Selecting the right drives and motors for an industrial automation system may seem straightforward at first glance—but as any experienced engineer knows, it’s a decision with far-reaching impact on system uptime, operational cost, and long-term reliability.
This article summarizes practical selection principles for Siemens SINAMICS drives and motors, including cost-performance trade-offs, product positioning, and load matching strategies.
01 Drive Selection: G-Series vs. S-Series
Since the launch of the SINAMICS family, Siemens drives are available in three main series:
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V-Series (Basic) – V20, V50, V70, V90
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Affordable but functionally limited; rarely suitable for demanding industrial applications.
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G-Series (General Purpose) – G120, G120C, etc.
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Flexible, cost-effective, suitable for most production-level applications.
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S-Series (High-Performance) – S120, S210
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Designed for high-end laboratory, testing, or precision applications.
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Our selection strategy focuses on profitability, reliability, and system fit:
1️⃣ Cost-Performance Principle
We prioritize the drive with the lowest cost that meets all functional requirements.
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Example: For fan/pump variable torque applications, both G120 and G120C support SLVC vector control, standard function blocks, analog and digital I/O, and PID process regulation.
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If both meet requirements, we select the G120C due to lower cost, improving system ROI without sacrificing performance.
2️⃣ Product Positioning
Different series match different application levels:
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G-Series → factory-level control systems for production and inspection.
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S-Series → high-end laboratories, testing centers, and R&D facilities.
This strategy allows tiered solutions aligned with user budget and performance expectations, while maintaining system reliability.
3️⃣ Avoiding Drive Overload
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For variable torque loads → select light-duty rating
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For constant torque loads → select heavy-duty rating
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Motors may be overloaded within specification, but drives must operate below rated limits to prevent thermal accumulation and reduce failure risk.
Example: A 15 kW motor requiring 1.5x overload → select a 22 kW drive (light or heavy-duty) to ensure continuous full-load operation, as required in 400-hour nonstop endurance tests.
Key takeaway: Correct drive sizing ensures lifecycle reliability, avoids costly replacements, and maintains uptime.
02 Motor Selection: Matching the Load
A motor is the power execution element of any drive system. Selecting the wrong motor can result in:
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Oversizing → wasted investment and energy
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Undersizing → failure to achieve required performance, costly retrofit
Motor Characteristics
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Four-Quadrant Operation – motors can rotate forward/backward, motoring or generating.
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Control via Variable Frequency Drive (VFD):
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Up to rated speed → constant torque within rated torque
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Above rated speed → constant power up to maximum speed
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Asynchronous AC Motor – at very low speeds (<10% rated), torque output is transitional; avoid continuous operation in this range.
Load Characteristics
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Determine the speed-torque or speed-power profile of the driven load
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Motor must cover the load curve without leaving gaps
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If the load curve exceeds motor capability, the motor cannot control the load effectively
Example: Propeller Load
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Speed range: 3000–7500 rpm (constant power range)
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Max power < 22 kW → select:
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AC Asynchronous Motor: 22 kW rated power
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Speed: 0–3000 rpm constant torque, 3000–9000 rpm constant power
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Drive: G120 22 kW heavy-duty
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Graphical curves: Replace with “Refer to motor speed-torque and speed-power curves; ensure load curve fully fits within motor limits”
Overload Considerations
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Method assumes 100% load and continuous operation
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For intermittent overload cycles, apply the same principle adjusting for duty cycle
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VFD control maintains constant flux in the basic speed range; in the field weakening range, torque reduces proportionally to maintain constant power
03 Summary: Key Principles for High-Reliability Selection
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Balance cost and functionality – choose the lowest-cost drive/motor that meets performance
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Respect product positioning – match G-Series and S-Series to different application tiers
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Avoid overloading drives – consider motor overload only where permitted
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Match motor to load curve – ensure torque and power curves fully cover load requirements
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Ensure long-term reliability – continuous operation without thermal or mechanical stress
Bottom line: Drive and motor selection is a combination of engineering judgment, cost optimization, and lifecycle reliability planning. A well-selected system reduces maintenance, improves uptime, and maximizes ROI