Eurotherm 584SV Series, Product Manual

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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 Eurothem Drives company.
•
Always use gold flash relays, or others designed for low current operation (5mA), on all
control wiring.
•
Remove all power factor correction equipment from the motor side of the Inverter before
use.
•
Avoid using motors with low efficiency and small cos ø (power factor) as they require a
larger kVA rated Inverter to produce the correct shaft kW.
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Although intended primarily for use with induction (asynchronous) motors, Inverters can also be
used for speed control of synchronous motors. Synchronous motors can offer economic
solutions in applications where tight control of speed is required together with the low
maintenance characteristics of an ac motor.
The two most common types of synchronous ac motor are permanent magnet and wound rotor.
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 can be kept constant by keeping the stator volts/frequency ratio constant, as with
an induction motor.
Torque is produced in the motor by an increase in load angle between the stator and rotor fluxes.
Maximum torque occurs when the load angle approaches 90
°
. If the load angle exceeds this
value then torque drops and the motor will stall. Systems involving synchronous motors need
careful design to ensure that the motor can accelerate the load and handle transient load changes
without stalling.
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Brake motors are used in applications requiring a mechanical brake for safety or other
operational reasons. The motor can be a standard induction motor fitted with an electro-
mechanical brake, or it could be a special conical rotor machine. In the case of a conical rotor
machine the spring-loaded brake is controlled by the motor terminal voltage as follows:
•
At rest the motor is braked.
•
When the motor is energised an axial component of the magnetic field due to the conical air-
gap overcomes the force of the brake spring and draws the rotor into the stator. This axial
displacement releases the brake and allows the motor to accelerate like a normal induction
motor.
•
When the motor is de-energised the magnetic field collapses and the brake spring displaces
the rotor, pushing the brake disc against the braking surface.
Inverters can be used to control the speed of conical rotor brake motors since the linear V/F
characteristic maintains the motor magnetic field constant over the speed range. It will be
necessary to set the FIXED BOOST parameter to overcome motor losses at low speed (see
FLUXING menu at level 3).