Application of Smart Grid Technologies in Line Loss Management of Low-Voltage Transformer Zones

As an essential component of the distribution network, low-voltage distribution areas (hereinafter referred to as "low-voltage transformer zones") directly affect the economic benefits of power supply enterprises and the quality of electricity consumption for end-users through their line loss issues. However, traditional management approaches have obvious shortcomings in terms of accuracy and efficiency. In this context, the application of smart grid technologies provides new solutions for line loss management. By introducing advanced technical means, not only can the refinement level of line loss management be effectively improved, but energy conservation and emission reduction goals can also be supported, which is of great significance for promoting high-quality development in the power industry.

1.Line Loss Issues in Low-Voltage Transformer Zones
Line loss problems in low-voltage transformer zones are primarily categorized into technical losses and management losses. Technical losses stem from inherent equipment losses and operational constraints—for example, iron and copper losses in transformers and power losses caused by line resistance. Taking a typical low-voltage distribution line as an example, when the conductor cross-sectional area is 50 mm² and the load current reaches 200 A, the power loss per kilometer of the line is approximately 4 kW.

When the conductor cross-sectional area is increased to 70 mm² under the same conditions, the loss can be reduced by about 30%. Management losses, on the other hand, are often caused by metering errors, electricity theft, or improper operation and maintenance. For instance, the metering accuracy of traditional mechanical electricity meters under light-load conditions is only about 85%, far lower than that of smart meters, which exceeds 99%. Additionally, three-phase imbalance can significantly increase line losses; if the three-phase current unbalance in a transformer zone exceeds 15%, the line loss rate will rise by 2% to 5%. The existence of these issues indicates that manual inspection alone can no longer meet the demands of refined management, and intelligent methods are urgently needed to enhance governance efficiency.

2.Smart Grid Technologies Applied in Line Loss Management of Low-Voltage Transformer Zones

2.1 HPLC (High-Speed Power Line Communication) Technology
The fundamental principle of HPLC technology is to use existing low-voltage distribution lines as communication media, coupling high-frequency modulated signals onto power lines via coupling circuits to achieve high-speed data transmission. This technology is mainly applied in scenarios such as real-time monitoring of line operating conditions in transformer zones, electric energy data collection, and user electricity information interaction.

During implementation, the first step is to conduct a site survey of the transformer zone’s line environment to evaluate channel characteristics and interference levels, thereby determining the optimal carrier frequency (typically within 1.7–30 MHz) and coupling method. Next, dedicated couplers and HPLC communication modules are installed at the low-voltage side of the distribution transformer, branch boxes, and user electricity meters to establish a communication network across the transformer zone. Meanwhile, a master station system is deployed to seamlessly integrate with upper-layer application systems through protocol conversion.

During the operation and maintenance phase, regular inspections and calibrations of equipment should be performed, communication signal quality should be monitored, and any anomalies must be addressed promptly. For example, if carrier signal attenuation exceeds 30 dB or the bit error rate rises above 1×10⁻⁴, line faults or electromagnetic interference sources should be investigated. If necessary, transmission power (typically ranging from –10 dBm to 30 dBm) should be adjusted or couplers replaced to ensure stable system operation. 

To enhance communication stability, HPLC systems usually adopt adaptive modulation schemes, dynamically selecting modulation modes based on channel quality. Different modulation schemes vary in data rate, noise immunity, and coverage range, requiring optimized configuration according to load fluctuations and noise conditions in the transformer zone. For instance, higher-order modulation can be enabled during nighttime when loads are lighter and noise levels are lower to improve data throughput, while switching to a robust mode during daytime peak hours ensures communication reliability. Table 1 lists three commonly used modulation schemes in HPLC systems along with their technical characteristics, providing reference for field parameter configuration.

Table 1 Technical Characteristics Comparison of Common Modulation Methods for HPLC

2.2 Intelligent Phase-Switching Switch Device
The principle of the intelligent phase-switching switch device is to measure three-phase currents and voltages, calculate the load imbalance in real time, and when the imbalance exceeds a preset threshold (typically 10%–20%), control the switching of loads to rebalance the three-phase loads. This device is primarily applied at the end of transformer zones, especially in areas with heavy single-phase loads.

During implementation:
First, an appropriate installation location must be selected—such as at branch boxes or the low-voltage side of distribution transformers—to ensure ease of construction and maintenance.
Second, a site survey should be conducted to understand the load distribution and reasonably configure the switch capacity (see Table 2). During the installation and commissioning phase, load simulation tests should be performed to optimize the control strategy and protection settings; for example, the overcurrent protection setting is generally configured at 1.2 times the rated current.
Third, the transformer zone’s operation monitoring system must be enhanced to enable information exchange and remote control with the switching device.
Fourth, during the operation and maintenance phase, preventive tests should be regularly carried out on the switch to promptly identify and address potential faults such as mechanical wear or poor contact, ensuring safe and reliable operation. Additionally, analysis of the transformer zone’s load variation trends should be conducted periodically to adjust the switch’s control logic and parameter settings as needed.

Table 2 Capacity Configuration Reference for Smart Switchgear

2.3 Low-Voltage Line Automatic Voltage Regulator
The basic principle of the low-voltage line automatic voltage regulator is to measure line voltage and current in real time, calculate parameters such as line impedance and power factor, and automatically adjust the position of the transformer tap changer based on the deviation, so as to maintain the output voltage within an acceptable range. This device is primarily applied in low-voltage distribution networks, especially in areas at the end of lines where voltage tends to become excessively high or low.

First, an appropriate installation location must be selected—such as the low-voltage side of a distribution transformer or a ring main unit—and a site survey should be conducted to understand the supply radius and user distribution along the line.
Second, the regulator capacity (see Table 3) and control strategy must be determined. During the installation and commissioning phase, no-load and load tests should be carried out to verify voltage regulation accuracy (typically required to be within ±1.5%) and response time (usually not exceeding 30 seconds), as well as to validate protection functions such as overvoltage and undervoltage.
Third, after commissioning, a comprehensive operation management system should be established, clearly defining requirements for inspection, operation, and maintenance to ensure safe and stable operation of the regulator. For example, if a single-phase voltage continuously deviates beyond ±7% of the rated value for 5 minutes, or if the three-phase voltage unbalance exceeds 2%, the cause must be promptly identified and corrective measures taken. Operational data analysis shows that properly configured automatic voltage regulators can improve line voltage compliance rates by 5% to 15%, significantly reducing line losses caused by voltage violations.

Table 3 Selection Reference for Low-Voltage Line Automatic Voltage Regulators

3.Technology Application

3.1 Case Background and Line Loss Issues
Transformer Zone A is located in the downtown area of an old urban district, with a power supply radius of 1.5 km, serving 712 residential customers and 86 commercial customers. The zone’s distribution infrastructure primarily includes one S11-M.RL-400/10 type distribution transformer with a rated capacity of 400 kVA; six low-voltage outgoing feeders—two with JKLGYJ-120 mm² conductors and four with JKLGYJ-70 mm² conductors—with an average line length of 510 meters per circuit; additionally, there are four HXGN-12 ring main units and 18 low-voltage integrated distribution cabinets.

In recent years, due to localized urban renovation and the expansion of commercial establishments, the load in this transformer zone has shown continuous growth. For example, in 2018, the peak load reached 285 kW, with electricity consumption increasing by 7.6% year-on-year, yet the line loss rate was as high as 9.7%, significantly exceeding the management target of 6.5% for the same period.

On-site inspections revealed the following key issues:

• Poor contact at connection points of the distribution transformer and lines caused localized heating and additional losses;

• Uneven three-phase load distribution, with a maximum imbalance reaching 18.2%;

• Unauthorized wiring and electricity theft by certain users;

• Aging metering devices with measurement errors exceeding ±5%.

These factors collectively contributed to persistently high line losses in the zone, creating a severe governance challenge.

3.2 Technology Selection and Implementation
To address the line loss issues in Transformer Zone A, a comprehensive solution integrating HPLC communication, intelligent phase-switching switches, and automatic voltage regulators was implemented after thorough evaluation.

First, HPLC couplers and communication modules were installed on the low-voltage side of the transformer, and corresponding equipment was deployed at each branch box and user meter, establishing a high-speed power line carrier communication network covering the entire transformer zone. This network enabled real-time monitoring of operational status, including voltage, current, power on busbars and branches, as well as critical indicators such as equipment temperature and harmonic distortion. Operation and maintenance personnel could thus promptly detect anomalies. Moreover, the high-accuracy energy metering data provided solid support for line loss analysis and management.

Second, six intelligent phase-switching switch units (rated for a maximum operating current of 250 A) were installed at major branch boxes and key load locations. These switches continuously measured three-phase current imbalance and automatically redistributed loads when imbalance exceeded 15%, effectively balancing the three phases. Field tests confirmed that switching actions were completed within 30 ms, with smooth transitions causing no disruption to users. Three months after commissioning, the three-phase imbalance in the zone decreased from 18.2% to 6.5%, and the line loss rate dropped by 1.7%.

Third, to address voltage violations at the end of the lines, a 200 kVA intelligent voltage regulator was installed 710 meters from the transformer. The regulator accepts an input voltage range of 210–430 V and maintains an output of 220 V ±2%. It automatically adjusts its turns ratio based on real-time voltage measurements at the line end, keeping terminal voltage consistently within the acceptable range. Since commissioning, the regulator has responded quickly through various load peaks and valleys, raising the voltage compliance rate at nine key monitoring points from 87% to over 98.5%.

Through a closed-loop management approach of “monitoring–control–optimization,” these measures have significantly improved the line loss performance of Transformer Zone A, achieving an estimated annual energy saving of approximately 120,000 kWh, with notable economic benefits. A comparison of key indicators is shown in Table 4.

Table 4 Key Index Comparison of Area A Before and After Comprehensive Governance

In actual implementation, the following points should also be noted:
First, regarding HPLC communication reliability, transmission power, channel coding, and other parameters should be reasonably configured according to the specific conditions of the transformer zone; if necessary, relay methods can be used to extend communication distance.
Second, the timing and interlock logic of phase-switching switch operations should be carefully set to avoid excessive or erroneous switching actions—for example, the switch may be configured to act only when the imbalance exceeds 15% and persists for 3 minutes.
Third, proper selection and capacity configuration of the voltage regulator should include a certain margin to prevent frequent adjustments that could cause mechanical wear; refer to Table 5 for guidelines on automatic voltage regulator selection and configuration.

Table 5 Model Selection Reference for Automatic Voltage Regulators

Moreover, a high-quality operation and maintenance team is also critical to ensuring the long-term stable operation of the system. Only by closely aligning with actual needs, selecting and optimizing technical solutions according to local conditions, and supporting them with a sound management mechanism can continuous improvement in line loss governance be truly achieved.

4.Conclusion
Line loss management in low-voltage transformer zones is of great significance for improving power supply quality and economic efficiency, and the application of smart grid technologies provides strong support in this regard. In practical work, technologies such as HPLC (High-Speed Power Line Communication), intelligent phase-switching switch devices, and low-voltage line automatic voltage regulators have become key focuses of research and implementation. With these technologies, real-time monitoring of transformer zone operating conditions, dynamic balancing of three-phase loads, and precise regulation of terminal voltage can be realized.

Taking Transformer Zone A in a certain county town as an example, after comprehensive remediation, the line loss rate decreased from 9.7% to 6.1%, and the voltage compliance rate improved by 11.5%, achieving significant economic and social benefits.

However, there are still areas needing improvement in current technology applications—for instance, further enhancing communication anti-interference capabilities and refining equipment self-adaptive control strategies. Looking ahead, the focus should shift toward integrated design and coordinated control of intelligent devices, and deeper exploration of line loss prediction models based on big data and artificial intelligence. Additionally, enhanced technical training for operation and maintenance personnel is essential to ensure the system’s long-term stable operation. These measures will deliver more efficient and sustainable solutions for line loss management in low-voltage transformer zones.