FAQ

An Un-interruptible Power Supply is a device that sits between a power supply (e.g. a wall outlet) and adevice (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device.

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 synchronized.

There are three typical types of UPS: OFF-LINE, ON-LINE, and LINE INTERACTIVE.

The online UPS is the most advanced and most costly UPS. The inverter is continuously providing clean power from the battery, and the computer equipment is never receiving power directly from the AC outlet. However, online units contain cooling fans, which do make noise and may require some location planning for the home user or small office.

Off-line UPS will supply power only when power failure. It draws current from the AC outlet and switches to battery within a few milliseconds break after detecting a power failure.

The line interactive UPS "interacts" with the AC power line to smooth out the waveforms and correct the rise and fall of the voltage outlet and switches to battery within a few milliseconds break after detecting a power failure.

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 it’s 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.

A UPS has internal batteries to guarantee that continuous power is provided to the equipment even if the power source stops providing power. Of course the UPS can only provide power for a while, typically a few minutes to many hours, but that is often enough to ride out power company glitches or short outages. Even if the outage is longer than the battery lifetime of the UPS, this provides the Opportunity to execute an orderly shutdown of the equipment.

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 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.

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.

Most UPS use Lead-acid maintenance-free batteries. This kind of battery is sealed so the UPS can be located with any direction and it does not void the poison gas during charging and discharging. So it also could be an indoor installation.

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 4-5 years.

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.

Rectifier
Converts AC voltage to DC voltage, recharges the batteries and maintains float voltage, handles overloads and buffers surges, 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.

There are things that can go wrong with UPS’s, and they require periodic maintenance to reduce costly repair. While the electronics in a UPS are likely to last for quite a while, the batteries will periodically need to be replaced. This will happen more frequently the more (and deeper) the batteries are cycled. Replacing the batteries every three years is a pretty typical vendor recommendation. Any UPS battery that has been in continuous service for five years probably should be considered suspect until proven otherwise. Like any other electronic device, a UPS can fail. You need to have a plan for this.

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.

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 230 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.

Air-Conditioning can be considered as a “dirty” load due to continual switching causing voltage and current spikes and surges. 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 toeth critical load is to have a seperate dedicated UPS for the A/C requirement.

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 senstive 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%.

When a ups fail, the UPS should be repaired and fully operational within a pre-agreed period.

UPS monitoring management is a software package to improve UPS efficiency. It helps users to control UPS and provide event records for the UPS. It also can automatically save files, shutdown operation systems, and shutdown UPS when power failure happens.

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.

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 compatibility problems.

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.

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.

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

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.