The Distribution Companies are required to restrict drawl of power from the grid to comply with the specified frequency requirements so as to overcome any threat to system security in an interconnected system on account of overdrawal from the grid. The Central Electricity Regulatory Commission (CERC) of India mandates manual as well as automatic demand disconnection from the distribution network under overdrawal conditions and on crossing the defined frequency limits. As the manual control at times become ineffective to decrease drawal by a certain quantum within the time limit and hence the automatic demand disconnection scheme assumes significant importance for Distribution Companies operating in developing countries like India to restrict drawl in its control area. The Automatic Under frequency Load Shed (AUFLS) and load relief by rate of change of frequency relay are the defence mechanism whereas Automatic Demand Management System (ADMS) acts as a tool for ensuring security and reliability of the interconnected system. A unique state-of-the-art Automatic Demand Management System (ADMS) has been implemented for the State Distribution System by the Transmission Utility of the State of Madhya Pradesh in India, which not only disconnects the interruptible loads but also restores the same automatically, on clearing the overdrawal conditions. Under this system real time information is gathered through the transmission Supervisory Control and Data Acquisition (SCADA) System and based on logics developed for the scheme, automatic load disconnection & restoration is achieved through the control output of Remote Terminal Unit (RTU) installed for SCADA System of State Transmission network.
Under this scheme, the transmission SCADA System has been integrated with State Load Despatch Center (SLDC) SCADA/EMS system via ICCP through which the data regarding frequency, schedule / drawal are obtained at Master Control Center, Jabalpur. An interface module for data transfer has been developed between transmission SCADA System and ADMS. Based on data received from transmission SCADA, the ADMS calculates the quantum of load shed and quantum of load restoration, as well as group-wise load shed / restoration separately for each Distribution Company. Thereafter the information is transferred to the respective SCADA Control Center for issue of command.
When Frequency is less than 50.00 (configurable) HZ and overdrawing of load is more than 12% (configurable) of schedule or 150 (configurable) MW whichever is less continuously for 15(configurable) minute duration, the shed quantum calculation will be triggered. On the other hand, if frequency is less than 50.05(configurable) HZ or underdrawing of load 12%(configurable) of schedule whichever is less, the normalize quantum calculation will be generated. When get the prorata quantum for each control center to shed/normalize command is given, the ADMS server shall determine which groups shall be shed/normalized. Once the groups for each control center to be shed /normalized are accessed, the ADMS process server shall send the control command to front end server which will issue control command to execute the ADMS process.
The load management in distribution system is an important issue for maintaining the reliability and security of interconnected system. The Automatic Demand Management Scheme has a significant role to reduce the gap in demand & availability of power. The ADMS System has been implemented by utilization & integartion of two hetrogenous SCADA/EMS system of the State Transmission Network and State Load Despatch Centre for Automatic Demand Management in distribution grid.