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Mounting and Installation
2.3
LTOP Line Transformer with Overvoltage Protection
Introduction
Dedicated lines are highly susceptible to the coupling-in and carry-over of external
potentials. Coupling-in of external potentials may be inductive or capacitive, e.g. as
the result of lightning. Direct galvanic coupling is also possible as a result of
insulation faults.
The LTOP (Line Transformer with Overvoltage Protection) limits interference
voltage and overvoltage to a non-critical level. The floating transformer provides
electrical isolation in addition, thus preventing potential carry-over onto other
sections of the line.
2.3.1
Design
Protective Mechanism
The protective mechanism consists of a combination of components whose
functions supplement one another (see Figs. 2-16 and 2-17):
·
Overvoltage suppressors filled with inert gas as coarse protection (G1, G2)
·
Inductors which limit rises in current (L1, L2)
·
Metal oxide varistor as fine protection (voltage-dependent resistance; R1)
·
Transformer for electric decoupling (T1)
·
Suppressor diode to limit the secondary voltage of the transformer (V1)
Fig. 2-16
Fig. 2-17
6NH7811-0AA22
2-32
Dedicated line
L1
G1
G2
L2
Circuit diagram of an LTOP unit
2
1
OPM
(1)
L1
L2
Location of circuit elements in an LTOP2 (viewed from above)
Modem
T1
R1
V1
X6
2
1
OPM
T1
(2)
T2
L3
L4
1
2
3
4
5
6
X1
© Siemens AG 2002 All Rights Reserved
MD2 Modem (07/2002)
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