Application of intelligent voltage stabilized power supply in street lighting-EEWORLD

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introduction

Nowadays, industrial plants generally have large working areas with many street lamps, which generally use high-pressure sodium lamps. However, the power consumption of these lamps is very large, which leads to unstable power supply voltage in the plant and large fluctuations. Especially in the second half of the night, the voltage is usually as high as 250V or more, resulting in extremely high bulb loss rate (up to 60% or more). In order to save energy, reduce waste and reduce costs, it is necessary to carry out energy-saving transformation.

1. Energy-saving transformation analysis

1.1 Power supply status

In order to avoid various losses during the transmission process and the adverse effects on electrical equipment caused by low voltage at the end of the line during peak hours, the power supply department supplies power to users at a voltage 10% higher than the nominal voltage (taking the single-phase 220V nominal voltage as an example, the actual power supply voltage is 220+22010%=242V) to ensure that the voltage at the far end of the power supply line will not be lower than 220-22010%=198V. Therefore, the voltage in most areas of the power supply line will be equal to or higher than the nominal voltage (220V). The standard transformation ratio of user transformers in my country is 10kV/0.4kV, but the actual power supply voltage of 10kV high-voltage lines is 11kV (10+1010%=11kV), so the actual single-phase output voltage at the low-voltage end can reach up to 254V (0.4V/10V11kV/1.732=254V).

1.2 Power usage

The normal operating voltage range (single-phase, i.e. phase voltage) of lighting electrical equipment (lamps) is 220 (110%) V (i.e. 198 V to 242 V). Usually, the power supply voltage in a city or region will increase as the power load in the area decreases, and this phenomenon is particularly prominent in industrial areas.

Especially late at night, the power supply voltage will be 10%~15% higher than the normal value of 220V.

Most lighting circuits supply power to lamps without reactive power compensation, with extremely low power factors. The reactive power loss of the circuit and the active and reactive power losses caused by reactive current in the circuit are relatively large, resulting in a huge waste of electrical energy .

1.3 Feasibility of power saving analysis

The calculation formula for the power consumed by the lamp during operation is:

Where P is the electric power consumed by the bulb; U is the voltage supplied to the bulb; R is the impedance of the bulb.

Once a light bulb leaves the factory, its impedance R is fixed. Therefore, if the supply voltage supplied to the lamp is changed, the power consumed by the lamp will drop rapidly as the square of the supply voltage drops.

1.3.1 Lighting energy saving transformation mainly consists of the following three aspects:

(1) Stabilize and control voltage to achieve energy saving

Install high-precision multi-period controllable slow slope linear real-time voltage stabilization and power saving equipment, and real-time voltage stabilization and control in different time periods. According to the conditions of lamps and power consumption sites, the unstable mains voltage can be accurately and stably controlled in real time to the voltage value required by lamps, which can greatly achieve energy saving while ensuring normal lighting. It can also effectively protect the bulbs and extend the life of lamps.

(2) Improve power factor and achieve energy saving

The intelligent voltage-stabilizing lighting energy saver designed in this paper can implement reactive power compensation for the circuit when the circuit power factor is low, improve the power factor, reduce reactive power loss and active power loss of reactive power in the circuit, and achieve energy saving.

(3) Balance three-phase output, reduce zero-sequence current, and achieve energy saving

The intelligent voltage-stabilizing lighting energy saver has the function of automatically balancing the three-phase output voltage. With the assistance of installation and processing by engineering and technical personnel, it can greatly balance the three-phase power supply current, effectively reduce the neutral line current and ring phase current, greatly reduce line losses, and achieve energy saving.

1.3.2 Lighting source conditions

For high-power lighting in places such as roads and workshops, the light sources usually used are gas discharge lamps, such as metal halide lamps, high-pressure sodium lamps, etc. The following takes high-pressure sodium lamps as an example to explain the light source conditions.

(1) Low starting voltage

The technical parameters of high-pressure sodium lamps clearly stipulate that: high-pressure sodium lamps should be able to start at a voltage lower than 198V; when starting, the pulse peak voltage output by the trigger of the high-pressure sodium lamp should be 2kV (2~3kV), and a qualified high-pressure sodium lamp can generate a high-voltage pulse with a peak value of 2~3kV by inputting a 50Hz mains voltage of (17510)V to the lamp trigger when starting. In order to ensure that the trigger can smoothly generate a high-voltage pulse of more than 2kV, the power supply voltage should be greater than 175V to trigger the bulb to glow and allow the gas in the bulb to be fully freed and emit light normally.

(2) The bulb has a wide voltage range

The working voltage of the high pressure sodium lamp after starting is (10020) V, that is, the high pressure sodium lamp will work between 80 and 120 V after starting, and it cannot be lower than 80 V. To ensure this working voltage, the power supply voltage must not be lower than 176 V (220-22020%=176 V).

(3) High-pressure sodium lamps’ requirements for power supply voltage fluctuations

High-pressure sodium lamps have strict requirements on the fluctuation of power supply voltage during use. The power supply voltage of high-pressure sodium lamps cannot fluctuate too much. If the voltage suddenly drops by more than 5%, it may extinguish itself, and the fluctuation of power supply voltage has a greater impact on the luminous parameters. We believe that: since high-pressure sodium lamps belong to gas discharge lamps, excessive voltage and frequent fluctuations in power supply voltage will greatly shorten the service life of high-pressure sodium lamps.

(4) Factors affecting the service life of high pressure sodium lamps

a. The influence of voltage amplitude on the life of high pressure sodium lamp

In order for the trigger to smoothly generate a high-voltage trigger pulse of more than 2kV, trigger the bulb to start, and discharge the gas in the bulb and make it fully free and emit light normally, the power supply voltage should be greater than 175V. When the gas in the bulb is discharged and fully freed and emits light normally, the service life of the bulb is proportional to the speed of the gas molecules in the bulb. The higher the speed, the shorter the life of the bulb, and the speed of the gas molecules in the bulb is proportional to the terminal voltage of the bulb. It can be seen that in order to extend the service life of the high-pressure sodium lamp, the terminal voltage supplied to the high-pressure sodium lamp should be appropriately reduced as much as possible. Practice has proved that the life of a high-pressure sodium lamp working at a voltage of 180V~200V for a long time after starting is much longer than that of a high-pressure sodium lamp working at a voltage higher than 200V.

b. The impact of voltage fluctuation on the life of high pressure sodium lamps

High-pressure sodium lamps belong to the category of gas discharge lamps. The more stable the voltage input to the bulb, the longer the life of the bulb. Frequent sudden voltage jumps will cause the bulb to generate impact current and affect the free state of the gas in the bulb, thereby shortening the life of the bulb.

2. Working principle, characteristics and effects of intelligent lighting energy saver

2.1 Simple working principle of smart lighting energy saver

The design of the intelligent lighting energy saver is based on the principle of electromagnetic compensation and closed-loop tracking real-time voltage stabilization. It is a high-precision multi-period controllable slow slope linear real-time voltage stabilization energy saving device, which completely overcomes the drawbacks of chopper energy savers, fixed autotransformer step-down energy savers, step-adjusting autotransformer step-down energy savers, etc., such as waveform distortion, harmonic pollution, voltage instability, and flash-off impact (10~20ms). In the application of road lighting energy saving, the intelligent lighting energy saver is generally divided into three periods: the first period is the startup period, the second period is the first half of the night, and the third period is the second half of the night.

The working voltage and energy saving effect of each period are shown in Figure 1.

2.1.1 Composition of power saver

The intelligent lighting energy saver is mainly composed of four parts: main transformer, compensation supplier, data acquisition and programming processing, output and operation control (see Figure 2).

In the block diagram of the intelligent lighting energy saver, U1 is the AC input voltage, U2 is the secondary voltage of the main transformer, U3 is the output voltage of the compensation supply transformer (also the input voltage of the main transformer, or the primary voltage of the main transformer), and U0 is the output voltage of the energy saver.

2.1.2 Simple working principle

The intelligent lighting energy saver strictly stipulates the same-name terminals of the input and output windings of the main transformer and the windings of the compensation supply transformer in the design and production. As shown in Figure 2 and the electrical principle, the output voltage U0 of the energy saver is determined by U1, U2, and U3. That is, U0=U1-U2U2=nU3 (n is the transformation ratio of the main transformer, that is, n=U2:U3=1:5). U3 is the linearly changing voltage of the compensation supply transformer according to the output voltage requirements after closed-loop data acquisition and programming processing. The minimum continuous change of U3 is 0.5V, that is, the minimum continuous change of U2 is 0.1V.

After the energy saver is installed in the user's circuit, the time period, time constant and output voltage parameters need to be set according to the user's on-site power needs.

After the power is turned on, the power saver data acquisition and programming processing circuit will process the collected output voltage data and the set time period voltage parameters in real time, and according to the needs of U0=U1-U2 and U2=nU3, it will instantly control and instruct compensation to supply the transformer with accurate output U3 to ensure the output of accurate and stable output voltage U0.

Due to the use of the linear slow slope compensation principle, the three-phase main transformer can be manufactured independently in phase, and the three-phase output voltage shares a set of setting parameters. Therefore, no matter how the input voltage changes or how the load changes, the three-phase output voltage of the energy saver is basically equal and can withstand 100% unbalanced load on the three phases.

2.2 Characteristics of Intelligent Lighting Energy Saver

2.2.1 Stabilize the optimal operating voltage

In response to the phenomenon of high and fluctuating grid voltage, the control device can adjust the output of the optimal lighting working voltage online in real time according to the actual needs of the user on site, and can stabilize it within 2%, effectively improving the power quality, thereby achieving the effect of saving 10% to 40% of electricity.

2.2.2 Multi-period energy-saving operation

According to the user's actual lighting needs, the control device can also set energy-saving voltages for multiple time periods through a program, thereby meeting the user's needs for different light sources and at different times, and achieving the best lighting state and maximum power saving rate.

2.2.3 Effectively protect electric light sources and extend their service life

An important factor affecting the life of electric light sources is the impact of current and voltage on the light source during startup and operation. In order to effectively reduce current impact and extend the life of lamps, foreign high-end lamp products require lamps to have a soft start function.

The intelligent control device can realize the soft start and slow ramp control process of the lamp. When the lamp is started, it uses low voltage soft start and fully preheats. This process can reduce the starting current impact by 40% and effectively increase the life of the light source. In the process of voltage regulation and voltage stabilization, the intelligent control device uses slow ramp linear regulation to process the voltage, allowing the voltage to slowly transition within the set time, ensuring that the light source is not impacted by voltage and current fluctuations, thereby reducing damage to the electric light source and extending its service life.

2.2.4 Real-time voltage stabilization and control

In places with large voltage fluctuations, such as places with many electrical equipment, the voltage fluctuation within 1 minute can even reach more than 15% in some periods; the power supply voltage of street lights in the middle of the night can reach more than 240V on some roads. The highly stable optimal output voltage of the intelligent control device can extend the life of the electric light source by 2 to 4 times and greatly reduce the operation and maintenance costs by 30% to 50%.

2.2.5 Strong applicability and high reliability

Each phase of the control device can be adjusted independently, with strong operability, can withstand 100% unbalanced load of three phases, and ensure that the failure of a single phase does not affect the normal operation of the other two phases. The same device can carry different types of light source loads, and can also independently adjust the output voltage of each phase.

The control device adopts manual and automatic dual bypass system to ensure that the lighting equipment is powered on and operates normally and safely; the control part of the control device does not contain AC contactors, contacts and moving components , ensuring high reliability and low power consumption.

Optional GSM/GPRS global real-time (mobile phone) monitoring system can monitor equipment operation through display , sound and other signals, alarm for faults, and take protective measures in time.

This lighting energy-saving product can realize the functions of intelligent lighting control, effectively protect electric light sources, and reduce energy consumption.

2.3 The effect of using smart lighting energy saver

2.3.1 Direct Effects

After installing and using smart lighting energy savers, the electricity bill for street lighting has dropped by more than 33%, reducing the company's operating costs.

2.3.2 Indirect effects

Since the installation and use of intelligent lighting energy saver, the damage and replacement rate of bulbs has been greatly reduced, which indirectly reduces operating costs.

3. Conclusion

By installing intelligent voltage-stabilizing lighting energy savers, the average energy saving rate of lighting has reached more than 33%, greatly reducing the loss of bulbs. After a period of practice, significant energy-saving effects have been achieved. However, some large enterprises consume more electricity and need to increase energy-saving investment and carry out energy-saving and consumption-reduction work in a comprehensive and steady manner, which is of great practical significance for enterprises to improve their economic benefits.

Reference address：Application of intelligent voltage stabilized power supply in street lighting

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