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04.05
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):
U
>
BOD
R
ENT
I
D
The falling voltage at the resistor with the superexcitation current I
igniting voltage U
U
<
BOD
R
ENT
I
S
Re b) With option G11: The device is used for high-speed de-excitation:
The maximum current that occurs in the field circuit I
=
⋅
I
1.8
MAX
I
is the rated excitation current. To simplify matters, 3 I
E,N
characteristic of the current through the SICROWBAR device is approximately the same as that in
Fig. 1 in Section 3.5. The calculated I
Siemens AG 7VV3003-8TA74
SICROWBAR 7VV3003 DC-Surge Suppressor Operating Instructions
:
BOD
⋅
≈
⋅
2
I
2.6
I
E,N
E,N
is calculated as follows:
MAX
is also used in the calculation. The time
E,N
must be less than the permissible I
MAX
3 - Description
should be lower than the
S
(see Section 2.1).
MAX
ENGLISH
11
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