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.
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