Single-phase transformers: a new energy-saving system for urban lighting
Three-phase systems are commonly used in my country’s low-voltage power distribution systems. Currently, the power supply method in low-voltage distribution networks is characterized by “small capacity, dense distribution points, and short radius,” which reduces line losses in low-voltage distribution networks. The use of single-phase transformers is an important measure to implement this power supply method, and single-phase transformers and single-phase substation/distribution technologies have been listed as recommended energy-saving technologies. Advantages of single-phase distribution: reduced line losses, improved voltage quality, and relatively safer electricity use.
1. Technical advantages of single-phase transformers for power supply to lighting loads
(1) Lower losses, energy saving
Using the same materials and capacity, single-phase transformers have lower no-load losses than three-phase transformers; single-phase transformers allow high-voltage lines to be closer to the load point, reducing the low-voltage power supply radius and lowering low-voltage distribution network losses.
In a certain area, the line loss of a 50kVA single-phase transformer with the same capacity, after switching from a three-phase transformer to a single-phase transformer, was lower than that of a three-phase transformer. Using a D12-50 single-phase transformer for power supply can save 586kW of electricity per year compared to using an S11-50 three-phase transformer.
(2) Cost Savings
With a single-phase transformer, high-voltage branches are constructed with two wires, and low-voltage lines with two or three wires; while with a three-phase transformer, high-voltage branches are constructed with three wires, and low-voltage lines with four wires. In terms of engineering costs, using a single-phase transformer can save 10% on high-voltage lines and 15% on low-voltage lines.
(3) Power Supply Reliability
Using a single-phase transformer for power supply in small-capacity, densely distributed locations increases the number of users, increases the base for reliability calculations, and improves power supply reliability. At the same time, during periods of high load and power rationing, a single-phase transformer reduces the scope of power outages and minimizes the impact on user power supply reliability. (4) Facilitating the Implementation of New Nighttime Voltage Reduction and Energy Saving Technology for Streetlights
Urban streetlights are generally arranged along both sides of the road, using single-phase V/V0 transformers to supply power to the urban road lighting load. Under the premise of not affecting road lighting in the latter half of the night, single-phase transformers can replace three-phase transformers to supply power to the urban road lighting load, achieving a dual energy-saving effect of single-phase transformer energy saving and automatic voltage reduction for streetlights in the latter half of the night.
2. Single-phase Transformer
(1) The high-voltage connection of the single-phase transformer should be designed to ensure the balance of the three-phase current at the 10kV line outlet of the substation. If the three-phase current of the 10kV outgoing line is unbalanced, it will increase the additional losses of the main transformer and generate negative sequence voltage in the system. In severe cases, it may cause the main transformer’s backup composite voltage blocking overcurrent protection to open its blocking circuit, leading to malfunction of the protection device. Therefore, the 10kV side of the urban single-phase transformer should be alternately connected to the three-phase power supply to achieve a basic load balance.
(2) When supplying power with a single-phase transformer, the transformer should be placed as close as possible to the load point.
3. New Energy-Saving System for Single-Phase Transformer High-Pressure Sodium Lamp Lighting
Streetlights are single-phase loads, suitable for being powered by single-phase transformers. Taking urban road lighting loads as an example, we present a new energy-saving system powered by a single-phase transformer.
Currently, the main method for saving streetlight energy is electromagnetic voltage reduction. Streetlights typically use gas discharge lamps, with operating voltages between 210 and 200V. The lighting cabinet requires 220V to start, and after lighting, the output voltage is appropriately reduced and stabilized.
The single-phase transformer high-pressure sodium lamp lighting energy-saving system does not require additional autotransformers, compensating transformers, or reactors. At night, the transformer is connected in a V/V0 configuration; in the latter half of the night, the neutral line on the secondary side of the transformer is automatically disconnected via an electronic controller, switching to a V/V configuration; this automatically changes the lamp voltage from phase voltage to half of the line voltage. Since the line voltage on the secondary side of the transformer is 400V in the latter half of the night, this effectively reduces the lamp’s power supply voltage from 220V to 200V.
Post time: Dec-01-2025
