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Siemens 6RA70 Faq

Digital, compact units for connection to a three-phase ac supply.
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A&D LD CS 31 October 2007
FAQ for 6RA70 DC MASTER and SIMOREG CM
Question:
How can I manually record the field characteristic?
Answer:
The automatic optimization run P051 = 27 supports recording of the field characteristic. If this
routine cannot be used, the field characteristic needs to be recorded manually as described
below.
A field characteristic is required for motors which will also operate in the field-weakening
range. It must not be recorded for motors which will operate up to rated speed only.
Relationships:
The magnetic flux Φ is determined by the excitation current of the motor. When the excitation
current increases (up to its rated value), however, the flux Φ does not increase linearly
because the stator core becomes saturated. The relationship between the excitation current
and the flux is not linear and is represented by the field characteristic (magnetization
characteristic).
The induced motor voltage is the EMF of the motor.
EMF[V] = k * Φ * n[RPM]; the EMF reaches its rated value when the motor is operating at
rated speed. To prevent the motor EMF from reaching excessive values at speeds above the
motor rated speed, the flux Φ is reduced in this range and the EMF is regulated to a constant
value, i.e. the rated EMF value.
The following relation applies in steady-state motor operation: Ud – Id * Ra = EMF
Ud: Motor armature voltage, Id: Motor armature current, Ra: Armature resistance of motor
The maximum speed adjustment must be made before the field characteristic is recorded.
P741 for an analog tachometer or P143 for a pulse encoder. The maximum speed
adjustment must be made at a speed lower than rated speed.
The current controller and speed controller must then be optimized (Section 7.5 of Operating
Instructions). The field characteristic can then be recorded.
Recording of a motor field characteristic (magnetization characteristic):
To record the field characteristic, the magnetization characteristic is measured. This is done
by setting the field current setpoint
, starting at 100.0 % of the rated excitation current of
I
fset
the motor
, e.g. in the following increments: 91.0 %, 83.0 %, 76.0 %, 70.0 %,
I
field
rated
motor
65.0 %, 60.5 %, 56.5 %, 53.0 %, 50.0 %, 47.0 %, 44.0 %, 41.0 %, 38.0 %, 35.0 %, 32.0 %,
29.0 %, 26.0 %, 23.0 %, 20.0 %, 17.0 %, 14.0 %, 11.0 %, 8.0 %.
At a given speed, therefore, a specific actual EMF value
is measured at each actual
EMF
act
value of the field current. The actual speed value
at the individual measuring points is
n
act
not decisive, but it is important that the speed is maintained at a constant value for each
single measuring point.
The EMF value
for each measuring point is displayed in parameter r037. The actual
EMF
act
speed value is displayed in parameter r025.
1

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  • Page 1

    A&D LD CS 31 October 2007 FAQ for 6RA70 DC MASTER and SIMOREG CM Question: How can I manually record the field characteristic? Answer: The automatic optimization run P051 = 27 supports recording of the field characteristic. If this routine cannot be used, the field characteristic needs to be recorded manually as described below.

  • Page 2

    Φ The flux values normalized to rated flux which are reached at specific field current fset setpoints are determined according to the formula defined below from the actual EMF fset and speed values calculated and measured respectively and entered in a table of flux values. Φ...

  • Page 3

    The field characteristic can be plotted on the basis of the field currents and calculated normalized flux values entered in the table. The field current values corresponding to linearly graduated (in increments of 5%) flux values can then be read off this plot and stored in the field characteristic parameters P121 (field current at 5% flux) to P139 (field current at 95% machine flux) (see Figure 1 below for an example of a field characteristic plot).

  • Page 4

    EMF controller. Settings: P081 = 1 P117 = 1 P273.01 = 0 The motor rating plate: SIEMENS DC - Motor 1GG6286-0NG40-1VV1-Z No. N R7 1145783 010 001 / 2004 EN 60034 Wärmekl./Th.Cl. H...

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Simoreg cm

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