Design and application of intelligent voltage-stabilized power supply in street lighting system

introduction

Nowadays, industrial plants generally have large working areas with many street lamps. High-pressure sodium lamps are generally used, and 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 a very high loss rate of bulbs (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 Analysis of energy-saving transformation

1.1 Power supply status

In order to avoid various losses in the power transmission process and the adverse effects of low voltage at the end of the line on power-consuming equipment during peak power consumption, 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 on the power supply line will be equal to or higher than the nominal voltage (220V). The standard transformation ratio of user transformers in China is 10kV/0.4kV, but the actual 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 consumption

The normal operating voltage range (single-phase, i.e. phase voltage) of lighting electrical equipment (lamps) is 220 (110%) V (i.e. 198V~242V). 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 lines supply power to lamps without reactive compensation, with extremely low power factor, and the reactive loss of the circuit and the active and reactive losses caused by reactive current in the circuit are relatively large, resulting in a huge waste of electric energy.

1.3 Feasibility of power saving analysis

The calculation formula for the power consumption of lamps during operation is:

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

Once the bulb leaves the factory, its impedance R is fixed. Therefore, if the power supply voltage supplied to the lamp is changed, the power consumed by the lamp will drop rapidly with the square of the power supply voltage.
1.3.1 The lighting energy saving transformation mainly consists of the following three aspects:

(1) Voltage stabilization and voltage control to achieve energy

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

(2) Improve the power factor to

achieve energy saving. The intelligent voltage stabilization 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 reactive current active power loss in the circuit, and achieve energy saving.

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

Intelligent voltage-stabilized lighting energy saver has the function of automatically balancing the three-phase output voltage. With the help of installation and processing by engineering and technical personnel, it can greatly balance the three-phase power supply current, effectively reduce the current in the neutral line and the ring phase current, greatly reduce line loss, and achieve energy saving.

1.3.2 Lighting source conditions

High-power lighting in places such as roads and workshops usually uses gas discharge lamps, such as metal halide lamps and high-pressure sodium lamps. The following takes high-pressure sodium lamps as an example to illustrate 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 of the high-pressure sodium lamp output by its trigger 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 when starting by inputting a 50Hz mains voltage of (17510)V to the lamp trigger. 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 start and allow the gas in the bulb to be fully freed and emit light normally.

(2) The bulb has a wide voltage range.

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

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

. High-pressure sodium lamps have strict requirements for power supply voltage fluctuations 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 the power supply voltage has a greater impact on the luminous parameters. We believe that: since high-pressure sodium lamps belong to the category of gas discharge lamps, excessive voltage and frequently fluctuating 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 service life of high -pressure sodium lamps

In order for the trigger to smoothly generate a high-voltage trigger pulse of more than 2kV, trigger the bulb to ignite and make the gas in the bulb discharge and fully ionize and emit light normally, the power supply voltage should be greater than 175V. When the gas in the bulb is discharged and fully ionizes 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 bulb life, 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 high-pressure sodium lamps, 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 high-pressure sodium lamps that work for a long time at a voltage of 180V~200V after ignition is much longer than that of those that work at a voltage higher than 200V.

b. The influence of voltage fluctuation on the service life of high-pressure sodium lamps

High-pressure sodium lamps belong to the category of gas discharge lamps. The more stable the voltage supplied 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 ionization state of the gas in the bulb, thus shortening the service life of the bulb.
2 Working principle, characteristics and effects of intelligent lighting energy saver

2.1 Simple working principle of intelligent lighting energy saver

The design of 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 saver, fixed autotransformer step-down energy saver, step-adjusting autotransformer step-down energy saver, etc., such as waveform distortion, harmonic pollution, voltage instability, and flash-off impact (10~20ms). Intelligent lighting energy saver is generally divided into three periods in road lighting energy saving applications: 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 the energy saver

The intelligent lighting energy saver is mainly composed of four parts: main transformer, compensation supply, 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 mains 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

In the design and production of the intelligent lighting energy saver, the same-name terminals of the input and output windings of the main transformer and the windings of the compensation supply transformer are strictly specified. 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 voltage that changes linearly according to the output voltage required by the compensation supply transformer 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 data acquisition and programming processing circuit of the power saver will process the collected output voltage data and the set period voltage parameters in real time, and according to the needs of U0=U1-U2 and U2=nU3, it will immediately control and instruct the compensation supply transformer to output accurate 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 made independently in phases, 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 power saver is basically equal, and can withstand 100% unbalanced load of the three phases.

2.2 Characteristics of intelligent lighting power saver

2.2.1 Stable optimal working voltage

For the phenomenon of high and fluctuating grid voltage, the control device can adjust the output 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%~40%.

2.2.2 Multi-period energy-saving operation

According to the actual lighting needs of users, the control device can also set multi-period energy-saving voltage through the program, so as to meet the needs of users with different light sources and different times, and achieve the best lighting state and maximum power saving rate.

2.2.3 Effectively protect the electric light source and extend its service life

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

Intelligent control devices can realize the soft start and slow ramp control process of lamps. When the lamp is started, low-voltage soft start is used for full preheating. 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 to ensure that the light source is not impacted by voltage and current fluctuations, thereby reducing the damage to the electric light source and extending the 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 in some periods can even reach more than 15%; the power supply voltage of street lights in the second half of the night can reach more than 240V on some roads. The high and stable optimal output voltage of the intelligent control device can extend the life of the electric light source by 2~4 times, and can greatly reduce the operation and maintenance costs by 30%~50%.

2.2.5 Strong applicability and high reliability

Each phase of the control device can be adjusted independently, with strong operability. It 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 adjust the output voltage of each phase independently.

The control device adopts manual and automatic dual bypass systems to ensure that the lighting equipment is powered on continuously 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.

The GSM/GPRS global real-time (mobile phone) monitoring system can be optionally equipped to monitor the operation of the equipment through display, sound and other signals, and fault alarms, and take protective measures in time.

This lighting energy-saving product can realize the functions of intelligent lighting control, effective protection of electric light sources, and reduction of power consumption.

2.3 The effect of using intelligent lighting energy-saving devices

2.3.1 Direct effect

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

2.3.2 Indirect effect

After installing and using intelligent lighting energy-saving devices, 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-saving devices, 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 economic benefits.