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Uninterruptible Power Supply For Backup Power

What is An Uninterruptible Power Supply?

An uninterruptible power supply (UPS) is a device that allows electrical equipment to continue operating normally when the main incoming electrical source is interrupted. The uninterruptible power supply most commonly encountered will be the device that keeps your computer running while you save your work and shut it down when the incoming grid is interrupted. While grid is available, the energy storage batteries in these units are kept charged or replenished after outages. Obviously, the more energy is stored, relative to the size of the load that needs to be carried, the longer electricity can be maintained in your electrical equipment in the absence of grid. The duration for which an uninterruptible power supply can provide electricity to its intended load is referred to as grid autonomy.

Any uninterruptible power supply will need some form of stored energy that can be converted into electricity when the grid fails. Although rechargeable batteries are the most common energy storage method employed, energy can be stored in many different ways. For instance, fossil fuel is a form of stored chemical energy. The kinetic energy, stored in water, used by hydro-electric generation systems is another good example of energy storage. Even conventional diesel and petrol generators can be considered a form of uninterruptible power supply depending on how they are set up and used.

Dynamic Uninterruptible Power Supply Systems

Dynamic uninterruptible power supply systems are usually employed in larger commercial operations that have sensitive electrical equipment that requires the guaranteed provision of continuous electricity. Server farms, data centres and medical facilities would typically employ this technology. Dynamic uninterruptible power supply systems are composed primarily of a large (several tons in mass) constantly rotating flywheel, an alternator which can also serve as an electric motor, control electronics and a diesel engine.

In normal operating mode, when the grid is present, electricity from the grid drives the alternator, which acts as an electric motor in this operating mode, to rotate the flywheel. The flywheel weighs several tons storing a substantial amount of rotational kinetic energy. This energy is available to energise loads in the event of a grid outage while the diesel engine is started, and the alternator is switched from motor to generator mode.

Dynamic uninterruptible power supply systems also act as electricity conditioning devices. An electromagnetic coil is used to condition the grid feed by eliminating voltage and current fluctuations that most utility grids are prone to. Although these fluctuations are common, most end users are not adversely affected by them so are unaware that they occur. Sensitive, sophisticated, computer and other IT-based systems however need stable current and voltage to avoid malfunctions or disturbances in their operation. Poor quality of grid electricity or interruptions in electricity provision can be catastrophic for hospitals, data centres or production facilities that run sensitive production processes. Poor quality of grid electricity or interruptions in electricity provision may result in substantial financial losses.

When the grid fails, dynamic uninterruptible power supply systems act immediately with no interruption. A portion of the energy stored in the flywheel is used to drive the generator while it starts up, so that electricity from the alternator is available immediately. The stored rotational energy is used to facilitate very fast start-up of the diesel engine. After the shortest possible time the diesel engine ramps up to its rated output producing electricity via the alternator and stabilising the flywheel. The system ensures that no gap in the electrical provision occurs and no deterioration in its quality is created, making the technology a truly ‘uninterruptible power supply’. Most of these systems require no battery storage at all.

Battery-Based Systems

By far the most commonly encountered uninterruptible power supply units are battery-based systems. Batteries have characteristics that make them excellent electrical ‘shock absorbers’ allowing them to smooth out large changes in demand. They are also good for maintaining steady, consistent, voltage to an inverter. Electricity delivered from a battery via an inverter is clean and steady. A full-time or full double conversion system is considered one of the most effective systems. Incoming utility electricity is always going to be an alternating current (AC) source. This is the electrical energy type used by most household and information technology equipment. Energy stored in batteries is delivered as direct current (DC). This means that electrical energy stored in batteries needs to be converted to alternating current to make it suitable for most appliances. So, by definition all battery-based units must first convert or ‘rectify’ the incoming AC electricity to DC electricity to charge the batteries and must also be able to provide AC output from the energy stored in the battery to energise commonly encountered appliances and IT equipment. DC electricity must be converted (inverted) back to AC using a device called an inverter.

In a double conversion uninterruptible power supply, electricity flows continuously through the rectifier and then through the inverter to the AC appliances that it powers. This arrangement means that the output voltage and frequency are completely isolated from the input voltage and frequency making these systems voltage and frequency independent of VFI devices. This helps the device clean up fluctuations in grid voltage and frequency. Some form of surge protection device (SPD) is usually also fitted to absorb potentially harmful voltage spikes such as those caused by lightning strikes on grid lines or, in the South African context, load-shedding switch-on and switch-off cycles. A well-designed uninterruptible power supply will also clean up voltage sags or brownouts before they get through to the output. When grid falls away, the battery continues delivering energy to the inverter, which then delivers clean electricity via the output to energise connected appliances. When the grid is restored, AC electricity flows through the rectifier, which feeds the inverter and recharges the batteries.

Speak to The Experts

While PacB are industry leaders in the provision of diesel generators, we also offer renewable energy solutions and uninterruptible power supply systems. If you need an uninterruptible power supply of any type, talk to PacB. We have identified the need for a reliable range of uninterruptible power supply systems and are the proud suppliers of the MAKELSAN UPS product range. We can assist with units as small as 1 kVA through to and including an 800 kVA UPS unit. The MAKELSAN UPS range that we provide is neutral and short circuit protected which is an essential feature to ensure that your equipment is properly protected. Our competent technical team is always available for telephonic assistance to support our units. Contact PacB today for anything related to uninterruptible power supply systems.

Our qualified technicians offer support and advice in the selection of the right power solution for your needs by calculating your power requirements.

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