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POWER FREQUENCY MAGNETIC
FIELD MANAGEMENT IN POWER
DISTRIBUTION SUBSTATION
Prof. Ahmed A.HOSSAM-ELDIN
Prof. Ahmed S.FARAG
Electrical Engineering Department, Alexandria University -Egypt
Ibrahim K.MADI
Hanaa M.KARAWIA
Alexandria Electrical Distribution Company-Egypt
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
ABSTRACT
Levels of Electromagnetic Fields (EMFs) in
our environment have increased steadily
over the past 50 years.
 There are many ways to mitigate the
power frequency magnetic field (PFMF)
either by design modification of electrical
facilities and equipment, or by shielding
using Conductive shielding (Aluminum and
Copper) or Ferromagnetic shielding (mumetal).

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

In
this
paper
the
magnetic
field
management
was
applied
using
a
developed SUBCALC program, also the
magnetic field measurements were taken
at distribution substation with and without
shielding.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

Different shielding materials are used in
the measurements. The materials used
were 3% silicon steel, primarily used for
transformer core, mu-metal, and copper
sheets. These materials were placed just
adjacent to the transformer at the low
voltage side and measurements were
taken.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
The comparative results at each location
are presented.
 Comparison
between
the
different
materials is shown.
 A comparison was made between the
experimental results and the simulated
ones.

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
INTRODUCTION

In Egypt, it is usual, especially in dense
area, to locate distribution substation in
the ground floor inside buildings. These
locations are very close to the public and
to workplaces. Power frequency magnetic
field (PFMF) emitted will interact with the
living organisms and with the electronic
equipments
in
the
surrounding
environment.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
So, magnetic field management becomes
a very important aspect. Firstly, to
minimize the impact of possible health
effects of PFMF while maintaining power
system reliability, and safety.
 Secondly, when the PFMF is higher than 1
µT, it will produce interference with
electronic beam devices such as TV,
computer monitors, and industrial aspects.

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
MAGNETIC FIELD MITIGATION

There is a real demand for effective and
low-cost mitigation of extremely low
frequency (ELF) magnetic fields. Due to
these reasons, remarkable efforts have
been devoted to search for suitable
techniques
to
achieve
the
desired
reduction of magnetic fields generated by
distribution
substations.
Several
techniques have been applied to mitigate
the magnetic field.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

Intrinsic methods, when they act on the
basic factors affecting the field strength,
such as phase arrangement.

External shielding techniques, would
mean the use of shields made of
ferromagnetic or conductive materials.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Intrinsic methods
Magnitude of phase currents:
At power frequency,the magnetic field strength
is proportional to the phase current
magnitude. Line currents on substation
buses,
vary widely in both their
magnitudes and phase angles. Utilities
normally calculate magnetic fields using
estimated current magnitudes.
With
unbalanced currents the magnetic field
strength is greater than the balanced ones.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
A.
Frankfurt (Germany), 6-9 June 2011
Height of
Increasing
carrying
magnetic
B.
conductors above/below ground:
the height of the currentconductors will reduce the
fields at or near ground level.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Conductor configuration:
The magnetic field level in substation is the
sum of the fields produced by the currents
in all conductors and is dependent upon
the distance between the observer and
each current -carrying conductor. Placing
the three conductors as close together as
possible creates greater field cancellation
and the magnetic field at or near ground
level is reduced.
C.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
EXTERNAL SHIELDING TECHNIQUES

Field management can also be achieved
through the use of shielding materials. AC
magnetic shielding uses either conductive
materials or ferromagnetic materials.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
(I) Conductive Materials (flux cancellation)

Conductive materials (e.g. copper and
aluminum) act as a shield because
induced eddy currents produce a magnetic
field that opposes the main existing
magnetic field.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
(II)Ferromagnetic Materials (flux-shunting)

Ferromagnetic materials such as iron or
steel, shunts the magnetic flux. Iron and
steel have high permeabilities, but some
alloys such as mu-metal( which is a mix of
nickel, iron, copper and chromium) have
higher permeability. These alloys with
higher permeability are more effective
than just iron or steel but they are more
expensive.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
MEASURMENT AND SIMULATION CASE
STUDY

A typical indoor distribution substation for
a residential area which houses a
(delta/star) transformer rated at 1MVA
with 11kV circuit breakers and 3phase, 4
wire 380/220 V distribution panel as
shown in Fig.1. The Magnetic field
measurements were carried out at height
of one meter above the ground level and
the results are indicated in the measuring
grid of (0.5m×0.5 m) Fig (2)
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Fig.1. Low voltage panel
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
6
transformer
1000 kVA
95.59
4
5
3
1
2
37.7
LV
MV
29.91
1
37.75
Low tension Panel
164.3
145.7
64.16
61.98
68.78
28.32
24.52
173.9
29.69
18.63
87.32
28.37
15.94
2
16.88
12.33
3
90.39
48.9
48.32
24.68
20.77
12.77
14.21
10.68
12.11
8.181
4
9.101
7.63
5
29.23
16.14
9.403
8.495
7.793
6.464
6
Fig.2. The magnetic field measurement
inside transformer distribution substation
Frankfurt (Germany), 6-9 June 2011

The 3D representation is illustrated in
Fig.3.The currents measured during the
magnetic field measurement is of an
average value of 200A, and the neutral
current was 48.7 A. The measurements
were taken during the day.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Fig.3. 3D representation for the magnetic field
measurements
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

Magnetic Fields Modelling Program was
developed to model, simulate and
calculate the magnetic field at any point
on the grid. The program models the
power
frequency
magnetic
fields
substation.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

In this research, the program is used to
model the magnetic field in 11/0.4 kV
distribution substation. The magnetic field
output of the simulation program for the
same measured substations and for the
same loading conditions is also presented
in 3D format for the simulated output of
the substation model as shown in Fig.4.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Fig.4. 3D format for the magnetic field
simulation
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
COMPARISON BETWEEN MEASUREMENTS
AND SIMULATION RESULTS
 It can be observed that the simulation
profile agrees with the measurements
profile on the overall distribution of the
magnetic
field.
This
indicates
the
effectiveness of the developed program.
This good agreement will encourage us to
use the program in applying many
modifications in the LV cables and the low
voltage panel boards arrangements.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Management application

The developed program was used to find
out the effect of the new arrangements in
the distribution substation with the same
current loads. The new arrangements
were as follows:


Reduce the separation distance between the
LV cable side
Re-arrange the low voltage panel boards by
making the LV busbars in the same horizontal
level with lateral distance between phases of
5cm, instead of the vertical arrangement
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
These new arrangements are applied and
the simulated results are presented in 3 D
format as shown in Fig.5. The maximum
calculated magnetic field was 250µT, while
before these modifications the maximum
values was about 600µT.
 This means that we can reduce the
magnetic field emission without added
cost.

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Fig.5. 3D format for the magnetic
field simulation
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
External Shielding Experiments

Measurements were taken over the LV
cables trench before shielding and after
putting shielding and were compared for
the different materials used.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
sheets of electrolytic copper 1mm
thickness, and area 0.5×0.5 m2, with
conductivity σ=58×106 S/m, and Relative
Permeability μr=1.
2. Aluminum sheets 2mm thickness and
area 0.5×0.5 m2 ,σ= 38× 106 S/m, and
μr=1.
3. Low-loss
silicon steel with 0.5mm
thickness , 0.5×0.5m2, and μr = 1000.
4. and mu-metal 90µm thickness and area
Prof. Ahmed HOSSAM-ELDIN
Session 26– Paper
ID 0119
0.5×0.5m2,– Egypt
σ=– 2×10
S/m,
μr = 105.
1.
Frankfurt (Germany), 6-9 June 2011
Magnetic field measurement results were
taken along the z-axis at a different
heights of 0.5 m over the shielding
material. As shown in Fig.7
 To discuss the shielding effectiveness we
should calculate the shielding efficiency
(SE) which depends on the ratio of the
field measured at the point (x,y,z) for two
different circumstances with shielding and
without shielding.

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
measured magnetic field,µT
120
100
80
60
40
20
0
0.05m
0.5m
1m
1.5m
Hieght, meter
without shielding
cu
Al
µ metal
steel
Fig.7. The measurements before and after shielding
with different material
Frankfurt (Germany), 6-9 June 2011

For power frequency magnetic field
Shielding effectiveness the following
equation can be used:
SE  20 log
Where:


Bo
:
Bshielding
present.
:
Bo
Bshielding
dB
is the field without shield,
is the field when the shield is
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
Fig.8. illustrates the shielding efficiency for the
different used materials
distance, meter
1.5m
1m
steel
µ metal
0.5
Al
cu
0.05m
0.00
1.00
2.00
3.00
Shielding Efficiency,dB
Fig.8. Shielding efficiency results
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
4.00
Frankfurt (Germany), 6-9 June 2011
RESULTS AND DISCUSIONS

The results indicates that the magnetic
field measured is the highest one at
distance 1.5m. This is because in this
position the magnetic meter was adjacent
to the low voltage panel.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

The best shielding efficiency value was for
the low-loss silicon steel which reaches
3.81dB, then for the mu-metal
which
reaches 2.17 dB taking into consideration
that the mu-metal thickness was 90µm
and the low-loss silicon steel thickness
was 0.5mm.Their high permeability attract
the field lines.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
RESULTS AND DISCUSIONS

The shielding efficiency for Aluminum and
copper were the lowest values. The reason
may be because that the penetration
depth (δ at 50 Hz) for copper is 9.44 mm
and for Aluminum is 12.33 mm, while the
penetration depth in magnetic materials
(low-loss silicon steel or mu-metal) are
much smaller than that of aluminum or
copper.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

Therefore, it is common to regard
conductive flat shielding with thin nonmagnetic materials at power frequencies
as inherently inefficient (since any
practical shield would have thickness less
than the penetration depth δ)
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
CONCLUSIONS

This paper useds the developed SUBCALC
simulation program to find out the results
of the magnetic field managements by
rearranging the distribution substation
components.
These
applicable
managements gave the best reduction
values for the magnetic field exposure
without additional cost.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011

For the shielding experiment the obtained
results show that the use of low-loss
silicon steel give best shielding results,
then the mu- metal which is very thin
compared to the rest of the used materials
;but it has higher cost. Their high
permeability makes them attract the field
lines.
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
The conductive materials (copper and
aluminum)
are
not
good
shielding
materials for power frequency magnetic
fields.
 It is recommended to apply the intrinsic
method (no cost or low cost solution)
before external shielding which has higher
cost.

Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119
Frankfurt (Germany), 6-9 June 2011
THANK YOU FOR YOUR
ATTENTION
Prof. Ahmed HOSSAM-ELDIN– Egypt – Session 2 – Paper ID 0119