earth leakage circuit breaker in low voltage distribution system
Street light distribution fault protection analysis
The characteristics of street light distribution are: first, long line laying; second, distributed electricity load; third, it is easier for people to reach. The fuse or circuit breaker automatically cuts off the power supply when the system has an open circuit fault. For ground faults, due to the characteristics of street light distribution, the protection device is slow to act and cannot cut off the circuit quickly when the fault occurs, and the protection device is difficult to operate reliably. Quickly cut off the faulty line, increasing the risk of electric shock.
In the past, in the grounding protection systems such as metal lamp posts and seat boxes, if a ground fault occurs, the grounding current = power supply voltage / grounding resistance at the source + grounding resistance at the lamp post.
In the past, in the zero-connection protection system that connected the metal lamp post and the seat box with the PE line or PEN line of the system, if a ground fault occurs, it is: ground current = power supply voltage / “phase-zero loop” impedance
Small-section wires are commonly used in street light distribution systems, with a resistance value of about 1 ohm per kilometer. Theoretically, the grounding current can reach 100 amps, but the actual grounding current is much smaller than the above calculated value because the grounding fault is often not a metallic connection.
Similarly, because the fault current of the line is small, it is difficult for the protection device to make reliable actions, and there will be dangerous voltage on the lamp post and the seat box, so that the danger of electric shock exists.
Leakage circuit breaker selection
(1) The quality of the leakage circuit breaker is better.
(2) The tripping rated current of the leakage circuit breaker is about 1.3 times of the normal operating current.
(3) The rated leakage current of non-action is about 2 times of the normal leakage current.
Choose the correct installation site
(1) Street lamp trunk line protection. The leakage circuit breaker for protection can be installed at the head end of the street lamp trunk line, and its protection scope is the street lamp low-voltage power distribution trunk line and its power distribution device. When the above-mentioned electrical equipment has a single-phase grounding fault, the leakage protector will act immediately to cut off the power supply to prevent the accident of electric contact between people, and at the same time, it will serve as the backup protection of the leakage protection device on the branch line.
(2) Street lamp branch protection. The secondary protection is street lamp branch protection. This protective leakage protection device is installed in each branch circuit of the street lamp. The main purpose of this protection is to prevent direct contact with electric shock, and the respective protection areas are small to ensure uninterrupted power supply of other non-faulty branches.