Research on Smart Distribution Transformers and Integrated Communication Applications

Article co-authored by Fortune Electric’s Hao-Min Chang, Wei-Ming Lu, Wen-Kuei Wei, and Ping-Chen Wu.

This article is published by EEPower as part of an exclusive digital content partnership with Bodo’s Power Systems.

With the large-scale integration of intermittent renewable energy sources and the rapid growth of emerging loads such as electric vehicles and charging facilities, fluctuations in generation and demand within distribution systems have become increasingly significant, resulting in feeder voltage variations. However, conventional transformers lack real-time voltage regulation capability and therefore cannot effectively mitigate overvoltage and undervoltage conditions.

To address these needs, this study proposes a smart distribution transformer architecture that integrates an advanced sensing transformer, an externally mounted active voltage compensator, and an AMI communication platform. Its voltage compensation capability is further evaluated through experimental validation to improve feeder voltage quality and the management efficiency of distribution equipment.

Image used courtesy of Freepik

Advanced Sensing Transformer

In this study, multiple monitoring devices are installed around the smart distribution transformer to continuously monitor its operating conditions. The collected data are transmitted through the communication system, which also issues alarms when abnormal conditions are detected. The system can also be integrated with a geographic information platform for substation equipment, enabling rapid identification of fault areas during equipment abnormalities or power outages and assisting maintenance personnel in scheduling inspections and repairs. Furthermore, accumulated long-term operating data can be used for fault trend analysis and preventive maintenance, thereby improving inspection efficiency, shortening repair time, and reducing the risk of equipment failure. The following sections describe the monitoring devices and their functions.

Oil Temperature Monitoring

Overheating of the insulating oil accelerates its degradation. Therefore, real-time oil temperature monitoring helps reduce the risk of equipment damage and extend the service life of the transformer.

Oil Level Monitoring

Long-term transformer operation may lead to oil leakage due to environmental conditions or equipment aging. A digital oil-level sensor enables real-time monitoring of oil-level changes, helping prevent short circuits, equipment damage, or power interruptions caused by insufficient insulation.

Load Monitoring

The load condition is estimated through voltage and current measurements to support transformer capacity allocation and regional power planning, thereby reducing equipment degradation and failure risks caused by prolonged overloading.

Copper Terminal Temperature Monitoring

Loose connections, increased contact resistance, or abnormal loading may cause localized temperature rises. Therefore, copper terminal temperature monitoring can help identify overload conditions or connection abnormalities.

Voltage and Current Monitoring

Voltage is measured using a voltage sensing circuit, whereas current is measured using a Rogowski coil. The Rogowski coil provides fast response, a wide measurement range, and immunity to magnetic saturation, making it suitable for high-frequency and high-magnitude AC current measurements.

Figure 1. Schematic Illustration of Smart Transformer Application Scenarios. Image used courtesy of Bodo’s Power Systems [PDF]

The sensors described above will be used in two monitoring configurations. For existing transformers, the primary monitoring parameters include voltage, current, and copper terminal temperature. For new transformers, additional parameters, including insulating oil temperature and oil level, will also be monitored.

Transformer Terminal Unit (TTU):

The TTU is externally installed on an existing distribution transformer. Monitoring devices collect the transformer’s actual operating data and transmit them to the TTU, which then forwards the data to the backend platform.

Transformer Smart Unit (TSU):

The TSU is applied to new transformers. It is a newly designed transformer monitoring and control terminal capable of integrating multiple monitoring devices and collecting their measurement data. The TSU packages the transformer operating data and transmits it to the backend platform through the Device Language Message Specification (DLMS) protocol.

Figure 2. TTU and TSU System Diagram. Image used courtesy of Bodo’s Power Systems [PDF]

Design of the Transformer-Side DLMS Server:

The transformer-side DLMS server is designed primarily in accordance with Taiwan Power Company’s AMI communication specifications. It includes dozens of interface classes, such as Data, Register, Profile Generic, Clock, and Association, with corresponding attributes and methods defined for each class.

Active Voltage Compensator

To achieve both reliability and controllability, this study adopts an externally mounted active voltage compensator that integrates power electronics technology with a conventional distribution transformer. This configuration only processes the portion of power associated with the voltage deviation and does not affect the original power-transfer function of the transformer. Therefore, the required converter rating, power loss, and implementation cost can be reduced while improving feeder voltage regulation and power quality.

The circuit adopts a back-to-back topology consisting of two conventional single-phase full-bridge converters. Each converter is composed of four switching devices and operates using a unipolar voltage-switching scheme. This simple topology allows the output filter to be designed based on twice the switching frequency, thereby reducing the required inductance of the high-frequency magnetic components.

Figure 3. System circuit configuration and voltage compensation principle. Image used courtesy of Bodo’s Power Systems [PDF]

A single controller is used to coordinate both the series and shunt converters, ensuring proper operation of the voltage compensation function. The required interface and control circuits are designed and implemented according to the system’s functional requirements.

For the voltage compensation software, when a voltage sag or swell occurs in the grid, the system automatically compensates for the voltage deficiency or excess on the feeder, thereby providing a stable voltage to downstream loads.

AMI Communication System Integration

This study integrates the existing lowvoltage AMI smart meter communication architecture of Taiwan Power Company. A smart transformer communication system compliant with the P1 interface and Route A communication path specifications is developed. The main components include a transformer-side DLMS server, a Route A communication module, a Data Concentrator Unit (DCU) interface, and a head-end interface, enabling transformer monitoring data to be transmitted to the backend information platform.

The backend Mini MDMS platform is responsible for receiving, parsing, storing, and displaying the monitoring data. Transformer data will be converted into XML messages compliant with Taipower’s P6 specification and integrated with feeder information to present equipment locations and real-time operating conditions.

Experimental Validation

This study verifies through prototype testing whether the voltage compensation performance meets the expected research and development objectives. The load is set to 25.6 kW. When the utility voltage is 212 Vac, the load-side output voltage is expected to be regulated to 220 Vac. The experimental measurement results are presented below:

The experimental results show that when the utility input voltage decreases to 212 Vac, the voltage regulation system can effectively regulate the load-side voltage to 220 Vac, as indicated by CH2_V_Load, thereby achieving the development objective of this study.

Figure 4. Experimental results (Note: “CH5_V_Series” refers to Converter Output Voltage, “CH2_V_Load” refers to Load Voltage, and “CH4_I_Series” refers to Converter Output Current). Image used courtesy of Bodo’s Power Systems [PDF]

Conclusion

This study proposes a smart distribution transformer architecture integrating condition monitoring, active voltage compensation, and AMI communication. Transformer operating data are transmitted to a backend platform to support abnormal-condition warnings, fault identification, and maintenance management. Experimental results show that, under a 25.6 kW load and a utility input voltage of 212 Vac, the proposed system regulates the load-side voltage to 220 Vac, verifying its voltage compensation capability. The proposed architecture improves feeder voltage quality and equipment monitoring efficiency and provides a practical approach for the intelligent upgrading of existing distribution transformers.

This article originally appeared in Bodo’s Power Systems [PDF] magazine and is co-authored by Chia-Ching Lin, Hao-Min Chang, Wei-Ming Lu, Wen-Kuei Wei, and Ping-Chen Wu, Fortune Electric, Taiwan