Specifications

U.S. Electrical Motors
Specification Guide
841 PLUS® to IEEE 841 STANDARD 841- 2001 (Revision of IEEE Std 841-1994)
Severe Duty - Totally Enclosed Fan Cooled (TEFC) Squirrel Cage Induction Motors – Up to and including 500 HP

SCOPE

This standard applies to high efficiency efficient totally enclosed fan-cooled (TEFC) horizontal and vertical single speed, squirrel cage, polyphase induction motors, 1 through 500 HP, in NEMA frame sizes 143T and larger for severe duty applications.

1 PURPOSE

1.1 The purpose of this standard is to cover the requirements that deal with mechanical & electrical performance, electrical insulation systems, corrosion, and electrical & mechanical testing for the US Motors line of 841 PLUS motors which have been designed to exceed the requirements of IEEE Standard 841-2001.

2 RATINGS

2.1 841 PLUS motors are 3 phase induction machines rated continuous duty at 60 HZ, single voltage with across-the-line full voltage start. Dual voltage motors are acceptable only for 2300/4000 volts. 

2.2 Production motors are available in 143T through 5811 frames at speeds of 3600, 1800, 1200, and 900RPM. 

2.3 Stock motors are available in 143T through 447T frames 1-200HP at speeds of 3600, 1800 and 1200RPM, 460 and 575 volt designs. 

2.4 Motors comply with the frame size assignments of NEMA MG 1 –1998 part 13. 

2.5 All motors have 1.15-service factor.

3 ENCLOSURES

3.1 Motors are TEFC and have a degree of protection of IP55 on 143 to 5811 frame. Motor bearings have a degree of protection of IP56 via the use of a non-contact bearing isolator.

4 SERVICE CONDITIONS

4.1 Motors are suitable for continuous duty operation without derating under the following service conditions:

4.1.1 Exposure to ambient temperatures from -25C to 40C 

4.1.2 Exposure to altitudes up to 1000meters (3300feet)

4.2 Suitable for use in indoor or outdoor applications involving severe duty conditions such as high humidity or chemical laden, corrosive or salty atmospheres.

4.3 Motors are capable of successfully accelerating inertia loads equal to what is specified in section 12.54 of NEMA MG 1-1998. 

4.4 Variable Frequency Drive (VFD) or Full voltage, across-the-line starting.

5 ELECTRICAL DESIGNS

5.1 Motors are NEMA Design B as defined in  NEMA MG 1-1998 part 12. 

5.2 Motors operate successfully at rated load under the combinations of voltage and frequency variations specified in sections 14.30 – 14.36 of NEMA MG 1-1998. 

5.3 Motors operate successfully under running conditions at rated load and frequency when voltage unbalance at the motor terminals does not exceed 1%. 

5.4 Motors are premium efficient designs that exceed the efficiency values in Table 1 of IEEE Standard 841-2001. Efficiency testing is done in accordance with IEE standard 112-1996. The nominal efficiency, ¾ load efficiency and guaranteed minimum efficiency are stamped on the motor's nameplate.

5.5 841 PLUS motors utilize a non-hygroscopic, chemical and humidity resistant insulation system. The thermal rating of the system is Class F as defined in section 1.66 on NEMA MG1-1998. 

5.6 The stator windings for 1-200HP and under 600 volts are random or form wound with copper wire utilizing US Electrical Motors' Insulife 2000 and Inverter Grade Insulation system that meets and exceeds NEMA MG1-1998 Part 31. 

5.7 Stator is double dipped and baked in varnish to form a heavy build that exceeds the test criteria of moisture resistance per NEMA MG-1. 

5.8 When operated at rated horsepower, voltage and frequency, the temperature rise of the stator winding does not exceed 80C when measured by winding resistance. 

5.9 Motors shall utilize the US Electrical Motors Inverter Grade insulation system, which consists of at a minimum Class F or better insulation materials with additional phase insulating material, extra end-turn bracing and Class H spike resistant wire. The resultant system shall withstand 2000 volt transients without premature motor failure and have no cable limitations in motor application.

5.10 Motors shall operate successfully under inverter running conditions at rated load with variation in the voltage or the frequency not exceeding the following conditions:

5.10.1 +/-10% rated voltage at rated constant volts/hertz ratio except for specific torque boost situations. 5.10.2 Motors shall operate successfully under running conditions at rated load and volts/hertz ratio when the voltage unbalance at the motor terminals does not exceed one percent.

5.11 Inverter Operating Characteristics - With rated volts/hertz ratio applied, motor performance shall be as follows for critical operating characteristics:

5.11.1 Torques - Motors shall meet or exceed the minimum locked rotor (starting) and breakdown torques specified in NEMA Standard MG1 Part 12 for Design B for the rating specified when on sine wave power. 

5.11.2 Currents - Locked rotor (starting) currents shall not exceed NEMA Design B values for the specified rating on 5:1 constant torque or less and variable torque motors. NEMA Design A values are allowed for 6:1 constant torque or higher value constant torque rated motors. Motors shall be capable of a 20 second stall at six times full load current without injurious heating to motor components.

5.12 Motors shall be rated for a 1.15 service factor on sine wave power and 1.0 service factor on VFD power in a 40C ambient.

6 MECHANICAL DESIGN

6.1 Motors are equipped with ball bearings or roller bearings to meet the requirements of 6.5 below. Ball bearings have AFBMA C/3 clearances and shall be the same size on both ends (with exception of 440T frame - minimum 6318 on Drive end bearing). 

6.2 Bearings are regreasable without disassembling the fan or fan cover and provide for the elimination of purged grease through fittings extending beyond the fan cover. Polyurea thickened grease is supplied. 

6.3 Inner bearing caps are provided for bearing retention and to prevent harmful amounts of lubricant from entering the motor interior. 

6.4 For direct coupled motors, stabilized bearing temperature shall not exceed a temperature rise of 45C for 4 and 6 pole motors and a maximum temperature rise of 50C for 2 pole motors as measured by a thermocouple on the surface of the bearing house.

6.5 Bearings provide for an L-10 life of 50,000 hours per ABMA 9-1990 or  ABMA 11-1999, as applicable based on NEMA belting application limits per NEMA MG1-1998, section 14.42.

6.6 Horizontal motors are modifiable to accommodate oil mist lubrication. The insulation system and motor leads are compatible with mineral oil. 

6.7 Enclosures have a degree of protection IP55 (per NEMA MG1-1998 part 5). Bearing isolators are provided on both ends of all 143 to 5811 'T' frame motors to minimize entrance of moisture and contaminants into the bearing chamber.

6.8 Condensation drain holes are provided at the low points in the end brackets and are supplied with corrosion resistant, breather drain plugs. 

6.9 Frame, brackets, fan cover and conduit box are a minimum of grade 25 cast iron. 

6.10 Rotor cage construction shall be of cast aluminum. The maximum permissible shaft runout at the end of the shaft extension of the assembled motor shall be:

6.10.1 0.875" to 1.625" diameter inclusive TIR < 0.001 6.10.2 Over 1.626" to 6.50" diameter, TIR, 0.0015 (ball bearing) and, 0.002 (roller bearing)

6.11 Motor mounting feet, when placed on a flat granite surface, shall not exceed 0.005" between the granite surface and the motor feet at each mounting bolt hole. 

6.12 A drilled and tapped hole is provided in the motor frame on the same side as the conduit box for grounding purposes. Motor frame feet are flat within 0.005 inch as an assembled unit.

6.13 Ventilating fans are of non-sparking conductive plastic material. Most ratings use bi- directional fans. On ratings where uni-directional fans are used, the rotation of the fan is indicated by a permanent label on the outside of the motor. 

6.14 Conduit box is diagonally split, rotatable in 90 degree increments, and exceeds requirements for  NEC minimum volume.  A ground lug is provided in the box. Gaskets are provided between the conduit box and frame and between conduit box base and cover providing a moisture resistant barrier.

6.15 Shouldered eyebolts with a minimum safety factor or 10 are provided for motor lifting. 

6.16 All fastening hardware is hex-head bolts or socket head cap screws with a grade 5, zinc/cadmium plating. 

6.17 Motor cast iron components are oxide primed and painted with vinyl phenolic paint to surpass 250 hour salt spray test per ASTM B117-97.

6.18 Motor nameplate is stainless steel and secured with 4 stainless steel drive pins. Nameplates are capable of meeting 720 hour salt spray test per ASTM B117-97. Each nameplate contains the following information in addition to that noted in section 10.40 of NEMA MG1-1998.

6.18.1 AFBMA bearing ID 

6.18.2 Manufacture date code 

6.18.3 Compliance with IEEE Standard 841-2001 

6.18.4 Motor weight 

6.18.5 Guaranteed minimum efficiency 

6.18.6 Maximum space heater surface C temperature, if provided, when operating at rated voltage in a 40C ambient 

6.18.7 Balance

6.19 Machined frame to endshield joints are protected by an application of corrosion preventative material to the machined surfaces before assembly. 

6.20 Corrosion protection is further enhanced by a resin and hardener that is applied to the stator, the rotor and the shaft from bearing journal to bearing journal and the exposed interior frame of the motor.

7 AIRBORNE SOUND

7.1 Motor sound power level when measured at a no load condition shall not exceed 90 dBA when determined in accordance with NEMA MG 1 –1998 part 9.

8 VIBRATION

8.1 Motor vibration measured in any direction on the bearing housing meets the levels listed below when tested per part 7 of NEMA MG1-1998:

8.1.1 Unfiltered vibration at rated voltage and frequency does not exceed 0.08 in/s peak velocity for 2, 4 and 6 pole motors and .06 in/s peak velocity for 8 pole motors. 

8.1.2 Filtered vibration does not exceed 0.05 in/s peak velocity at a frequency of 2f (twice line frequency) 

8.1.3 Unfiltered axial vibration does not exceed 0.06 in/s peak velocity on bearing housing (does not apply to roller bearings)

9 PRODUCTION TESTS

9.1 The following tests are performed on all motors:

9.1.1 Measurement of winding resistance 

9.1.2 No load readings of current, power, and speed at rated voltage and frequency

9.1.3 Mechanical vibration check as described in 8.1, using either elastic or rigid mount 

9.1.4 High potential test in accordance with section 12.03 of NEMA MG1-1998

9.2 The following test information is recorded and inserted in the motors' shipper.

9.2.1 Winding Resistance 

9.2.2 No load current, voltage and speed 

9.2.3 The following five unfiltered vibration readings, measured as described in 8.1: drive end (horizontal, vertical, and axial) and opposite drive end (horizontal and vertical)

10 WARRANTY

10.1 Motor components shall have a full five year performance warranty on sine wave power and three year warranty on inverter power.

REFERENCES

 

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