Uninterruptible Power Supply

Hello friends, I think you are all most familiar with the device UPS. Today I am going to share some information about UPS...

UPS i.e. Uninterruptible Power supply is an electrical device which supplies the power to the load when there is sudden fail in the mains.

Now a days most of the instruments or appliances are operated from ac mains & if there is a sudden failure in the ac mains then it may cause the improper functioning of the instruments. Since most of the modern systems use microprocessors, computers and hardware including semiconductor devices any interruption in the power supply may lead to uncompleted work and may make the system ineffective to use, in order to avoid these problems an UPS can be used.

According to me one who uses UPS should have to know the working of it.      The above diagram shows basic diagram of an UPS which consists of two power sources and a switch.

The two power sources can be named as primary power source and another one is secondary source. Usually AC mains are used as primary power source and battery as a secondary source. (It may be different according to the type of UPS)  The secondary source is used when the primary source is interrupted. And the switch is used as a controlling device. It changes from primary source to secondary when it detects failure in the primary source. It automatically switches from the secondary power to the primary when it is detected that primary source has returned to its normal. The power available from mains is ac and all batteries provide dc hence, in UPS there is a circuitry to convert ac to dc for battery charging called as converters. Similarly there is a device converting dc power from battery to ac power as required by the load called as inverter.

Based on the mode of operation UPS can be classified into two types. They are:-

1.      ON-LINE UPS

2.      OFF-LINE UPS

1.      ON line UPS:-

ON-line UPS

The online UPS is also called as true UPS; there are two power sources and a transfer switch that selects between them. The main feature of this UPS is that it uses the battery as Primary source and the load is connected to the inverter. The UPS converts the 230V input AC mains supply to DC power which is then used to charge the battery. The dc output of the battery is then converted into ac by using an inverter. As this regenerates the complete ac power, it will be free from any mains borne interference such as spikes and voltage variations. Online UPS can withstand large fluctuations on the main voltage. Upon the mains failure, the battery continues to drive the inverter without any break. Online UPS also has various failsafe and self diagnostic features that will instantly transfer the load onto the mains power if there is a power failure in UPS hardware or UPS is overloaded. This is done with the help of transfer switch.

There are a few advantages of On-line UPS, and a few of them can be given as:

• This provides Failsafe/overload protection.
• This is a true No-Break power supply.
• This is mainly used for large servers

 This contains a very few disadvantages, and are:

• Size and cost of ON-Line UPS is more then other types of UPS.
• The power dissipation is very high due to conversion from ac-dc-ac.
• Since the heat generated is very high hence it reduces the life of the battery.

 Applications:

·         Telecommunication systems.

·         Voice mail and Email systems.

·         Network servers.

·         Electronic equipments.

·         Test and diagnostic equipments.

2.      OFF-LINE UPS/ Standby UPS:

OFF-line UPS

OFF line UPS is also called as the standby UPS. In this, the primary source is the mains power and the secondary power source is the battery. In this UPS, the battery and inverter are normally not supplying power to the load. The battery charger is using the line power to charge the battery but battery and inverter are waiting in standby mode till they r needed.

Hence the name standby UPS. As main line is primary source, it is also called as line preferred UPS. The spike protector and filter are used to filter the line noise and surges and to protect the loads from severe mains conditions. When the ac mains power goes out, the transfer switch detects it and automatically switches from primary to secondary. Thus battery starts supplying the load through inverter.

Some of the merits are:

• Low cost.
• Silent operation.
• Efficient.

          Demerits are:

• Minimal power protection-not suitable for places where voltage fluctuation is severe.
• Poor output voltage regulation.
• Break-transfer to battery mode because of switch over delay.
• UPS will drop the load if there is overload current and or inverter failure.

 Applications:

• Workstations and peripherals.
• Modems
• Office and home PC’s
• Business centers

  Hoping that this helped you…. Please comment….