UPS Systems Help

UPS systems come in 2 main categories:

Line interactive UPS systems
Online double conversion UPS systems

Definitions

Line interactive Modified sine-wave UPS system

· Low to medium levels of protection for your equipment · Relatively inexpensive · Sizes - 500VA - 1000VA · Considered entry level units · Most commonly used for PC back-up · Not Suitable for generators · Offers minimal protection

Line interactive Pure sine-wave UPS system

· Medium levels of protection for your equipment · Sizes - 1000VA - 3000VA · Considered industry standard · Can be used as a long runtime unit · Tower or rack mounted form · Not Suitable for generators

Online double conversion UPS system

· High levels of protection for your equipment · Sizes - 1000VA - 3.6MVA · Considered Up market · Used for general AC Back-up and protection on sensitive equipment. · Can be used as a long runtime unit · Tower or rack mounted form · Offers total protection · Only option Suitable for generators

Operations

Please note we have excluded the ferro resonant type UPS systems, as the technology use for these UPS systems is outdated and the unit is very wasteful of energy due to the inefficiencies of the unit.  

If you are looking for a protection system for expensive or very sensitive equipment, then you need an online double conversion UPS system.

▲ Online Double conversion UPS system topology

The load on an online UPS system runs constantly off the Inverter and the batteries, mains (Eskom supply) is only used to charge the batteries, therefore your supply power or lack there of has no effect on the running of your equipment. Online UPS systems are also used were a stable 50Hz frequency is required.

Online UPS systems can also be fitted with isolation transformers, this will further protect your UPS system and your load, isolation transformers are recommended for UPS systems 10kVA and larger.

Please note: Only online UPS systems can be used on generators as they are not effected by the generators varying frequency.

A line interactive UPS system and a entry level UPS system are very similar in there construction, both have a transfer switch, both supply power directly from the mains, the actual difference is in the level of protection that they offer mainly a line interactive unit supplies your load a pure sine-wave under power failure conditions and has a larger and more effective AVR, where as a entry level UPS system under power failure conditions supplies your load a modified sine-wave and offers little protection in the form of an AVR.

▲ Line interactive UPS system topology

Under normal conditions your supply power goes straight trough the unit and regulated by an AVR, while a small portion of that supply power is used to charge the batteries. Under a power failure condition the unit switches over to run from the batteries and the inverter.

Pure Sinewave

Normal AC Mains, given to us from Eskom is of a pure sinewave nature, it has very little harmonic distortion, subject to outside interference, such as lightning and large AC Loads ETC. All AC equipment in the stores today have been designed to run off a Pure sinewave wave form, including Computers, Motors, certain Lights ETC.

The internal components of the inverter/UPS inverts the incoming DC Voltage into a sinewave wave form, but because of the sophistication of these components, this makes the Inverter/UPS more expensive.

Modified Sinewave

Modified sinewave has been created to save cost, modified sinewave inverters and UPS systems just switch their DC supply between positive and negative poles to give you a simulated sinewave wave form.

Modified sinewave inverters and UPS systems are very cheap to produce but could be very costly if installed onto the incorrect equipment, for example, motors, Fluorescent globes with standard ballasts, anything with a high inrush or speed control or anything that has sensitive information stored on it, or is of a sensitive nature itself.

Please note, some UPS systems most notably the 600VA, under the desk type UPS systems are modified sinewave, but because a PC only runs off the inverter for a short period, when there is a power failure, they are less likely to be damaged as a result from the modified wave form.