How to solve the transmission fault of high-voltage fully insulated copper tube busbar?

The tubular busbar plays an irreplaceable role after the rectangular busbar. There are many branches in the busbar

With characteristics such as high current (12000A), high mechanical strength, good insulation, and wide applicability, it is increasingly recognized and accepted by more and more customers.

With the rapid development of our country's economy, the demand for electricity in the entire society is increasing day by day. At present, both 110kV and 220KV substations use voltage levels of 10kV and 35kV on the low-voltage side. As the capacity of the main transformer increases, the rated current on the low-voltage side of the transformer's incoming line is also constantly increasing.

Conventional rectangular busbars are becoming increasingly difficult to meet the requirements of busbar heating and short-circuit electrodynamics in terms of technology and structure, resulting in additional losses, increased skin effect coefficients, decreased current flow capacity, and uneven current distribution. Especially when the capacity of a single main transformer is 180MVA or above, the 10kV outgoing side of the main transformer not only has the electric power and heating problems of the busbar bridge itself, but also the heating problems caused by eddy currents induced in the electromagnetic field of the busbar bridge pillar insulators, steel frames, and reinforced concrete columns and foundations near the busbar bridge. Tube shaped busbars serve as a substitute for rectangular busbars.

With the emergence of modern engineering facilities and equipment, the power consumption of various industries has increased rapidly, especially with the emergence of numerous high-rise buildings and large factory workshops. Traditional cables, as transmission lines, can no longer meet the requirements in high current transmission systems. The parallel use of multiple cables has brought many inconveniences to on-site installation and construction connections. Plug in bus duct, as a new type of distribution wire, has emerged. Compared with traditional cables, it fully demonstrates its superiority in high current transmission. At the same time, due to the use of new technologies and processes, the contact resistance and temperature rise at the connection points of the bus duct at both ends and the junction of the distribution port are greatly reduced. High quality insulation materials are used in the bus duct, thereby improving the safety and reliability of the bus duct and making the entire system more complete.

Copper busbar plays a very important role in power transmission. Copper tube busbars have the advantages of smooth surface, no deformation, and good conductivity. If the transmission system is used for too long, it is easy to cause some minor malfunctions.

1. Eliminate closed metal loops

(1) Connection with steel cored aluminum wire. At the existing connection location, steel cored aluminum wire is used for connection, which is convenient for construction, unrestricted in site, and requires less investment.

(2) Connect with copper bars. This solution has the same drawbacks as the above solution.

(3) Increase the distance between the joint and the reactor to reduce or eliminate the influence of strong magnetic fields on the joint. The construction period of this plan is long, the workload is large, the investment is high, the power outage time is long, and it is limited by the site.

2. Use sealed protective materials

Using sealing protective materials (such as hybrid grease) is a simple, fast, and effective method. Electric composite grease, commonly known as conductive adhesive, can prevent external water vapor, dust, and corrosive media from entering, protect the contact surface from corrosion, reduce contact surface resistance, and suppress heat at the joint.

The copper busbar with high current carrying capacity is a hollow conductor with a large surface area and uniform electric field distribution

Low skin effect, low power loss. Insulated copper tube busbar has a low skin effect coefficient (KF ≤ 1) and low AC resistance, which can reduce the power loss of the busbar

Good heat dissipation conditions, low temperature rise. The copper tube busbar is a hollow conductor with good heat dissipation conditions. The inner diameter air duct of the busbar can naturally form air convection (there is a pressure difference between the inside and outside of the tube)

The allowable stress' σ 'is large and the mechanical strength is high. The allowable stress of copper tube busbars is 4 times that of rectangular busbars. The short-circuit current that can be borne by the operating load is large, and the mechanical strength is high, which increases the support span of the busbar and reduces the corresponding pillar insulators, busbar fittings, and civil structure foundation area

The electrical insulation performance is strong. The insulated copper tube busbar adopts a multi-layer sealed shielding insulation method, and the shell is grounded with a potential of zero. Make the electric field distribution uniform, control the potential and limit the electric field; Characteristics such as avoiding partial discharge on insulation surfaces, conducting leakage and charging currents, and protecting against dangerous contact voltages

The insulation material used for insulated copper tube busbars has a high temperature coefficient, and the main insulation material is suitable for working in temperatures ranging from -250 ℃ to+250 ℃. It has excellent electrical performance and chemical stability, low dielectric loss, flame retardancy, aging resistance, and long service life

Strong anti electrical vibration force, directly fix the copper busbar on the steel frame or concrete supportCancel wall bushings and post insulators, which have strong seismic resistance

Not affected by environmental interference, highly reliable insulated copper tube busbar is shielded and sealed, with no condensation generated inside and free from grounding and phase to phase short circuit faults caused by external moisture, dust, and foreign objects. The operation has a high degree of reliability. Compared with the same period last year, rectangular busbars exposed to the environment are prone to grounding and short circuit caused by accidental contact with people, animals, and other objects, which is not conducive to safe operation

The ends of the two bus conductors that need to be connected should be partially parallel and aligned with each other, and a docking type bus duct should be used. Insert the copper connecting piece and insulation partition into the end of the busbar, and clamp one copper connecting piece on each side of the busbar for each phase of the neutral gear. Place an insulation partition between the copper connecting pieces. After confirming that there are no issues, insert the insulation bolt and pay attention to whether the connection holes of the copper connecting piece, busbar end, and insulation partition are aligned, whether the copper connecting piece and insulation partition are in place, and tighten the bolt. The plug-in box cannot be unplugged without disconnecting the switch. Generally, three plug-in boxes can be connected to a 2-meter straight bus duct. Due to the low current of the plug-in boxes, the plug-in boxes are directly connected to the bus duct through connectors with corresponding interlocking. For external output, cables are usually used to confirm that there are no issues. Then, connect the two bus ducts to the connector bus and check the conductor connection surface at one end of the bus duct and whether the connector is damaged or bumped. The bus duct conductor should be inserted into the connector and secured in place using a torque wrench.

It is mainly composed of an outer shell, an insulated plug, and a metal busbar. The outer shell plays a role in dust prevention and protection. There are ventilation holes on the shell to complete the heat dissipation function, and the built-in busbar can be made into a single or double pole according to the current size. If the shell is made of metal, it also has the function of grounding protection. From the perspective of insulation, sufficient distance should be left for safety; From the perspective of heat generation, sufficient space should also be left for heat dissipation to ensure that heat is dissipated into the air through convection. There are ventilation holes on the shell to complete the heat dissipation function, and the built-in busbar can be made into single or double according to the current size. If the shell is made of metal, it also has the function of grounding protection. Taking the three-phase bus duct as an example, the main structure.

Tube type busbar is one of the key equipment (materials) in the power transmission and transformation system, playing a crucial role in the safe and reliable operation of the transmission and transformation system and power equipment.

It has a high current（12000A）Due to its high mechanical strength, good insulation, and wide applicability, it is increasingly recognized and accepted by more and more users

It is mainly used as an overcurrent conductor in China's power construction projects, replacing traditional rectangular, slot shaped, bar shaped busbars and flexible conductors, for connecting conductors between power grid transmission lines and substation transformers, jumper wires in transmission lines, connecting conductors in power equipment, and overcurrent conductors in high current DC melting devices.

Comparison between bus duct and cable:

1. Multiple bus ducts can meet the rated current of 6300A, which is superior to cables.

The insurance cost for installing busbars is relatively low, while the cost for cables is relatively high.

3. The sub interface of the bus duct can add sub circuits, and the cables need to be laid from the distribution room.

4. The busbar is equipped with standard installation brackets and does not require any other support; Cables need to be laid using separate cable trays or pipelines.

5. Bus ducts can be controlled at the nearest location to the equipment, while cables need to be controlled in the distribution room.

6. The bus duct has a long service life and can be reused. And the cable has a short lifespan and cannot be reused.

Bus ducts have the following characteristics compared to cables:

(1) Bus duct is a flat conductor, which has the characteristics of good heat dissipation, low impedance, and high current carrying capacity compared to circular conductor cables or pre branch cables. Compared with cables or pre branch cables with a current carrying capacity of 630A or above, bus ducts with a current carrying capacity of 630A or above can save 10-35% of copper materials and reduce energy loss by more than 15% under the same current carrying capacity.

(2) The bus duct carries a large amount of current on weekdays, which facilitates the connection of feeders and reduces energy consumption together. It is very suitable for AC power supply and can withstand long-term operation at a given voltage value. Under the condition of alternating current within one minute, the bus duct will not be broken down and there will be no flashover. The withstand current and short-term peak current it can carry will meet the standards.

(3) The service life of bus ducts is approximately 2-3 times that of cables and branch cables. Hong Kong, Macau, and some European countries have clear regulations that the service life of cables is 12-15 years. In fact, the service life of bus ducts is as long as 30 to 50 years. Bus ducts can be divided into air insulated and fully insulated categories. In general, the inherent structure of bus ducts with air insulation is simple, covered with insulated bus ducts with heat dissipation characteristics and high current levels. The electrical shafts and bus ducts installed in high-rise buildings are equipped with a certain socket diameter, and the installation of such joints should consider multiple human disturbances. However, the initial capacity of the bus duct is large, and the structure is compact, which also has advantages in situations with high loads.

(4) The use of bus duct current carrying function ensures stability and avoids unnecessary power loss. The maximum temperature increment current (i.e. the rated current of the bus duct) that satisfies the standard rules for bus duct standards is very important. This current can control the current carrying function of the bus duct. The rated current of a cable is determined by its cross-sectional area. The calculation load varies, the number of cables in the cable tray varies, and different cable trays are used. The temperature inside the tray changes according to these factors, and the current carrying function of the cables also changes accordingly. So the current carrying capacity of the cable calculated by multiplying the reduction factor by the rated current of the cable is inaccurate. The installation method of this sealed cable tray also adds energy loss.

(5) It can be concluded that the capital is low, and there are copper and aluminum conductor materials for bus ducts. Copper conductor bus ducts are more expensive than copper cables, and the price of copper conductor bus ducts above 630A is similar to the cost of cables; Aluminum conductor bus ducts are 25% to 35% cheaper than copper conductor cables. The higher the current, the lower the cost of bus ducts compared to cables. For this reason, using bus ducts for transmission lines with a current carrying capacity greater than 630A is more economical and reasonable than using cables.

(6) Requirements for argon gas

The purity of argon gas should be controlled at 99.9% or above, with impurity oxygen below 0.005%, hydrogen below 0.005%, moisture below 0.02mg/L, and nitrogen below 0.015%. The increase in oxygen and nitrogen exacerbates the cathodic atomization effect. If the oxygen content exceeds 0.3%, the tungsten electrode will be burned more severely. If the oxygen content exceeds 0.1%, the weld surface will be dull or blackened. If the nitrogen content exceeds 0.05%, the fluidity of the molten pool will deteriorate, and the welding surface will be poorly formed.

(7) Joint form

Graphics and dimensions at the joint

(8) Welding requirements

To fix the tubular conductor and reduce deformation, the welding sequence should be spot welding first to fix the main pipe and reduce bending at the joint. Spot welding should be carried out symmetrically, and the argon flow rate is generally set at 30-50L/min

(9) Composition of welding wire (or welding rod)

(10) Joint strength coefficient