What is a UPS and why do I need one?
An Uninterruptible Power Supply (UPS) is a piece of electrical equipment that will provide emergency power to a critical load in the event of failure of the input power source, typically mains power from a utility provider. A UPS system can also be used to 'bridge the gap' whilst a standby generator is started and synchronised.

Its constituent parts are a Battery which provides the emergency power; an Inverter which converts DC voltage to AC voltage; a Rectifier which converts AC voltage to DC voltage and recharges the batteries; and, a Static Bypass which ensures that the load drops automatically onto the mains input feed if the Inverter fails.

Which type of UPS system is right for me?
This depends, quite simply, on the type of installation to be protected and the level of power protection required. Is it an existing or new installation? Which items of equipment need to be protected? What is the criticality of the business? How susceptible is the area to power fluctuations?

Solutions range from simple offline (low cost, limited protection) solutions for home and small business, to more complex online solutions (high end, isolating the load from virtually all types of power supply problems) for rack environments, computer rooms and data centres.

What are Bypass Switches?
These switches are used to bypass UPS normal operation. Static switches allow service and isolation for safety purposes. External maintenance switches, in addition, allow total isolation and removal of the UPS from site without disrupting power to the critical load.

What are the main features of the various UPS configuration options – transformers, redundancy, phase, filters?
Transformer-less UPS, typically used from the smallest ratings up to 80kVA, is cost effective and suited to IT applications and environments. Transformer-based UPS is suitable for industrial applications, available from 10kVA, and typically is standard technology from 100kVA upwards.

Cascade Redundancy uses standard units with one feeding the load whilst the other sits in the bypass line of the main unit ready to support the load in the event of a system malfunction. Under mains failure conditions the first unit would feed the load via battery until the batteries are exhausted and then the load would be transferred to the second unit via the static bypass and the second battery bank would then feed the load. Parallel Redundancy is designed to increase reliability (redundant systems) or to increase load handling capability (full capacity systems). Under mains failure conditions all units would feed the load until the batteries were exhausted or until a generator takes up the supply.

Single phase units are rarely available beyond 20kVA. Above this size it is usually necessary to use a three phase input for the rectifier, even where the inverter output is single phase. When feeding this type of system via a generator it is important to remember that the bypass line will be single phase, demanding a higher current on one phase only.

Larger systems usually require some form of input filtering to meet the recommendations for lower levels of input harmonics (THDi). Twelve pulse rectifiers can improve upon more standard 6 pulse systems and offer the ability to correct the problem across the whole load range. Passive input filters added to 6 pulse designs are usually cost effective and improve the input power factor, but often only effective at higher load levels, typically above 50%. For very large installations it is quite common to have a combination of a 12 pulse rectifier with extra input filtering, to dramatically reduce harmonics as a result of a restricted input supply or standby generator limitations.

Can I add more UPS modules to the system when my load increases?
Yes, a plug and play parallel system allows additional units to be added to an existing system. Additional UPS units can be added to either provide redundancy or extra capacity if the load increases.

Can I support Air-Conditioning on my UPS?
Yes, but not recommended. The duration and level of current spikes and surges typically associated with AC units is generally far greater than the UPS' capability. Therefore it is advised not to support AC on a UPS, but to supply it with a generator.

What are Brownouts and Blackouts?
A brownout is a "dip" in the voltage level of the electrical line; the voltage drops from its normal level to a lower voltage and then returns. Brownouts are extremely common and can wreak havoc with IT loads. They can be worse than blackouts as devices may continue to get power but at a reduced level, and some devices will malfunction rather than fail totally.

A blackout is a total failure of the power supply. The damage caused depends on its timing. If the system is idle, there may be little or no damage when the power returns. If the system is active there may be considerable damage and data loss.

What is ECO or 'Active Standby' mode?
This means that the UPS runs in bypass for normal conditions and transfers the load, without break, to an inverter when the mains fail. This is mainly used on sites where the general mains supply is relatively stable or the load is not sensitive to mains interference.

What is a Static Inverter?
A static inverter is virtually the same as a UPS system except it is configured to operate in 'active standby' mode with the bypass supplying the load during normal conditions. When a mains failure occurs contactors are used to transfer to inverter with the standby batteries then supporting the load.

What should I know about Batteries in UPS systems?
'BS or British Standard' is the generic term given to high integrity batteries that fully comply with BS6290 part 4 (and IEC60896-2) in terms of construction, performance and design life.

'Design life', typically between 5-12 years for VRLA batteries, is an indication of battery quality. It relies on several factors including environment, temperature, maintenance, number of discharge cycles, charging regime etc. Generally, a good quality 9-10 year design life product is likely to need replacement in 6-8 years.

'Autonomy' refers to battery duration at a specified load level. A UPS battery can be sized to support loads from a few minutes up to several hours. However the cost of a large battery at a high load level can sometimes mean that a Diesel Generator should be considered.

'Temperature Compensated Charger' refers to specialist circuitry that compensates for any variations in the ambient temperature and makes the recharge voltage temperature dependant, i.e. the higher the temperature, the lower the recharge voltage. This optimises battery performance and helps to prolong battery life.

When would I need a Generator?
Generators are usually used where the load cannot be off for any length of time and/or in areas where the mains supply is less than reliable. If your business would suffer significantly from long-term power outages, it would benefit from a generator installation.

If generators are installed, a bypass isolation transformer should be considered to earth the UPS output neutral and eliminate the problem of losing the traditional neutral-earth reference which occurs with the use of four pole changeover switchgear or contactors when transferring from mains to generator.

If a UPS and Generator combination is employed the two components need to be carefully matched and attention paid to aspects such as input harmonics, load acceptance, poor frequency regulation, voltage intolerance and poor response times.

How can I remotely monitor my UPS system?
Several options are available.

A Remote Alarm Panel (RAP) that connects to the UPS interface board and is capable of providing full operating status and alarm conditions.

A more advanced Remote LCD Panel that connects to a serial port on the UPS and offers the same features as the RAP with the advantage of full digital metering.

Both panels incorporate a multi function audible alarm with mute facilities and lamp test.

Network Adaptors, CS121 or NetMan, that provide full UPS status and measurement values via a web-browser with facilities to send alarms using email, SMS messaging, SNMP traps or directly to an existing BMS system.