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Fault tracing
3ADW000379R0501 DCS550 Manual e e
The overload phase is calculated using M1LoadCurMax (31.10) and M1OvrLoadTime (31.11). The recovery
phase is calculated using M1RecoveryTime (31.12). In order not to overload the motor, the I
2
t-areas of
overload phase and recovery phase have to be identical:
timeeryreIItimeoverloadII
redanomanomaa
cov)()(
2222
max
∗−=∗−
In this case, it is ensured that the mean value of the armature current does not exceed 100 %. To calculate
the recovery current following formula is used:
)(
cov
22
max
2
nomaanomareda
II
timeeryre
timeoverload
II −∗−=
With parameters follows:
[ ]
222
%)100()10.31(
)12.31(
)11.31(
%)100( −∗−=
reda
I
After an overload phase, the armature current is automatically reduced / limited to I
a red
during the recovery
phase. The current reduction during the recovery phase is signaled by means of A108 MotCurReduce.
Field overcurrent
The nominal value of the field current is set with M1NomFldCur (99.11).
Set the overcurrent level by means of M1FldOvrCurLev (30.13). Exceeding this level causes F515
M1FexOverCur.
Armature current ripple
The current control is equipped with a current ripple monitor. This function can detect:
1. a broken fuse or thyristor
2. too high gain (e.g. wrong tuning) of the current controller
3. a broken current transformer (T51, T52)
The current ripple monitor level is set by means of CurRippleLim (30.19). Exceeding this level causes either
F517 ArmCurRipple or A117 ArmCurRipple depending on CurRippleSel (30.18).
Current ripple monitor method is based on comparing positive and negative currents of each phase. The
calculation is done per thyristor pair:
Current ripple monitor method
CurRipple (1.09) is calculated as abs (I
1-6
-I
3-4
) + abs (I
1-2
-I
5-4
) + abs (I
3-2
-I
5-6
). By low-pass filtering with 200 ms,
CurRippleFilt (1.10) is generated and compared against CurRippleLim (30.19).
Current ripple monitor calculation
Note:
The load influences the error signal CurRippleFilt (1.10).
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