What is load shedding and why is it carried out?
When the supplying company receives more demand for electrical
power than its generating or transmission or installed capacity can
deliver, the company has to resort to rationing of the available
electricity to its customers. This act is called load shedding.
Load shedding can also be referred to as Demand Side Management
or Load Management
Demand Controller devices are used to shed loads when a pre-set
Kw reading has been reached.
These devices are tied in to circuits supplying electric heat,
stoves, dryers, hot tubs--anything that tends to use a lot of
power. When set properly, Demand Controllers can be very effective
at reducing your energy bill.
This question may be referring to the kind of load shedding
which often occurs in places where the total electrical power load
which can be taken by consumers greatly exceeds the available
amount of energy which can be generated by the local power station
or national network of power stations. This is a situation which is
common in many developing countries. As soon as total power
demanded exceeds a certain percentage - usually 98% - of the
maximum possible power that can be generated, parts of the
distribution network have to be disconnected. Such disconnections
are known as "load shedding".
If loadshedding was not done the generating equipment's overload
breakers would automatically shut down the whole power station to
protect its alternators (electrical generators) from very severe
damage. Such damage would be extremely expensive to repair and
would take a lot of time to do.
So in practice, to keep the power stations running 24/7 under
such conditions, loadshedding is applied to different parts of the
distribution network at various set times throughout a regular
"power availability" period of, usually, a week. For example, parts
of the network supplying homes and small business offices may only
get power for two or three hours at a time every day or every other
day, whilst important places - such as hospitals, major factories
and, typically, government offices - may get power almost 24/7.
Load shedding, normally used in industrial, large commercial,
and utility operations, is monitoring electric usage continuously
(usually by automated instrumentation) and shutting down certain
pre-arranged electric loads or devices if a certain upper threshold
of electric usage is approached. there are two reasons for doing
it, both of them financially motivated.
Power companies sometimes set up an industrial customer or a
school with an electric billing rate in steps, i.e. if you are
pulling less than this amount of electric current during certain
times you get billed at one rate for the electricity you use. If
you are pulling MORE than this amount of electric current during
that time, you get billed at a higher rate, even if you use the
same amount of electricity overall. The highest current you draw
during the time period in question is your "peak demand". The power
company has to have generating capacity built and in place to
generate the sum of all of the "peak demands" of its customers
during the highest peak demand period. Say that period is 10 am to
12 am during weekdays. If the highest peak demand exceeds the
capacity of the power company to generate, they either have to
build another power station to cover that 2 hour period each day,
which is a waste of money, or they have to buy power from some
other power company during those 2 hours which is also expensive.
So power companies look for ways to cut down on the highest peak
demand. They encourage their large customers to cut back on peak
demand during those "highest peak demand periods" by charging them
more if they exceed a certain peak demand. Customers can stay below
this set peak demand limit by monitoring their electric demand and
cutting off unnecessary electric loads if they get too close to
their demand limit. That is one form of load shedding.
The other way is for the power companies to ask their small
customers for permission to install a piece of equipment in their
home or business and wire one or two appliances to the equipment
which will shut down the appliances based on a radio signal from
the power company. The appliances are usually electric water
heaters. The power company gives a discount to these customers.
Then, if the power company sees that it's demand is coming close to
its generating capacity, it sends out a signal and cuts off all
these appliances. That is also called load shedding.