January 1, 2022 2:29 pm

ELECTROMAGNETIC FIELDS IN HIGH VOLTAGE AND EXTRA HIGH VOLTAGE ELECTRICAL LINES Author: Ing. Jorge Pinto Rocha ENDE Transmisión – Planning Management INTRODUCTION The Trunk Interconnection System (STI) of Bolivia is made up of high voltage electrical lines and substations (HV) in 69, 115 and 230 kV, and extra high voltage (EAT) in 500 kV. These […]

ELECTROMAGNETIC FIELDS IN HIGH VOLTAGE AND EXTRA HIGH VOLTAGE ELECTRICAL LINES

Author: Ing. Jorge Pinto Rocha

ENDE Transmisión – Planning Management

INTRODUCTION

The Trunk Interconnection System (STI) of Bolivia is made up of high voltage electrical lines and substations (HV) in 69, 115 and 230 kV, and extra high voltage (EAT) in 500 kV. These facilities generate electromagnetic fields of industrial frequency (50 Hz), the intensity of which depends on the voltage level, electrical power of the transport, geometry of the structure, number of sub-conductors, height of the sub-conductors with respect to the ground, etc. The electromagnetic fields in transmission lines are calculated using typical structures and conductors, and a comparative analysis is presented with respect to the maximum limits recommended by the International Commission on Protection against Non-Ionizing Radiation (ICNIRP 2010).

DEVELOPING

The calculation of the electric field (E) and the magnetic field (B) of electric transmission lines in Bolivia is carried out using the methodology of the book EPRI AC Transmission Line Reference Book 200 kV and Above 3rd. Ed., Whose typical characteristics are the following:

U

(kV)

Ternas

Cond./fase

Setting

De fases

Conductors

Separation

Haz Cond. (m)

SIL/terna

(MW)

69

1

1

Horizontal

ACSR Partridge 266.8 MCM

12

115

1

1

Triangular

ACSR Ibis 397.5 MCM

35

230

1

1

Horizontal

ACSR Rail 954 MCM

130

230

2

2

Vertical

AAAC Flint 740.8 MCM

0.45

175

500

1

4

Delta

ACAR 750 MCM

1.10

1000

Estructuras típicas en 69, 115, 230 (1 terna), 230 (2 ternas) y 500 kV.

Frequency (Hz)

E_general (kV/m)

E_ocupational (kV/m)

B_general (µT)

B_ocupacional (µT)

50

5

10

200

1000

The maximum electromagnetic fields were calculated within (E_ocupacional, B_ocupacional for workers) and outside (E_general, B_general for the general public) of the minimum safety band established in the Bolivian regulation AE 409/2019:

U

(kV)

Girdle

Security (m)

Minimun height

Condition – floor (m)

E_ocup.

(kV/m)

E_gen.

(kV/m)

B_ocup.

(µT)

B_gen.

(µT)

69

23

6.6

0.96

0.38

2.81

0.66

115

31

6.9

1.64

0.43

3.88

0.97

230

38

7.6

3.88

0.96

10.21

2.07

230

38

7.6

6.48

0.20

9.28

3.48

500

61

11.7

10.0

1.68

18.33

3.85

The cross-sectional profile of the electric and magnetic fields at the closest point of the conductors with respect to the ground (maximum deflection condition) are as follows:

U (kV)

Electric field

(V/m)

Magnetic field

(1µT=10mG)

69

115

230

(1)

 

230

(2)

 

500

CONCLUSIONS AND RECOMMENDATIONS
  • Electric fields for high voltage lines in 69, 115 and 230 kV oscillate between 0.96 and 6.48 kV / m within the safety band, values that are below the maximum limit of 10 kV / m recommended by ICNIRP; Outside the safety band, the values range between 0.20 and 0.96 kV / m, well below the maximum permitted limit of 5 kV / m for the general public.
  • The electric fields in 500 kV extra high voltage lines usually determine the installation height of the conductor to comply with the limits recommended by ICNIRP, consequently, it was necessary to increase the minimum conductor-ground height to 11.7 m in order not to exceed 10 kV / m within the safety band; Outside of it, the value obtained was 1.68 kV / m, which does not exceed the permitted limit of 5 kV / m for the general public.
  • Magnetic fields for high and extra high voltage lines, in general, are well below the limits recommended by ICNIRP. Within the safety range it ranges from 2.81 to 18.33 µT, and does not exceed the recommended limit of 1000 µT; Outside the safety range, it ranges between 0.66 and 3.85 µT, values below the maximum allowed limit of 200 µT for the general public
  • The comparative analysis shows that the high voltage lines in 69, 115 and 230 kV easily comply with the limits proposed by the International Commission on Non-ionizing Radiation Protection (ICNIRP) for electric and magnetic fields.
  • The electrical gradient for transmission lines at 500 kV calculated at occupational distances (maintenance) marginally meets the limits established by the Standard (ICNIRP 2010). Therefore, geometric variations in the design and construction stage must be reviewed as indicated in the AE 409/2019 standard, in section X. ADDITIONAL CRITERIA, it is recommended to “verify the width of the security strip, and the minimum height of the conductors with respect to the ground and other obstacles in extra high voltage lines (EAT) ”.
REFERENCES
  • EPRI AC Transmission Line Reference Book 200 kV and Above 3rd. Ed., 2003.