Variable speed drives with Process performance motors
Squirrel cage induction motors offer excellent availability, reliability and efficiency. With a variable speed drive (VSD) – a frequency converter – the motor performance can be further improved.
Instead of running the motor continuously at full speed, the VSD enables speed adjustment according to actual need. The VSD makes it possible to control the process accurately and in some cases even to improve the capacity of the process by operating at higher than nominal speeds.
In contrast with conventional applications operating with a direct- on-line (DOL) supply, a VSD makes smooth starting possible. This significantly reduces the stress on the motor and driven application. Smooth starting also means that the supply network will not be affected by high starting current transients, a fact that can be taken into account in the design of the network.
The use of ABB industrial drives together with Process performance motors usually provides substantial energy savings as the speed and therefore the power required by the process can be optimized.
Process performance motors are designed for both DOL and variable speed operation. A wide range of options is available, so motors can be adapted to the most demanding applications. When selecting Process performance motors for VSDs, the following points must be taken into consideration.
ABB’s new generation process performance premium efficiency motors deliver maximum value over their entire life cycle. Their IE3 efficiency rating makes them an ideal environmental choice for motor users seeking to save energy and reduce their carbon footprint.
New levels of efficiency
Rising energy costs and increasing concerns about the environment are focusing attention on ways to further reduce energy consumption. Motor-driven systems account for 65 percent of all the electricity used in industry, giving motors a major role to play in efforts to reduce energy use. Cutting-edge design, quality materials and advanced manufacturing techniques make ABB’s process performance premium efficiency motors extremely reliable and energy efficient, even under the most challenging conditions.
Future-proof solution
ABB motors comply with the latest efficiency standards and requirements. ABB closely follows developments in the global regulatory environment and ensures that its products stay ahead.
Process performance premium efficiency motors with the IE3 efficiency rating already meet the requirements of the EU MEPS (European Minimum Energy Performance Standard). These motors are available now for delivery from stock.
Excellent all-round performance
Process performance premium efficiency motors offer enhanced operating performance, low starting currents, and an excellent torque curve. They produce less noise, are subject to lower mechanical stresses, and run cooler than less efficient motors. Cooler running is a big advantage. Reducing the temperature of the bearings and windings extends the lubrication intervals and increases the useful life of the motor. This translates into higher reliability, easier maintenance, and a longer life cycle – factors which reduce the overall cost of ownership. As a result, ABB’s process performance premium efficiency motors have longer warranties than many other types of motor. With an extensive range of accessories available, ABB’s process performance premium efficiency motors are particularly suitable for industrial and OEM use. They are ideal for all applications demanding efficiency and reliability, especially under challenging conditions.
1. Dimensioning
The voltage (or current) fed by the VSD is not purely sinusoidal.This may increase motor losses, vibration, and noise level. Further,a change in the distribution of losses may affect the motors temperature rise. In each case, the motor must be correctly sized according to the instructions supplied for the frequency converter.
ABB’s DriveSize program utilizes dimensioning rules that are based on comprehensive motor and drive type tests. Please use DriveSize for selecting the correct motor and drive combination for a desired load profile. In case of manual dimensioning, note that the loadability (or load capacity) curves provided in this catalog and in the respective manuals are indicative only. Values for a specific motor and drive are available on request.
In addition to thermal dimensioning, an adequate torque margin must be maintained for stability. The maximum torque of the motor must be at least 30 % higher than the load torque over the whole duty range. Voltage drop in the supply cable must also be taken into consideration, especially in cases where long supply cables are needed
2. Operating speed, vibrations and shaft seals
Process performance motors are designed to work over a wide speed range and also at significantly higher than nominal speeds. The maximum speeds can be found on motor rating plates or in DriveSize. In addition to motor speed, make sure that the maximum or critical speed of the entire application is not exceeded. If a particularly low level of vibration is required, motors with improved balancing (variant code 417) should be used. In high speed applications, the use of labyrinth seals (variant code 783) instead of V rings should be considered.
3. Ventilation
When the motor is operated at low speeds, the cooling capacity of the fan decreases, which again reduces the motor’s load capacity. A separate constant speed fan (variant codes 183, 422,514) can be used to increase cooling capacity. At high speeds, the use of metal fans (variant code 068) instead of plastic ones should be considered. If a low noise level is required, unidirectional low-noise fans (variant codes 044 and 045) are recommended.
4. Lubrication
In variable speed applications, bearing temperature varies as a function of speed and motor load. In such cases, the most accurate relubrication intervals can be obtained by measuring the bearing temperature under normal operating conditions. If the measured temperature is higher than +80 °C, the relubrication intervals specified on the lubrication plate or in the maintenance manual must be shortened, or lubricants suitable for high operating temperatures must be used. See ABB low voltage motor manual.
In case of continuous operation at very low speeds and at very low temperatures (below -20 °C), the lubrication properties of standard greases may not be sufficient, and special greases with additives are needed.
Operating temperatures also affect bearing life. When motors are equipped with sealed bearings, that is, bearings greased for life, it must be noted that if the operating temperature differs from the design temperature, the bearing life will also be different. More information on bearing lifetimes can be found in section Mechanical design of this catalog and in the relevant manuals.
The use of so-called conductive greases for elimination of bearing currents is not recommended because of their poor lubrication characteristics and low conductivity.
5. Winding insulation
To ensure that motors operate reliably, the effects of non-sinusoidal output voltages from the converter must be taken into consideration when selecting the correct insulation system for the motor and output filters for the converter.
The allowed phase-to-ground voltage peaks at motor terminals:
- 1300 V peak: standard insulation
- 1800 V peak: special insulation, variant code 405
The higher curve, Special insulation, applies to motors with special winding insulation for frequency converter supply, variant code 405. Standard insulation applies to motors with standard design.
6. Bearing currents
Bearing voltages and currents must be avoided in all motors to ensure reliable operation of the entire application. With ACS800 or ACS550 drives and uncontrolled DC voltage, insulated bearings (variant code 701) and/or properly dimensioned filters at the converter must be used. For information on other converter types, contact Sales. When ordering, clearly state which alternative will be used.
Common mode filters
Common mode filters reduce common mode currents and so decrease the risk of bearing currents. Common mode filters do not significantly affect the phase of main voltages on motor terminals. For more information, see ABB drives catalogs.
Insulated bearings
ABB uses bearings with insulated inner or outer races. Hybrid bearings, that is, bearings with non-conductive ceramic rolling elements, can also be used in special applications.
7. Cabling, grounding, and EMC
The use of a variable speed drive sets higher demands on the cabling and grounding of the drive system. The motor must be cabled using shielded symmetrical cables and cable glands providing 360° bonding (EMC glands, variant code 704). For motors up to 30 kW, asymmetrical cables can be used, but shielded cables are always recommended, especially if there are sensitive components in the driven application.
For motor sizes IEC 280 and above, additional potential equalization is needed between the motor frame and the machinery, unless the motor and the driven machine are installed on a common steel base. When a steel base is used for potential equalization, high frequency conductivity of the connection must be checked.
To meet EMC requirements, special EMC cables must be used in addition to appropriate cable gland mounting with special earthing pieces. Refer to ABB drives manuals for more information.
8. Motor loadability with frequency converter drives
These loadability curves can also be used for preliminary dimensioning of motors used at frequency converter duty, but it must be noted that the harmonic content and control algorithms vary between frequency converters, so the motor temperature rise will also be different. The curves show the maximum continuous load torque as a function of frequency (speed), which results in the same temperature rise as operation with the rated sinusoidal supply at nominal frequency and full rated load.
Normally, Process performance motors operate according to class B temperature rise. For these motors, dimensioning should be done according to temperature rise B curve, or the motor can be slightly overloaded. In other words, it can be dimensioned according to temperature rise F curve.
However, if only class F temperature rise with a sinusoidal supply is indicated for the motor in the technical data section, dimensioning must be done according to the temperature rise curve B.
If the motor is loaded according the temperature rise F curve, it will be necessary to check the temperature rise in other parts of the motor and ensure that the lubrication intervals and grease type