| The design of the Uninterruptible Power Supply is | | | | switch. This is generally termed- True On-line UPS - |
| determined to a large extent by the required function | | | | The term 'True On-Line' is used because this type of |
| and what level of critical cover is expected to | | | | UPS will really protect your mission critical equipment |
| protect the load . | | | | to the point that if you remove its power source and |
| At the bottom end of the scale are ' Desk Tops' the | | | | then re-instigate the power , there will be no effect |
| Offline UPS system , generally below 1kVA, as its | | | | on your equipment. |
| name suggests it provides an unregulated filtered | | | | How is it work then? The True On-Line |
| supply to the load at the same time maintaining the | | | | Uninterruptible power supply works by having a |
| state of charge of the battery by a separate | | | | rectifier, which converts the utility mains ac supply to |
| charger. | | | | dc, has the dual function of providing a dc supply for |
| When the utility mains fails or goes out of tolerance | | | | the inverter and also a supply to recharge the |
| the inverter turns on and is connected to the load via | | | | battery. Therefore in the event of the utility mains |
| a relay. There is a short break while this operation | | | | failing or going out of tolerance due to voltage or |
| takes place and the duration of this break is called | | | | frequency causing the rectifier to switch off the |
| the transfer time. | | | | battery will seamlessly continue to provide the dc |
| The Offline UPS system is not suitable where there | | | | supply for the inverter. |
| are large variations in the local utility mains supply, as | | | | The inverter then converts the dc supply back to an |
| the load will be directly affected. To overcome this | | | | ac supply that is voltage and frequency controlled to |
| problem a Line Interactive UPS system can be used, | | | | supply the load. The load is therefore completely |
| the technology operates in a very similar way to the | | | | protected from any surges, spikes or sags from the |
| Offline UPS systems whereas the inverter does not | | | | utility mains supply. |
| provide supply to the load unless a utility mains failure | | | | The double conversion Uninterruptible Power Supply |
| or brownout has occurred. | | | | has the added advantage of what is generally called |
| The Line Interactive UPS system uses an active | | | | the static switch; this is an electronic changeover |
| voltage regulator (AVR) to control the voltage seen | | | | power switch, which selects the supply required for |
| by the load during normal operation; this method | | | | the load. The supply can be either the unprotected |
| insures that the load has a constant voltage applied | | | | utility mains supply or the fully protected inverter |
| to it. Again these Uninterruptible Power Supplies are | | | | supply. This feature can be very useful in the event |
| more suitable for smaller office environment loads | | | | of an overload occurring, which is beyond the rating |
| and generally are restricted to a maximum of 10kVA. | | | | of the inverter, the load will be automatically |
| Traditionally for larger load requirements the Double | | | | transferred without loss to the utility mains supply, |
| Conversion UPS system has been favoured, basically | | | | transferring back to the protected inverter supply |
| it consists of a rectifier, battery, inverter and static | | | | when the fault has been removed. |