Load Shedding
What is Load Shedding?
Load shedding is used for the essential shedding of deemed non/less essential loads on a system. This isolates power from certain designated supplies to reduce the overall load on the system
What is Load Shedding Used for?
Load shedding is most commonly used for implementation with generator systems, this due to two reasons:
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Generator Start Up
Matching the generator to the exact load current may well still cause implications when the generator is to take a full load, this is due to when switching to the generator you ask the generator to accept the full load immediately, which system dependant this sometimes cannot be achieved. Therefore a percentage of the load is calculated to be shed and commonly reintroduced in stages, commonly every 5 seconds to slowly introduce the full load onto the generator, moving from a partial load to full load to ensure the generator doesn't stall, this can either be completed manually or automatically.
2. Generator under rating
Occasionally generators are underrated compared to the main incoming supply, this is typically implemented as under mains failure the system will run on generator but only supply deemed essential supplies, due to the underrated current supply of the generator certain outgoing ways are required to be opened to limit the current capacity of the load to the current capacity of the generator system, this can either be completed manually or automatically.
How to implement Load Shedding?
There are various ways of load shedding, here are but a few of described examples, varying in complexity:
1.Manual
This involves the manual load shedding of breakers (load) by isolating individual supplies, physically switching deemed nonessential loads off to reduce the overall total load. Once complete and undersupply of the generator the load will either match the maximum generators requirements or allow further manual reinstatement of the shed loads.
2.Undervoltage
This involves the automatic load shedding of breakers (load) by isolating individual supplies, under voltages works as soon as the voltage is sensed to be lost on a breaker or breakers, this automatically trips the breaker switching off deemed nonessential loads to reduce the overall total load. Once complete and under supply of the generator the load will either match the maximum generators requirements or allow further manual reinstatement of the shed loads.
3.Timer & Relay Circuits
This involves the automatic load shedding of breakers (load) by isolating individual supplies, this with the use of shunt trips or under voltages, working by losing voltage or a driven open signal to open a breaker or breakers, this automatically trips the breaker switching off deemed nonessential loads to reduce the overall total load. Once complete and under supply of the generator the load is commonly reinstated via the timer and relay circuit, typically in stages to gradually increase the load of the system supplied by the generator.
4.Programmable Logic Controller (PLC)
This involves the automatic load shedding of breakers (load) by isolating individual supplies, this with the use of shunt trips or under voltages, working by losing voltage or a driven open signal to open a breaker or breakers, this automatically trips the breaker switching off deemed nonessential loads to reduce the overall total load. Once complete and under supply of the generator, the load is commonly reinstated and monitored via a PLC, typically in stages to gradually increase the load of the system supplied by the generator. However, PLC is quite complex devices and can be used to monitor the generator and using sequential control undertake protocols as per the programs. Basically, a PLC can be used for various functions and increases the accessibility and the amount of control that can be required when controlling said breakers.