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Marathon MP Series Brushless Three Phase AC Generator

Jan. 03, 2020

Description of Marathon MP Series Generator

Marathon MP series three phase AC synchronous brushless generator is a new generation brushless generator, which based on MAGNA PLUS generator of Marathon electric co. USA.

MP generator may be combined with diesel engine (internal-combustion engine) to make fixed or movable electrical power. It is suited for commercial buildings, hospitals, factories, farms, fields, etc, as power and lighting. The generating set may be used for the prime power or stand by.

MP series generators are of unique design, advanced construction, excellent performances, reliable operation, easy use, small volume and light weight.

Marathon MP Series Generator


1. MP series generators are manufactured in accordance with NEM ODP type. It consists of main generator, AC brushless exciter, rotating rectifiers, AVR, conduit box, etc.

2. Class H or Class F insulation system.

3. The frame is made by steel plate. the design of stator lamination is unique. If necessary, 12 lead wires may be supplied.

4. Main rotor apply the single piece 4-pole salient pole lamination, coupled with die cast or welding damping winding, field winding to form a unirotor construction. The field winding is a layer wound with thermo settings epoxy for high mechanical and electrical integrity.


1. MP series generator may be operated continually at rated load under following conditions:

a. Ambient: Air temperature ≤ 40, well ventilation, marine use, ≤ 45

b. Elevation ≤1000m over sea level

2. Electrical performances

a. Steady voltage regulation ≤1.0%

b. transient voltage regulations ≤+20%, -15% (60% in, cos= 0.4 lag)

c. Adjustable Voltage range 95-105% Un

d. Waveform distortion at no-load, ≤5% (line voltage)

e.  Starting motor ability, (no-load, three phase, 4p, cage motor)


Motor Capacity

Up to 40KW


50. 64. 75KW


90. 120KW


150. 200. 250KW




Principle of Operation:

MagnaPlus generators are a brushless, self excited, extremely voltage regulated, synchronous AC generator. The generator is made of six major components: main stator (armature), main rotor (field), exciter stator (field), exciter rotor (armature), rectifier assembly, and voltage regulator. In understanding the above terminology, note the following: stators are stationary, rotors rotate, a field is an electrical input, and an armature is an electrical output. 

The generator's exciter consists of a stationary field and a rotating armature. The stationary field (exciter stator) designed to be the primary source of the generator's residual magnetism. This residual magnetism allows the exciter rotor (armature) to produce AC voltage even when the exciter and fed directly to the main rotor (field). As the generator shaft continues to rotate, the main rotor (field) induces a voltage produced by the residual magnetism of the exciter allows the automatic voltage regulator to function. The regulator provides voltage to the exciter resulting in a build-up of generator terminal voltage. This system of using residual magnetism eliminates the need for a special field flashing circuit in the regulator. After the generator has established the initial residual voltage, the regulator provides a controlled DC field voltage to the exciter stator resulting in a controlled generator terminal voltage.


In the event that the generator is not to be installed on its prime mover immediately, it is recommended that the unit be stored in a cleaned, fry area which is not subject to rapid changes in temperature and humidity.

In the event of long term storage, the generator should be tested cleaned and dried as required, before being put into service. See the maintenance section of this manual for further.

Installation and adjustment

1. Generator must be mounted at the clean, dry and well ventilation place. The prime mover and generator should be installed on a public frame, never put them on the cement floor, and ensure the public frame underformed.

2. Single bearing generators.

Single bearing units are provided a SAE flywheel housing adapter and flexible drive discs to match the engine. Close tolerances are maintained in the manufacture of the generator to promote ease of alignment.

Special stell drive discs are bolted the shaft. In some case spacer are used to achieve the proper :XG" dimension. Holes are provided in the periphery of the coupling discs which correspond to tapped holes in the engine flywheel. The outside diameter of the drive discs fit in a rabbet in the flywheel so that concentricity is assured.

CAUTION: Grade 12.9 place to the flywheel. Do not use split type lock washers, they will cause stress rises, and may result in disc failure. 

The SAE flywheel housing adapter and the engine flywheel housing are designed to match each other, with no further alignment necessary.

Shims may be necessary under the generator feet to insure a solid mounting. Do not force the feet to an uneven mounting surface, serious problems could result. ENDPLAY TEST PROCEDURES:

After the generator has been assembled to the engine, check for endplay of the assembled set. Using a suitable lever, force the engine flywheel forward so that the crankshaft is pressed against its thrust bearing. When force is removed, the engine crankshaft should remain in position. Apply force in the opposite direction forcing the crankshaft towards the generator, and observe if the crankshaft remains in the position after force has been removed, refer to the engine manual for proper or recommended endplay. If the crankshaft springs away in either direction after force has been removed. It is an indication that the generator shaft is not moving freely, and normal life of the thrust bearing could be impaired. Probably cause of this problem are:

a. Improper "XG" dimension of either the generator or the engine flywheel, or both. Generator bearing may be bottoming out in its bearing bracket.

b. Misalignment.

a) Improper seating of generator drive discs in the engine flywheel.

b) Improper mating of the generator frame to the engine flywheel housing.

c) Set sub-base is not true. Generator and or engine feet repair shims. See mounting instructions.

3. Two bearing generators.

If generator couples with engine by flange rabbet. It is easy to mount. If it coupled by other way, should pay more attention to installation, it may be necessary to shim the generator feet for proper support and alignment. Aligning the generator and engine as accurately as possible will reduce vibration, increase bearing life, and minimize coupling wear.

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