Distribution

                               Power distribution

After transmitting power to the load centers it is distributed with low voltage (230V line to neutral). But sometimes distribution section may involve with medium voltages (11kV/33kV).  Here i'm going to discuss about some equipments used in distribution section.

Auto Recloser

Auto recloser is a type of circuit breaker. Operation is as follows. When there is a temporary fault in overhead lines, such as touching a tree branch due to wind, the auto recloser will trip. But after some time period it will automatically recloses and therefore the power flow in transmission lines continue. But at the time when it reclose if the fault is not cleared recloser will trip again. This process will continue again and again up to certain times (this number of terms and the waiting delay can be programmed). So after certain trip and reclose cycles this device will lock out. Because fault occur was not cleared and therefore it should be a permanent fault. When the device is lock out it should be manually close after clearing the fault. In manually closing situation there is a cold load pick feature in auto reclosers. 

Cold load pick up feature

Think that there is no power supply in longer period. So refrigerators, air conditioners and such devices are completely off. When the power supply is restored these devices extract large load current to operate. As an example think about refrigerator in your home. It is operating until the temperature becomes to a certain level. After that it stops. When temperature increase to a threshold value it start operating again. But after a long term power failure the temperature inside the refrigerator increases to a very high value. So when power supply is restored refrigerator have to work more to reduce the temperature. It means it require more power. But after some time it operates normally and don’t require such large power.

Therefore it is clear that after long power failure, when we restore the power supply the load current will be greater. This is known as cold load. Cold load pick up feature means supply that large power without tripping.  

DDLO (Drop down Lift Off switch)

In field sometimes this is called as cut out. This equipment connect seriously with the power line. The main purpose is protect power system/ equipment from high current flow. There is a metal string inside the fuse. When high current flows it melt. Hence due to gravity circuit become open.