Siemens MICROMASTER 420 - Manual (Page 67)

Issue 07/04 3 Functions
MICROMASTER 420 Operating Instructions
6SE6400-5AA00-0BP0 67
I
1 1
2
U
12
3
U
1N
I
1N
Z
N
Z Z
I I I
3 2 1
= =
U 3 U U U
1Ν 31 23 12
⋅ = = =
Z 2
I
U
1
12 ⋅ =
3
Z
Z
Y 12,
∆ 12,
=
U
3
U
Y 12,
1
∆ 12,
=
I
1 1
2
U
12
3
I
12
Z Z
Z
I
3
1
I I I
1 31 23 12
⋅ = = =
U U U
31 23 12
= =
I
3
1
I
Y 1, ∆ 1,
=
Z
3
2
I
U
1
12 ⋅ =
Fig. 3-19 Star / delta circuit configurations
87 Hz characteristic
When a motor with a delta circuit configuration (e. g. V
N ∆ , motor
= 230 V) is fed from a
frequency inverter, where the rated voltage corresponds to the star circuit
configuration (e.g. 400 V frequency inverter), then it is important to proceed as
follows and observe the following:
The motor must have the appropriate voltage strength.
Above the rated motor frequency, the iron losses in the motor increase over-
proportionally. This is the reason that above this frequency, the thermal motor
torque should be reduced.
For the quick commissioning, the rating plate data for the delta circuit
configuration should be entered or the rating plate must be appropriately
converted.
The drive inverter must be designed for the higher current (delta circuit
configuration).
The 87 Hz characteristic is independent of the control type.
When using the 87 Hz characteristic, the mechanical motor limits must be
taken into account (refer to Catalog M11).
For the 87 Hz characteristic, the ratio between the voltage and frequency (V/f
characteristic) remain constant. This is the reason that the following relationships
apply:
P = power P
U
U
P
N∆
N∆
N1
N1
⋅ =
f
U
U
f
N∆
N∆
N1
N1
⋅ =
( )
n f f n
∆ N∆ N1 N1
p
min
s
60
+ −






=
f
f
N1
f
N ∆
U
U
N ∆
U
N1 f = frequency
n = speed
p = pole pair No.
(400 V)
(230 V)
(50 Hz) (87 Hz)
Fig. 3-20 V/f characteristic