4. HIGH-EFFICIENCY MOTORS

Consider specifying high-efficiency motors for new equipment and when standard motors require replacement or repair

The major advantage of high-efficiency motors (HEMs) is the energy savings they provide. They use from 1% to 4% less electricity than standard motors and are generally more reliable, last longer and result in lower transformer loading. HEM design enhancements include

• 20% to 60% more copper and up to 35% more high-quality electrical steel laminations
  
  
• lower loss rotor bar design
  
  
• optimized manufacturing methods and production techniques that reduce losses

Benefits of Choosing High-Efficiency Motors

• extended winding and bearing life
  
  
• increased ability to cope with short-term overloads
  
  
• capable of withstanding higher voltage fluctuations or phase imbalance

4.1 LIFE-CYCLE COSTING

Consider both initial cost and energy consumption over the life of the motor

Wherever possible, companies should try to purchase the most efficient motors available. When it comes to electric motors, the true measure of what the item will really cost is seen only when we examine both initial price and operating costs. A standard motor costing $2,400 may consume over $144,000 of electricity in a 10-year operating period. An equivalent HEM may cost 15% to 20% more but may save over 600% of its initial incremental cost during the same period. This results in a payback of about 1.5 years or less.

Purchasing High-Efficiency Motors (HEMs): Rules of Thumb

• specify HEMs for new installations operating more than 3500 hours per year
  
  
• select HEMs for motors that are loaded greater than 75% of full load
  
  
• buy new HEMs instead of rewinding old, standard-efficiency motors
  
  
• specify HEMs when purchasing equipment packages
  
  
• use HEMs as part of a preventive maintenance package
  
  

4.2 FEDERAL MOTOR EFFICIENCY REGULATIONS

Ensure that the motors you purchase exceed these minimum efficiency levels

Canadas Energy Efficiency Regulations for 1-hp to 200-hp polyphase, single-speed, NEMA design A or B induction motors, amended in December 2002, specify minimum energy efficiency standards for motors sold in Canada. The "vendor" — not the "user" of the motor — is responsible for complying with the Regulations.
Two classifications are addressed:

• Totally enclosed fan-cooled motors are used in dusty and corrosive environments. They use an integral fan for cooling.
  
  
• Open drip-proof designs draw ambient air through the motor for cooling. They are used in clean environments and will tolerate limited dripping liquids that strike the enclosure from any angle up to 15 degrees downward.

NEMA MOTORS – ENERGY EFFICIENCY STANDARD

POWER IN kW   HP	OPEN (PERCENTAGE)				ENCLOSED (PERCENTAGE)
	2-pole	4-pole	6-pole	8-pole	2-pole	4-pole	6-pole	8-pole
0.75    1	75.5	82.5	80.0	74.0	75.5	82.5	80.0	74.0
1.1    1.5	82.5	84.0	84.0	75.5	82.5	84.0	85.5	77.0
1.5    2	84.0	84.0	85.5	85.5	84.0	84.0	86.5 (85.5)*	82.5
2.2    3	84.0	86.5 (84.0)*	86.5	86.5	85.5	87.5 (84.0)*	87.5	84.0
3    —	84.0	84.0	86.6	86.5	85.5	84.0	87.5	84.0
37.5    5	85.5.	87.5	87.5	87.5	87.5	87.5	87.5	85.5
4    —	85.5	87.5	87.5	87.5	87.5	87.5	87.5	85.5
5.5.    7.5	87.5	88.5	88.5	88.5	88.5	89.5	89.5	85.5
7.5    10	88.5	89.5	90.2	89.5	89.5	89.5	89.5	88.5
11    15	89.5	91.0	90.2	89.5	90.2	91.0	90.2	88.5
15    20	90.2	91.0	91.0	90.2	90.2	91.0	90.2	89.5
18.5    25	91.0	91.7	91.7	90.2	91.0	92.4	91.7	89.5
22    30	91.0	92.4	92.4	91.0	91.0	92.4	91.7	91.0
30    40	91.7	93.0	93.0	91.0	91.7	93.0	93.0	91.0
37   50	92.4	93.0	93.0	91.7	92.4	93.0	93.0	91.7
45    60	93.0	93.6	93.6	92.4	93.0	93.6	93.6	91.7
55    75	93.0	94.1	93.6	93.6	93.0	94.1	93.6	93.0
75    100	93.0	94.1	94.1	93.6	93.6	94.5	94.1	93.0
90    125	93.6	94.5	94.1	93.6	94.5	94.5	94.1	93.6
110    150	93.6	95.0	94.5	93.6	94.5	95.0	95.0	93.6
132    175	94.5	95.0	94.5	93.6	95.0	95.0	95.0	94.1
150    200	94.5	95.0	94.5	93.6	95.0	95.0	95.0	94.1

* Energy efficiency standard percentage when using kW to measure power output.

These efficiency levels should be considered as a baseline when making a motor purchase. Depending on their size, HEMs are generally 1% to 4% more efficient than those that meet the minimum standards set out in Canadas Energy Efficiency Regulations.

4.3 MOTOR INSTALLATION AND APPLICATION CONSIDERATIONS

Changes in application can change the performance of the system

Power Factor

An induction motor requires both real and reactive power to operate. The real power (kW) produces work and heat. The reactive power (kVAR) establishes the magnetic field in the motor.

Induction motors are the principle cause of poor power factor. Electric utilities often levy a penalty for power factors that fall below a certain level, typically 90%. Some strategies for correcting poor power factor include

• minimizing operation of idling or lightly loaded motors
  
  
• ensuring correct supply of rated voltage and phase balance
  
  
• installing capacitors to decrease reactive power loads
  
  

Efficiency Gains Versus Motor Speed

A motors rotor turns slightly slower than the rotating magnetic field in the stator. The difference between these two speeds is called the slip speed. Standard NEMA Design B motors run with a slip of 3% to 5% at rated load. Some HEMs operate with less slip, resulting in a slightly higher full-load speed of 5 to 10 rpm. For centrifugal loads, even a minor change in speed translates into a significant change in flow and energy consumption. When replacing standard motors, select an HEM of the same or lower speed when possible. If necessary, adjust sheaves and pulleys to capture the full energy savings benefits.

Motor Sizing

Motor efficiency is fairly constant down to approximately 50% of rated load, below which it drops off quickly. Care should be exercised in leaving an adequate but not excessive safety margin. The motor should be sized for the peak load expected. Oversized motors can significantly increase costs since all electrical components must be sized to the motor rating. Using HEMs makes additional sense because they are more efficient across a wider load range than standard motors.

4.4 MOTOR POLICY

Develop a motor policy to help assure continued productivity and efficiency

The purpose of a motor policy is to help plant personnel manage their motor systems in order to minimize lost production time and expense. A motor policy has three distinct aspects: planning, replacement guidelines and repair procedures. The following information can help design a policy that is suitable to your needs. Values shown are typical industry norms.

Planning

Sometimes in trying to get a motor back into service as quickly as possible, decisions are made that satisfy the short-term goal but negatively impact long-term efficiency and motor life. Implementing a comprehensive motor policy can help avoid this situation.

• All motors operating one or more shifts per day should be inventoried, assigned an individual equipment number and catalogued. Records should include nameplate rpm and hours of operation.
  
  
• Spare motors should be inventoried and assigned an individual equipment number. Recorded information should include nameplate data and the application(s) for which the motor is suitable.
  
  
• A plan should be developed for replacing all motors, including the source (inventory, supplier and repair) and the type of replacement motor (HEM, standard, repaired).
  
  
• All motors to be discarded should be partially dismantled, with the nameplate removed to prevent reuse, and disposed of in an environmentally suitable manner.
  
  
• The purchase of motors and repairs should be conducted with a selected number of high-quality suppliers who provide value-added services to ensure lowest total cost.
  
  
• Motors supplied with new equipment must meet Canadas Energy Efficiency Regulations. The full load nominal efficiency must be equal to or higher than those shown on the table in Section 4.2. Motors must also be designed for the voltage and frequency in which they will operate.
  
  
• New equipment purchases should specify that HEMs are used.
  
  
• Motors will be ordered based on CSA-C390-98 test standards.

Repair or Replacement Guidelines

When a motor fails or burns out, maintenance personnel have three options to consider:

• the cost of rewinding considering the age of the motor, its general condition, the availability of a new motor and special mechanical and electrical features
  
  
• rewinding versus purchasing a new standard motor
  
  
• purchase of a new, high-efficiency motor

The following chart will help determine the replace/repair decision breakpoint.

Select the hours that the motor operates and draw a horizontal line until it intersects with the average electric cost curve. Then draw a line down until it intersects the motor size on the x-axis. Any motor size to the left should be replaced with a HEM; any motor size to the right should be rewound.

Motors to be Refurbished

• No motor with a defective stator core should be rewound. If the core cannot be restored to its original integrity, the motor should be replaced with an HEM.
  
  
• Motors that are 100 hp or larger with an annual operating time of less than 4000 hours should be rewound if core iron specifications are acceptable.
  
  
• Motors that are 50 hp or more should be rewound a maximum of three times, after which the motor should be replaced.
  
  
• All motors below the repair/replace breakpoint, as determined by the chart on page 15 (20 hp in this example), should be replaced with new HEMs and not be rewound.
  
  
• No standard efficiency motor should be rewound if the cost of the repair exceeds 60% of the cost of an HEM.

Repair Procedures and Specifications

• Motor repair shops should be EASA-Q or ISO 9000 registered.
  
  
• Companies may pay a nominal fee to shops for the testing, tearing down and quoting for a motor repair when a decision is made to purchase a new motor from another source.
  
  
• Repair the motor to its original design with respect to number of turns, winding design and coil configuration, wire cross-sectional area, bearing size and type and insulation quality.
  
  
• Damaged cores should be repaired or replaced.
  
  
• Stripping should occur in an oven with a water-quench temperature-suppression system with temperature not exceeding 400ºC (750ºF).
  
  
• The repair shop should endeavour to determine the cause of failure and report its findings.

Impact of Rewinding on Efficiency

The quality of workmanship and materials used in a motor rewind can vary significantly. The impact of a poorly rewound motor may not be immediately apparent; however, the results can include greater energy consumption and shorter life due to higher operating temperatures. When selecting a repair shop, consider its capabilities, experience and workmanship — not just the cost.

4.5 MAINTENANCE

An effective maintenance program affects reliability, performance and productivity

The purpose of maintenance is to keep equipment from failing prematurely, ensure optimum performance and minimize unscheduled downtime. Well-maintained machinery is also more energy efficient and exhibits lower frictional losses and decreased operating temperatures. The following sections cover major motor maintenance issues and make recommendations on servicing and testing.

Cleaning

Dirt attacks the insulation of a motor through abrasion and/or absorption. It can contaminate lubricants and damage bearings. Dirt buildup on the motor housing, fan and inlet openings increases the motors temperature, which reduces efficiency and shortens motor life.

Lubrication

Larger motors require periodic bearing greasing. One problem is over-greasing, which causes increased friction, leading to failure. Excess grease can be forced onto the windings, also causing failure. Clean the fittings before injecting grease in order to avoid contamination.

Vibration

A noticeable increase or change in motor vibration is an indication of a bearing problem, load imbalance, a bent shaft, a coupling misalignment or electrical irregularities. Incorrect belt tension and alignment can increase power consumption and decrease motor life.

Voltage Testing

Motors that operate outside a design range of plus or minus 10% of nominal voltage operate at decreased efficiency and have a shorter motor life. Unequal phase voltage can cause extremely large rotor currents, resulting in higher temperatures and dramatically increased motor losses. Measure and log the voltage at the motors terminals while the machine is loaded. Comparing measurements against established norms can help identify problems.

Insulation Testing

Resistance testing of critical motors on a routine basis is an important predictive test that can reveal degradation of insulation. Readings should be taken once or twice a year. Long-term trending provides a good picture of winding quality. Shown here are measured insulation resistance readings (upper graph), which are corrected to a common temperature base (lower graph), providing an accurate basis for comparison. In this case a significant downward trend occurs at the four-year mark. This motor should be removed from service and sent for a cleaning and "dip and bake" servicing, avoiding a full rewind and at about one third of the cost.