Electrical automation

Is a VSD Electrical or Mechanical ?

18 December 2017

In today's VSD market, the number of manufacturers and different models are constantly increasing to cater for the vast range of applications that they can be used for.  Therefore selecting a VSD to suit an application is becoming more important to ensure the required mechanical performance levels are achieved.

As a supplier of complete drive systems, Technidrive believe the first question should be: “What is the mechanical application?” or “What load on the motor shaft?

Is it a conveyor / fan / pump / crusher etc?

Does it require high torque at low speed?

What is the operating speed range?

What acceleration / deceleration rates are required?

Once we have established what performance is required, we evaluate the required electrical control and communication network etc.

Achieving the required mechanical performance to suit the application, combined with the optimised electrical control provides the benefits of improved efficiency, protection, lifetime and overall performance. For constant torque applications we recommend WEG Inverter models with Optimal Flux

Combining a WEG Variable Frequency Drive (VFD) with a WEG Motor results in Optimal Flux.

How? The design characteristics of a WEG motor are pre-loaded into the WEG VFD.  The Optimal Flux control algorithm increases motor flux at low speeds, thereby allowing the same torque to be developed with lower current.  The results are optimal motor flux at low speeds to produce full torque while minimising motor losses.

Why Optimal Flux was developed.

Historically variable speed, constant torque applications were driven by DC motors fed from DC variable speed drives.  The DC motors were typically cooled by a separately driven blower, allowing full load operation to very low speeds.  However, design factors typically limited the speed range to 20:1. In the 1990's, consumers migrated to AC motors powered by VFDs.

AC powered applications however were limited to variable torque applications due to cooling limitations on the available AC motors.  The air flow (cooling) from the shaft mounted fan is dramatically reduced as speed decreases.  If the loads were not also reduced as speed decreased, the reduced cooling would result in motor overheating.  As demand for VFD technology grew, motor designs were modified to provide adequate cooling at low speeds.

This was accomplished by up- sizing motors or by fitting a separately driven forced ventilation in place of the shaft mounted fan.

WEG developed Optimal Flux (patented) to specifically address the needs of constant torque VSD market.  Specifically, those applications with +/-0.5% speed regulation without an encoder and a speed range of 10:1. Optimal Flux allows the operation of WEG motors from a speed range approaching 5Hz upwards, without thermal damage and the need for speed feedback from a shaft mounted encoder, the fitting of forced ventilation to the motor or derating.

How does Optimal Flux achieve lower motor losses?

Most of the heat in motors is the result of losses.  If motor current can be reduced even slightly, the resultant losses are significantly reduced.

Variable torque loads inherently accomplish this since they require less torque (less current demand) as their speed is reduced.  Constant torque loads require full torque at low speeds.  Merely reducing the current would reduce both losses and torque, which would be unacceptable.  The design characteristics of WEG W22 motors are loaded into the CFW11 VFDs which allows the Optimal Flux® control algorithm to adjust motor flux at low speeds thereby allowing the same torque to be developed with lower current


What are the advantages of WEG VSD's and Optimal Flux?

. Doubled motor insulation life as operating temperature is reduced by approximately 11% (vs. Non-Optimal Flux Control VFD).  Typically, for each 10 degrees C of temperature reduction, motor insulation life is doubled.

. Elimination of motor & drive incompatibility as WEG has tested the drive and motor combinations under full load conditions.

. Single source customer support for motor and drive.

. Less down time resulting in cost savings.

. Elimination of costs associated with a separately driven fan, including the forced ventilation motor and starter, additional cable run to the fan motor, installation costs and the energy to operate it.

. Elimination of Output reactor for motor cable runs to 100m.

. Reduced spares and inventory.

. Reduction in energy use for both IE2 and IE3 designs

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