Consider the following when designing or servicing your gear units

  • Mounting Position: The orientation of the gear unit determines the amount of oil. M1 contains the least; M2 and M4 contain the most. Whenever possible, design your system for M1.
  • Input Speed: The faster the oil churns, the higher the churning losses. Therefore, a gear unit with 4-pole motor (~1475 rpm) will run cooler than with a 2-pole motor (~2800 rpm).
  • Synthetic Oil: Synthetic oil is known to reduce friction by 25%, which can be significantly on worm gear units or large gear units. Synthetic oil allows the gear unit to run cooler, doubling the oil service life, which reduces your maintenance interval and costs.
  • Viscosity: The “thicker” the oil, the more resistance it has to flow and the more energy it requires moving. Always use the correct viscosity, considering the type of application and ambient temperature.

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The Truth about Premium-Efficient Motors

1. The motor is only part of the efficiency equation.

As you have seen, a motor is at best one-sixth of the total energy loss potential for an electro-mechanical drivetrain. And, what’s more, it typically isn’t even the most inefficient part. Mechanical devices, such as external transmission elements, have far more inefficiencies than electrical devices do. So, look there first to find your largest energy savings.

2. By revamping your entire drivetrain, you may actually be able to use a
smaller motor and save even more.

Right now, you are probably using a motor of a particular power rating to produce a certain output from your drivetrain. You may be pleasantly surprised to find that, by upgrading your gearbox, drive, and external transmission components, you will have gained enough efficiency that your motor power is now higher than you actually need. Therefore, you may be able to save additional costs by purchasing a lower horsepower motor. For example:

Before: 45 kW load ÷ 53.5% efficiency = 84.1 kW (use 90kW motor)

After: 45 kW load ÷ 72.5% efficiency = 62.1 kW (use 75kW motor)

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SPIROPLAN Right-Angle Gear Units

3. Motors are most efficient when integrated with other drivetrain components
from the same manufacturer.

Systems where the VFD, motor, and gearbox are all engineered by the same company are by nature designed to work well together, eliminating unnecessary inefficiencies and allowing additional energy savings. For example, integrating an SEW-EURODRIVE DRP motor, helical-bevel gear unit, and VFD will provide dramatically higher energy savings than simply replacing the motor.

4. The motor must be well-suited to your application.

Just placing a premium-efficient motor on the line may not automatically solve all your energy problems, even if all the other components are as efficient as possible. Ensure that the specifications of the motor fit your application, especially if you have a high-cycling application that is greater than 10 to 30 cycles/hour. If so, use a premium efficient motor designed for such an application with an appropriately sized integral brake.

Also, where possible, use the smallest motor for the application so that it is loaded near 80% and operates as close to it nameplate efficiency as possible.

5. Mechanical efficiencies matter, too.

Worm gear units, which are common in the industry, have an efficiency range of 50 to 88 percent, depending on the number of starts (teeth) on the worm gear or gear ratio, as shown below.

number of starts —– typical efficiency range
1                                        50-69%
2                                        70-79%
5                                        80-88%

Their poor efficiency is due to sliding gear contact. Since sliding produces friction, much of the energy is wasted through heat. Conversely, helical bevel gear units use rolling friction, so they lose only 1.5% of efficiency for each stage. Thus, a three-stage helical bevel gearbox is 95.5% efficient.

Although helical-bevel gear units are higher in initial cost, they will save money in energy over the lifetime of the system. If you are an end-user, consider specifying helical-bevel gear units the next time you purchase equipment for your plant. It is in your best interest.

6. Gearmotors eliminate even more efficiency losses.

Gearmotors inherently yield tremendous increases in efficiency compared to the average flexible transmission system. Since a gearmotor contains a motor that is rigidly coupled and precisely aligned with the gear unit, the connection is nearly 100% efficient. By eliminating the friction and slippage associated with v-belts, pulleys or chains, you can quickly yield a potential 12-15% increase in efficiency. You will save even more on the replacement and maintenance of belts. And, don’t forget about safety.

7. Oil may be costing you.

Oil plays a role in energy savings because it creates heat as it churns inside a gear unit. And, the amount of heat increases as the oil volume increases. Not only does heat increase your energy bill, it also damages gears and seals. Excessive heat is especially problematic for larger gear units – typically with an output shaft diameter greater than 60mm.

 

Common Premium-Efficient Motor Misconceptions

1. Efficiency automatically equals savings.

Not necessarily; it depends on the application. Current Australian MEPS requirements mandate that new motor efficiencies be as a minimum IE2 High Efficiency motor or IE3 Premium Efficiency with efficiencies based on AS1359.5:2004, which “roughly” aligns with the international IEC60034:30 standard on induction motor energy efficiency. The efficiency levels are typically based upon 80-100% loading with the motor connected to constant power source (i.e. across the line). So purchasing a High or Premium Efficiency motor from one manufacturer will very likely give you a motor with basically the same efficiency as a High or Premium Efficiency motor purchased from another manufacturer.

If you only install a premium-efficient motor, you are not automatically saving all the money you could be saving. There are multiple reasons why this might be possible, as discussed below:

  • Your new motor may only be a few percent more efficient than your previous motor. Therefore, in cycling or intermittent duty applications, the savings you recognize are so small that they are outweighed by the higher cost of the new motor.
  • Your new motor may not be well-suited to saving energy in your type of application, e.g. high-cycling applications.
  • Your new motor may be over-sized for the application, yielding much less efficiency than what the nameplate says.
  • Other parts of your drive-train may be much less efficient, causing higher-than necessary energy consumption from your efficient motor.

While a premium-efficient motor is important, it’s critical to evaluate your entire drive-train for efficiency and to realize that the motor is just a single part of the overall equation.

2. Replacing my motor will give me the best bang for my buck.

It depends. A motor is only one component in the drive-train (and, truth be told, motors for some time have been comparatively efficient). Each component in a system will inherently have some inefficiency and these energy losses multiply together to provide an overall system efficiency. Just one component with poor efficiency will quickly drag down the rest of the system. Consider the following theoretical example where every component has an almost-impossible efficiency of 99%:

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You’ll see that even in this example with 6 components of ideal efficiency, you are still
losing almost 6% of the energy.

Now, to consider two more realistic examples:

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You can see in both examples that you are losing over 42% of the energy going into the system. You can also see that replacing your motor with a premium-efficient model will save you just over 4% efficiency, even though the new motor is 7% more efficient that the old motor. That is because the other, less efficient components in your drivetrain are still wasting energy. Therefore, the investment you have made in a premium-efficient motor will take longer to recoup than you had planned.

3. Replacing my motor will automatically make my line more efficient.

Well, yes- but by less than you can expect. However, replacing some of the other components along with your motor can provide some very substantial efficiency gains. Consider, for instance, that you replace the gear unit as well as the motor. Worm gear units, which are installed in many manufacturing environments, are inherently inefficient, as the gears are essentially sliding against one another causing heat (energy loss). Sure, there are instances on which worm drives are necessary for the application (e.g. withstanding heavy shock loads, or providing back-driving resistance). But, in many applications a helical-bevel gear units, which operates with rolling contact, will be much more efficient.

Take the previous “real world” example and replace both the motor AND the gear unit.

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Now you are quickly recognizing substantial, double-digit efficiency grains- nearly 20%- and your line begins to become much more efficient.

To gain even more efficiency, consider changing or eliminating your transmission elements. Replacing a v-belt with a direct drive or use a shaft-mounted gear unit. Shaft-mounted units, such as the TorqLOC® from SEW-EURODRIVE, offers a keyless, taper hollow shaft with a shrink disc that has a liberal tolerance so it installs easily. It can even retrofit onto an existing keyed shaft.

4. A premium-efficient motor is an appropriate energy-saving choice for all applications.

Again, it depends. Most premium-efficient motors used in continuously-running applications will begin to show at least modest energy savings (depending, as previously shown, on the other elements in the drive-train).

But, motors used in high-cycling applications may never recognize the entire efficiency gain of a premium-efficient motor, due to the start-and-stop nature of the application fighting against the higher rotor inertia of many premium-efficient motors. Hence, the extra investment in a high-efficiency motor may not ever be completely recouped.

However, some Premium Efficiency motors, such as the DRP motor from SEW-EURODRIVE are engineered to make them more efficient in high-cycling applications. These motors are designed with low losses, and less heat accumulation in the windings, which increases efficiency and provides a very high number of starts and stops per hour.

Be sure that you consider all the options available to you, and be careful to choose the premium-efficient motor that is best suited to your need.

5. Adding a variable frequency drive (VFD) will automatically make my line more efficient.

Maybe. As the efficiency equation shows, a VFD is a load. It produces heat (losses) from electricity conversion, switching frequency, and harmonics. So by itself, it will decrease your system efficiency. What’s more, many VFD’s have an adjustable carrier frequency that reduces audible noise during operation. Unfortunately, when the carrier frequency increases, so does the heat. In fact, the heat produced as a high carrier frequency can be so significant that a room full of VFD’s may require a substantial increase in air conditioning.

Thus, the key to energy savings is to use a VFD to reduce other losses in the system (i.e. smart control), as in the following applications.

  • Regenerative Energy: When a motor is trying to stop a high inertia load or lower a load, it acts as a generator. All of the kinetic or potential energy stored in the machine has to be removed. All of the kinetic or potential energy stored in the machine has to be removed. Typically, it is wasted as heat through a braking resistor. But, a regenerative VFD can put the energy back onto the grid. Some even allow the energy to be directly given to another VFD as it accelerates, such as in a storage retrieval system.
  • HVAC: Typical systems used in HVAC contain mechanical dampers with motors that run continuously. Using a VFD to turn off the motor or to optimize the motor speed is much more efficient, especially since the load decreases more than four times at half the speed.
  • Soft Start: Using a VFD to control the acceleration on a cycling application lowers the motor starting current. So, the motor runs cooler since less energy is converted to heat.
  • Motor Efficiency Correction: Motor nameplate is usually rated at 80% loading. Therefore, when a large motor is applied to a small load (e.g. 1 kW used instead of 0.25 kW), its actual efficiency decreases considerably. Using a VFD with vector control (or VFC technology) optimizes the motor efficiency, regardless of the loading conditions.

The bottom line? If properly used, VFDs can have some big efficiency benefits when added as part of a complete drive-train efficiency solution.

Energy Efficiency Legislation Regulations

DOE & EISA Ruling Explained

In March of 2010, the DOE (Department of Energy) instituted a ruling that incorporates small motors into their Energy Efficiency Programs. The DOE, as required by law, is mandated to review the readiness of the Energy regulations based on current materials and manufacturing technologies. This SMR (Small Motor Efficiency Rule) includes motors that are described in the information below. This rule goes into effect on March 9th, 2015. Motors requiring outside agency approval, such as UL or CSA, have a 2-year extension
and need to comply by March 9, 2017.

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W22 Severe Duty Super Premium Electric Motor

In addition, in May of 2014, the DOE released communications with required expansions of 3 phase, single-speed, low voltage, integral HP motors, 1-500 HP to meet NEMA Premium efficiency levels, excluding some exceptions. This ruling expands current motor
regulation for motors that were not previously covered in the EISA 2010 regulations. These families of motors are also listed in the information below. This rule goes
into effect on June 1, 2016.

This new rule is predicted to save approximately 7 quads of energy and result in approximately $41.4 billion in energy bill savings for products shipped from 2016 – 2045. This rule is also predicted to reduce 395 million metric tons of carbon dioxide emissions.

FOR THE SMR, THE MOTORS THAT ARE IN SCOPE INCLUDE:

  • 2-digit frame numbers – 42, 48 and 56 frame motors and their IEC equivalent frame size motors
  • The Speed or Poles of the motors would include 2, 4 and 6 pole designs from 1/4 to 3 HP
  • Open construction motors that are either 3 phase (Polyphase), Cap Start – Induction Run or Cap Start/Cap Run designs
  • Continuous duty rated and also meet NEMA Service Factor

EXEMPTIONS TO THIS RULE INCLUDE:

  • Definite or Special Purpose OPEN construction design motors
  • Motor speeds that are outside of the 2, 4 and 6-pole speeds
  • Enclosed motors
  • Motor types that are not classified as being 3 phase, Cap Start – Induction Run or Cap Start/Cap Run
  • Intermittent duty motors as well as designs outside the HP and frame size listing as described above
  • Motors that are already covered by other efficiency legislation are also not covered by this rule

EISA Expansion Rule

The EISA (Energy Independence and Security Act) expansion and compliance rule, or sometimes referred to as the EISA Expansion Rule, expands the following list of motor designs to meet NEMA Premium efficiency: 1 – 500 HP, NEMA Design A, B & C (1 – 200
HP only today for Design A & B motors); IEC Design N, H, 8 Pole designs, enclosed 56 Frame IHP (1 HP and larger) that are either of General Purpose, Special or Definite Purpose design electric motors.

The Efficiency levels must meet NEMA Premium levels as listed in Table 12-12 (IE3 – 60Hz).

MOTORS NOW AFFECTED BY THIS EXPANSION RULE INCLUDE:

  • NEMA Design A & B motors from 201 to 500 HP
  • NEMA Design C motors from 1 to 500 HP
  • All voltages ≤ 600 volts
  • 8-pole motors
  • Electric motors with non-standard end-shields, flanges or shafts
  • Motors with moisture resistant windings, like encapsulated or sealed windings
  • Motors that use any non-standard mounting like a base or cradle
  • Motors that do not have a base or cradle footless designs
  • Partial designed electric motors but not rotor and stator sets
  • Vertical hollow shaft motors
  • TENV designed motors
  • JM and JP Pump motors
  • Electric motors having thrust or roller bearings
  • Integral brake motors
  • Motors with separately cooled blowers on them
  • Enclosed 56 frame 1 HP and larger – 56 Open motors are covered by the SMR
  • Gearmotors if the motor can be removed from the reducer and work as independent motor

EXEMPT MOTORS FROM THE 2010 EXPANSION RULE INCLUDE:

  • Fire pump motors
  • Liquid cooled motors
  • Submersible motors
  • Air over design motors
  • Component sets (stator, rotor sets)
  • Small electric motors below 56 frame – see SMR rules
  • Advanced Motor Technology motors which include PMAC, ECM, Brushless DC, etc.
  • Inverter duty only motors

What’s the Difference Between Spur, Helical, Bevel, and Worm Gears?

by Carlos Gonzalez

Gears are a crucial part of many motors and machines. Gears help increase torque output by providing gear reduction and they adjust the direction of rotation like the shaft to the rear wheels of automotive vehicles. Here are some basic types of gears and how they are different from each other.

Spur Gears

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Spur Gear

Spur gears are mounted in series on parallel shafts to achieve large gear reductions.

The most common gears are spur gears and are used in series for large gear reductions. The teeth on spur gears are straight and are mounted in parallel on different shafts. Spur gears are used in washing machines, screwdrivers, windup alarm clocks, and other devices. These are particularly loud, due to the gear tooth engaging and colliding. Each impact makes loud noises and causes vibration, which is why spur gears are not used in machinery like cars. A normal gear ratio range is 1:1 to 6:1.

Helical Gears

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Helical Gear

Helical gears have a smoother operation due to the angle twist creating instant contact with the gear teeth.

Helical gears operate more smoothly and quietly compared to spur gears due to the way the teeth interact. The teeth on a helical gear cut at an angle to the face of the gear. When two of the teeth start to engage, the contact is gradual–starting at one end of the tooth and maintaining contact as the gear rotates into full engagement. The typical range of the helix angle is about 15 to 30 deg. The thrust load varies directly with the magnitude of tangent of helix angle. Helical is the most commonly used gear in transmissions. They also generate large amounts of thrust and use bearings to help support the thrust load. Helical gears can be used to adjust the rotation angle by 90 deg. when mounted on perpendicular shafts. Its normal gear ratio range is 3:2 to 10:1.

Bevel Gears

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Bevel Gears

The image above shows two different configurations for bevel gears: straight and spiral teeth.

Bevel gears are used to change the direction of a shaft’s rotation. Bevel gears have teeth that are available in straight, spiral, or hypoid shape. Straight teeth have similar characteristics to spur gears and also have a large impact when engaged. Like spur gears, the normal gear ratio range for straight bevel gears is 3:2 to 5:1.

Spiral teeth operate the same as helical gears. They produce less vibration and noise when compared to straight teeth. The right hand of the spiral bevel is the outer half of the tooth, inclined to travel in the clockwise direction from the axial plane. The left hand of the spiral bevel travels in the counterclockwise direction. The normal gear ratio range is 3:2 to 4:1.

Hypoid gears are a type of spiral gear in which the shape is a revolved hyperboloid instead of conical shape. The hypoid gear places the pinion off-axis to the ring gear or crown wheel. This allows the pinion to be larger in diameter and provide more contact area.

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Pinion & Gear

The pinion and gear are often always opposite hand and the spiral angle of the pinion is usually larger then the angle of the gear. Hypoid gears are used in power transmissions due to their large gear ratios. The normal gear ratio range is 10:1 to 200:1.

Worm gears are used in large gear reductions. Gear ratio ranges of 5:1 to 300:1 are typical. The setup is designed so that the worm can turn the gear, but the gear cannot turn the worm. The angle of the worm is shallow and as a result the gear is held in place due to the friction between the two. The gear is found in applications such as conveyor systems in which the locking feature can act as a brake or an emergency stop.

 

5 Common Motor Myths

by Stephen Mraz

Electric motors are incredibly common in manufacturing and many engineers are well-versed in their operation and principles. But the average consumer, and even a few non-electrical engineers are unaware that what they think is true about motors and efficiency just isn’t true. Here are five of the more common myths about motors.

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Baldor 1-Phase AC Motors

1. Higher temperatures have little effect on electric motors. Properly designed motors fall into specific insulation classes. The class determines the motor’s maximum operating ambient temperature rating. That rating, which includes some level of load, accounts for the threshold temperature the motor should remain beneath. For each 18°F this threshold is exceeded, the motor’s life is cut in half.​

2. Frequent startups do not hurt a motor. If a motor is not designed for frequent starts, then subjecting it to them will shorten its operational life. The initial rush of starting current generates extra heat, which usually dissipates while the motor runs. But if the motor does not run long enough between starts, there’s no time to shed the extra heat and the motor could exceed its maximum operating temperature.

3. Power-factor corrections save a lot of energy. Power-factor correction can reduce energy use, but only by a small amount. So unless your utility requires power-factor correction or charges penalties for low power factors, improving it will not affect your electric bill. The amount of energy saved depends on several site-specific factors, including the mix of electrical loads connected to your meter, the type and length of conductors, and where power-factor-correction equipment is placed (i.e., closer to the meter or closer to the motor loads). However, even in extreme cases, it is unusual for electrical consumption savings to be greater than 2%.

4. High-efficiency motors save more energy than standard-efficiency motors. In fact, an induction motor’s operating speed is somewhat less than its synchronous speed. The motor turns at the synchronous speed if the motor shaft’s rotation matches the frequency of the ac electricity powering the motor. The difference between synchronous and actual speed is called “slip.” Many energy-efficient motors operate with less full-load slip or at slightly higher speeds than comparably sized efficiency motors.

For centrifugal fans and pumps, even minor changes in a motor’s operating speed translate into a major change in the imposed load and annual energy consumption. Fan and pump “affinity” laws indicate that horsepower loading on motors by centrifugal loads varies as the third power or cube of its rotational speed. So a small increase in motor speed of 20 rpm can cause a 3.5% increase in electrical load.

5. Soft-start equipment on big electrical motors cuts utility demand charges. Soft-start equipment can lower your utility bills, but it will not significantly reduce demand charges. When motors start, they draw an “inrush” of current, often five to six times the motor’s full-load running current. This creates heat, a motor’s enemy. Soft starters increase the voltage applied to motor terminals over time, and this limits the inrush current and reduces heat buildup. In doing so, soft starters extend motor lifetimes, in particular, for motors frequently stopped and started.

Demand charges from utilities, however, are not affected. If electrical kilowatt demand is measured and billed on your utility account, the electric meter measures the average kW consumed over each 15 or 30-minute period. In contrast, soft starters affect motors’ power draw over the course of just a few seconds. The motor’s lower power draw over that short period is insignificant compared to the time period when demand charges are calculated.