Application Notes
13-1
631 Digital Servo Drive 07-01-08-02-E-V0500
13
A
PPLICATION
N
OTES
Application advice is available through our Technical Support Department, who can also arrange
for on-site assistance if required. Refer to Chapter 8: “Routine Maintenance and Repair” for the
address of your local Eurotherm Drives company.
•
Always use gold flash relays, or others designed for low current operation (5mA), on all
control wiring.
Controlling Synchronous Motors
Synchronous motors can offer economic solutions in applications where tight control of torque,
speed, position and high dynamics is required together with the low maintenance characteristics
of an ac motor.
The most common types of synchronous ac servo motors are
permanent magnet
types.
In contrast to induction motors, synchronous motors run at synchronous speed whether on full
load or no load. Synchronous speed is set by the frequency of the supply applied to the stator.
The stator flux is controlled by controlling the current phase vector. This is possible by using a
feed-back system which senses the rotor position, e.g. by Resolver.
Using Line Chokes
Line chokes are not required to limit input current to Eurotherm Drives Servo drives.
Line chokes may be used to reduce the harmonic content of the supply current where this a
particular requirement of the application or where greater protection from mains borne transients
is required.
Using Output Contactors
The use of output contactors is not recommended. However, if you are required to use output
contactors, we recommend that this type of operation is limited to emergency use only or in a
system where the drive can be inhibited before closing or opening this contactor.
Using Motor Chokes
Installations with long motor cable runs in the range of 50m may suffer from nuisance
overcurrent trips. This is due to the capacitance of the cable causing current spikes to be drawn
from the servo drive output. A choke may be fitted in the servo drive output which limits the
capacitive current.
Motor chokes may also be used to increase the value of load inductance in those cases where the
motor inductance does not reach the required minimum value.
Refer to Eurotherm Drives for more information.
