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UPS | Continuous power

An Overview of UPS Basics

An uninterruptible power supply (UPS) is a device that powers electrical equipment when the normal grid power fails. An example that most will be familiar with is the small unit that keeps a desktop computer powered up for a short time while work is saved, and the PC is shut down in a controlled manner when grid power is interrupted.

An uninterruptible power supply relies on some form of stored energy to provide substitute (backup) electrical power during power outages. While the grid is available, the energy stored is kept in reserve in case of an interruption of grid power. Any energy consumed during an outage is replenished once the grid is restored.

UPSs come in a vast range of sizes and designs to suit applications, from backing up a desktop computer for a few minutes to providing utility scale power for extended periods to facilities such as server farms. They can be designed to provide single- or three-phase alternating current (AC) output. The total amount of stored energy, relative to the load that needs to be powered, determines the duration for which equipment will run in the absence of the grid.

Rechargeable batteries are the most common energy storage method employed, but this is not the only type of stored energy that can be used. The kinetic energy stored in water or a flywheel are also possible sources of energy that can be used to provide backup power for continuous power provision. Even energy stored in compressed air or liquefied air can drive devices that convert their stored energy into electricity to keep critical electrical equipment powered up.

 

Battery-Based UPS Systems

The majority of uninterruptible power supply units are battery-based systems. Batteries have characteristics that make them an excellent source of stored energy for UPS systems. Batteries are good at rapidly providing large amounts of current. This characteristic allows batteries to handle smoothing out large variations in demand.

Batteries work well with the inverters required to convert the Direct Current (DC) they provide into Alternating Current (AC), as they are good at maintaining constant voltage to an inverter over extended periods. Electrical power delivered from a battery and inverter is typically clean and stable.

 

A UPS Versus Alternative Backup Solutions

A battery-based UPS offers instant, automatic power backup, which continuously keeps critical or sensitive electrical equipment energised. Power interruptions to medical equipment, for instance, could literally be a matter of life or death. Sensitive electronic equipment and server farms are exposed to the risk of damage, or data loss, by unexpected power outages or from power quality issues and grid failures.

A properly specified UPS eliminates the dangers that sudden shutdowns expose sensitive equipment to. They also mitigate the effects of the poor power quality that comes with the initial return of the grid, which is potentially worse than the initial interruption.

In operation, a UPS system produces no carbon emissions, making it more environmentally friendly than a fossil fuel-powered generator. Unlike a generator, it requires no maintenance, although the batteries do have a finite lifespan and will need replacing at some stage.

The primary limitation of a UPS is that, no matter how large the battery storage component is, the amount of stored energy is finite. A diesel generator designed for primary power provision can run continuously for very long periods if properly maintained and fuel is kept topped up.

 

Which Design?

While a battery-based UPS can be designed in several ways, a full-time, or full double conversion, system is considered the most effective system. Incoming grid power is an AC source and is the electrical current type used by almost all households and most commercial and industrial electrical equipment. The energy stored in batteries is DC, which means that electrical energy stored in batteries needs to be converted to AC to power most electrical appliances.

Battery-based units must first convert or “rectify” the incoming AC electricity to DC to charge the batteries and then must also be able to provide AC output from the energy stored in the battery to power the AC loads. DC electricity must be converted back to AC using an inverter.

In a double conversion system, electricity flows continuously through the device to the AC appliances connected to it. The design results in the output voltage and frequency being completely isolated from the input voltage and frequency. The design allows the UPS to clean up fluctuations in grid voltage and frequency and provide clean, stable output.

A surge protection device (SPD) is usually also provided to absorb voltage spikes or electromagnetic pulses, typically caused by lightning. A well-designed UPS will also take care of voltage sags (brownouts), preventing them from getting through to the output side of the device. When the grid falls away, the battery continues delivering energy without interruption to the inverter, which, in turn, delivers clean, continuous electricity to connected appliances. When the grid is restored, AC electricity is restored to the rectifier, which recharges the batteries and simultaneously feeds the inverter, powering the connected loads.

 

Single versus Three Phase

A single-phase UPS has a single input and output source to the electrical equipment. With just one sine wave voltage, it only requires two wires to complete the circuit, a conductor and a neutral. A three-phase UPS uses three separate conductors and provides three sine waves, each out of phase and spaced 120° apart from each other, to provide continuous power. A three-phase system needs a minimum of four wires, namely three conductors and a neutral.

A three-phase unit can deliver more electrical power than a single-phase unit because it uses all three phases. A three-phase UPS is typically used in industrial and business settings, where single-phase systems are more suited to domestic appliances or equipment with lower power requirements.

A single-phase unit will usually cover loads up to 10 kVA and will be used for smaller installations, such as telecoms or computer systems or domestic loads. They will power devices that typically run on a standard three-pin plug.

A three-phase UPS will be specified for larger installations, industrial applications, and medical environments, and the protection of equipment with large electric motors, such as lifts, pumps, and fans.

 

Speak to The Experts

We at PacB are an industry leader in the provision of diesel generators and also offer renewable energy solutions and UPSs. A UPS and genset working in tandem is the gold standard in uninterruptible power. Combining these technologies ensures continuous, clean, and stable electrical power to electrical equipment.

If you need a continuous power supply system of any type, consider PacB. We can assist with units from as small as 1 kVA through to and including utility-scale devices. We can assist with uninterruptible power supply units for any application. We can also design and engineer custom tandem systems. Contact us today for anything related to power supply systems, whether genset, UPS, or renewable energy.