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The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.

Ultra-high-voltage AC power transmission has outstanding advantages of high transmission capacity, long distance of power transmission, low line loss, small coverage, etc., which is an energy-saving and eco-friendly advanced power transmission technology. At present, China has three 1000 kV AC UHV projects completed in operation in total [

Domestic and foreign studies on UHV AC power transmission line induction are more concerned with parallel construction. In Literature [

In this paper, field measurement is made on induced voltage and current of 110 kV crossing lines below UHV line in Jinhua, Zhejiang, simulated model is set up by CDEGS software to compute and analyze fluctuations in induced voltage and current of 110 kV lines under different transmission currents of UHV line, different crossing distances and crossing angles between UHV and 110 kV lines, precautions in shutdown overhaul of low-voltage lines under UHV line are presented, and reference basis is offered for layout design of crossing lines.

Put into operation at the end of 2014, Zhebei-Fuzhou 1000kV UHV AC Power Transmission Project is constructed in two circuits all the way. Line Jianglian I, Line Jianglian II and 110 kV Line Xianchi 1555 (construction in two circuits on the same tower) cross in Jinhua. Their crossing distance is 18.3 m and crossing angle is 60˚.

ly; 7 and 8 refer to ground wires. Parameters of conductors and ground wires of crossing lines are shown in

The simulated model of induced power of crossing lines is set up in the HIFREQ module in the simulation software of CDEGS as shown in

In order to study and master effects of UHV line on induced power of power transmission lines below, field measurement is made on 110 kV Line Xianchi 1555 in Jinhua as shown in

In the measurement, three-phase conductors of Circuit I and Circuit II at the No.15 Support below the crossing point or Conductor 1 - 6 in

1) Induced voltage of all phase conductors is measured before earthing switches on both ends of line are closed following substation shutdown;

2) After earthing switches on both ends of line are closed, induced voltage of all phase conductors is re-measured;

3) Temporary ground wires are attached to locations near both sides of a measuring point to measure induced current of temporary ground wires.

It is known by measured results that while earthing switches in the substation are not closed, higher electrostatic induced voltage arises on the 110 kV line and induced voltage of Conductor 1 that is the closest to UHV line attains as high as 12.24 kV; while earthing switches on both ends of substation are closed, induced voltage on the line is almost zero; due to lower running load of UHV line in

Line type | Line Jianglian | Line Xianchi 1555 |
---|---|---|

Conductor | 8 × JL/G1A-630/45 | 1 × LGJ-240/30 |

Ground wire | LBGJ-185-20AC | LGJ-50/30 |

Load Parameter | Name of UHV line | |
---|---|---|

Line Jianglian I | Line Jianglian II | |

Active power/MW | 246 - 275 | 241 - 271 |

Reactivepower/Mvar | 405 - 416 | 11 - 21 |

Current/A | 261 - 271 | 127 - 154 |

Conductor No. | Induced voltage of conductor/kV | Induced current of ground wire/A | |
---|---|---|---|

Earthing switches are unclosed | Earthing switches are closed | ||

1 | 12.24 | 0.002 | 0.07 |

2 | 10.47 | 0.002 | 0.06 |

3 | 8.70 | 0.002 | 0.02 |

4 | 12.22 | 0.001 | 0.07 |

5 | 10.47 | 0.001 | 0.06 |

6 | 8.70 | 0.001 | 0.02 |

measurement, after temporary ground wires are attached to both ends of the crossing point, the measured induced current flowing through the ground wires is very low as well, which is lower than 0.07A.

The maximum value in

It is known by table that results of simulated computation and field measurement are close to each other, proving the accuracy of simulated model. Different transmission currents of UHV line, crossing distances and crossing angles are taken to make simulated computation and analysis on induced voltage and current of 110 kV line.

The maximum transmission capacity of the UHV line is 6000 MW in one circuit. However, since it is put into operation lately and experiences no peak of power consumption, it keeps running in a lower load. In order to ensure personal safety in shutdown overhaul of 110 kV line below, it is necessary to study induction in the state of high load. While UHV line is in the transmission powers of 2000 MW, 4000 MW and 6000 MW respectively, transmission current of each phase conductor is 1.15 kA, 2.31 kA and 3.46 kA respectively. Crossing distance of 18.3 m and crossing angle of 60˚ are taken to compute induced voltage and current of 110 kV line under different transmission currents as shown in

While earthing switches in the substation are not closed, induced voltage of 110 kV line is generally electrostatic coupling component and electrostatic induction is irrelevant with transmission current. Therefore, induced voltage of conductors is almost unchanged; after earthing switches on both sides of station are closed, induced voltage of 110 kV line is generally electromagnetic coupling component and electromagnetic coupling voltage rises as transmission current rises in direct proportion and induced voltage is 12.3 V while UHV line is in

Conductor No. | Induced voltage of conductor/kV | Induced current of ground wire/A | |
---|---|---|---|

Earthing switches are unclosed | Earthing switches are closed | ||

1 | 12.77 | 0.0016 | 0.067 |

2 | 11.08 | 0.0013 | 0.057 |

3 | 9.58 | 0.0014 | 0.044 |

4 | 12.76 | 0.0016 | 0.067 |

5 | 11.07 | 0.0013 | 0.057 |

6 | 9.58 | 0.0014 | 0.044 |

Transmission current/kA | Induced voltage of conductor/kV | Induced current of ground wire/A | |
---|---|---|---|

Earthing switches are unclosed | Earthing switches are closed | ||

1.15 | 12.77 | 0.0047 | 0.20 |

2.31 | 12.78 | 0.0085 | 0.38 |

3.46 | 12.78 | 0.0123 | 0.56 |

full-load operation; induced current flowing through temporary ground wires is very low, which is lower than 1A.

Transmission current of 3.46 kA of each phase conductor and crossing angle of 60˚ are taken to compute induced voltage and current of 110 kV line under different crossing distances as shown in

The farther UHV line is away from 110 kV line below, the lower electrostatic induced voltage and electromagnetic induced voltage of 110 kV line will be. As crossing distance rises from 20 m to 50 m, electrostatic induced voltage falls from 12.43 kV to 8.93 kV and electromagnetic induced voltage falls from 12.2 V to 11.0 V; induced current of temporary ground wires slightly declines as well.

Transmission current of 3.46 kA of each phase conductor and crossing distance of 18.3 m are taken to compute induced voltage and current of 110 kV line under different crossing angles as shown in

While crossing angle changes from 0˚ (parallel construction) to 90˚ (vertical crossing), induced voltage and current of 110 kV line show greater change. In parallel construction of two lines, electrostatic induced voltage attains 100.84 kV, electromagnetic induced voltage attains 358 V, and induced current of ground wires attains 16.3 A, much higher than those in the situation of line crossing. Even though crossing angle is only 30˚, electrostatic induced voltage falls 59.3%, electromagnetic inducted voltage and induced current of ground wires fall as much as 89.7% and 89.4% respectively.

Crossing distance/m | Induced voltage of conductor/kV | Induced current of ground wire/A | |
---|---|---|---|

Earthing switches are unclosed | Earthing switches are closed | ||

20 | 12.43 | 0.0122 | 0.56 |

30 | 10.84 | 0.0118 | 0.54 |

40 | 9.755 | 0.0114 | 0.53 |

50 | 8.930 | 0.0110 | 0.51 |

Crossing angle | Induced voltage of conductor/kV | Induced current of ground wire/A | |
---|---|---|---|

Earthing switches are unclosed | Earthing switches are closed | ||

0˚ | 100.84 | 0.358 | 16.3 |

30˚ | 41.02 | 0.0367 | 1.72 |

60˚ | 12.78 | 0.0123 | 0.56 |

90˚ | 10.94 | 0.00088 | 0.039 |

While 1000 kV Line Jianglian is in liveoperation in Jinhua, Zhejiang, field measurement is made on induced voltage and current of conductors of 110 kV Line Xianchi 1555 that is 18.3 m below the above line and in a crossing angle of 60˚ with the above line. The electrostatic induced voltage attains 12.24 kV. Due to lower line load in measurement, the electromagnetic induced voltage is lower than 2V and induced current of ground wires is lower than 0.07A.

Results of simulated computation show that while UHV line is in full-load operation, electrostatic induced voltage is12.78 kV, electromagnetic induced voltage is 12.3 V and induced current is lower than 1 A in the 110 kV line below; as the crossing distance rises, the induced voltage and current gradually fall; while two lines are in parallel construction, the electrostatic induced voltage is 100.84 kV, electromagnetic induced voltage is 358 V and induced current of ground wires is 16.3A, much higher than those in the situation of line crossing. The higher the crossing angle is, the lower induced voltage and current will be.

Though induced voltage and current of the crossing line below the UHV line are lower than those in parallel construction, greater electrostatic induced voltage may arise. In shutdown overhaul, it is necessary to ensure that earthing switches on both sides of line in the substation are closed. While crossing angle of lines is lower than 30˚, electromagnetic induced voltage of lines will be higher than human safety voltage of 36 V after earthing switches are closed. Thus, in line overhaul, it is also necessary to attach temporary ground wires on both sides of a working point to ensure personal safety.

Pan, W.W., Miu, S.C., Yu, G.K., Wu, T. and Zhang, B. (2017) Measurement and Simulation of Induced Voltage and Current on 110 KV Crossing Transmission Lines under UHV AC Trans- mission Lines. Energy and Power Engineering, 9, 635-643. https://doi.org/10.4236/epe.2017.94B069