System Listings

Uninterruptable Power Supplies

System Overview
It is often necessary to provide certain equipment in a building with an electrical supply that is both reliable and stable. It is in these situations where UPS is utilised.

The most common modern use for UPS systems is where computers or related electronic equipment is installed. Such equipment would suffer loss of data or possible damage to electronic internal components if a power surge were to occur or if a small interruption of supply occurred.

It is vital that if an extended power cut were to occur, the UPS can operate for a sufficiently long time to enable users to shut down the equipment safely.

Some installations are able to continue to function normally in a power outage through use of UPS systems combined with standby generation. Hence, clear commercial advantage is gained.

Systems Available and Applications

•  Static Systems. Ranging in size from the smallest of desktop units maybe 100VA to large free standing units able to serve hundreds of KVA. A static UPS has no moving parts and relies upon rechargeable batteries to provide output whilst the main supply is deenergised. During normal use the batteries are kept fully charged and in optimum condition. The systems generally combine a charging circuit with a line conditioner. The unit is controlled by a static switch which automatically changes over the supply from mains to battery when needed. Commonly used with computer equipment for UPS cover over both short and long durations. (1min - 1hr). Also used in conjunction with standby generation to provide a stable supply whilst the generator started and run up.

•  Rotary Systems. At one time common, this relies upon a form of flywheel which is run up to high speed during normal operation by a motor. During a power failure the motor acts as a generator and for a short duration, the unit can generate an output that is stable enough to serve a load for a short duration if connected in parallel to it. This technology has been superceded with the introduction of modern static UPS systems. However, flywheels have been used in hybrid schemes where the flywheel is run in parallel with rechargeable batteries to extend supply duration. Small standby generation plant also uses flywheels. In this case the generation plant itself is a form of UPS.
  Modern developments in flywheel technology   using low friction bearings look set to cause new developments in the UPS industry. In which case, the rotary UPS may well come back into fashion.
  

Legislation & Guidelines
UPS systems are governed by a range of regulations and legislation  

British Standards.

Also refer to The British Standards Institution

• BS 7671:2001 "Requirements for electrical installations". IEE Wiring Regulations. Sixteenth edition. This is the all encompassing "Bible" in relation to the design, installation and use of electrical installations and equipment in buildings.
  

Combined Standards

• 
  BS EN 50091-1:1993 "Specification for uninterruptable power systems (UPS). General and safety requirements". Applicable to electronic indirect a.c. convertor systems with an electrical energy storage device in the d.c. link.
• BS EN 50091-1-1:1997 "Specification for uninterruptable power systems (UPS)". General and safety requirements for UPS used in operator access areas
• BS EN 50091-2:1996 "Specification for uninterruptable power systems (UPS). EMC requirements" This product EMC standard will take precedence over all aspects of the generic standards and no additional testing is necessary.

International Standards

See also IEC search page

• .Project : IEC 62040 Ed. 1.0  Uninterruptable power systems (UPS): Electromagnetic compatibility (EMC) requirements

Legislation

• Health & Safety at Work Act 1974 - Massive item of legislation which encompasses all aspects of Health & Safety in the workplace. This has been constantly added to over the years. It now comprises and references a whole series of separate regulations and codes of practice documents
• Electricity Act 1989 - In the words of the official HMSO title. "An Act to provide for the appointment and functions of a Director General of Electricity Supply and of consumers' committees for the electricity supply industry; to make new provision with respect to the supply of electricity through electric lines and the generation and transmission of electricity for such supply; to abolish the Electricity Consumers' Council and the Consultative Councils established under the Electricity Act 1947; to provide for the vesting of the property, rights and liabilities of the Electricity Boards and the Electricity Council in companies nominated by the Secretary of State and the subsequent dissolution of those Boards and that Council; to provide for the giving of financial assistance in connection with the storage and reprocessing of nuclear fuel, the treatment, storage and disposal of radioactive waste and the decommissioning of nuclear installations; to amend the Rights of Entry (Gas and Electricity Boards) Act 1954 and the Local Government (Scotland) Act 1973; and for connected purposes."
• Electricity at Work Regulations 1989 - Regulations covering the whole aspect of ensuring that the workplace is safe in regards to the use of electrical equipment. (a part of the H&S at Work act)
• Construction (design & management) regulations 1994 - Another wide reaching set of regulations which cover the whole process of construction safety. It focuses on carrying out risk assessments and altering the design or management process to account for such risks. Again this forms part of the H&S at work act 1974.

Related Links

Links relating to the design and installation of Uninterruptable Power Supply systems can be found here

Manufacturers

Many if the above illustrations have been provided by MGE UPS Systems to whom thanks is expressed. Other manufacturers are listed here