IEEE Electrification Magazine - September 2016 - 46
3 kV dc
25 kV ac
Suspended Earthing Wire
Suspended Earthing Wire
IB
IB
IB
D1
D3
IB
JTS
IB IB
JB
JF
IB
Buried Earthing Wire
IB
IB
IB IB
D4
D2
D5
IB
Key
JST: Track Insulating Joint at ST
JB : Track Insulating
Joint at Border Post
JF : Track Insulating
Joint at Filter
IB: Impedance Bonding
Figure 5. An overview of a border post with the related earthing systems.
unwanted connections are present and bypass any
insulating joint, no disturbance variations are recorded.
Figure 5 reports reference values of ac current flowing
in a 3 kV dc system as a function of the effectiveness of
insulation of rail joints while a steady current of 100 A
flows in a 25 kV ac system.
Periodic Test
Achievements
After more than ten years of experience in placing into
service and managing the interconnection between the
different electric traction systems, the reference scenarios
are clearly identified (see Figure 8) in terms of the reduction of disturbances provided by the technical solutions
adopted by Rete Ferroviaria Italiana.
The benefits introduced by the different technical solutions can be summarized as follows:
xx
The parallel resonant filters practically suppress 50-Hz
currents through the rails and the contact line in the
sections where they are installed.
Z50Hz (Ω )
The filters installed in a 3 kV, as anticipated, are made
by an inductance and a capacitance connected in parallel to the track insulating joint and in parallel to the
OCL air gap. Starting from design values, inductance
can vary as a function of the location in which the
inductor is installed. Installation in the container (see
Figure 6) or the presence of a metallic path in the surrounding reactor can affect the related magnetic circuit
and, consequently, introduce a small deviation from
the inductance design value. For this reason, proper
tuning of the filter is required before it enters into service. The filter tuning is done by selecting the appropriate value of the capacity to be connected to the filter,
which can be between 2,450 and 3350 nF (2,900 + 350 nF)
with steps of about 15 nF.
The value of the capacity can be affected by several factors, like temperature or capacitor aging, etc. For this reason, a periodic inspection of the filter impedance value at
50 Hz is required at least twice per year. Taking into account
all the variables already presented, the typical value of the
impedance at 50 Hz is about 80-90 X (see Figure 7).
Track Filter
Inductor Box
46
Capacitors Box
Filter Impedance as a Function of Capacity Value
90
80
70
60
50
40
30
20
10
0
2,500 2,550 2,600 2,650 2,700 2,750 2,800
C (µF)
OCL Filter Inductor Box
Figure 6. An installation of a filter in a container on a double track
Figure 7. The typical values of filter impedance calculated at 50 Hz
line. (Image courtesy of RFI Technical.)
as a function of capacity value.
I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2016
Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2016
IEEE Electrification Magazine - September 2016 - Cover1
IEEE Electrification Magazine - September 2016 - Cover2
IEEE Electrification Magazine - September 2016 - 1
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IEEE Electrification Magazine - September 2016 - Cover3
IEEE Electrification Magazine - September 2016 - Cover4
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