January 1, 2022

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)	N° Ternas	N° 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.

October 13, 2021

ABI: Electric power coverage is expected to reach 94.6% of Bolivian homes until December

Within the framework of the principle of universalization of basic services and thanks to the economic reactivation led by President Luis Arce, the works to expand the coverage of electric power in the country were resumed and it is expected that until December it will be extended to 94.6 % of Bolivian households, reported the Vice Minister of Electricity and Alternative Energies, José María Romay.

August 6, 2021

FM ALBA: They will restart the work for the Yaguacua-Tartagal electrical interconnection

Province announced that it will resume the electrical interconnection work that will link the Yaguacua Thermoelectric Station with the Tartagal Transformer Station, which represents the union of the Argentine Interconnection System; SADI; with Bolivia. The work will restart in the next few days and it is expected to finish in the month of November. The agreement to carry out the union was signed in 2015. During the de facto government of Jeanine Áñez, the works were interrupted despite the progress registered, more than 70 percent, in laying the line. In a virtual meeting, the Secretary of Mining and Energy of Salta, Flavia Royón; the general manager of the Bolivian National Electricity Company (ENDE) Ing. Jorge Durandal; and the project manager ENDE Transmission Argentina S.A. Ing. René Córdova, agreed on the technical guidelines to advance in the completion of the work of the High Voltage Line (LAT 132 kV) Yaguacua-Tartagal (Juana Azurduy de Padilla). The work will restart in the next few days and its completion is scheduled for next November.

July 13, 2021

As part of the improvements to the protection control systems, for the 2021 management the renovation of the protection control panels of the Kenko substation has been planned. The Kenko substation is an important node for injection of power by the SIN and withdrawal of energy by the distribution company DELAPAZ. A Kenko substation was reached with an important 115 kV Kenko – Mazocruz transmission line. This line is the main means of supplying energy to this substation.

Currently the Kenko substation control panels are more than 30 years old, some of them, and initially they were supplied with electromechanical relays that were gradually withdrawn and replaced by more modern ones. However, the first relays that replaced the original relays have also reached their useful lives, so their replacement is necessary. Taking advantage of this second or third relay replacement cycle, it has been found convenient to replace the complete board with another one according to the new standards that ENDE Transmission handles.

Figure 1. Current Control and Protection Boards in SE Kenko’s control room

or this renovation, new empty boards were acquired, which were assembled and assembled with the new relays and accessories in the La Maica warehouse workshops of ENDE transmission. The main relays were purchased in advance as part of the Mazocruz -Pallina project. All protection control and plan design engineering was carried out by specialist protection engineers with the help of a draftsman.

Figure 2. Control and Protection Board assembled in La Maica Warehouse – ENDE Transmission

With the new board scheme adopted by ENDE transmission, the three existing boards: 1 for line protection, 1 for bay control and another for alarm annunciator, will be replaced with a single board that fulfills the same functions. The new board houses two modern line protection relays RED 670 from ABB as Main Protection 1 and a SIEMENS 7SL87 relay as Main Protection 2. Both relays will communicate with the control center through an RTU in MMS protocol of the IEC standard 61850, in this way, considerably reducing the signal wiring to SCADA. Following the ENDE Transmission architecture, both relays will be able to control the maneuverable equipment in the bay of the Kenko-Mazocruz line, obtaining redundancy that leads to an improvement in the reliability of the Control and Protection System.

The panel also has a GPS clock that allows the time synchronization of the equipment through the SNTP protocol and a communications switch that allows remote management of the equipment and the transmission of information for the SCADA.

At the La Maica Store, the board underwent pre-commissioning tests to verify the satisfactory operation of the Control and Protection functions of the installed equipment. For this purpose, an analog signal injection equipment was used to simulate conditions similar to those present in the power system where it will be installed (115 kV Kenko-Mazocruz Line).