When buying an electric motor, the first things most buyers look at are power (kW), speed and efficiency class. Yet a motor's true value only becomes clear in how many years it runs without failure. IE5 synchronous reluctance motors (SynRM) stand out exactly here: the absence of permanent magnets and windings on the rotor means fewer failure points, a lower rotor temperature and therefore a longer service life compared to classic asynchronous or permanent-magnet motors. In this article we examine the lifespan of the IE5 synchronous reluctance motor, the concept of MTBF (mean time between failures), how the magnet-free rotor contributes to reliability, bearing life, drive life and total system reliability from the buyer's perspective. The aim is to judge a motor not only by the efficiency figure on its nameplate, but by the continuous uptime it delivers over its lifetime. (This article makes no fixed-price or numerical promises; the goal is to explain the right approach.)

IE5 synchronous reluctance motor magnet-free rotor, MTBF and longevity advantage

Why Is Lifespan Different in an IE5 Synchronous Reluctance Motor?

The main factor determining a motor's life is how fast its internal components wear. Winding insulation ages with temperature, bearings wear under grease and load, and the rotor is exposed to both thermal and mechanical stress. The advantage of the IE5 synchronous reluctance motor is that it eliminates some of these wear sources by design. The SynRM rotor has no conductor bars (unlike the cage of an asynchronous motor), no permanent magnets (unlike a PM motor) and no rotor windings. The rotor consists only of specially shaped laminations forming reluctance barriers. Since no current-carrying element rotates, rotor copper or conductor losses are almost zero, which means the rotor runs much cooler.

A low rotor temperature creates a chain of life advantages. A cooler rotor transfers less heat to the bearings through the shaft; cooler bearings mean slower grease degradation and longer bearing life. Likewise, the absence of magnets entirely removes the risk of demagnetization (loss of magnet strength) at high temperature. To understand the fundamental differences between asynchronous and synchronous reluctance technologies in more detail, the IE4 asynchronous vs synchronous reluctance comparison covers the topic in depth.

Magnet-Free, Winding-Free Rotor: Fewer Failure Points

Reliability engineering has a simple principle: the fewer moving and stressed parts a system has, the lower the probability of failure. The SynRM rotor is the concrete embodiment of this principle. In permanent-magnet motors, the magnet bond can weaken over time, magnets can crack under high temperature or shock loads, and partial demagnetization can occur. In asynchronous motors, rotor cage bars can break, especially under frequent starts and high inertia; this is a failure type often seen in the field. You can find the symptoms and causes of broken rotor bars in the broken rotor bar in asynchronous motors article.

Because the SynRM rotor has neither magnets nor conductor bars, these two large failure families are eliminated from the outset. The remaining main wear sources are the bearings, winding insulation and external cooling system; with good design and correct maintenance these remain long-lived. That is why the IE5 SynRM is increasingly preferred in continuous processes where uptime is critical. The IE5 synchronous reluctance vs PM motor article details the structural difference and helps clarify this choice.

What Is MTBF and Why Does It Matter in Motor Selection?

MTBF (Mean Time Between Failures) is a reliability metric showing how long, on average, equipment runs between two failures. A high MTBF means the equipment fails less often and therefore experiences fewer unplanned shutdowns. For a plant running continuous production, the stopping of a motor means the stopping not only of that motor but of the entire line; this is why MTBF directly relates to production loss and cost.

The factors that most affect a motor's MTBF are: winding insulation temperature, bearing operating temperature and lubrication condition, rotor mechanical strength, cooling system effectiveness and drive (VFD) compatibility. The IE5 SynRM offers an advantage in almost all of these. Because rotor losses are low, the total heat load is reduced; less heat protects both the winding and the bearing for longer. To correctly read all the information on the motor nameplate and assess data such as the temperature class that affects MTBF, we recommend reviewing the IE5 synchronous reluctance motor nameplate reading guide.

The Relationship Between Rotor Temperature and Bearing Life

Bearing life is the most frequently replaced component of a motor in practice and usually determines the motor's total life. Two main factors determine bearing life: mechanical load (bearing load, alignment, vibration) and thermal load (the temperature the bearing is exposed to). Grease roughly halves in life for every 10-15 degree rise in temperature; so a cooler-running bearing directly means a longer relubrication interval and longer bearing life.

The cool rotor of the IE5 SynRM plays a decisive role here. In an asynchronous motor the rotor heats up due to cage losses, and a significant part of this heat is conducted to the drive-end and non-drive-end bearings via the shaft. Since this loss is almost absent in the SynRM rotor, the bearings run at a lower temperature and the grease retains its function much longer. For selecting the right grease type, NLGI consistency and relubrication interval, the electric motor bearing greasing guide and, for general bearing-life quality markers, the bearing and bearing life in cast iron motors article are useful references.

Relationship between low rotor temperature and bearing life in IE5 SynRM

Winding Insulation, Temperature Class and Life

The most critical element determining a motor's electrical life is the winding insulation. The insulation material ages with temperature; the insulation class (F, H) and the actual temperature rise (for example ΔT 80K) determine how many years the insulation will last. As a general rule, when the continuous operating temperature is kept below the permitted limit, insulation life is significantly extended. Because the IE5 SynRM has low total losses, it reaches a lower winding temperature under the same load; this allows operation with a Class B temperature rise even when Class F insulation is used (an "F/B" design), providing an extra life margin.

To understand the effect of insulation class on life and the F/H difference in more depth, the winding and insulation class in IE3 motors article and the temperature rise class article are directly helpful. For plants wishing to continuously monitor winding temperature, the motor winding temperature monitoring article describes a practical investment that increases reliability.

Thermal Behavior and Heating in Drive Operation

IE5 synchronous reluctance motors always run with a variable frequency drive (VFD); they cannot be connected directly to the grid. This is both an opportunity and a caution from a life perspective. The opportunity: the drive keeps the motor running at the required speed and load at all times, preventing unnecessary heating and reducing mechanical stress with soft starting. The caution: high-frequency switching from the drive can cause bearing currents and shorten bearing life if correct filtering and grounding are not applied. You can find the thermal behavior of the SynRM and correct sizing in drive operation in the IE5 thermal behavior and cooling article.

Bearing currents and harmonic-induced extra heating are reliability topics to watch in every drive-fed motor. Shielded cable, EMC-compliant grounding and, where necessary, insulated bearings largely eliminate this risk. To go deeper, the VFD and harmonic-induced bearing current article and the motor grounding and EMC article provide a comprehensive framework.

Drive Life and Total System Reliability

The IE5 SynRM should be evaluated as a package: motor + drive. System reliability depends on the weakest link, so not only the motor's but the drive's life matters too. The main factors determining drive life are capacitor aging, cooling fan life, operating temperature and electrical stress. A well-ventilated panel, a correctly sized drive and regular dust cleaning significantly extend drive life. Drive supply voltage and DC bus selection also affect reliability; we covered this in the IE5 drive DC bus voltage and supply article.

Total system reliability also covers the mechanical connection alongside the motor and drive. Coupling alignment, foundation fixing and vibration level directly affect both motor and bearing life. For correct coupling selection and shaft alignment, refer to the flexible vs rigid coupling article, and for vibration acceptance values the ISO 10816/20816 vibration and balance article. You can see how the SynRM's already quiet, low-vibration operation contributes to life in the IE5 noise and sound level article.

Maintenance, Failure Management and a Longevity Strategy

Long life is achieved not only by buying the right motor but also with the right maintenance strategy. The maintenance burden of the IE5 SynRM is low because the consumable that needs replacing is basically limited to bearings and grease; there are no hard-to-repair components like magnets or cages. Still, regular vibration measurement, bearing temperature tracking and a greasing plan maximize MTBF. We detailed SynRM-specific maintenance and failure management in the IE5 synchronous reluctance motor maintenance article.

For a general motor maintenance schedule, the electric motor maintenance and periodic check schedule, and for early failure causes the electric motor lifespan and early failure causes article are complementary resources. If you want to compare total cost of ownership across efficiency classes, the IE5, IE4 and IE3 TCO comparison article makes the effect of lifespan on cost concrete. You can reach the IE5 ultra premium motor transition guide in our product range and all our electric motor solutions via our homepage.

Partial-Load Efficiency, Heat Load and Life

In real plants, motors often run below rated load, under variable load profiles. In applications like pumps, fans and compressors the load changes constantly throughout the day. One of the strongest aspects of the IE5 synchronous reluctance motor is that it keeps its efficiency high even at partial load. High efficiency at low load means fewer losses and less heat; less heat again extends winding and bearing life. This is not only energy saving but also a direct reliability and life advantage.

The point to watch here is correct sizing. A heavily oversized motor runs constantly at very low load, which lowers both efficiency and power factor. You can examine why the SynRM's partial-load efficiency curve is superior in the IE5 efficiency curve and partial load article. For selecting the right power margin and load ratio, the motor load ratio and correct sizing article offers a practical framework, and why oversizing eats savings is in the IE4 partial and low-load efficiency article.

How Long Life Reflects on the Purchasing Decision

A motor's price tag is only a small part of the total cost of ownership. In a continuously running motor, energy and maintenance costs far exceed the initial investment. The long life and high MTBF of the IE5 SynRM provide a two-way gain in this equation: both energy loss decreases and unplanned downtime and spare-part costs fall. In a plant running continuous production, the cost of a single unexpected motor stoppage is often far higher than the motor itself.

For this reason, in critical applications the purchasing decision should be made not only on power and price but on lifespan, MTBF, maintenance burden and total cost of ownership. To clarify the investment decision between efficiency classes, the IE5 vs IE4 investment payback article and the above-132 kW IE5 investment article are resources to consult. For critical spare-motor planning, the critical spare motor list article rounds out your reliability strategy.

Frequently Asked Questions

Is the IE5 synchronous reluctance motor's life really longer than an asynchronous motor's?

By design, the SynRM rotor has no magnets or cage bars, so rotor-related failures are largely eliminated and the rotor runs cooler. Lower temperature extends bearing and winding insulation life, which in practice means higher MTBF and fewer unplanned shutdowns. Actual life is still determined by correct mounting, alignment, maintenance and drive compatibility.

Can I request the MTBF value when ordering?

Yes. For continuously running critical applications, it is advisable to request the expected bearing life (L10), insulation class and temperature rise data before ordering. These data provide a realistic estimate of the motor's uptime. If you share your requirement with us, we will determine the suitable range together.

If the drive fails, does the IE5 motor keep running?

No; the synchronous reluctance motor cannot be connected directly to the grid and must run with a drive. Therefore, in total reliability, the drive must also be correctly sized, well ventilated and, in critical plants, redundant. System reliability is maximized by considering the motor and drive together.

Get a Quote

Let us plan together the IE5 synchronous reluctance motor solutions that offer high MTBF and long life for your continuously running plant. For the right power, speed and drive matching for your application, you can reach us at +90 (532) 345 49 86 or create a request via our contact page.

Purchasing and Selection Checklist

  • Clarify the daily/annual operating hours and continuity requirement of the application (MTBF is critical in continuous processes).
  • Define the required power (kW), speed range and load profile (constant/variable torque).
  • Request insulation class (F/H), temperature rise (ΔT) and expected bearing life (L10) data.
  • Evaluate the motor + drive as a package; plan drive sizing and panel ventilation.
  • Prevent bearing-current risk with shielded cable, EMC grounding and, if needed, insulated bearings.
  • Check coupling alignment, foundation fixing and vibration acceptance values before mounting.
  • Add grease type, relubrication interval and temperature monitoring (PT100/PTC) to the maintenance schedule.
  • Settle lead time, warranty and spare-motor strategy during procurement.