Street lighting is a significant part of the communal economy of settlements. Costs for this coverage make up to 30-40% of all energy supply costs. To reduce electricity costs and improve the comfort of lighting system maintenance, new methods are being introduced, including automated control of street lighting.
Tasks of automation
The main tasks of street lighting automation include:
- uninterrupted lighting of streets and transport highways;
- ensuring energy savings while maintaining lighting quality;
- reduction of maintenance costs of lighting systems.
To implement these tasks, both autonomous equipment and automation systems are used.
Lighting systems and their characteristics
The latest elements of lighting systems are LED lamps, which are very economical and reliable. But the conversion of street lighting to such light sources will require a lot of money and time. Meanwhile, most of the streets are lit by gas-discharge lamps.
Ballasts are used to control such lamps. There are two types of ballasts:
- induction;
- electronic.
With the help of an induction ballast, a current jump is created in the circuit, due to which a high voltage of 2-3 kV occurs at the moment of switching on and the gas discharge lamp is ignited. During the operation of the lamp, such a ballast, which is a choke, limits the power.
The induction ballast has the following disadvantages:
- the presence of a bulky throttle and an unreliable starter;
- flickering of light with the network frequency (strobing);
- low efficiency.
At the same time, this type of ballast increases the phase shift (decreases cos φ). To correct this effect, it is necessary to include additional capacitors and use circuits for counter switching on lamps.
An electronic ballast is an electronic device that ignites the lamp and maintains the voltage necessary for burning at its terminals.
The circuit of the electronic ballast includes the following blocks:
- filter;
- rectifier with a smoothing filter;
- inverter;
- throttle.
The filter is designed to filter interference from the network and interference that occurs in the lamp power circuit. The rectifier is designed to obtain a constant voltage that powers the inverter.
The inverter produces oscillations with a frequency of 10-20 kHz. The load of the inverter is a transformer, which generates the voltage to light the lamp, as well as the voltage to maintain the burning.
When using an electronic ballast:
- flickering is eliminated;
- the brightness of the lamp radiation increases;
- the dimensions of the device components are reduced;
- ccd increases;
- when using the latitudinal pulse modulation mode, it is possible to adjust the brightness;
- the service life of the lamps increases due to the programmed ignition start. At the same time, the cathode of the lamp is first heated, and then the arc is ignited.
Management methods
Street lighting can be controlled in the following ways:
- manual;
- light sensor;
- timer;
- microprocessor systems.
Manual control of street lighting is turning on / off power according to a certain schedule directly at the substation by the operator. The disadvantage is the involvement of additional personnel and uncomfortable working conditions.
The light sensor controls the switching on of lamps based on the intensity of natural sunlight. disadvantages:
- limitations in sensor calibration;
- impact on the sensor of dust, dirt and snow;
- impossibility of using energy-saving methods.
The time relay is oriented to the set time parameters. Hence the main drawback of such street lighting control:
- constant adjustment of relay settings, taking into account the length of day and night in the seasons.
The most advanced are control systems that use processors and, in particular, automatic control systems (ACS). Typical automatic control systems include:
- server;
- automated workplaces;
- modems and communication lines with control objects;
- cabinets and light source control units.
How the ACS works
The street lighting control system performs the following tasks:
- automatic and manual control. It includes the dispatcher’s commands, and the accounting of the readings of the light sensor, etc.
- control of the operation of starting devices;
- automatic removal and fixation of network readings. Thanks to this, it is possible to analyze the operation of the lighting system, including the determination of burned-out lamps, directly at the dispatch center, without going to the site.
When controlling according to the schedule, the lamps are turned on according to the date and time of day. After entering the schedule, the automatic control system can control the lighting throughout the year without the intervention of the operator.
After the formation of the software, the control command over the communication line is transferred to the ballast, which in this case represents the executive mechanism.
As communication lines are used:
- low current communication lines (twisted pair);
- radio communication;
- cellular communication;
- HF signal transmission via cable.
In each case, the advantages and disadvantages of the communication line are taken into account. For example, when using twisted pair, you can send commands to each lamp, but for this, each lamp must have its own unit installed. At the same time, such a line requires mandatory adjustment of the timer.
A communication line using GSM does not require large costs for its implementation, but SIM cards are required for its operation and the operator must be paid for its use.
Such a communication line works only in the coverage area of the communication operator, and its reliability depends on the load of the GSM system by other users.
Using power cables to transmit commands can lead to errors when the cable breaks. The length of such a communication line should not be more than 1 km.
When using a radio channel, you need transmitting and receiving equipment, the operation of which may be subject to the influence of radio interference or the influence of zones of no signal.
According to service possibilities, a twisted-pair communication line can be used in a small town or a large city area, a GSM communication line – in a city or the nearest suburb, a power cable communication line – within a block, and a radio line – in a city , suburbs and along highways.
Lighting automation equipment
Along with ACS-type means, the following devices are used to control the lighting of a street, house or suburban area:
- light sensor;
- motion sensor;
- timer;
- astronomical relay;
- dimmer switch
Light sensor
The light sensor (twilight switch) is designed to automatically turn on and off the lighting depending on the lighting of the area.
The principle of operation of this sensor is that the light flux affects the light-sensitive element (photoresistor, phototransistor, photodiode), which is included in the electronic circuit. As a result of the change in the current flowing in the circuit, the relay included in this circuit is triggered. The relay contacts open and the lamp turns off.
The main characteristics of the light sensor:
- power or load current;
- trigger threshold;
- activation delay;
- degree of protection.
The most important parameter of the sensor is the load power. When choosing a sensor, it is necessary that the power of the lamp is equal to or less than the permissible power. This power for most industrial sensors is in the range of 1.5-2 kW.
The trigger threshold of the sensor is determined by illumination. In most light sensors, this parameter can be adjusted. Its value ranges from 2 to 200 lux.
When setting the sensitivity of the sensor, it should be taken into account that an illumination of 5 lux corresponds to the darkness at which individual objects can be distinguished, and at an illumination of 2 lux total darkness occurs.
The trigger delay is designed to protect the trigger of the sensor from false signals that occur, for example, when a shadow from a tree or light from headlights falls into the working area of the sensor. This delay is equal to 15-60 seconds.
When the sensor is placed outside, it can be affected by dust or moisture. Therefore, light sensors should have a higher degree of protection (no worse than IP44).
Motion sensors
Along with light sensors, motion sensors are used to automate lighting control on the street. Sensors can be both built-in and remote.
The principle of operation of such sensors is to respond to the appearance of a moving object. For the most common infrared sensors, information about the change in light emission in the IR range is used. The main parameters of such sensors:
- load power;
- range of action;
- viewing angle;
- activation delay time.
After installing such a sensor, its parameters are adjusted. In most models of motion sensors, the following are regulated:
- sensitivity (SENS);
- illumination (LUX);
- delay time (TIME).
With the help of the first adjustment, the range of the sensor activation is set, with the help of the second – the threshold of activation according to illumination, with the help of the third – the duration of the sensor’s activation time.
Timer
The timer includes turning off the lighting based on certain hours of the day. The disadvantage is the need to adjust the device due to the daily change in the time of sunrise and sunset.
A more accurate option is a digital astronomical clock, which has a program for determining the time of sunset and sunrise based on the latitude and longitude of the place of work of the light source. In accordance with this information, lighting is turned on and off.
Such a timer can switch a purely active load with a current of 16 A (for switching an inductive load, this current is equal to 4 A). To connect more powerful lighting lamps, it is necessary to connect a magnetic starter. Astronomical timers can be installed in the switchboard, and their degree of protection does not exceed IP20.
Dimmers
Autonomous dimmers are used for small lighting systems for which it is economically unprofitable to use centralized brightness control of lighting lamps.
For example, a K2303 type dimmer can switch the lighting to a reduced energy consumption mode at night (up to 75-50% of the nominal value). This allows you to save energy consumption.
The dimmer can work both with gas-discharge lamps and with LEDs. The device is installed in each street lighting fixture. With the help of special switches on the dimmers, the operating mode is set, as well as the time schedule for switching to reduced power. This type of dimmer can also work with a motion sensor. At the same time, if there is no moving person or car in the area of the sensor, the lighting lamps will burn dimly, and when a moving object appears, they will burn at full power.
Conclusions
- To control street lighting, in which gas-discharge lamps with induction or electronic ballast are used, both separate autonomous means of automation and complex automatic control systems can be used.
- Light, motion sensors, time relays, and dimmers are used as autonomous means of lighting automation.
- Low-current communication lines, cellular communication lines, communication lines using power cables and radio lines can be used to ensure communication between the lighting control point and the lamps.