is placed between the power supply network and the equipment to be protected, in order to provide energy to the devices even in the event of black-out.
By receiving any power grid input, it’s capable to transform it and give its output a well-stabilised alternating voltage, in value and frequency, without any interruption in the supply, even when the energy supplied by the public distribution network is missing.
In order to do so, the UPS draws energy from pre-charged batteries contained inside the UPS and makes it available at its converted output.
The UPS is also able to filter all anomalies that may appear on the network by not allowing spikes, surge and other transients to reach the equipment.
As power plants are located at kilometres away from users, energy is distributed through electricity networks that split thousands of kilometres. During this journey, there are numerous electrical disturbances that put at risk the efficiency and functionality of the devices and/or installations.
The causes of these disturbances may be external or internal to the network.
The most frequent disturbances that may cause damage to electronic and electrotechnical equipment are:
• Voltage peaks caused by electrostatic discharge
• Voltage adhesives
• Frequency changes
• Micro-interruptions of grid voltage
• Transitional phenomena
• Interferences — noise
• Rapid voltage changes
• Distortion of waveform.
In case of lack of preparation and protection, these phenomena can lead to rather disastrous consequences.
Often, by mistake, Uninterruptible Power Supplies are used when these events have already happened and when the first damage has occurred. The damages caused by these network disturbances can be:
• Total/partial loss of files and data
• Hardness, wear or rupture, of hardware
• Data processing errors
• Unplanned system crash
• Errors at peripherals and terminal
• Problems of control of production processes
• Abnormal solicitation of electronic components
An UPS therefore has two functions:
1. Eliminate disturbances in the distribution network, protecting electronic equipment and thus avoiding breakdowns and malfunctions.
2. Protect against voltage and black-out changes in order to allow data to be saved and operations to continue properly even in the absence of energy, for a time dependent on the charging and capacity of accumulators connected to the Uninterruptible Power Supply.
Sizing an Uninterruptible Power Supply means determining the power required to protect the loads connected to it.
The sum of the power absorbed by the loads shall be identified, taking care to distinguish between active power (W = Watt) and apparent power (VA = VoltAmpere).