Load Cycling-Rejection Automation

Why is Load Rejection Performed?

Since the power of the power plant or generator used as an energy source is insufficient for the loads to be activated, it is necessary to install a load cycling-rejection system in order to prevent the power plant from overloading or operating at low load. 

Two different operating scenarios arise here;

1- Static Load cycling - rejection system

Preventing the system from overloading by deactivating a certain fixed load. This is, for example, the case where a block load is deactivated so that the source (usually the generator) that is activated in the event of a power failure or a power plant that falls into the islanding are not overloaded. This can be easily implemented with a simple automation. This deactivated load is permanently deactivated until the transformer/network, which is the main source, is back.

This can also work the other way around. For example, it can also be in the form of commissioning of a particular load bank so that the low-load backup source (usually the generator) does not fail due to low load operation in the long run.

2-Dynamic  Load cycling - rejection system

The load cycling-rejection sequence is the continuous controlled deactivation or activation of more than one point that can be adjusted by an automation system to prevent overloading of back-up power supply or a Co-Gen system that goes into islanding. However, in order to prevent the continuous de-energization and return of the load, the number of deactivation or activation can also be limited.

It is also possible to divide such systems into two.

2a- Fast load rejection

If the overload capacity of the source is limited, it is the state of switching off the load within a maximum of 100 ms by controlling the load increase continuously. In such fast systems, load control must be done with a transducer that can measure the changing load information every 20-50 ms and give it analogously (4-20 mA or 0-10V).In addition, the analog output of this transducer must be connected to an RTU system that updates the status information every 1 ms. However, in this way, the load(s) can be disabled within 100 ms max, taking into account the breaker opening time, which is around 60 ms.

The biggest mistake made in such systems is to take an analog output from an energy analyzer or to read data from the data port of the analyzer. In this case, the delay time will be around 500-1000 msec, which is sufficient for the source to be disabled from overload.

Another method shall be using RTUs specially designed for load shedding. These products can perform fast load rejecting in the same way by operating according to the reverse frequency/time curve.

2b - Slow load rejecting

It is the state of load rejecting within 1 second in sources with excessive load resistance. In this case, this load rejecting process can be easily done with relatively simple / inexpensive systems such as PLC + energy analyzer.

Our company can make all kinds of load rejecting systems from generators to power plants with its engineering professional staff of Fesis Automation. In fact, it is possible to easily manage the load rejecting scenario with the EMS module of the  HYPERLINK "https://www.sge.com.tr/kategori-zenon-scada-159.html" o "zenon" t "_blank" xenon scada, which of we are distributors.