Field Heating When In "Off"-State; The Purpose Of Emf Controller - ABB DCS 500B Description

Functional Software description
Field heating
when in "OFF"-
state
EMF_CONTROL
function block
The Purpose of
EMF Controller
60
The motor field can have a small value in order to avoid condensa-
tion when motor is in "OFF"-state. The function can be activated by
means of parameter:
FIELD HEAT SEL (914)
The used current references are the same as with the field reduc-
tion function:
F1 RED REF (1314)
F2 RED REF (1511)
The function is activated when command "ON" is 0, ie., the main
contactor is open. The function closes the field contactor.
U
I exc.
Field Weakening Point
Figure 44 Field weakening as a function of speed
The EMF-controller has two main control functions:
1. When the motor is run above the base speed, the EMF-
controller reduces the motor field to keep the EMF-voltage
constant at a maximum level. This must be done to avoid ar-
mature overvoltage and on the other hand, a maximum EMF is
needed to keep the FLUX as high as possible.
2. When an accurate torque controller loop is needed, the EMF
controller can be used to form an accurate FLUX value. The
application program in the DCS 500B calculates the required
value of the motor EMF at the used speed and used FLUX
reference. The EMF-controller then adjusts the field current so
that the measured EMF corresponds to the EMF-reference.
reference for the first motor
reference for the second motor in the
case of shared motion.
U armature
Excitation
Speed
DCS 500 Software Description