23-11-2012, 12:11 PM
Seminar on Uninterruptible Power Supplies
1Uninterruptible Power.ppt (Size: 183.5 KB / Downloads: 58)
Introduction
Power supply used in residentials,industries and for commercial purposes is not safe, many disturbances and failures occurs.
Stable interruption free power supply is of utmost importance.
Computers are more sensitive to power disturbances and power supplies.
Uninterruptible power supply is an alternative source to protect the systems from power losses and black outs.
UPS-An Overview
Also known as a uninterruptible power source or battery back up.
A device which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available.
UPS are designed so that there is one source of power that is normally used, called the primary power source, and another source that kicks in if the primary is disrupted, called the secondary power source.
UPS come in different sizes and shapes.
The size of the UPS is primarily dictated by the size of the battery; the larger the battery, the more time our equipment can run on battery power before shutting down.
Different UPS have various other additional features, including warning signals, PC control software, and conditioning circuitry for the AC power source.
Common power problems
There are various common power problems that UPS units are used to correct.They are as follows:
Power failure
Voltage sag
Voltage spike
Under voltage (brown-out)
Over- voltage
Line noise
Frequency variation
Switching transient
Harmonic distortion
Types of UPS
On- line UPS
Off- line UPS
Line interactive UPS
In the On-Line UPS, whether the mains power is on or off, the battery operated inverter is on all the time and supplies the ac output voltage.
When the mains power supply goes off, the UPS will be on only until the battery gets discharged. When the mains power resumes, the battery will get charged again.
On-line UPS
The switching times of these supplies is considered less than 5ms.
Sealed maintenance free batteries are used.
The running time of the inverter is low (approx. 10 to 30 minutes).
Cost is high.
Also known as power conditioner or line conditioner.
Off-line UPS
In Off-Line UPS , inverter is off when the mains power is present and the output voltage derived directly from the mains is the same as the mains supply voltage.
The inverter turns on only when the mains supply goes off.
The Off-line Standby Power Supply (SBS) offers the bare bones power protection of basic surge protection and battery backup.
Its switching time is less than 5 ms.
Sealed batteries or lead acid batteries are used.
The running time of these supplies is also low (about 10 to 30 minutes).
Sine wave or square wave inverters are used.
Line-interactive UPS
The Line-interactive UPS offers surge protection and battery back-up.
It has the added feature of minimal voltage regulation while operating from the utility source.
A “brown-out” happens when the utility voltage remains excessively low for a sustained period.
The inverter/converter unit is always connected to the output, powering the equipment.
Cost is high.
Commonly used in units for home and business use, available in sizes up to 3,000 VA or so.
UPS or UPS/software combinations provide the following functions:
Automatic shutdown of equipment during long power outages.
Monitoring and logging of the status of the power supply.
Display the Voltage/Current draw of the equipment.
Restart equipment after a long power outage.
Display the voltage currently on the line.
Provide alarms on certain error conditions.
Provide short circuit protection.
Benefits of parallel architecture
All parallel UPS systems comprise two or more UPS modules operating in parallel to feed a common critical load bus.
UPS modules are paralleled for three reasons:
To increase the power rating of a UPS system..
To increase the availability of a UPS system.
To ensure the power rating of the UPS always matches the power requirements of the load.
Transformer less UPS systems are more energy efficient than their transformer based.