The electrical design scope of the landscape engineering mainly includes the exterior design and the landscape design in the garden. Compared with the electrical design of the building interior, it has its own particularity. Intelligent power supply and distribution system
1. Box change and lighting distribution box setting principles
(1) Characteristics of landscape design
The power supply area is large, the power points are scattered, and the load is small. Before taking over the landscape design, the location and number of outdoor boxes should be determined according to the scope of the landscape project. When the general park is within 400 m, a box can be used to supply power. If the length is exceeded, the number of boxes should be increased. For example, the Shangrao City Forest Park is 800 m long and uses two boxes to supply power. Of course, if there is a large building in the park, the power of the landscape lighting can also be drawn from the substation of the building. (2) Arrangement of outdoor distribution box
Generally, the power distribution box has a power supply radius of about 150 m. If the distance exceeds this distance, the number of distribution boxes should also be increased.
2. Lighting distribution system
(1) Division of distribution circuits in the box
According to the different functions of the light fixtures, they are divided into different power distribution branches. In general, lamps used for functional lighting (courtyard lights, lawn lights) and landscape lighting (tree lights, wall lights, buried lights, etc.) should be routed differently, and each circuit is behind a circuit breaker. Contactors are installed as manual or automatic switch lamps. Each loop contactor is connected to the weak current controller through the control line, enabling intelligent automatic control.
(2) Distribution system design
According to the requirements of the specification, the main switch of the lighting distribution box shall adopt a four-pole isolation switch. This is mainly due to the safety of electrical maintenance. When the power supply for the lighting in the park is led out by the substation in the park, the neutral line of the TT system and the total equipotential bonding system are not connected. When the neutral line has a fault voltage into the building, the total equipotential bonding system is ground potential, and this fault voltage will cause an electrical accident.
Therefore, in order to ensure the safety of maintenance, the main switch of the outdoor lighting distribution box should adopt a four-pole isolation switch.
(3) Outdoor lighting distribution box equipment selection
A surge protector should be installed in the box, and both the phase line and the neutral line need to be installed. This is because the neutral line in the TT system is no longer grounded after being led out from the substation and is in an insulated state to the ground. It can induce lightning impulse voltage as well as the phase line. Different from indoor lighting, there is no special regulation on the number of lamps in each individual lighting circuit of outdoor lighting. Generally, it is a low-power LED lamp. Usually, the power of each lamp is only 1~3W, forming 30~40 bands per circuit. Even more lights. However, for high-powered high-intensity discharge lamps, the number of lamps in a single circuit should be appropriately reduced. The single-phase loop current is ≤ 16 A. When calculating the actual power consumption of each circuit metal halide lamp, it is the discharge. The total installed power of the lamp is 1.5 times. 3. Setting of residual current action protector
(1) Use of protector (RCD)
Since the outdoor lighting of the garden adopts the TT grounding system, when a ground fault occurs in the system, the fault current needs to be returned to the power supply through the two grounding resistors of protective grounding and system grounding. Due to the limitation of the two grounding resistors, the fault current is insufficient to make the circuit breaker open. The device operates effectively. To ensure safety, it is necessary to use a RCD with high sensitivity to cut off the power.
(2) Setting of residual operating current value
The length of the garden outdoor lighting distribution line is 100-200 m, or even longer. In addition, the luminaire and the cable itself have a certain leakage current, and the leakage current of the distribution circuit is large during normal operation. If the residual operating current is set to 30 mA, a malfunction trip will often occur, which will greatly reduce the reliability of the power supply. Therefore, in order to ensure the reliability of the power supply of the outdoor lighting device, the rated residual operating current I Δ n of the leakage protector (RCD) should be correctly selected. Since the leakage current data of various devices and lines are incomplete and cumbersome to calculate, the following simple calculation methods can be used:
1) For single phase lighting circuits. RCD rated residual operating current Iâ–³n> circuit actual supply current / 2 000.
2) For three-phase four-wire power lines. RCD rated residual operating current Iâ–³n> circuit actual supply current / 1 000.
Article 5.2.4 of the "Safety Regulations for Night Scene Lighting" also stipulates that the operating current of the residual current protection of the end branch of the lighting distribution in outdoor places should not be greater than 100 mA, and the operating time should not be greater than 0.5 s. This will not cause a malfunction trip.
TT grounding system
1. Practical application of the grounding system
According to 10.9.1.3 of the “Electrical Design Code for Civil Buildingsâ€: TT grounding should be adopted for installations installed in outdoor landscape lighting > 20 m from the external wall of the building. However, there are different grounding practices for different types of lamps. (1) Street lamp, garden lamp grounding
Due to the large spacing of the above-mentioned luminaires, a grounding pole is provided next to each luminaire. The grounding pole is made of 2 500 mm, φ 50 mm galvanized steel and 40 mm × 4 mm galvanized flat steel, which is directly connected to the luminaire. At this time, the first luminaire from the cable led by the outdoor lighting distribution box to each lighting branch is PE-free.
(2) Grounding of lawn lamp and buried decorative lamp
This kind of luminaire is characterized by its small size and short spacing, so it is not applicable to set the grounding pole next to each luminaire. The TT grounding system in this case is: 2 500 mm, φ 50 mm galvanized steel pipe is used as the grounding pole next to the first luminaire of each branch, so the PE wire is drawn from the ground pole (between each loop luminaire) The PE wire) is reliably connected to the lamp housing and metal rod. The grounding resistance is required to be ≤10Ω. If the grounding resistance does not meet the requirements, it is necessary to increase the grounding pole and the spacing of the grounding poles of each branch is > 20 m. At this point, the first fixture from the outdoor lighting distribution box to the respective lighting branch cable has no PE line.
2. Ground fault protection of the grounding system
Article 7.7.7 of the "Electrical Design Code for Civil Buildings" stipulates that the operational characteristics of the ground fault protection of the TT system shall comply with the following requirements:
RA × Ia ≤ 50 V (1)
Where RA is the sum of the resistance of the protective conductor of the grounding electrode and the exposed conductive portion, Ω; Ia - the operating current of the protective device, A.
50 V is the safe voltage limit for normal environments. In the outdoor lighting design, the outdoor lighting fixtures are fixed-use electrical equipment, but the environment should be considered in the rain and snow, and the safety voltage limit should be 25 V. Then equation (1) becomes:
RA × Ia ≤ 25 V (2)
That is, RA ≤ 25 V/Ia is required. When Ia = I△n = 100 mA, RA ≤ 25/0.1, RA ≤ 250 Ω. This resistor is very large and very easy to implement. Therefore, the leakage protection can be used as the ground fault protection of the outdoor lighting device of the TT system. In actual work, the grounding resistance of the luminaire is generally required to be ≤ 100 Ω, which is far less than the specification, thus ensuring the safety of the human body in the event of leakage.
4. The neutral line of the grounding system is not grounded repeatedly.
When the grounding system of a project uses the TN-C-S system, its neutral power should be grounded repeatedly when entering the building. This can prevent the three-phase voltage imbalance caused by the neutral point drift from burning the single-phase equipment accident after the neutral line break of the incoming power supply; but in the TT grounding system, the power supply is neutral when entering the outdoor main distribution box. The line should not be grounded repeatedly, because repeated grounding will cause the following problems:
(1) The circuit breaker malfunctions
If the neutral line of the TT system is repeatedly grounded, the load current on some neutral lines will return to the power supply through the ground to become stray current. If the circuit breaker at the head end of the line is equipped with an RCD, this part of the stray current will cause it to malfunction.
(2) Initiating electric shock and casualties
Once a ground fault occurs at the substation, the neutral line is raised to ground potential, and the fault voltage is conducted along the neutral line to the outdoor lighting main distribution box. If the neutral line is repeatedly grounded, the potential of the grounding resistance of the total lighting distribution box will increase due to the fault voltage, and the grounding resistance potential of the protective grounding of the nearby lighting fixture will also rise, which will protect the grounded PE along the TT system. The wire is conducted to the outer casing of the lighting fixture, so that the lamp housing is charged, and there is a possibility of electric shock and injury.
Therefore, the neutral line of the TT system must never be grounded repeatedly. In order to prevent the neutral line from breaking, only the method of increasing the mechanical strength of the neutral line and increasing the cross-sectional area is adopted. According to IEC requirements, copper wire ≥ 6 mm2. Therefore, even if the area of ​​the park is small, the power consumption of landscape lighting is very small, the outdoor lighting distribution box is very close to the substation, and the minimum incoming power of the lighting distribution box should be YJV22 - 4 × 6, which should be attract people's attention.