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  • UPS
  • Bypass
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Do I require a 12 Pulse rectifier or Input filter with the MHT range of UPS?

By selecting a UPS from our MHT range you can rely on the advanced rectifier design to dramatically reduce input current harmonics to < 3% thereby eliminating the need for a 12 pulse rectifier or input harmonic filters.

What are the main components of a UPS system?

Rectifier Converts AC voltage to DC voltage, recharges the batteries and maintains float voltage, handles overloads and buffers surges, can can accept wide input voltage fluctuations.
Inverter Converts DC voltage to AC voltage, regulates and filters AC voltage. Static Bypass Automatically connects load to mains supply if overload or fault occurs. Battery Provides emergency power source when mains supply fails.

Considerations when choosing a UPS and Generator combination?

It is usually beneficial to deal with one supplier for both items as this eliminates the potential conflict if the equipment does not work well together. Typical problems are related to input harmonics, load acceptance, poor frequency regulation, voltage intolerance and poor response times.

Single or Three phase UPS?

Here are many aspects which affect the choice of module. Totally single phase units are rarely available beyond 20 kVA, above this size it is 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 units with three phase input/output are more easily distributed across generators and can also be used to feed single phase loads, and with good load balancing, need not be oversized.

Can I support Air-Conditioning on my UPS?

Air-Conditioning can be considered as a “dirty” load due to continual switching causing voltage and current spikes and surges. The The UPS module can cater for a certain level of overload for a small duration, however the duration and level of current surges typically associated with A/C units is far greater than the UPS’ capability. Therefore, it is advised not to support the AC on a UPS and supply this element with a generator only if possible.

If there is no option but to support the AC using a UPS, it is normal to oversize the inverter by 4-5 times to ensure that the unit will cater for this more demanding load and eliminate any risk to the critical load. Another sensible approach to reduce any risk is to the critical load is to have a separate dedicated UPS for the A/C requirement.

How can I remotely monitor my UPS system?

There are two ways in which you can monitor your UPS remotely. One option is to install a wall mounted Remote Panel (MultiPanel) that connects. to the UPS to a serial port on the UPS and offers the advantage of full digital metering (available for all UPS models - 400 m cable max and required 240 Vac UPS backed mains supply). The panel incorporate a multi-function audible alarm with mute facilities and lamp test.

The alternative option is to utilise the computer network with our NetMAN network adaptors to 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. This device can also offer temperature monitoring and unattended server shutdown when combined with optional modules.

Why do you need a UPS?

An Uninterruptible Power Supply (UPS) is used to protect critical loads from mains supply problems, including spikes, voltage dips, fluctuations and complete power failures using a dedicated battery. A UPS system can also be used to ‘bridge the gap’ whilst a standby generator is started and synchronised.

What should be considered when buying a UPS system?

Existing Installations Consider a central back-up system to eliminate expensive re-cabling. Wise to involve a company specialising in power conditioning. New Installations Access the level of power protection required. Some installations may demand that every item is supported by UPS, others may only require UPS for a central server and one or two workstations.

Type of Client/Application Emergency services, financial institutions, Industrial etc. This can have an impact on the system specification. Site Location Inner city areas may be more susceptible to power fluctuations. Rural areas may be affected by weather conditions on power lines. More remote areas may be located at the very end of the power line.

Can I add more UPS modules to the system when my load increases?

Yes, the MST, MPS and MHT ranges employ a plug and play parallel system that allows additional units to be added to an existing system at a at a later date. Additional UPS units can be added to either provide redundancy or extra capacity if the load increases. Sometimes it’s worth investing in additional switchgear early on so that more units can be accommodated much more easily.

Why choose 'Transformer-based' or 'Transformer-less' UPS?

Transformer based Traditional technology, typically available from 10 kVA, suitable for industrial applications, galvanic isolation with inverter output transformer, typically standard technology from 100 kVA upwards. Transformer-less Typical technology from the smallest ratings up to 120 kVA, more compact footprints, lower weights, more suited to IT applications and environments, high efficiency across the load range, generally more cost effective.

What is a 'Line Interactive' UPS?

Line interactive technology sits between offline and online. The load is fed from mains during normal operation, however unlike 'offline', this technology incorporates various filters to provide voltage stabilisation and help suppress spikes and transients.

Why install a Bypass Isolation Transformer?

When generators are installed, it is common to use four pole changeover switchgear or contactors when transferring from mains to generator resulting in the traditional neutral-earth reference being lost during transition. This can cause the phase voltages to rise alarmingly and any sensitive single-phase loads could be damaged. By adding a bypass isolation transformer, it allows the electrical contractor to earth the UPS output neutral, thereby eliminating this problem. Single phase bypass transformers are also installed on small systems where the client requires the UPS output neutral to be earthed.

What is a Bypass Switch?

Static Bypass switches are used to bypass the UPS normal operation, in cases of high inrush or fault conditions. Manual bypass switches are an added benefit to allow service and isolation for safety purposes. Correctly designed systems should enable these operations to be performed without loss of power to the load. External maintenance bypass switches add the facility to remove the UPS from site, offers local isolation capabilities and enables all ac cabling to be completed prior to the UPS delivery.

What are the benefits of an External Maintenance Bypass Switch?

Capability for total isolation for UPS maintenance, with no disturbance to the load. Greatly reduced cost and size when compared to other systems using ‘Key interlocking.’ Totally safe and user friendly, simple switching sequence, no risk of back-feeding UPS. Use of electrical interlocking ensures ‘no-break’ transfer without complex & expensive key interlock arrangement. No need for additional Maintenance switches or key exchange boxes (cost savings) Standard system using top quality switchgear, which is readily available (prompt delivery) Can easily be customised to incorporate larger terminals for oversized cables. Can be built to include full MCB/MCCB protection or just isolation depending on site requirements. Unit can also incorporate shunt trip facilities for ‘emergency power off’ (EPO) on input and by-pass switches. Can be installed outside normal hours, by a competent electrician, to enable UPS to be installed during normal hours without a further shutdown. Capability for ‘ two input’ systems giving greater flexibility and security for the critical load. Local MCB/MCCB allow downsizing of cables locally without extra protection devices.

When would I need a Generator?

Generators are usually used where there is likelihood that the load cannot be off for any length of time or in areas where the mains supply is less than reliable. Life critical systems always demand long-term support and large computer or data installations, relating to telecoms, call centres and financial institutions usually have similar needs. Any company that will suffer significantly from long-term power outages would benefit from a generator installation. If being used to support a UPS or rectifier as part of the load, the generator and control system should be carefully selected to avoid.

What should be considered when selecting a battery?

Type of enclosure - Sealed or Vented - Design life 5, 8 to 10 or 10+ years - Standard or BS6290 part 4 compliant - Battery Autonomy – Floor loading, ambient temperature.

What is a BS battery?

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. Usually costing slightly more than standard sealed lead acid products, they offer 10-12-year design life, threaded copper insert terminals, flame retardant case material (UL94-VO) and are generally selected for premium installations such as Hospitals and Telecommunications.

What does the 'Design Life' of a battery mean?

Battery quality can be determined by the ‘design life’, typically between 5-12 years for VRLA batteries. The ‘design life’ is not and never will be a guaranteed life expectancy and relies on several factors including environment, temperature, maintenance, number of discharge cycles, charging regime etc. From experience, we generally expect a good quality 9-10 year design life product to need replacement in approx 6-8 years.

What is a Brownout?

A brownout, sometimes also called a ‘sag’, is a "dip" in the voltage level of the electrical line. When a brownout occurs, the voltage drops from its normal level to a lower voltage and then returns. UPS systems can handle a reduction in the nominal voltage due to its input voltage window. If the voltage falls outside this window the battery can take over without any disturbance to the load.

Brownouts are extremely common and can sometimes be detected by lights flickering or dimming; often during heavy load periods or severe weather conditions. As demands power increase, so does the risk of brownouts.

Brownouts can wreak havoc with IT loads. In many ways, they are worse than a blackout. In a blackout, the power just goes off, but with a brownout the device continues to get power but at a reduced level, and some devices will malfunction rather than failing totally.

What is a Blackout?

A blackout is when the power totally fails. The damage that a blackout causes to your system depends a great deal on its timing. If the system is idle when the power goes out, probably nothing will be wrong with the system when the power comes back on. However, if the power fails whilst writing data to a disk you're likely to have a problem. Also the power doesn't fail cleanly, but with spikes and jitters both when it ends and when it comes back on. Some systems survive the power going off and back on without too much difficulty, but the potential for large amounts of damage is there; and of course, you lose any unsaved work.

What is a Static Inverter?

A static inverter is virtually the same as a UPS system except they are 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 (typically for 1 hour or 3 hours depending on application). This type of product is generally used in emergency lighting applications, offering efficient backup with reduced running costs, although provides no filtering or protection for more sensitive loads such as computer equipment. All our UPS modules can be configured to operate as a static inverters, however please note this is a factory fitted option.

What does Autonomy mean?

The battery duration at a specified load level is referred to as the battery “autonomy”. 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. Increasing the ‘autonomy’ is achieved by adding extra battery strings connected in parallel, however it is important that the charging capability of the UPS system is considered.

What are the differences between 'Online' and 'Offline'?

Off-line (VFD) systems are usually low-cost products designed for a simple one or two user PC installations, they offer little or no protection against most supply problems and really only give support for short-term power loss. The load is fed from the mains during normal operation, hence 'off-line'. On-line (VFI) UPS systems are regarded as 'high-end' and employ more sophisticated technology which uses a rectifier and inverter, hence 'double-conversion'. This effectively isolates the load from virtually all types of power supply problems.

Cascade or Parallel redundancy?

UPS systems can be designed to operate in parallel to increase reliability (redundant systems) or to increase load handling capability (full capacity systems). These modules would include extra paralleling circuitry and would usually share the load during normal operation. Each individual unit is sized to support the load in the event of a single system malfunction and naturally a seamless transfer is ensured. Under mains failure conditions all units would feed the load until the batteries were exhausted or until a generator takes up the supply.

Cascade Redundancy uses totally 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. Since the second is brought online by activation of the first Bypass Switch a seamless transfer is ensured. 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.

What is a Temperature Compensated Charger?

Variations in ambient temperature presents the greatest threat to battery installations. Special circuitry can be incorporated in the UPS to compensate for any variations in the ambient temperature making the recharge voltage temperature dependant - the higher the temperature - the lower the recharge voltage. This feature ensures optimum battery performance and helps to prolong their life.

Input filters or 12 pulse rectifiers?

With current recommendations demanding lower levels of input harmonics (THDi) it is more common for larger systems to require some form of input filtering to achieve this. 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 of the load, 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. Recent developments in rectifier design have resulted in IPFC (input power factor corrected) IGBT rectifiers offering very low THDi and a high Input PF as standard.

What is ECO mode?

ECO mode is often referred to as 'Active Standby' and is mainly used on sites where the general mains supply is relatively stable or the load is not sensitive to mains interference. The UPS runs in bypass for normal conditions and transfers the load, without break, to inverter when the mains fails. This configuration is available on our entire UPS range upon request. This mode provides an improved system efficiency of around 98%.

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