Here You Go.

You sent an electric motor out for repair. Now it is back.

What are all these tags that were not there before?

Good question! 

The idea of this article came to me when I walked past the motor shown in the image. I noticed lots of tags and badging on the motor. For a simple 125HP, 1800RPM Siemens motor we had a lot of visual aids on the motor. Many of these aids are standard from HECO. Others are a result of working with a specific client. So, who benefits from all these visual aids, or tags as we call them?

Are your electric motor bearings wearing out long before they should? The problem might be bearing fluting … and the good news is that there are ways to prevent it.

What is Fluting?

Fluting is a form of electrical damage suffered by electric motor bearings when alternating (AC) or direct (DC) current actually passes through the metal bearing. As the currents pass through the bearings, they can leave behind surface damage that results in premature bearing failure.

Electric motor bearings are supposed to provide support, reduce friction, and constrain motion so that it only occurs in certain directions (e.g., radial, axial). When they can't do that anymore, they need to be replaced. However, before replacing a bearing in one the electric motors or drive trains you are responsible for, you need to be aware of certain key factors that affect bearing suitability and have an understanding of the different types of bearings you may encounter.

The winding insulation on your electric motor has a major impact on its life expectancy and reliability, which means that using the wrong insulation class could be very costly. The best way to avoid this mistake is to be familiar with the basics of NEMA insulation classes.

Medium voltage drives (also called VFDs or variable frequency drive) are adjustable speed drives used to control the torque and speed of AC motors. The use of VFDs in industrial powertrains is increasing, in part due to a reduction in their cost and size. If you are in the market for a VFD or you need to replace one, there are certain basics that you need to know.

Basis for VFDs

The equation representing the relationship between power, voltage, and currents is extremely simple: P = VI, or power = voltage x current. From this simple relationship we can see that at a given power level, the voltage and current are inversely proportional. In other words, the higher the supply voltage, the lower the current draw will be.

For AC motors used in high-power applications, operating at a low voltage causes the motor to draw a very high current, resulting in higher energy usage, lower efficiency, and higher cost -- and none of that is good. However, based on the power equation we just discussed, we can see that the current draw can be reduced by increasing the voltage supplied -- and that is the basis for medium voltage drives.

Rotary encoders monitor the position and movement of electric motor shafts -- but how do they work?

And what kind do you need?

What is an Encoder?

An encoder is a device used to provide feedback to a control system by sensing a change in position. Rotary encoders work with electrical motors to sense rotational motion related to the motor shaft. Depending on the type of encoder used, they can provide information about change in position, absolute position, and even the speed of the shaft.

Encoders are invaluable to the small servo motors that function with great precision and accuracy in a 3D printer. They are just as critical to the massive motors used with cranes to lift heavy, cumbersome objects. In fact, encoders are found in just about every industry, from petrochemical to paper and pulp manufacturing.

Not all the motors in your facility may be larger motors, and size is not an indicator of how critical a motor may be to your processes. That's why at HECO we've made sure that we can repair and recondition small motors just as effectively as we can large motors.

Repairing Small Motors

Small motors, just like their larger counterparts, need repairs and those repairs aren't necessarily cheaper because the motor is smaller. That's why it's important to make sure you're making the right decision about who you want working on your small motors.

In another post, Electric Motor Repair vs. Replacement - How to Choose?, we talked about a steel company that was sending out 5HP, 1800RPM motor fans for repairs that cost an average of $3000 each -- and they needed about 54 repairs per year on these motors. Oh, and the lifespan of these motors was 6 months. It turns out that they considered these to be emergency repairs, which meant their repair vendor was simply fixing the motor as quickly as possible without regard to what was causing the repeated problems.

That is not a good plan, especially given the expected life of the motor. When there are repeated failures of the same type of motor, either the source of those problems needs to be sought out and addressed or the motor needs to be replaced.

Small Motors: Repair or Replace?

Sometimes it is more cost-effective to replace a smaller motor than it is to repair it. There are several factors that you should take into account when deciding whether to repair or replace an electric motor (small or large!), including ...

• What caused the motor to fail?
• How is old the motor?
• What is the size of the motor?
• What are the annual operating hours for the motor?
• What are the capabilities of your repair shop?
• What will the repair cost?

To be sure, size is a major factor in the choice to repair or replace. If the repair costs for a motor exceed 60 - 70% of replacement cost, then you should replace the motor.

One of your mission-critical motors failed and while it's out for repairs or rebuild, you installed a new one. There are no words to describe how you felt when that brand new electric motor failed, as well. You’ve got more downtime now, along with additional repair costs.

Why did that new electric motor fail?

A Historical Perspective on Motor Durability

Today's electric motors aren't made the same as they used to be: modern motors are made with less steel, many times not as much service factor, and sometimes they aren't as durable. These changes are actually reflected in the motor frame classifications. Back in 1954, U frame motor classifications were introduced with standardized dimensions. These motors were heavy, rugged, and reliable with the right maintenance. In fact, some would say that they were over engineered: more powerful and heavier than they really needed to be to get the job done.

Things to Consider When a New Motor Fails

If you’re trying to figure out why your new motor just failed, you should consider what happened with the previous motor, the environmental conditions, the operating conditions, whether the motor was installed correctly, and the common failure modes for electric motors.

Aerator and well pump motors can pose some special challenges -- and many times those challenges lead to premature motor failure. Here at HECO, we've learned how to address the challenges faced by electric motors used in wet environments using VPI (Vacuum Pressure Impregnation).

Well Pump Motors for a Pharmaceutical Company

Over twenty years ago, HECO started servicing electric motors for a local pharmaceutical company. One of the recurring issues they encountered was well pump motors that were failing within months of installation. We helped them track down the source of the problem: water was getting into the winding. Once that water got in, it caused the winding to ground and led to catastrophic motor failure. To remedy the damage, the motor would have to be rewound.

Rather than just settling for rewinding electric motors after they failed, our experts here at HECO decided to stop the problem for good. They took a new motor and insulated the windings using the VPI process as opposed to the traditional dip and bake. Once this new motor was installed, the premature electric motor failures stopped. The problem was completely solved and we managed to save our customer money and downtime.

That's when HECO started performing the VPI process on specialty applications on new motors -- not just motors in for repair and rewind. This approach successfully prevents this common type of winding failure and significantly extends the useful life of the motors used in applications such as well pumps.

You've got a electric motor in for repair and the repair shop indicates that your problem lies in the windings. Maybe when you are reviewing the quote you see the acronym VPI in connection with the rewinding process.

Before you sign off on the repair, you want to know what is involved with VPI or Vacuum Pressure Impregnation, and whether its a smart choice for your motor. If that's you, you've found the right place.

Why Motor Winding Insulation is Important

Insulation of motor windings / coils serves three key purposes:

• Insulate the windings from potential contaminants (electrical and physical)
• Dissipate heat generated by the windings
• Make the windings rigid and secure

These are all vital for efficient operation of your electric motor.