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Importance of the parallel operation of transformers

 

 

Transformers are placed in parallel by electric utilities when they want to provide a 'stronger' voltage source and will result in higher available fault current that can be delivered downstream. Usually the utility transformer can serve its own load but two are put together to achieve with a ties primary and secondary bus to 'stiffen' the voltage to ride through system load changes. Because here we have more transformers connected in parallel. So even if, one of the transformers gets into a fault or is taken out for maintenance or repair, the load can continued to be serviced. Therefore by this we can reduce the spare capacity also.

Before two or more transformers connected in parallel and to share a common load satisfactorily, there are some conditions to be satisfied. Those are the voltage ratio (turns ratio) and the per unit impedance of each machine on its own base must be the same. When two transformers are connected in parallel, the impedances of the transformers must match (within 10%) to divide the load approximately equally between the two transformers or to divide the load according to the rating of each transformer. If the transformers to be connected in parallel are equipped with load tap changing windings, then the impedances for each of the tap changer positions must match. If these conditions are not met, then one of the transformers could conceivably carry a continuous overload, resulting in overheating.

Also the polarity must be the same, so that there is no circulating current between the transformers.
The polarity of connection in the case of single phase transformers can be either same or opposite. Inside the loop formed by the two secondary the resulting voltage must be zero. If wrong polarity is chosen the two voltages get added and short circuit results.     The phase sequence must be the same and no phase difference must exist between the voltages of the two transformers. When these requirements are satisfying we can have a good parallel operation of transformers which is very useful and favourable in practice.

 

Generally, application of parallel transformers allows achieving the following benefits:

 

1. Reducing the total capacity of electrical transformers (as compared to separate their work). The decrease of total installed capacity is reached:
   

• by lowering the overall  demand load to the diversity of loads connected to different transformers
  
• by using a higher load rate of parallel transformers
  
• less required backup in case of electrical transformer failure
  

2) Reduction of electricity losses in electrical transformers due to a possible disconnection of unloaded transformers

3) Improving the power quality due to the stable level of short circuit current throughout the network

4) Increasing the reliability of operation of protective devices in the case of phase-to-earth short circuits in the network.

5) Possibility of placing electrical transformers in operation phase-by-phase

Importance of the parallel operation of transformers

Transformers are placed in parallel by electric utilities when they want to provide a ‘stronger’ voltage source and will result in higher available fault current that can be delivered downstream.  Usually the utility transformer can serve its own load but two are put together to achieve with a ties primary and secondary bus to ‘stiffen’ the voltage to ride through system load changes. Because here we have more transformers connected in parallel. So even if, one of the transformers gets into a fault or is taken out for maintenance or repair, the load can continued to be serviced. Therefore by this we can reduce the spare capacity also. 

Before two or more transformers connected in parallel and to share a common load satisfactorily, there are some conditions to be satisfied. Those are the voltage ratio (turns ratio) and the per unit impedance of each machine on its own base must be the same. When two transformers are connected in parallel, the impedances of the transformers must match (within 10%) to divide the load approximately equally between the two transformers or to divide the load according to the rating of each transformer. If the transformers to be connected in parallel are equipped with load tap changing windings, then the impedances for each of the tap changer positions must match. If these conditions are not met, then one of the transformers could conceivably carry a continuous overload, resulting in overheating.

Also the polarity must be the same, so that there is no circulating current between the transformers. The polarity of connection in the case of single phase transformers can be either same or opposite. Inside the loop formed by the two secondary the resulting voltage must be zero. If wrong polarity is chosen the two voltages get added and short circuit results.     The phase sequence must be the same and no phase difference must exist between the voltages of the two transformers. When these requirements are satisfying we can have a good parallel operation of transformers which is very useful and favourable in practice.

Generally, application of parallel transformers allows achieving the following benefits:

1)      Reducing the total capacity of electrical transformers (as compared to separate their work). The decrease of total installed capacity is reached:

·         by lowering the overall  demand load to the diversity of loads connected to different transformers

·         by using a higher load rate of parallel transformers

·         less required backup in case of electrical transformer failure

      2)   Reduction of electricity losses in electrical transformers due to a possible disconnection of unloaded transformers

      3)    Improving the power quality due to the stable level of short circuit current throughout the network

      4)  Increasing the reliability of operation of protective devices in the case of phase-to-earth short circuits in the network.

     5)   Possibility of placing electrical transformers in operation phase-by-phase

Windows 7 released

      Windows 7 finally released today.The interest for the new OS from Microsoft has been huge, making Windows 7 the biggest pre-order item in the history of Amazon UK and a perpetual trending topic on Twitter. The reactions from users and reviewers have been mostly positive, but after the lukewarm it’s-ok-but-why-should-switch-from-WinXP attempt that was Vista, the fact that people can’t wait to get their hands on Windows 7 is hardly a surprise.
And, for the most part, it’s true. Annoying security features such as UAC have been fixed in Windows 7 (you can now manually set its annoyance level), the system feels speedier and more responsive (although it really isn’t that much faster when you actually measure it (for example, boot time on both systems is pretty much the same on my computer), but it feels that way, and it’s all that matters), compatibility issues have been fixed. In short, it’s more of a really, really good service pack for Vista than a new OS, but it’s definitely enough to switch from the eight year old Windows XP.
If you’re interested in making the switch, the price is $319 for Windows 7 Ultimate, and $299 for the Professional version ($219 and $199 for the upgrade, respectively). Windows 7 Home Premium will set you back $199, and an upgrade from either Vista or XP will cost you $119.

QUICK START GUIDE & USER’S MANUAL

Table OF Content

Welcome 1

Check Components 3

Installation 4

Configuration 5

Troubleshooting 5

Welcome to the PC Remote control system which will give you a easy handling on presentations and multimedia activities. PC Remote Control lets you control all aspects of your computer from a remote control without using a keyboard or mouse you can use any remote control to configure the PCRC You Can do lot of actions as mentioned below.

Remote actions

Keyboard key press simulation.

You can specify if you want to use Alt, Ctrl or Shift.

Mouse

Movement and click control.

Execution

Of external applications.

Post Message

API function access which lets you send Windows type messages.

Volume

Control on volume.

Miscellaneous

Actions: Computer log off, reboot or shutdown.

On Screen Display

Of system parameters or free text

Installation

Installation

YOU should follow each step carefully as shown below in order to guarantee proper operation of PCRC set.

• Connect the Rs 232 terminal to the computer using appropriate cable
  
• Connect the USB cable to a USB port of the computer.
  
• If it is good, the blue LED is indicated.
  
• Try sending some signal to the receiver, if red led is blinking while sending signal then system sends signal to the computer.
  

PLACE THE PCRC SET

• Place the device on the system unit or any other appropriate place where IR beam can easily pointed by IR sender.
  
• Do not place the unit where external IR noises are high.
  
• Avoid direct exposure to sunlight.

Configuration

You must configure device before using it. You may find lot of software which can configure IR receiver models. But we recommend using PC remote control by moises cambra. Other best option is use the winlirc. WinLIRC is the Windows equivalent of LIRC, the Linux Infrared Remote Control program. it is open source free software, but configuring it is little bit confuse for local usres.If you are using Linux, you have to use LIRC.

Configuring using Pc remote control is easy. Follow the instructions given by the help file and configure. You can configure four actions with the trial version of the software. You have to register the program to activate more commands.

Troubleshooting Tips

• No Signal display when configuring
  

Check system is power on and serial cable is properly connected

• Incoming signals are not identical for same button on remote
  

This can be happen if your serial port does not have enough serial port voltage. Especially, with the latest laptop computers that using low power RS232 interfaces ICs.