ABB DCS550 Series, Manual

Page: 76 / 316

76
Firmware description
3ADW000379R0501 DCS550 Manual e e
Field Heating
Overview
Field heating (also referred to as “field warming and field economy”) is used for a couple of reasons.
Previous generations of DC-drives used voltage-controlled field supplies, meaning that the only thing the field
supply could directly control was the field voltage. For DC-motors to maintain optimal torque, it is important to
maintain the field current. Ohm’s law (U = R*I) tells us that voltage equals resistance multiplied by current. So
as long as resistance remains constant, current is proportional to voltage. However, field resistance increases
with temperature. Therefore, a cold motor would have a higher field current than a warm motor, even though
voltage remained unchanged. To keep the resistance and thus the current constant, the field was left on to
keep it warm. Then the voltage-controlled field supply works just fine.
The new generation of drives, including the integrated field exciter used with the DCS550, is current
controlled. Thus, the field supply directly controls field current. This means that field heating may no longer be
necessary when the DCS550 is employed.
Another reason field heating is used is to keep moisture out of the motor.
Use following parameters to turn on and control field heating:
−
FldHeatSel (21.18),
−
M1FldHeatRef (44.04)
Modes of operation
There is one mode of operation in which the field current will be at a reduced level, determined by
M1FldHeatRef (44.04). With FldHeatSel (21.18) = OnRun the field heating is on as long as On = 1, Run = 0
[UsedMCW (7.04) bit 3], Off2N = 1 and Off3N = 1. In general, field heating will be on as long as the OnOff
input is set, the Start/Stop input is not set and no Coast Stop or E-stop is pending.
On [UsedMCW
(7.04) bit 0]
Run [UsedMCW
(7.04) bit 3] Off2N [UsedMCW
(7.04) bit 1]* Result
0 x x field is turned off
1 0 1 reduced field current**
1 1 1 normal field current
1 1

0 1 normal field current, then reduced** after stop
1 x 1

0 field is turned off as motor coasts to stop and
cannot turned back on again as long as Coast
Stop is pending
*see Off2 (10.08)
**the field current will be at the level set by means of M1FldHeatRef (44.04) while motor is stopped
E-stop
A pending E-stop - see E Stop (10.09) - switches the field off. It cannot be turned back on again as long as the
E-stop is pending. If the E-stop is cleared while in motion, the motor stops according to E StopMode (21.04)
and then field and drive will be turned off.