Communication protocols are needed to connect different control and protection systems to SCADA in Hydropower Plants. These protocols, either standard or custom, work over serial connections to send information between the control center and remote locations. They use different methods like phone lines, cables, fiber optics, and radio signals such as broadcast, microwave, and satellites. The most commonly used communication protocols are listed below.
1. Modbus
Modbus is a communication protocol developed by Modicon Corporation. It is commonly used in industrial automation and is now considered the standard in the industry. The point-to-point Modbus protocol is widely used for communication between RTUs (Remote Terminal Units) and PLCs (Programmable Logic Controllers). When devices communicate on a Modbus network, the protocol helps each controller identify its address, recognize messages meant for it, decide what action to take, and extract any data attached to the message. There are several updates and improvements made to address its limitations.
2. Distributed Network Protocol (DNP)
Distributed Network Protocol Version 3 (DNP3) is an open and efficient protocol designed for SCADA systems, especially in the utilities industry. It is a member-restricted protocol, used in some electric power systems. The DNP protocol has been updated several times, and the latest version is 3.0. The DNP association has rules that limit how the protocol can be used, and many major SCADA software providers have been slow to adopt it.
3. IEC 60870
IEC 60870 is a set of open standards developed by the International Electrotechnical Commission (IEC) for transmitting SCADA control and information. It is mainly used in power transmission and distribution systems. IEC 60870-5-101 is a standard for telecontrol of electric power transmission systems and is widely used in many countries.
IEC 60870 part 5 defines the communication methods for sending basic telecontrol messages between two systems that are directly connected by permanent data circuits. The IEC TC 57 WG3 group developed a protocol standard for telecontrol, teleprotection, and telecommunications for electric power systems, which resulted in IEC 60870-5. There are five main documents in the IEC 60870-5 series:
- IEC 60870-5-1: Transmission Frame Formats
- IEC 60870-5-2: Data Link Transmission Services
- IEC 60870-5-3: General Structure of Application Data
- IEC 60870-5-4: Definition and Coding of Information Elements
- IEC 60870-5-5: Basic Application Functions
Additionally, the IEC TC 57 group created companion standards to support various tasks:
- IEC 60870-5-101: Transmission Protocols for basic telecontrol tasks
- IEC 60870-5-102: Standard for transmission of integrated totals in electric power systems (less commonly used)
- IEC 60870-5-103: Transmission Protocols for protection equipment interfaces
- IEC 60870-5-104: Network access for IEC 60870-5-101 using standard transport profiles
These companion standards support telecontrol, protection data exchange, and network access for the various IEC 60870 standards.
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