ABB REG316 4 Series - Page 246

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-208
E. Setting instructions
Settings:
Magnetic flux for enabling char. V/f-Setting
Reference value VB-Setting
Minimum operating time t-min
Maximum operating time t-max
10 values defining the inverse t [V/f = 1.05] ... t [V/f = 1.50]
time operating characteristic
Reset time t-Reset
The overfluxing function protects the iron cores of generators
and power transformers against excessive flux.
The magnetic flux is not measured directly. Instead the volt-
age/frequency ratio which is proportional to the flux and easier to
measure is monitored.
Overfluxing can result from either an increase of system voltage
or a reduction of system frequency.
For example, 10 % overfluxing at constant frequency is equiva-
lent to increasing the value of the V/f ratio to 1.1 VB /f
N
.
The limit curve for the maximum magnetic flux (V/f) permissible
for electrical machines is defined in
· standards
· data supplied by manufacturers.
Providing compensation using the reference value of the A/D
channel has not been made, the reference voltage VB for the
protection is calculated from transformer rated voltage U
TN
and
the v.t. rated voltages U
N1
and U
N2
as follows:
VB U
U
U
TN
N
N
=
2
1
The setting is the ratio VB/UN, where UN is the rated voltage of
the protection, otherwise “VB-Setting” would be 1.0 UN.
The overfluxing curve of the generator must be known in order to
set the times t-min and t-max and enter the table of 10 values
t [V/f = 1.05] ... t [V/f = 1.50].