What is the reason for short circuit in enclosed bus duct? What are the ways to handle it?

Short circuit is a common problem, often caused by the use of low-priced and low-quality insulation materials during production. Copper bars contain impurities and have protrusions, burrs, welding errors, no water spraying function, or waste enters the shell of the bus duct during installation, which can lead to short circuits in the bus duct. So what should we do when a short circuit occurs?

If there is a problem with the busbar trunking of the double busbar connection, attention should be paid to the operation method of busbar maintenance during the process of handling the problem. If necessary, the busbar maintenance should be stopped for a short period of time. After the bus voltage disappears, the dispatcher shall immediately pull off the switch (including the bus coupler switch) that may call, and notify the operation team to check the bus externally.

When the voltage of the bus duct disappears due to a malfunction and there are obvious short-circuit signs (such as fire, explosion sound, smoke, etc.), the operation team personnel shall not resume operation on their own and shall conduct a detailed inspection of the bus equipment.

If there is a malfunction in the components connected to the busbar or if the branch switch refuses to operate, resulting in a circuit breaker that causes the busbar to lose voltage, a detailed inspection should be conducted. Immediately isolate the faulty components in the busbar slot or open the knife switches on both sides of the faulty branch switch, and then quickly restore the operation of the busbar and send out other branches.

Generally, the busbar cross-section should be selected based on the long-term operating current. And verify the short-term thermal stability and dynamic stability of the bus duct under short-circuit cable conditions. Due to factors such as resistance in conductors and the AC current trend when multiple conductors are in close proximity, heating can occur when current passes through the bus duct. The allowable temperature for heating during long-term operation of copper and aluminum bare bus ducts is 70 ℃. However, when the touch surface is reliably covered with tin (such as ultrasonic tinning), the allowable temperature advances to 85 ℃. Constrained by this continuous heating allowable temperature, bus ducts of different materials and sections provide corresponding long-term allowable current values. When selecting a bus duct section, the actual long-term operating current of the bus duct should be lower than the long-term allowable current value of the selected section bus duct. In situations where the average annual load is high and the bus duct is long (such as outdoor distribution equipment bus ducts), the bus duct is generally selected using the economic current density method. Economic current density is a comprehensive consideration of bus duct losses, annual repair and depreciation costs for bus ducts and associated equipmentThe current flowing through the unit cross-sectional area of the bus duct at this moment. The cross-sectional area of the bus duct is obtained by dividing the economic current density by the long-term operating current that does not include overload. The cross-sectional area of the bus duct selected by the economic current density method is generally larger than that selected by the long-term operating current.

Structural features:

1. This series of enclosed busbar trunking has excellent short-circuit resistance performance. Due to the protection of the aluminum (or weak magnetic steel plate) shell, it can effectively reduce the structural heating caused by eddy currents or circulating currents, lower the temperature of the enclosed busbar shell, reduce electrical energy loss, increase current carrying capacity, and reduce electric force.

2. This series of enclosed busbar trunking structures * can have installation and maintenance holes set at the upper or lower part of the enclosed busbar. For high current indoor enclosed busbars, ventilation louvers are installed on both sides and the lower part of the shell to enhance heat dissipation and reduce temperature rise.

3. This series of busbar trunking structures can have installation and maintenance holes set at the upper or lower part of the busbar trunking. For high current indoor busbars, ventilation louvers are installed at the two sides and lower part of the shell to enhance heat dissipation and reduce temperature rise.

4. The use of double insulation and multi-point connection grounding of the shell significantly reduces maintenance workload and improves safety performance.

5. The use of corrugated pipe expansion joints is simple to install and can achieve adjustment of two degrees of freedom in both horizontal and vertical directions. It not only meets the expansion and contraction requirements caused by different temperature drops and thermal expansion and contraction, but also compensates for errors caused by foundation settlement, solving the problems of poor protection level, inconvenient installation, and unreliable operation of traditional sliding plate expansion and contraction devices

characteristic:

(1) Single bolt clamping terminal

The bus duct design adopts a single *Bolt clamping terminal is a connecting component for busbar trunking units. Due to its special structure, it can prevent incorrect installation operations. At the same time, by tightening one bolt, two busbar trunking units can be reliably and quickly connected.

(2) High protection level socket

The bus duct is designed with a safety protection baffle at the socket, and the plug-in box can only be inserted when the protective baffle is opened. When the socket is not in use, the protective plate can be closed to prevent dust and foreign objects from entering at the socket, thereby improving the protection performance of the bus duct, preventing misoperation, and greatly improving the safety of the bus.

(3) Number of shell (protective shell) levels

The bus duct is designed with 5 current levels and only 3 levels of enclosures are used. In this way, when the system changes capacity according to adjacent levels, there is no need to replace the casing of the bus duct. For example, when 400A changes to 630A, the casing size is the same. Therefore, it greatly facilitates installation.

(4) Large transmission of electrical energy

The bus duct is designed as a separated air insulated type, which improves the heat dissipation of the bus duct, lowers the impedance, and achieves economical power transmission through the bus duct.

(5) Good completeness

The bus duct is designed with various functional connection units to meet the needs of all power transmission and distribution projects.

1. Reduce grounding faults and avoid phase to phase short circuits. Enclosed busbars with enclosures can prevent grounding faults caused by external moisture, dust, and foreign objects. Adopting phase to phase enclosed busbars also prevents the occurrence of phase to phase short circuits

2. The use of shell shielding for isolated phase enclosed busbars in steel structures can fundamentally solve the problem of induced heating in steel structures

3. Reduce the short-circuit electromotive force between phases. Due to the dual shielding effect of eddy currents and circulating currents on the shell, the short-circuit electromotive force on the phase conductors is greatly reduced

4. Improve the safety and reliability of operation. The pot type insulators in this factory are pressed with SMC to form a busbar enclosure, which prevents insulator condensation. At the same time, hydrogen and temperature measuring devices are used, and the measurement signals can be displayed on site or transmitted to the DCS system to improve the safety and reliability of operation. The busbar enclosure also creates conditions for the use of ventilation cooling

The 5 enclosed busbars are produced by the factory in a complete set with guaranteed quality, low operation and maintenance workload, easy construction and installation, and no need to set up mesh barriers, simplifying the requirements for civil engineering

6. The shell, including branch circuits, is electrically connected and grounded at multiple points within the same phase, greatly simplifying and eliminating the risk of personal electric shock