Optimizing Motor, Drives and Gearbox Systems to Ensure Best Performance and Total Cost of Ownership: Questions and Answers

William Finley answers questions about optimizing motor, drives and gearbox systems to ensure best performance and total cost of ownership.


William Finley, Chief Technology Officer, Drive Technologies, Siemens Industry, Inc.1. Q: Can Variable Frequency Drives be used as Soft Starters?

A: Yes.

2. Q: Have you done any retrofit projects, or are you more focused on new construction projects?

A: Yes, we have performed retrofit projects as well as new construction projects. An example of retrofit projects include: replacement of steam turbines with variable frequency drives and motors.

3. Q: Does it matter when a motor is located far away from the drive?

A: It does if drive is not equipped with output filter and have sufficient output voltage margin to compensate for voltage drop across long cables. Different topologies have different limitations. Perfect Harmony allows connection of standard (MG-1) induction motor at distance with total motor cable length up to 2200meters without using output filters of any kind.

4. Q: What is the usual HP range that might be cost effective to consider integrated drive systems as a retrofit measure with potential incentives for energy conservation from utilities?

A: We have a white paper discussing the topic, there is no recommended HP range, per se, but it depends on the application and duty cycle to come up with an exact energy savings dollar value.

5. Q: Is a fin-cooled the same as TEFC as shown on page 24?

A: Yes, it is the same.

6. Q: Let's presume that OEM is asking belt conveyor drive trains from Siemens. End customer has specified that the drive train has to be frequency controlled. OEM itself, when inquiring from Siemens, has no idea how the end customer is using his drive train-- which speed and so on. Question: Where the OEM could guess the way of usage (load spectrum)? Is there help for OEMs?

A: I could imagine all kinds of scenarios for conveyors and their duty cycles. Motors can be rated for constant torque throughout a speed range by over sizing the motor or added auxiliary ventilation. The motor and converter frequency controller can also support an overload condition for a short period of time. The OEMs can supply the duty cycle of the torque (load spectrum) and we (Siemens) can help in sizing the motor power rating and sizing of the converter.

7. Q: When motor is in very high and very low temperature how is driver function affected?

A: We have a white paper discussing the topic, design features may be required to protect the motor. For example, system de-rating may be required for high ambient temperature above 40 degree Celsius. Additionally, below 5 degrees Celsius special design modifications may be required to accommodate.

8.  Q: A question from Mechanical Drives (MD), concerning belt conveyors for mining. In general how much IDS is more accurately than earlier and save in his energy costs? You show that it depends on overloading (%) and kind of drives configurations (options)... please clarify it again. 

A: Siemens custom motors can be engineered to minimize full load current and AFD cost. Or voltage reduced to minimize the number of power cells. As a result, in either case the overall system cost is reduced. While minimizing the current may require raising the motor voltage to satisfy power requirements, many times this can reduce the size of the AFD without affecting the drive input voltage. Though the motor cost may increase a small amount this is normally small compared to the AFD savings

9. Q: Again from MD, which kind of gearbox types would be suitable for IDS?

A: It depends on the application and, to a lesser degree, the system design.

10. Q: What is the typical overspeed limit (%) when applying variable torque or constant torque loads?

A: Electrically, when a motor increases frequency past the base speed and the voltage remains constant, it is called constant horsepower. Overload or breakdown torques will decrease with an increased frequency in this range. A Typically an increase in frequency from 60 to 70hz will decrease the breakdown torque by 25%.

11. Q: In the presentation you mention a white paper available on VFD induced shaft currents and bearing currents. Where is this white paper available?

A: This white paper is available upon request. In the future, our sales force will be supplied these papers that will be available for any customer request. In addition, the papers will be published online and made available to customer through the Siemens IDS website.

12. Q: Are there some issues that we should care of if we connect a synchronous machine to a Voltage Source inverter IGBT based instead of an LCI converter?

A: With respect to Perfect harmony there are typically no issues in connecting 3 phase synchronous motor with AC excitation  previously operated from single channel LCI drive to voltage source Perfect Harmony VFD. Existing motor exciter powers supply compatibility may have to be reviewed and very require to be replaced with new exciter power supply which we can provide with VFD. Applications for dual channel LCI drives (2 windings motors) will have to be reviewed on case by case basis.

Also LCI drives have inherent regenerative capability when some voltage source drives do not. So requirement for VFD regenerative capability shall be considered when selecting VFD for the application.

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