Siemens SINAUT ST7 - LTOP Line Transformer with Overvoltage Protection; Design

Mounting and Installation
6NH7811-0AA22 © Siemens AG 2002 All Rights Reserved
2-32 MD2 Modem (07/2002)
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 T
ransformer 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 Circuit diagram of an LTOP unit
Fig. 2-17 Location of circuit elements in an LTOP2 (viewed from above)
L1
L2
V1
T1
G1
G2
R1
Modem
Dedicated line
12
3
4
5
6
X1
X3
21
S2
S1
X2
21
12
12
X6
OPM
(1)
OPM
(2)
L1
L2
L3
L4
T1
T2