AMC-300-1

SEPTEMBER 1988

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA)

ATLANTIC MARINE CENTER

STANDARD SPECIFICATION AMC-300-1

OVERHAUL OF ELECTRICAL ROTATING MACHINERY

1. SCOPE. This specification contains the general requirements and procedures to be used in overhauling electrical motors and generators on and for NOAA ships and boats.

2. REFERENCES.

None

3. REQUIREMENTS.

3.1 General.

3.1.1 The contractor shall provide all labor, material, services, tools, supervision, and technical expertise needed to accomplish the required work. All material and replacement parts used or installed in the machinery shall be new and shall be equal or superior to the materials and parts used in the original manufacture.

3.1.2 Removal and reinstallation of the electrical machine

by the contractor is required only if specifically required by the detail specifications or other procurement document. If removal and reinstallation is specifically required, the contractor shall be responsible for all handling and work related to the removal and reinstallation, including the removal and restoration of all interferences.

3.1.3 The contractor shall notify the Contracting Officer's

Technical Representative (COTR) at least 24 hours in advance of performing the tests and inspections. The COTR may witness all or any portion of the tests and inspections.

3.1.4 The contractor shall submit to the COTR a written

report of all inspection findings and test results, including a record of all measurements and readings taken.

3.2 Standard Overhaul.

3.2.1 Removal. If removal is required by the detail

specifications or other procurement document, proceed as follows:

a. Verify that electric power has been secured and tag out the motor controller. Disconnect electric wiring and tag individual wires to aid in proper reinstallation. Wrap wire ends to protect them from damage and prevent electric shock in the event the wire are inadventently energized. Record hook-up data.

b. Measure and record thrust readings. Measure and record air gap readings and bearing clearances for machines having sleeve bearings.

c. Inspect couplings for cracks, broken segments, wear, and misalignment.

d. Remove the machine to a suitable electric shop.

Tag and retain chocks, shims, shock mounts, and other accessories associated with the machine installation.

e. Inspect foundations for cracks, distortion, and excessive deterioration.

3.2.2 Disassembly. Completely disassemble the machine.

3.2.3 Cleaning. Clean all mechanical parts with lint-free

cloths moistened with a suitable solvent. Do not let solvent come in contact with varnished surfaces or commutators. Steam detergent clean and dry the stators and rotors as follows:

a. Remove all loose accessible carbon, dirt and other foreign particles from the windings by using a vacuum suction.

b. Prepare an appropriate amount of cleaning solution by mixing 15 to 20 pounds of steam cleaning compound and one quart of butyl alcohol per 1000 gallons of fresh water. Heat the solution to 185-190 degrees Fahrenheit and maintain the temperature throughout the cleaning.

c. Completely immerse the windings in a tank with the hot cleaning solution. Rotors shall be placed in the tank with the commutator/slipring end up. Stir the cleaning solution with an air agitator to circulate it through the windings and out through commutator risers. Continue stirring the solution while the windings are immersed for 8-10 hours.

d. In lieu of immersing the windings for 8-10 hours as specified above, the Contractor may elect to use a steam spray machine such as a steam jenny to apply the cleaning solution.

The temperature of the cleaning solution impinging on the windings shall not exceed 194 degrees Fahrenheit and the pressure at the windings shall not exceed 30 pounds-per-square-inch-gage.

Avoid any live steam impinging directly on the windings. If this optional cleaning method is used, all subsequent re-cleaning necessary to obtain acceptable insulation resistance readings shall be the Contractor's responsibility.

e. Thoroughly flush windings with clean hot fresh water after cleaning. Remove surface moisture with clean lint-free cloths to keep the amount of water which soaks into the insulation as low as possible.

f. Immediately after cleaning, thoroughly dry the windings in an oven. Slowly increase the oven temperature to a maximum of 220 degrees Fahrenheit. Do not exceed 165 degrees Fahrenheit during the first hour. After drying in the oven for eight hours (minimum), take and record megger readings of the windings every two hours. Continue drying until four consecutive megger readings of the same value have been obtained.

g. Allow the windings to cool to within 50 degrees Fahrenheit of ambient temperature.

3.2.4 Inspections.

a. Conduct complete visual inspections of all parts for cracks, deterioration, excessive wear, eccentricity, and other defects which could prevent continued safe operation of the machine.

b. Tighten all connections. All wedges, binding bands, soldered connections, and bolted connections are to be checked, and tightened where needed.

c. Examine all windings and connections for cracks in taped surfaces, brittle condition, crystallization, and loose connections.

d. Inspect rotor shaft journal areas, bearings, and bearing housings. Measure and record diameters of all journals, commutators, and sliprings.

3.2.5 Electrical Tests. As soon as practical after

cleaning, conduct the following electrical tests:

a. Insulation Resistance Tests. Using a 500-volt megger, conduct separate tests of the stator circuits and the rotor circuits in accordance with Appendix A. Record all readings. If any readings are less than those allowed in Appendix A, contact the COTR prior to proceeding.

b. DC High Potential Tests. Conduct tests in accordance with Appendix B on all windings of motors rated over five horsepower and all generators rated over 4 kilowatts. Do not perform this test on smaller machines or on squirrel cage armatures.

c. Voltage Surge Comparison Tests. Conduct AC surge comparison tests for phase balance, continuity and voltage drop on all windings in accordance with the test equipment manufacturer's operating instructions. Use a tester which is able to vary voltage smoothly from zero up to the maximum. The test voltages to be applied shall be 1.4 times the values computed from the following table.

ARMATURE FIELD SHUNT FIELD

CIRCUITS OF AC CIRCUITS OF CIRCUITS OF

AND DC MACHINES AC MACHINES DC MACHINES

Generators and motors, 2/3(2E + 1000) 7E but in no 2/3(2E plus including propulsion case less 1000) generators and motors, than 1000 but excluding all volts nor machines listed below. more than

2300 volts.

Generators and motors 600 600 600 of not more than 250 volts and not more than 0.25 kilowatts (generators) or 0.5 horsepower (motors), except machines listed below.

Bracket fan motors 400 400

Generators and motors 350 350 350 of not more than 35 volts, except engine starting motors

Engine starting motors 500 500 not more than 36 volts.

Note: "E" equals the operating voltage of the machine.

The above values are for windings which have been reconditioned but which have not been rewound or renewed. For rewound or renewed windings, the values shall be increased by 50 percent.

3.2.6 Repairs.

a. Mount the rotors in a lathe and check for trueness.

Resurface commutator and slipring surfaces using surfacing stones or a rounded diamond point tool. Eccentricity shall not exceed

0.001 inch total indicated runout (TIR). Take very light cuts (.010 inch maximum), and remove the minimum amount of metal necessary to restore the commutators and sliprings to a true and otherwise good condition. If cut with a turning tool, finish the commutators and sliprings with a surfacing stone. Undercut mica, chamfer commutator bar edges, and burnish commutator and slipring surfaces.

b. Clean brush rigging. Renew existing brushes with new brushes of same size, type and hardness as existing.

Reassemble brush rigging, using new springs and brush tension arms.

3.2.7 Evaluation. After each phase of the overhaul and

whenever any condition is noted which needs correction, the Contractor shall submit an inspection and evaluation report to the COTR before proceeding with the overhaul. The inspection and evaluation report shall indicate the existence of all conditions and inspection results and shall recommend corrective actions needed to restore the machine to a condition of reliability equivalent to a new machine.

3.2.8 Varnish treatment. After acceptable insulation

resistance readings have been attained and all needed repairs have been completed, treat the rotors, stators, and coils with varnish dip and bake in accordance with Appendix C.

3.2.9 Balancing. Statically and dynamically balance the

rotors. The mass to be balanced shall include all rotating parts which form a part of the rotor assemblies.

3.2.10 Final Electrical Tests. After windings have cooled

following varnish treatment, repeat the electrical tests required in paragraph 3.2.5 above.

3.2.11 Reassembly. Reassemble the machine.

a. Install new seals, gaskets, brushes, and fasteners.

New fasteners shall conform with MIL-S-1222, Type I or II, Grade 5 or 8, zinc coated.

b. Renew bearings on all machines of less than 25 horsepower or 20 kilowatt rating. Properly lubricate bearings.

c. Adjust brushes and brush rigging. Measure and record air gaps between field and stator coils.

3.2.12 Reinstallation. When the detail specifications or

other procurement documents require, reinstall the machine.

a. Renew foundation fasteners with fasteners conforming to MIL-S-1222, Type I or II, Grade 5 or 8, zinc coated and self-locking hexagon nuts conforming to MIL-N-25027. (This requirement is not applicable to body-bound bolts.)

b. Align the machine onboard the ship.

c. Remake all connections and test run the machine for one hour to demonstrate satisfactory operation.

APPENDIX A

INSULATION RESISTANCE TESTS (MEGGER READINGS)

A-1. All insulation resistance measurements are to be made with the test voltage applied between the copper conductors and the metallic structure in which the winding is embedded. If necessary, a good connection shall be assured by removing paint and corrosion at the point of the contact on the structural part.

All bare copper surfaces and terminals must be suitable for making the copper contact.

A-2. All insulation resistance readings taken shall be corrected to 25 degrees Centigrade (77 degrees Fahrenheit).

A-3. Insulation resistance readings are to be taken and recorded for each applicable winding circuit listed in A-5 below. When measurements are being made on one winding, all other windings shall be connected to ground.

A-4. The complete armature circuit of a dc machine includes the armature, brush rigging, connections to machine terminals, and all fields which carry armature current, such as commutating field, compensating field, and series field. The stator circuit of polyphase generators and motors include all phases.

A-5. After cleaning in a shop, the minimum acceptable insulation resistance readings for windings shall be as specified below. If any low readings are obtained, contact the COTR prior to proceeding.

a. DC motors and generators (except propulsion).

(1) Complete armature circuit 1.0 megohms

(2) Armature alone 2.0 megohms

(3) Armature circuit less armature 2.0 megohms

(4) Complete shunt field circuits 2.5 megohms

Notes

1. The above figures are applicable for machines rated at 250 volts or less. For machines having a higher voltage rating, multiply the figures by E/250. (E = rated voltage of machine)

2. Small machines usually have one of the shunt field leads connected internally to the armature circuit. In such cases, the complete armature circuit and the complete shunt field circuit may be measured without breaking the connection. If necessary, the armature can then be isolated by lifting all brushes. With brushes left in place, the complete armature circuit will include armature, armature circuit, and the permanently connected shunt field circuit. With the brushes lifted, the armature circuit less armature and the complete shunt field circuit will be measured and considered to be "armature circuit less armature".

b. AC motors and generators.

(1) Stator circuit 2.0 megohms

(2) Rotor circuit of wound rotor induction motors 1.0 megohms

(3) Field circuit of generators or of synchronous motors 4.0 megohms

c. DC propulsion generators and motors.

(1) Complete armature circuit Rx3 megohms

(2) Armature alone Rx5 megohms

(3) Armature circuit less armature Rx5 megohms

(4) Complete shunt field circuit Rx10 megohms where R = ______E_________ W + 1000

E = rated voltage of machine W = kilowatt rating of machine divided by 100 (kilowatt rating equals 0.746 times the horsepower rating)

APPENDIX B

DC HIGH POTENTIAL TESTS

B-1. The dc high voltage tester must be able to vary voltage smoothly from zero up to the maximum required, and is to be provided with a protective current relay which can be set to trip at any given percentage of the micro-ammeter scale. The micro-ammeter is to have sufficient ranges to provide readings from less than 1 to at least 2500 microamperes.

B-2. The maximum voltage to be applied to the windings during the tests is 1.1(2E plus 1000), where E is the operating voltage of the windings. Separate test voltage must be calculated for exciter windings.

B-3. Apply approximately 25 percent of the maximum test voltage with the positive terminal of the tester attached to the copper and the negative terminal of the tester attached to the iron.

Measure and record the leakage current. Set the protective current relay of the tester to approximately four times the recorded leakage current. The current relay may be adjusted upward for gradually rising current values.

B-4. Gradually increase the dc voltage in steps up to the maximum. Stop at a minimum of eight steps and allow the leakage current to stabilize. Measure and record the leakage current and the machine temperatures for each voltage step. Should a sharp rise in the leakage current occur at any step, stop the test and notify the COTR.

B-5. Plot the current and voltage values on cross-section paper at the completion of the test.

B-6. After completion of the test, ground the copper for a sufficient time for the machines to become completely discharged.

After the ground wire has been removed, check for remaining charge by attaching the dc high potential tester with its dial in the discharge position. When the meter switch is turned to the low scale position, the micro-ammeter will move off zero if any charge remains.

APPENDIX C

VARNISH TREATMENT (DIP AND BAKE)

C-1. Insulate windings having Class A, B, or F insulation as follows:

a. Put into an oven and bake for 4 hours at 300 degrees Fahrenheit. Cool to 100 degrees Fahrenheit and immerse the windings in clear baking varnish conforming to MIL-I-24092, class 155, composition I until bubbling ceases. Immerse the rotor vertically or near vertical with sliprings, leads and commutators up (out of the varnish). Maintain the varnish at a temperature 75 to 90 degrees Fahrenheit, with a viscosity between 250-350 centipoises.

b. Remove and drain the windings. Air-dry for one hour, rotating components 90 degrees every 15 minutes to prevent pocketing of varnish.

c. After draining and before baking, clean the metal surfaces of the rotors, the bore of the stators, and the pole faces of the field structures with a cloth moistened with a solvent.

d. Put the windings in an air-circulating, forced exhaust, baking oven and bake for 6-8 hours at a temperature of 300 degrees Fahrenheit.

e. Remove from the oven and cool to approximately 125 degrees Fahrenheit.

f. Repeat the varnish dip and bake treatment, except immersion in the varnish shall be limited to one minute.

C-2. Insulate windings having Class H or N insulation as follows:

a. Put into an oven and bake for 4 hours at 300 degrees Fahrenheit. Cool to 100 degrees Fahrenheit and immerse the windings in clear baking varnish conforming to MIL-I-24092, class 200, for a minimum of 4 minutes and a maximum of 5 minutes.

Immerse the rotor vertically or near vertical with sliprings, leads and commutators up (out of the varnish). Maintain the varnish at a temperature 75 to 90 degrees Fahrenheit, with a viscosity between 125-225 centipoises.

b. Remove and drain the windings. Air-dry for one hour, rotating components 90 degrees every 15 minutes to prevent pocketing of varnish.

c. After draining and before baking, clean the metal surfaces of the rotors, the bore of the stators, and the pole faces of the field structures with a cloth moistened with a solvent.

d. Put the windings in an air-circulating, forced exhaust, baking oven and bake for 2 hours at a temperature of 390 degrees Fahrenheit.

e. Remove from the oven and cool to approximately 125 degrees Fahrenheit.

f. Repeat the varnish dip and bake treatment, except immersion in the varnish shall be limited to one minute. During baking, raise the temperature to 450 degrees Fahrenheit and bake for 8 hours.

END OF SPECIFICATION