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CONSIDERATION OF MAGNETIC FIELD LEVELS IN DESIGNINGTRANSMISSION LINES AND SUBSTATIONS FOR RESIDENTIALLY

CROWDED AREAS IN EGYPT

FATMA MOUSTAFA* ENAYET MOUSTAFA AHMED HAL

MOHAMED ISMAIL MONA RAAFAT FOUAD TAHER

MINISTRY OF ELECTRICITY AND ENERGY

EGYPT

This paper includes measurements of the magnetic field carried out: (1) inside four extra high voltage

substations 500/220/66 kV, (2) at the vicinity of some extra high voltage transmission lines and (3) at

residential areas close to one substation. These sites were chosen in crowded inhabited areas in Cairo

the Capital of Egypt. The purpose of the measurements is to determine the suitability of the network

design to limit the magnetic field to values less than those recommended by the International Radiation

Protection Association (IRPA) guides for magnetic field levels [1].

Measurements were carried out around the hour of the load flow in the transmission lines to measure

the field at the maximum current. Results showed that in some areas that the magnetic field exceeded

the IRPA permissible limits, where mitigation measures or precautions have to be applied.

The paper includes example of the design of a 220 kV substation, and a 220 kV transmission line,

which are used in the Egyptian network. Also, the paper includes the measurements taken (only the

values which exceed the limit) and the comments and recommendation to manage the subject.

Keywords: Magnetic Field – Substations - Design – Transmission - Lines – IRPA Guides – Mitigation -

Measures-Precautions.

1. INTRODUCTION

Cairo the Capital of Egypt is characterized by high population density, highly increasing percentage in

annual electricity consumption and a limitation of unoccupied land areas suitable for new power

projects or even transmission lines (TL). This situation led to a very tight limitation for the right of way

clearances for both transmission lines and substations, either for the existing installations, due to the

movement of residence towards them, or to the new installations due to rare unoccupied land areas.

*Dr. Fatma Ahmad MoustafaMinistry of Electricity and Energy, 11517- Cairo, Egypt. E-mail: [email protected]

21, rue d'Artois, F-75008 Parishttp://www.cigre.org © CIGRÉ

Session 2004C4-201

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On the other hand, the worldwide concern to limit the magnetic field levels either for public or for

workers in power plants [1,2] and the rules set by the Egyptian Electricity Holding Company (EEHC) to

apply the IRPA guides for electromagnetic fields level for the new power projects and transmission

lines, necessitated that the issue of magnetic field level has to be managed and taken into consideration

[3]. The first step was to consider the matter in the design of all new substations and transmission lines

for all voltage levels. The second step was to conduct measurements for the magnetic fields inside,

outside and close to some substations, also under and at the vicinity of some high voltage transmission

lines.

2. DESCRIPTION OF THE SITUATION

The Egyptian unified power network includes voltage levels of 500, 220, 66 kV beside the primary

distribution voltage levels of 22 and 11 kV [4]. Cairo, the Capital city of Egypt has an area of 453 km

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and a population of about 16 million. All of these voltage levels are inclusively found in Cairo

substations and transmission lines (overhead and underground) ,of which are three substations of

voltage level 500/220 kV and 18 substations of 220/66 kV of voltage level with total capacity

10452.5 MVA, in addition to about 3500 Km of 220 and 66 transmission lines and underground cables.

The City network loads vary from 3200 MW to 4600 MW. Table (1) includes the substations of Cairo

and their capacities.

Some of these substations and transmission lines cross residential crowded areas where citizens live in

overpopulated neighborhoods with insufficient space that they live very close to a distance sometimes

less than the right of way width. These citizens may be subjected to magnetic fields of unacceptable

levels. In addition, workers in the substations and maintenance staff of transmission lines may also be

subjected to magnetic field of unacceptable level.

For this reason, the Extra High Voltage Research Center of the EEHC carried out a program for

measuring the magnetic fields in some critical sites. Four substations were chosen that exist in the most

crowded areas, Measurements were carried out in every place for each substation. Two of these are old

ones , the other two are newly built . These substations are:

1-Motamadia 220/66/11 kV– 625 MVA, operated in year 2000

2-Heliopolis 220/66/11kV– 475 MVA, operated in year 2000

3-Bassous 500/220 kV- 500 MVA, operated in year 1989

4-Cairo East 220/66/11 kV-450 MVA operated in year 1979.

Measurements were performed also under and at the vicinity of three sections of overhead transmission

lines, these are:

1-Bassous/Cairo West – of voltage level 500 kV

2-Cairo East/Sakr Koraish - of voltage level 220 kV

3-Bassous /Cairo North - of voltage level 220 kV.

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Measurements were also carried out in the residential area close to Motamadia substation.

Measurements were carried out during the months of July and August 2003 (Summer Season) at Hours

1 PM and 10 PM where loads are expected to be high in these hours in this season. The measurements

were repeated many times in different days (working days of the week). Measurements were performed

using the Magnetic Field Meter MFM 10 ELF, a portable Magnetic Field Meter of frequency range 5 to

2000 Hz. Measurements were taken at a height of 1 meter above the ground.

Table (1) Cairo Substations Capacity

No. Name of

substation

Voltage

kV

Capacity

MVA

No. Name of

substation

Voltage

kV

Capacity

MVA

1 Bassous 500 / 220 1 x 500 11 Metro 220 / 30 4 x 50

2 Abu Zabal 500 / 220220 / 66

66 / 11

1 x 5003 x 125

3 x 25

12 Wadi Hof 220 / 6666 / 6.6

66 / 6.6

3 x 1252 x 30

2 x 253 Tebbin 500 / 220 1 x 500 13 Tebbin South 220 / 66 3 x 125

4 Cairo North 220 / 6666 / 11

4 x 1255 x 25

14 6th October 220 / 6666 / 20

3 x 1256 x 25

5 Bahteem 220 / 6666 / 11

3 x 1253 x 25

15 Motamadia 220 / 6666 / 11

4 x 1255 x 25

6 Heliopolis 220 / 66

66 / 11

3 x 125

4 x 25

16 Saptia (2) 220 / 66

66 / 11

3 x 125

5 x 25

7 Cairo East 220 / 66

66 / 11

3 x 125

3 x 25

17 Basatin 220 / 66

66 / 11

4 x 125

7 x 25

8 Sakr Koraish 220 / 6666 / 11

3 x 1253 x 25

18 Katamia 220 / 6666 / 20

3 x 1253 x 25

19 Ein El Sera 220 / 66

66 / 11

3 x 125

4 x 20

9 Saptia (1) 220 / 66

66 / 11

3 x 125

5 x 301 x 12.51 x 10

20 Stad 220 / 6666 / 11

3 x 1253 x 25

10 Hadaba ElAhram

220 / 6666 / 11

4 x 1253 x 30

21 Cairo South 220 / 66 3 x 75

3. MAGNETIC FIELD EXPOSURE LIMITS

The International Radiation Protection Association (IRPA) has specified guides for the magnetic fields

exposure at power frequencies [1]. The Egyptian Electricity Holding Company (EEHC) applies these

limits in its specifications for the erecting of substations of transmission lines. These limits are shown in

Table (2):

Table (2) Specific levels for Magnetic Fields at Power Frequencies in IRPA

Few hoursµT

Long periodµT

Area

5000 maximumexposure duration is 2 hours per work days

500for whole working day

Occupational

1000for up to a few hours per day and can be

exceeded for a few minutes.

100for up to 24 hours a day

recreational areas, meeting grounds

General

Thus, the level of 100 µT is taken as a limit for maximum magnetic field exposure in the specifications

and design of EEHC.

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4. DESIGN CONSIDERATIONS

The Design Center of the Egyptian Rural Electrification Authority (REA) is responsible for carrying out

the following designs: (1) over head TL and towers for all voltage levels, (2) distribution substations up

to 66 kV and (3) Put the specification for the design of high and extra high voltage substations. One of

the main design considerations is the magnetic field levels inside, outside and adjacent to these

installations. Figures (1 & 2) are examples of tower designs for 500 kV and 220 kV levels [5].

Figure (1) Examples of 500 kV Tower

Design.

A) Erected in 1968

B & C) Erected in 1980

Figure (2) Examples of 220 kV Tower

Design.

D) Conventional tower

E) Compact Tower

5. MEASUREMENTS AND CORRECTIVE MEASURES

5.1. Substations

5.1.1 Measurements in Motamadia 220/66/11 kV-625 MVA Substation.

Motamadia substation is one of the newly built substations, operated in year 2000. It exists in a very

crowded area in west of Cairo to face the huge increased loads in the area and to decrease load

bottleneck in the west Nile area. The substation which is of a conventional type, was designed according

to the Egyptian requirements and specification, supplied and erected by an Egyptian company.

The high voltage section of the substation includes, four transformers 220/66kV-125MVA each and 6

feeders 220 kV connecting the substation to the network through underground cables. The mediumvoltage section includes five transformers 66/11 kV – 25 MVA each and 22 feeders 66 kV. The low

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voltage side of 11 kV includes 58 feeders. As mentioned above, measurements were carried out in every

place in the substation (28 point measurement) and repeated at variable times, most of the

measurements were low (much less than the 100 µT). Table (3) includes only those measurements of

magnetic fields that exceeded or were close to the limit of magnetic field in the IRPA guide (100 µT)

and the corresponding current passing in the circuits (cables, wires, TL transformers ..etc) .

Table (3) Magnetic Field Measurements in Motamadia substation

Place of Measurement M F

µ T

Current

A

At the terminal of transformer no. 3 - 66/11 kV at the 11 kV side. 95 1020

At the terminal of transformer no. 4 - 66/11 kV at the 11 kV side. 110 1110

5.1.2 Measurements in Heliopolis 220/66/11 kV-475 MVA substation.

Heliopolis substation also, is one of the newly built substations, operated in November 2000. It is

situated in a very crowded area in east of Cairo. The substation was established in this area to replace an

old substation which was incapable of facing the huge increased loads in the area. The substation which

is of a GIS type, was designed according to the Egyptian requirements and specification, however

supplied and erected by a foreign company under the supervision of the Egyptian personnel. The high

voltage section of the substation includes three transformers 220/66kV-125MVA each and 8 feeders

220 kV. The medium voltage section includes four transformers 66/11 kV – 25 MVA each and 15

feeders 66 kV. The low voltage side of 11 kV includes 35 feeders.Measurements of magnetic fields

were carried out in 51 spots in Heliopolis substation and repeated in different days. Table (4) includes

only those values which exceed the 100 µT and the corresponding current value.

Table (4) Magnetic Field Measurements in Heliopolis substationPlace of Measurement

(a & b are two circuits of a line)

M F

µ T

Current

A

point of cable 1 - 220 kV buried underground 299 250

point of cable 2 - 220 kV buried underground 784 782

point of cable 3 a- 66 kV buried underground 232 190

point of cable 3 b- 66 kV buried underground 221 190


point of cable 4 b- 66 kV buried underground 200 200 point of cable 5 a- 66 kV buried underground 268 180





At the terminal of the transformer no. 2 -66/11kV at the 11 kV side. 781 1020

At the terminal of the transformer no. 4 -66/11kV at the 11kV side. 263 990

5.1.3 Measurements in Bassous 500/220 kV-500 MVA substation.

Bassous substation, is in operation since 1989. It is situated in a very crowded industrial area named

Shoubra El Kheima. The substation is of a GIS type, was also designed according to the Egyptian

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requirements and specification, supplied and erected by foreign company under the supervision of the

Egyptian personnel. It includes one transformer 500/220 kV – 500 MVA, three feeders 500 kV and 18

feeders 220 kV. It is connected to other substations through one 500 kV TL, 9 over head 220 kV TL and

4 underground 220 kV cables. Measurements of magnetic fields were carried out in 38 spots in the

substation. Table (5) includes only those values which exceed the 100 µT and the corresponding

current value.

Table (5) Magnetic Field Measurements in Bassous substationPlace of Measurement M F (µT) Current (A)

point of cable1 a - 220 kV buried underground 219 550


5.1.4 Measurements in Cairo East 220/66/11 kV-450 MVA substation.

Cairo East substation, is in operation since 1979. It is situated in an industrial , commercial and

residential area in Nasr City. The substation is of a conventional type open air switchgear. It includes

three transformers 220/66 kV–125 MVA, three transformers 66/11 kV each 25 MVA,10 feeders 220kV,

15 feeders 66 kV and 11 feeders for future expansion. It is connected to other substations through 4 over

head 220 kV TL and 2 underground 220 kV cables. Measurements of magnetic fields were carried out

in 34 spots in the substation. Table (6) includes only those values that exceed the 100 µT and the

corresponding current value.

Table (6) Magnetic Field Measurements in Cairo East substation

Place of Measurement M F (µT) Current (A) point of cable1- 220 kV buried underground 481 390

point of cable 2- 220 kV buried underground 433 670

At the terminal of Transformer no. 1- 66/11kV from the 11 kV side 924 662



5.1.5 Comments on the measurements inside the four substations

• The magnetic field level inside the Motamadia substation was acceptable in general. No

corrective measures were required.

• Magnetic field levels inside the Heliopolis substation were acceptable except at the points of

cables' burial underground, where the values are extremely high.

Although that the substation staff are not allowed to be present in these spots, but a note was

sent to the substation managers to consider preventing the presence of any person in such spots

to avoid the exposure to high magnetic field level.

• The magnetic field leveld inside the bassous substation were acceptable in general, only two

points out of 38 were in a level a little bit high. These points were also at the entrance of the

cables burrying. In general, the substation is considered of acceptable magnetic field level. No

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corrective measures were applied, but an attention was given to the substation managers to

consider the matter.

• In Cairo East substation also, the high level of magnetic field appeared at the points of cables'

burial. Some values are considered high. A note was sent to the substation managers to consider

preventing the personnel from being in these locations.

5.1.6 Measurements around the Motamadia Substation 220 / 66 kV:

The substation lies in a residential and agricultural area. Two of its sides are adjacent to agriculture

land, one side to residential and the fourth side to traffic road. Measurements were carried out all around

the substation. The values were between 0.7 to 2 µT in the agricultural area, between 1.3 to 1.8 µT at the

residential area close to 220 kV feeder, between 3.8 to 4 µT at the residential area close to 66 kV feeder

and between 1.2 to 1.5 µT at the traffic road. All of these values are considered acceptable.

5.2 Transmission Lines Measurements and Mitigation

5.2.1 Mitigation Measures

The transmission Lines Cairo North / Bassous double circuit 220 kV was laying in a very crowded

residential area in the middle of Cairo. It was designed to cope with the load for a long period of

time. As the time passed energy consumption increased resulting in the increase of transformed

electric current, which in turn resulted in the increase of magnetic field emission from it. On theother hand, the residence buildings moved towards the transmission to a distance less than the right

of way in some sections of the line, and even in some critical sections right under the line. For the

sack of human beings protection, mitigation measures were carried out. A part of about 8 km of the

transmission line was replaced by an underground cable double circuit XLPE type.

5.2.2 Measurements under and at the vecinity of Transmission Lines

The purpose of the measurements is to check the suitability of the design of towers to the issue of

magnetic field. Three transmission lines were chosen:

1-Bassous / Cairo West 500 kV, single circuit, the three phase are in horizontal configuration with

three conductors in a bundle (tower B in Figure 1)

2-Cairo East / Sakr Koraish 220 kV, double circuits, the three phases are in vertical configuration with

two conductors in a bundle (tower D in Figure 2)

3-Bassous / Cairo North 220 kV, double circuits, the three phase are in vertical configuration with two

conductors in a bundle (tower D in Figure 2)

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Lateral measurements were taken at mid span between two towers in a direction perpendicular to the TL

rout every 5 meters starting from the TL center. The highest value measured for all of these over head

transmission lines were right under the outer conductor of the TL as in Table 7.

Table (7) Highest value of magnetic field measured under the Transmission Lines Transmission Line Magnetic Field µT

Bassous / Cairo West 500 kV 2.4

Cairo East / Sakr Koraish 220 kV 2.9

Bassous / Cairo North 220 kV 3.2

The right of way clearance in the Egyptian Law, for the different voltages, measured from the tower

center, is as shown in Table (8):

Table (8) Right of Way Clearance in the Egyptian LawVoltage (kV) Clearance from tower Center (m)

500. 220 25

66 13

211 5

5.2.3 Comments on the measurements of magnetic field:

Magnetic field levels under and at the vicinity of HV transmission lines mentioned above are low,

considered acceptable and does not require any modifications in the tower design.

6. CONCLUSIONS

1-Measurements of Magnetic field levels inside four High Voltage Substations (500 & 220 kV)

and at the Vicinity of three HV Transmission Lines (500 & 220 kV) in Cairo proved that the

design of these installations are suitable for this purpose and conform with the requirements of IRPA.

2-The Egyptian Law for Right of Way Width is quite sufficient to protect the citizens from the

magnetic field health hazards go through the surface of the ground.

3- High values of Magnetic field exist at the points of where underground cables. Instructions

were given to the substation managers to prevent the approach of any personnel to these

points.

7. REFERENCES

[1] Interim guidelines on limits of exposure to 50/60 Hz electric and magnetic fields, International

Non-Ionizing Radiation Committee of the International Radiation Protection Association, Health

Physics, 58, 113-122, 1990.

[2] B.J. Maddock, Standards for exposure to electric and magnetic fields at low frequencies,

paper 17, International Commission on Occupational Health, Paris, October 1992.

[3] Regulations for safety and health protection in the workplace for exposure to electric,

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magnetic or electromagnetic fields, Berufsgenossenschaft der Feinmechanik und

Elektrotechnik, June 1995.

[4] Annual Report of the Egyptian Electricity Holding Company (EEHC) 2002.

[5] The Egyptian Experience for Electric & Magnetic Fields and Radio Noise With Compact

and Traditional Towers- Cigre Session 1998.

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