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500kV and above large section overhead cable technology!

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-02-20

1 The Principle

At present, with the rapid development of national economy, the domestic (especially in East China, North China and South China and other economically developed region) electricity load surge, power grid construction has lagged behind the development of economy, accelerate the construction of power grids are increasingly vocal. However, the erection of an important factor in restricting the power grid construction is transmission line. The large cross section conductor technology can solve the outlet circuit and the limited line corridors problem. The same conditions (voltage grade, mitotic count, conductor material), the conductor cross-sectional area increased 1 times, according to economic current density calculation, transmission capacity conductor can improve more than 90%, according to wire heating condition calculation, transmission capacity can increase about 50%, significantly improve the efficiency of transmission corridor. The use of large cross-section conductor, can improve the electric performance and mechanical performance of line, improve the effect of the line on the environment.

1.1 electrical performance

The electrical properties of large cross-section conductor is the first consideration, which mainly consider the corona characteristics and resistance characteristics of circuit. Corona is a potential gradient exceeds a certain critical value after free of air caused by the wire around the a luminous discharge phenomenon. Through calculation, the wire section is greater, the lower surface potential gradient lines, corona loss conductor unit length is smaller; at the same time, in the same transmission capacity, loss resistance wire per unit length is smaller.

East China Electric Power Design Institute in the Three Gorges converterstation line 500kV DC transmission line design, compares several maximum surface potential gradient, corona inception voltage gradient and corona loss.

According to the USA Electric Power Research Institute (EPRI) of the "± 600kV high voltage direct current transmission line design parameters Handbook" and Canadian TESH MONT consulting company

recommended formula, calculation results of 500kV bipolar DC conductor surface gradient is shown in Table 4 - 1.

The conductor surface potential gradient table 4-1 various wires

Wire splitting type 4×LGJ-630/55 ACSR-720/50 4×LGJ-800/70
Gradient(kV/cm) 20.18 19.42 18.44

The reference DC ge - Shanghai line formula and TESH formula recommended MONT consulting company, corona inception gradient results in Table 4 - 2.

Table 4-2 various initial conductor corona gradient

Wire splitting type 4×LGJ-630/55 4×ACSR-720/50 4×LGJ-800/70
The positive lead g(kV/cm) 18.74 18.66 18.57
The negative wire g(kV/cm) 18.02 17.92 17.82

The project total corona loss and loss of bipolar good weather (L ~ 900km) in Table 4 - 3.

Table 4-3 equivalent corona loss and total corona loss

Wire 4×LGJ-630/55 4×ACSR-720/50 4×LGJ-800/70
The height of wire(cm) 1600 1600 1600
Unit corona P(kW/time·km) 2.479 2.094 1.601
Total corona(kW) 2231 1885 1445

According to the resistance loss of the Pl = I2 * r, the lead resistance loss and line loss in Table 4 - 4.

Table 4-4 wire resistance loss and line loss

Wire 4×LGJ-630/55 4×ACSR-720/50 4×LGJ-800/70
Current I(kA) 3 3 3
20℃ DC resistance(Ω/km) 0.04514 0.0398 0.03574
Resistance loss Pl(kW) 91409 80595 72374
Corona loss PP(kW) (H=1250cm) 1124.2 952.2 729
Bus loss(kW) 92532.7 81547 73103
Corona loss accounts for% of the bus 1.215 1.17 0.997

The above comparison results show that, wire section is greater, then line corona and corona loss is small.

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