1.COMPARISON OF THREE CONDUCTOR MATERIALS: Copper Bar, copper-aluminum composite bar and aluminum bar

The comparison of the electrical performance parameters of the three conducting materials is shown in Table 1. From the comparison of the comprehensive indexes in Table 1, it can be seen that the service reliability and service life of the three conducting materials are.

(1) Copper Busbar is next to silver in electrical conductivity, reliable, but heavy, high price, and will be higher and higher.

(2)Aluminum buses are light, inexpensive, and second only to copper in electrical conductivity, but if lap joints have the following fatal weaknesses.

the surface of aluminum is easy to oxidize, which will increase the contact resistance at the lap surface and cause heat, even burn out. 

 the material is soft, the creep speed is fast, after fastening the time is long easy to loosen, because of the contact bad and gives off heat even burns out.

Because of the above reasons, after long-term electrification, the surface contact resistance gradually increases, easy to produce electric property decay and even lose conductivity.

Table 1

Experimental Verification 1: Conductor surface lap performance test

In 2003, the Electric Power Laboratory of British Columbia, Canada, carried out 2000 hours salt spray corrosion cycle test and electric current burst test on the lap joints of copper and copper, copper and aluminum, aluminum alloy and aluminum alloy, the high current burst test is used to study the aging of conductor joint.

The results show that the reliability of aluminum conductor is far different from that of copper and copper under the same environment. The resistance of copper-copper connections increased only in 30% of the samples, while the resistance of aluminum-aluminum connections increased more than 70% , and more than 40% of them lost their conductivity. The experimental results show that the direct lap joint of aluminum alloy has the advantages of rapid aging and short electrical life. (the original text of the experiment was a 2005 IEEE (Society of electrical and electronic engineers) award-winning paper.)

The research and development of copper-aluminum composite bus-bar is to solve the fatal weakness of aluminum bus-bar in electric conductivity, and to reduce the cost on the premise of ensuring safety, reliability and service life. Copper-aluminum composite busbar surface is copper, therefore, the oxidation resistance is the same as copper. Mutual Lap is the lap of copper and copper, long-term electrification of its electrical life and copper bus. After special treatment, the creep deformation is small, the performance is close to copper, the fatal weakness of aluminum bus bar is overcome, the reliability is the same as copper bus bar, its performance is essentially different from aluminum bus bar, it can replace copper bus bar, but the price is greatly reduced.

Experiment # 2:

Whether the service life of copper-aluminum composite bus-bar can meet the requirements, the above conclusion is confirmed by test: The service life test of conductor material is based on GB/T9327-2010"test methods and requirements of CRIMP and Mechanical Connection Fittings for power cable conductors with rated voltage up to and including 35KV" , the Shanghai Cable Research Institute made 1000 thermal cycles (equivalent to 1000 temperature rises) for a brand composite row, and connected four 8 * 80 rows with 1535A current. Measure the temperature and DC resistance of the overlap part, calculate the resistance ratio, dispersion and so on after 1000 tests, the test lasted eight months, the test was qualified. The test proves that the material and the property of the interface between copper and aluminum have little change, which is in the range of the standard. The ability and reliability of the composite row to withstand thermal fatigue are proved, which shows that the conductivity will not decay after long-term electrification.

The above-mentioned test proves that the performance of copper-aluminum composite bus-bar is essentially different from that of aluminum bus-bar, and its electrical life is much longer and its reliability is much higher. It is as safe to use as copper busbar. At the same time, due to its light weight, easy installation, self-weight caused by the bending stress is small, longer life, is a cost-effective busbar.

In order to solve the problem of easy oxidation on the surface of aluminum bus bar, some enterprises adopt zinc plating and copper plating on the surface of aluminum bus bar, because the coating is very thin and the service life is limited, the most important is the creep problem has not been solved. In order to solve the creep, some enterprises use aluminum alloy row, aluminum alloy conductivity than pure aluminum, the use of cross-section to increase a lot. In short, to ensure the safe use of aluminum arrangements to increase the number of processing procedures, the cost is not low.

2.Safety and reliability of copper-aluminum composite row: Reliability test (thermal cycle and thermal fatigue test)

(1) thermal cycling test

After 100 cycles of 0-200 °C thermal cycling test, the interfacial bond strength (shear) was measured before and after the test. The interfacial bond strength did not decrease after the test. The test confirmed that the interfacial bond strength was within 200 °C, the stress produced by thermal expansion and cold contraction will not destroy the interfacial bonding strength. The normal service temperature of the whole set of electrical equipment does not exceed 110 °C, therefore, the stress produced by thermal expansion and cold contraction will not affect the interface bonding strength of copper and aluminum, and will not cause damage to the normal service of the whole set of electrical equipment. In accordance with the requirements of wind power industry, another 100 thermal cycle tests were carried out at-40 °c-120 °C, and the interfacial bonding strength did not decrease.

(2) thermal fatigue test.

At present, only GB/T9327-2010"test methods and requirements of CRIMP and Mechanical Connection Fittings for power cable conductors with rated voltage up to and including 35KV" is used to verify the service life of conductor materials. Shanghai Cable Research Institute did 1000 thermal cycles (equivalent to 1000 temperature rise) test on a brand composite row according to the highest requirement of this standard, connected with 48 * 80 rows and connected with 1535A current. Each measurement of the junction temperature and DC resistance, the calculation of the resistance ratio, dispersion, and so on, took eight months, the test qualified. This test proves that the material properties of the interface of cu-al composite row have little change after a long period of high current, which proves the ability and reliability of the composite row to withstand thermal fatigue.

Since 2008, the copper-aluminum composite platoon has been used in high-voltage and low-voltage switchgear and power bus trunking projects, including high-rise buildings, modern factories, commercial buildings, and Rail Transit. Hundreds of projects have been successfully operated for many years, nothing bad came back. 

Source: Tongxinbao

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