The influence of the over-speed protection control for the isolated grid stability

In thermal power plants, the over-speed protection control (OPC) is one of the most important functions in Digital Electro Hydraulic system (DEH), the objective is to inhibit the turbine speed soaring and protect the generator´s safe. However, if the OPC parameters selection is irrational, the isolated power grid which is tripped from the bulk power grid would appear the phenomenon of “power or frequency oscillation” at load rejection condition. If the oscillations are not disappeared in time, the whole grid would be collapsed, the isolated power grid is vital for resuming main grid after sudden unpredictable mistake. The mathematical model for isolated grid stability research is established in this paper, the Simulate reproduce power oscillations at the accidents. Several improvement proposals of OPC control logic are also discussed, the results show that increasing the OPC action speed point and removal speed point is benefit for preventing the grid oscillation. It´s significant for guiding adjusting the OPC parameters to ensure the isolated power grid safe and stable.