Cogeneration Power Plants Integration with State Load Despatch Centre

Cogeneration is typically defined as the sequential generation of two different forms of energy from a single energy source (Bureau of Energy Efficiency). This energy source can be fossil fuel or a renewable resource such as biomass. Cogeneration power plants have been in operation for quite some time in India. These power plants are used to cater to the needs of their load centres while being connected to the electricity grid. As a result, cogeneration power plants draw power from the electricity grid and inject power into the grid in case of surplus electricity. Cogeneration technologies have a wide range of industrial applications including agrochemicals, automobiles, diary industry, mining, oil and gas, steel, textiles, etc. The principle of electricity through cogeneration and the two-way power flow is illustrated below:

Under the architecture of the Indian power system, there are various load despatch centres set up at the national, regional and state levels to ensure integrated operation of the power system in the concerned region. These apex bodies exercise control over the inter-state (and intra-state, as the case may be) transmission system and have the power to issue directions and exercise supervision and control as may be required for ensuring the stability of the electricity grid. Cogeneration plants, like other sources of power generation which are connected to the electricity grid, are subject entities that have to follow the directions issued by the load despatch centres. In this blog post, we will review the obligations of cogeneration plants and how automation solutions can effectively enable generators to meet these requirements.

Obligations of Cogeneration Plants

As we have seen, there is a two-way flow of electricity in cogeneration plants connected to the electricity grid. This two-way flow of electricity demands a high level of monitoring by the Load Despatch Centres (LDCs). This is ensured through the integration of the cogeneration plant to the LDC. This data integration with LDC will enable stakeholders to regulate and monitor generation and utilization and thereby, ensuring that grid stability is maintained.  Furthermore, with the onset of “One Nation One Grid”, reporting of electrical parameters in real-time is essential to maintain grid stability.

Therefore, cogeneration plants connected to grid are statutorily required by the Indian Electricity Grid Code to submit all real time data to LDCs to ensure Grid stability.

Scope of Work

Through our considerable experience of executing various types of automation projects, we have understood that in the case of cogeneration plants, energy monitoring requires intervention from specialists in the subject matter. As experts in the field, we ensure that the requisite automation solutions are implemented so as to ensure adequate integration of cogeneration plants with LDC.

In this instance, a leading enterprise in the sugar industry had a cogeneration plant that was being used for its internal consumption while being connected to the grid. The objective of this project was to provide remote SCADA system and State LDC integration in two parts:

• Part 1 – SCADA system for plant end switchyard under the supervision of the State Transmission Utility: one line bay to be monitored through the proposed SCADA system remotely from 220/132/33kV substation via PLCC communication
• Part 2 – Real-time monitoring SCADA system for plant end switchyard: 132/11kV plant end switchyard to be monitored through real-time data monitoring system remotely from the State LDC via leased line point to point communication.

Work to be done

To implement this project, we used Remote Terminal Units (RTU) of Vizimax make, a state-of-the-art device marketed by SCOPE. The following was done for the integration of cogeneration plant with the State LDC:

1. Interfacing hardware at Co-Gen plant end: Typically, an RTU system with I/O modules for DI, DO, AI signals hardwiring, RJ45 Ethernet communication ports for interfacing soft signals from TCP/IP based devices such as relays, IEDs, BCUs etc., RS485 Serial communication ports for energy data interfacing of MODBUS communicable MFMs/MFTs/meters with all its related accessories, panels and cables
2. Communication infrastructure for plant data transmission to SLDC: As these plants are generally located far away from the SLDC control centre, the establishment of communication network infrastructure based on field application such as PLCC network, leased line network, wireless GPRS or MPLS network, OPGW network etc. is required
3. Plant data integration with existing SLDC SCADA: The data will be provided over an industry-standard protocol like IEC 60870-5-101 (serial) or IEC 60870-5-104 (TCP/IP based) for seamless integration with existing SLDC SCADA

The architecture of the solution post-installation is illustrated below:

Protocols used for Communication

The table below describes the protocols used for communication with RTU:

Communicable Devices	Protocols for Communication with RTU
Distance Protection Relay	IEC 61850
Backup Protection Relay	IEC 61850
Busbar Protection Relay	IEC 61850
Multifunction Meter	Modbus Serial
GPS clock	NTP
PLCC modem	IEC 101
Routers for data transmission to SLDC	IEC 104
Energy Meter	Modbus Serial
Digital Energy Meter	Modbus Serial
Multifunction 3 phase power meter	Modbus Serial
DI card	Modbus Serial
Serial to TCP/IP Converter	Modbus TCP/IP

The implemented solution is illustrated below:

Conclusion

In this manner, cogeneration plants can successfully ensure integration with the LDC and fulfil mandatory requirements to ensure grid stability. To know more about how your cogeneration plant can be effectively integrated to the LDC, please visit https://www.scopetnm.com/protection-solutions/rtu-automation-solution or write to us at marketing@scopetnm.com