In power automation, there are various "TU" devices. Here’s a detailed explanation of their definitions and distinctions. First, note that the first letter represents the function abbreviation. Except for industrial DTU, all other TUs are Terminal Units.
Industrial DTU
Data Transfer Unit (DTU), also known as a "data transmission unit, concentrator, converter, or repeater," typically functions as a router or gateway. It supports multiple industrial protocols (e.g., MQTT, IEC101, Modbus) for wired input and transmits data to remote locations via wired or wireless means. In modern networked systems, all other devices include a DTU unit, either built-in or external. The absence of "Terminal" in its name indicates that it focuses solely on data transmission, not control.
Industrial RTU
Remote Terminal Unit (RTU) is responsible for monitoring and controlling field signals and industrial equipment. It is a core component of enterprise integrated automation systems and is a general industrial term, not specific to the power sector.
Power FTU
Feeder Terminal Unit (FTU) is a specialized RTU for power feeders. It serves as the interface between automation systems and primary equipment, primarily used in distribution systems to monitor and control transformers, circuit breakers, reclosers, sectionalizers, pole-mounted load switches, ring main units, voltage regulators, and reactive power compensation capacitors. FTU communicates with the feeder master station, providing data for system operation control and management while executing control commands for distribution equipment. In practice, FTU often narrowly refers to automation terminals for switches, while distribution transformers are monitored by DTU or TTU. FTU combines control and data acquisition functions, with fast sampling rates and minimal data types, making it a core component of grid dispatch automation.
Power TTU
Distribution Transformer Supervisory Terminal Unit (TTU) is used in power supply and distribution systems to monitor and control distribution transformers. Compared to FTU, TTU collects more data types. Initially, TTU lacked control functions, but modern versions are incorporating features like reactive power compensation adjustment.
Power DTU
As mentioned earlier, industrial DTU is integrated into power distribution stations due to their larger size, combining data acquisition and transmission devices into a single enclosure or cabinet. These units include both DTU and RTU functionalities and are used in distribution networks. Power DTU is essentially a combination of industrial DTU and power RTU, similar to the relationship between a computer and its built-in network card.
Summary
DTU and RTU are industrial terms.
FTU, TTU, and DTU are classifications of RTU applied to specific power equipment.
Industrial DTU is essential for remote data transmission from FTU and TTU.
Two development directions for DTU:
Miniaturization and integration: FTU and TTU with built-in DTU (the power DTU model).
Unified transmission: Independent DTU supporting multiple data collection terminals (e.g., FTU, TTU, smart meters).
Power Distribution Automation System
A typical distribution automation system consists of:
Distribution Master Station: Located at the city dispatch center.
Distribution Sub-Station: Often set up in 110kV/35kV substations, responsible for communication with DTU/TTU/FTU devices in its area.
Distribution Remote Terminals (FTU, DTU, TTU): Interface with field equipment.
Communication Network: Connects the master station and sub-stations.
Detailed Descriptions of Power Terminals
Feeder Terminal Unit (FTU)
FTU is installed beside feeder switches (e.g., outdoor pole-mounted switches on 10kV lines, such as circuit breakers, load switches, and sectionalizers). Typically, one FTU monitors one switch, but in cases of shared pole installations, one FTU can monitor two switches.
Features:
Uses advanced DSP technology, multi-CPU integration, and high-speed industrial communication.
Runs on an embedded real-time operating system, offering high stability, reliability, and adaptability.
Combines remote measurement, signaling, control, protection, and communication functions.
Functions:
Remote Measurement:
AC electrical measurements (e.g., Ia, Ib, Ic, Uab, Ucb).
Calculates P, Q, f, cosφ, etc.
Records and uploads protection currents (Ia, Ic).
Monitors DC analog signals (e.g., battery voltage, temperature).
Remote Signaling:
Switch status signals (SOE).
Battery low voltage alerts.
Protection and abnormal signals.
Remote Control:
Switch operation (multiple attempts allowed during power loss).
Battery maintenance.
Remote protection signal reset.
Data Transmission:
Communicates with the master station.
Supports multiple protocols (e.g., IEC 60870-5-101/104, DNP3.0, Modbus).
Offers various communication interfaces (RS-232/485, industrial Ethernet, CAN).
Fault Identification, Isolation, and Recovery:
Provides overcurrent protection and reclosing functions.
Reports fault currents and switch trip information to the master station for fault isolation and power restoration.
Local Operation:
Includes local switch buttons and maintenance controls.
Ring Network Function:
Automatically controls switch operation based on PT status.
Distribution Transformer Terminal Unit (TTU)
TTU monitors and records the operating conditions of distribution transformers. It calculates voltage, current, active power, reactive power, power factor, and energy consumption every 1–2 minutes, storing data for a week or a month. TTU lacks control functions but may include reactive power compensation control.
Applications:
Suitable for monitoring 100–500kVA transformers in utilities, industries, and rural areas.
Supports GPRS communication for data transmission to management centers.
Functions:
Integrated Functions: Combines metering, power quality monitoring, transformer condition monitoring, and reactive power compensation.
Smart Reactive Compensation: Automatically adjusts capacitor banks for optimal power factor.
Flexible Networking: Compatible with existing power management systems.
Easy Installation: Modular design simplifies setup and maintenance.
Distribution Terminal Unit (DTU)
DTU is installed in substations, ring main units, and compact substations. It collects data on switch positions, voltage, current, power, and energy, while performing switch operations, fault identification, isolation, and power restoration. Some DTUs also include protection and backup power auto-switching functions.
Features:
Combines the functionalities of power DTU and RTU.
This detailed breakdown should help clarify the roles and distinctions between DTU, FTU, TTU, and RTU in power automation systems. Let me know if further details are needed!
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