08-16-2017, 09:05 PM
ppt for load scheduling load shedding
1.What is load shedding?
Load shedding is a measure of last resort to prevent the collapse of the power system country-wide. When there is insufficient power station capacity to supply the demand (load) from all the customers, the electricity system becomes unbalanced, which can cause it to trip out country-wide (a blackout), and which could take days to restore. When power is insufficient, Eskom can thus either increase supply or reduce demand to bring the system back into balance. As the difference between supply and demand becomes small, we refer to the system becoming tight . This implies that action has to be taken to prevent the system from becoming unstable. Eskom normally takes a sequence of steps to keep the system stable and to avoid load shedding. The steps include first asking large customers to reduce load voluntarily. However, if several power station units trip suddenly and unexpectedly, we may have to skip those steps and go straight to load shedding to prevent the system from becoming unstable. Scheduled load shedding is controlled by way of sharing the available electricity among all its customers. By switching off parts of the network in a planned and controlled manner, the system remains stable throughout the day, and the impact is spread over a wider base of customers. Load shedding schedules are drawn up in advance to describe the plan for switching off parts of the network in sequence during the days that load shedding is necessary. On days when load shedding is required, the networks are switched off according to
the predetermined plan, to ensure that, as far as possible, customers experience load shedding in accordance with the published load shedding schedules. In exceptional circumstances, if scheduled load shedding is not achieving the required load reduction and/or unexpected emergencies or failures occur, then System Control Centres will shed load outside the published schedules by using emergency switching in order to protect the network. Such events are rare, but if a state of emergency load shedding is declared, then all customers can expect to be affected at any time, and the planned schedules may not necessarily apply.
2. How does load shedding work?
The Load Shedding Schedules have been simplified for these reasons:
To make the schedules easier to understand and remember
To improve our ability to adhere to the planned schedules
To improve the stability and consistency of the schedules
To improve the predictability of being switched off
To improve the communication of the schedules and the status of the power system
To make the impact fairer across the entire customer base.
When load shedding is required, a fixed plan for Load Shedding Schedules will go into operation
These schedules are published in advance so that customers can find out the days and times when they will be affected if load shedding becomes necessary
Period of load shedding
Load shedding will only occur when required by the system
Where possible, Eskom will predict the tight periods in advance and a fixed period for scheduled load shedding (e.g. two weeks) will be identified before hand and communicated to customers in advance via the media
All customers could be affected
If there is load shedding outside the schedules, the media will be the main channel used for keeping customers informed.