04.05
3 - Description
Siemens AG 7VV3003-8TA74
ENGLISH 11
SICROWBAR 7VV3003 DC-Surge Suppressor Operating Instructions
Re 2. Selecting the maximum current , option G11
(Option G11 = high-speed de-excitation board)
Generally speaking, a distinction must be made between the following two cases:
a)
The device is only used for surge suppression (option G11 not required)
b)
The device is used for high-speed de-excitation (option G11 required).
Re a) The device is only used for surge suppression:
The SICROWBAR DC surge suppressor and dimensioned field discharge/discharge resistor form
one unit. Two general conditions must be considered for the purpose of dimensioning the resistor:
The maximum current that flows through the resistor should be lower than the maximum mean on-
state current of the thyristor (see selection table):
D
BOD
ENT
I
U
R
>
The falling voltage at the resistor with the superexcitation current I
S
should be lower than the
igniting voltage U
BOD
:
S
BOD
ENT
I
U
R
<
Re b) With option G11: The device is used for high-speed de-excitation:
The maximum current that occurs in the field circuit I
MAX
is calculated as follows:
E,N
E,N
MAX
I
2.6
I
2
1.8
I
⋅
≈
⋅
⋅
=
I
E,N
is the rated excitation current. To simplify matters, 3 I
E,N
is also used in the calculation. The time
characteristic of the current through the SICROWBAR device is approximately the same as that in
Fig. 1 in Section 3.5. The calculated I
MAX
must be less than the permissible I
MAX
(see Section 2.1).
Summary of Contents for 7VV3003-5AG32
Page 31: ......
