Main keywords for this article are DC Motor Diagram, DC Motor Working Principle, DC Motor Electrical Design, DC Motor Mechanical Design, DC Motor Balancing and Vibration.
DC Motor References
American National Standards Institute (ANSI)/American Society of Mechanical Engineers (ASME)
ANSI/ASME B1.1 Unified Inch Screw Threads (UN and UNR Thread form)
American Bearing Manufacturers Association (ABMA)
Std 9 Load Rating and Fatigue Life of Ball Bearings
Std 11 Load Rating and Fatigue Life for Roller Bearings
Anti-Friction Bearing Manufacturers Association (AFBMA)
Institute of Electrical and Electronic Engineers (IEEE)
113 Guide on Test Procedures for DC Machines
304 Test Procedure for Evaluation and Classification of Insulation Systems for DC Machines
National Electrical Manufacturers Association (NEMA)
MG-1 Motors and Generators
National Fire Protection Association (NFPA)
70 National Electrical Code (NEC)
DC Motor Working Principle
Following video is showing DC Motor Working Principle with good animation video.
DC Motor Diagram
Following is clear picture view of DC motor diagram and its components.
DC Motor Electrical Design
- Motor ratings shall be specified in kW. Full load armature and field current shall be specified at a 50 °C ambient temperature and at the base speed. Multiple armature design may be supplied on motors larger than 750 kW.
- Motors shall be supplied with standard NEMA frames, to the extent ratings permit.
Power Source
- DC power sources for motors shall be batteries; dc generator; variable speed drive; or rectified power supply.
- Motors shall supply rated output torque in continuous service, with variations of plus or minus ten (10) percent of the rated armature or field voltage, or both, without electrical or mechanical damage to the motor.
Motor Type
The type of motor furnished shall be suitable for the specific application.
a. Straight shunt wound
b. Stabilized shunt wound
c. Series wound
d. Compound wound
e. Permanent magnet
DC Motor Windings and Insulation
- The motors shall be designed to operate at the following dc voltage levels:
a. Armature 500, 600, 700 or 750 V dc
b. Field 150, 240 or 300 V dc - Motors shall be supplied with Class F insulation minimum. Insulation shall be limited to total temperatures based on NEMA MG 1 Table 23.9 for Class F insulation in a 40 °C ambient, but with temperature rise 10 °C less than would normally be allowed for Class F insulation due to the elevated site temperature.
- Field windings shall be encapsulated or epoxy resin impregnated and oven cured. Field windings shall be bonded to the poles.
- Motors rated above 150 kW (200 HP) shall be provided with at least two (2), 100 Ω platinum resistance temperature detector (RTD’s) in commutator or each interpole field winding, and wired to a terminal strip in a NEMA 4X or cast iron terminal box. The RTD’s shall be three (3) wire type, and shall be located where the maximum temperature is located.
DC Motor Armature
- Armatures shall have low inertia, and shall be dynamically balanced at highest rated speed to a value not exceeding those specified in NEMA MG-1.
- Armature coils shall be made of rectangular copper conductors, individually insulated and bonded together with separators. The fully formed coils shall be wrapped and taped with grounded wall insulation.
- The connections of the armature coils to commutator risers and the inner pole to pole face shall be tungsten inert gas (TIG) welded to give a high strength, low resistance and oxide free surface.
DC Motor Commutator and Brushes
- Commutator shall be constructed of insulation with silver-bearing copper commutator segments, and shall be easily accessible for maintenance.
- Brushes shall be copper or carbon, with current density not exceeding 50 percent of their nominal ratings, and shall be mounted in rigid, corrosion resistant brush holders. Brush springs shall be constant pressure, to provide stable brush position when motor is operated in either direction, and shall require no adjustment. Both brushes and holders shall be individually replaceable, and shall be easily accessible for maintenance. Replacement brush catalog number shall be listed on motor nameplate.
- Redundant or duplicate brush assemblies shall be provided, to minimize the periodic brush replacement.
- The brushes shall be provided with vibration dampening pads and brush wear monitoring system. The monitoring system brush leads shall be wired to a separate terminal box.
- A high-impact, clear poly-carbonate metal-frame window shall be provided, to allow visual inspection of the brushes and commutator while motor is in operation.
DC Motor Performance
- Motor starting current shall be limited to 250 percent of full load current.
- Motor shall be capable of multiple starts without injurious overheating and without permanent damage to motor.
- Motors shall be designed to meet the overload capacity specified in NEMA MG1-23.10 for general industries motors. In addition, the motors shall have the following overload capabilities at rated voltage throughout the rated speed range:
a. 1.15 times the rated kW (HP) for continuous operation
b. 1.25 times the rated kW (HP) for 2 hours - Motor torque shall be capable of overcoming maximum inertia and load torque on starting, and of accelerating the load to rated base speed under the rated and reduced voltage conditions specified in 5.2 during starting, without injurious heating.
- Motor base speed shall be determined based on rated field voltage and rated armature voltage. Motors shall be capable of delivering the maximum required load torque without exceeding the motor nominal base speed rating.
- Motors shall be capable of withstanding an overspeed of 25 percent above the rated base or highest operating speed, whichever is greater, for a period not exceeding 2 minutes.
Terminal Boxes
- Terminal boxes shall be cast iron, oversized and diagonally split for all cast metal frame motors.
- Separate terminal boxes shall be provided for main leads and auxiliary devices, for example space heaters, RTD’s, and vibration and brush monitoring device leads.
- Boxes shall be of weathertight or special construction, as required for classified locations. Terminal boxes shall be provided with threaded conduit openings or hubs on all motors.
- Motor terminal boxes shall be rotatable for connection from any one of four directions at 90° intervals.
- Terminal boxes on the horizontal motors shall be located on the right hand side when viewed from the end opposite the shaft extension.
- A motor lead seal and separator gasket shall be provided between the motor frame and terminal box on all motors.
Motor Leads
- Motor leads shall have the same class insulation as the windings, and shall be fitted with manufacturer’s standard terminals. Leads and terminals shall be permanently marked in accordance with NEMA MG-1.
- If bus bar leads are used in the terminal box, to accommodate connections of the power supply leads, the bus bars shall be fully insulated and supported.
- The motor connection diagram shall be attached to the motor, either inside the terminal box or on the motor frame on the same side as terminal box.
Auxiliary Cooling Fans
- Fan motors shall be rated 460 V, three-phase, 60 Hz, ac power supply.
The fan shall be of nonsparking, corrosion-resistant metallic material.
Fans shall have an air pressure switch to indicate loss of air flow.
Fan motors shall be interlocked with the dc motor, to ensure that the fan is running prior to starting the dc motor.
Space Heaters
- Sheath type heaters shall be provided, to prevent condensation when motors are idle.
- The sheath temperature of space heaters when operating at site conditions and at 110 percent of rated voltage shall not exceed 180 °C.
- The space heaters shall be rated at 230 V, but shall be operated at 115 V, single phase service. The heaters shall be energized through the motor controller on motor shutdown.
Provisions for Grounding
- Motors shall be provided with a visible, external tapped hole or lug in the frame foot located at the end opposite the drive shaft and on the terminal box side of the motor, for attaching the grounding conductor lug.
- For motors rated above 150 kW, all non welded parts of the motor assembly and accessories shall be bonded together with copper straps, and connected to motor grounding pad or grounding lug.
- Motor terminal boxes shall be provided with a grounding lug inside the box.
Conduit and Wiring
All power and control wiring within the confines of the motor assembly and accessories shall be heat, moisture, and abrasion resistant. All conduits shall be rigid galvanized steel (RGS) except for the areas subject to vibration, where liquid-tight conduits with UL approved fittings shall be used. All leads from alarm, auxiliary and control devices shall be brought out to terminal boards in the auxiliary terminal box.
Main keywords for this article are DC Motor Diagram, DC Motor Working Principle, DC Motor Electrical Design, DC Motor Mechanical Design, DC Motor Balancing and Vibration.
DC Motor Mechanical Design
Hazardous Areas
- Motors shall comply with the requirements of NFPA 70 for hazardous classified locations. If vendor does not receive complete area classification information (Class, Division, Group, and auto ignition temperature).
- Explosion proof and dust ignition proof motors shall bear labels by UL, or shall be labeled in accordance with requirements of approved certifying laboratories or authorities for proper class(es) and group(s), and shall have a suitable temperature designation. Explosion proof motors shall be furnished if they are available in the required rating. If an explosion proof motor is not available, the motors shall be made safe for the area, using one of the methods allowed by NFPA 70.
Motor Enclosures
- Motors shall be suitable for operation in severe environments associated with refineries and chemical plants. Motor enclosures, accessories and internal components shall be protected to resist chemicals, corrosion, moisture, and abrasives, for example particles, blowing sand and salt laden atmosphere.
- Motor frames shall be cast iron, rolled steel, or laminated steel construction.
- Enclosures shall be as in accordance with the following:
a. For hazardous areas, motors shall be totally enclosed explosion proof or totally enclosed pipe ventilated. All accessories attached to motors shall be approved for installation in the classified locations.
b. For non-classified locations, the motors shall be totally enclosed airover piggyback (TEAOP) for motors rated 150 kW and below. For motors larger than 150 kW the motors shall be totally enclosed dualcooled with air-to-air heat exchanger (TEDC-A/A) or totally enclosed dual-cooled with air-to-water heat exchanger (TEDC-A/W). No free exchange of air shall occur between the inside and outside of motor. - TEDC-A/A motors shall be furnished with stainless steel exchanger tubes. Separate ac motor driven blowers shall be used for circulating internal and external air through the exchanger.
- TEAOP and TEDC-A/A motors shall be provided with reusable stainless steel air filters. Filters shall be securely fastened in place and easily removable for cleaning during motor operation. Filters shall be provided with a differential pressure gage and alarm to indicate a dirty filter.
- TEDC-A/W motors shall have exchangers with removable tube bundles. These exchangers shall be fabricated with double tubes and flanges for in-plant cooling water. If a TEDC-AW enclosure is specified, plant cooling water data will be given in SES E06-X04. Exchanger tubes shall be 90-10 Cu-Ni. Vendor shall indicate in proposal the delta temperature and pressure across the exchanger, plus the required flow rate. Flow-sensing devices shall be provided in the water supply piping, to sense low and high flow, and inner tube leakage.
- TEDC-A/A and TEDC-A/W motors shall be supplied with two (2), 100 Ω, platinum RTD’s for input and output air temperatures.
- Motor shall have a corrosion resistant drain and plug in low point of the enclosure, accessible from the exterior of the motor. Seals and slingers shall be provided to prevent moisture from entering through the shaft opening.
- Cast iron fan shrouds shall be supplied on cast iron frame for totally enclosed motors.
- Motors shall be provided with eyebolt(s) or lifting lug(s).
- Motors shall be equipped with stainless steel hardware. Hardware and threaded openings shall conform to ANSI/ASME B1.1.
- Vertical jacking bolts shall be provided on motors 55 kW and larger.
DC Motor Bearings and Lubrication
- Motors shall be furnished with grease-lubricated, anti-friction ball bearings.
- Motors shall have noncontact labyrinth or taconite dust-resistant shaft seals.
- Grease-lubricated bearing shall be supplied with two (2) threaded ports. The grease supply ports shall have hydraulic fittings and shall be accessible from the exterior of the motor. The hydraulic grease fittings shall be industry standard design. Grease drain ports shall be supplied with pressure relief fittings.
- Anti-friction bearings shall be designed for a minimum L10 life of 40,000 hours under continuous duty at rated load and speed, calculated in accordance with AFBMA Standard 9 for ball bearings or AFBMA Standard 11 for roller bearings.
- The lower section of each bearing shall be provided with two (2), 100 Ω, platinum RTD’s, on motors rated 750 kW and above. The RTD’s shall be three (3) wire type.
- Motors rated 750 kW and above shall be provided with both bearings electrically insulated. Insulation resistance from the frame shall not be less than one (1) MW. Warning nameplates reading ‘Insulated Bearing’ shall be provided. Provisions shall be included to permit direct resistance measurements on the bearing insulation.
DC Motor Shaft
- Direction of shaft rotation shall be counterclockwise when viewed from the non-drive end, unless otherwise specified by the engineered equipment vendor.
Shafts shall be in accordance with NEMA MG-1 standard dimensions for NEMA frame motors. Shafts on horizontal motors shall be suitable for direct coupling, belt drive, or chain. - Shafts shall be complete with the motor half coupling factory mounted.
- Shaft runout shall not exceed 0.050 mm for horizontal, and 0.025 mm for vertical motors.
- Vertical motors shall have flanges similar to ‘P’ base, and shall have solid shafts.
- Motors rated 750 kW and above shall have motor shaft position (magnetic center) and rotor end play limits permanently scribed on the shaft. A permanent reference point shall be provided on bearing housing.
DC Motor Balancing and Vibration
- Motor armature shall be precision balanced. The use of solder or similar deposits for balancing shall not be acceptable. Parent metal removed to achieve dynamic or static balance shall be drilled out in a manner that does not affect the structural strength or electrical balance of the rotating element.
- The maximum amplitude (peak-to-peak) of motor vibration as measured at the bearing housing, and the method of measurement, shall be in accordance with NEMA MG-1.
- Each bearing shall be provided with two (2) vibration probes and oscillator demodulators. The probes shall be Bentley Nevada, Model No. 3300 series displaced 90° apart and 45° from the vertical at each bearing.
DC Motor Test and Inspection
All motors shall receive routine tests in accordance with NEMA MG-1 and IEEE 113 and 304.
Main keywords for this article are DC Motor Diagram, DC Motor Working Principle, DC Motor Electrical Design, DC Motor Mechanical Design, DC Motor Balancing and Vibration.