| Summary: | 碩士 === 國立高雄應用科技大學 === 電機工程系碩士班 === 95 === This thesis proposes an intelligent automatic load shedding method to design a PLC (programmable logic controller) based load shedding system to relief the scheduled load without the violation of system voltage and frequency as well as the production process should the power shortage is occurring from Taipower system. The right and quick decision is executing by the accurate computation and the complete information of loading and generation output acquired from switchgears. The designed system is first to install the power meter on 11.4kV switchgear to collect the current loading and convey to PLC located on switchgears. Both all switchgears’ loading and all generators’ output are transferred to master PLC via PLC’s network and the computation procedure in the PLC is then executed. Based on the priority of load shedding for all switchgears, the computation results are then referred to decide which group of loads waited for shedding and they are returned to set the candidate of switchgear via the PLC network. In this thesis, protective relays of lock relay are applied in terms of two-stage parallel connecting way to multiplex single contact into one hundred system contacts to form shed loops located on each switchgear. Each of these contacts are in series with corresponding digital output in waited for shedding on PLC to form real tripped contact of system. The PLC periodically computes the mismatch of generation output and loading in order to assign the waited for shedding switchgear. Once the power system disconnection has occured, the tripped contacts will enable each switchgear with waited for shedding status and the load shedding will function except for the other disable switchgear.
In order to justify the effectiveness and practicality of the designed load shedding strategy, the PLC based system is embedded into energy management system at one of the TFT company. After testing several outage events of the power system, the proposed system can efficiently finish the load shedding task without violating the deviation of system voltage and frequency in the company.
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