JQR 251.43 , 340.2, and 340.4

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340

Level 300 Training

 Testing and Varnishing Rewound Motors

 

Learning Objectives
You will be able to:

  • Conduct required postwinding test procedures to a rewound stator.
  • Correct any deficiencies found in the stator, or take action to have them corrected.
  • Test insulating varnish to ensure proper viscosity.
  • Varnish and bake a rewound stator in accordance with procedures listed in NAVSEA 0900-LP-060-2010 Series.
  • Inspect the stator after varnishing and baking to ensure the correctness of the procedures.

Background

During this lesson, we will be discussing and accomplishing the electrical tests that are required before varnishing (dipping) a rewound stator. We will then discuss and accomplish the required varnishing and baking procedures.

 

 

 

Postwinding electrical tests

Note.gif (1021 bytes) Record all test results in section 5 of the Typical Motor Data Sheet (Electrical).

Conduct insulation resistance to ground test with a megohmmeter or equivalent instrument. Record results.

Conduct phase resistance balance test with a Kelvin bridge or low-reading ohmmeter. Record results.

Conduct a surge comparison test with a surge comparison tester. Record results.

Take action as necessary if the winding fails any test. Complete the motor winding checklists (sheet 1 and sheet 2) before varnishing.

Prepare to varnish the winding when all tests are satisfactory.

 

 Click on image to enlarge.
Figure: Typical Motor Data Sheet (Electrical)

Typical Motor Data Sheet (Electrical)

 

Varnishing preparation

Insert bolts in stator bolt holes to keep the varnish from entering and plugging the holes.

Caution.gif (1040 bytes)The first dip will be accomplished with the connection side of the stator winding in the up position.

Attach a dipping harness or wire rope slings to the stator so that the stator bore will be in the vertical position during and after dipping.

Place the stator in the bake oven which has been preheated to 302°F (150°C) ±10 percent. Bake the stator for 4 hours.

Warning.gif (1054 bytes) Always wear thermo-insulated gloves when handling heated components.

At the end of the allotted baking time, remove the stator from the oven and allow it to cool to approximately 104°F (40°C).

 

Varnishes

• Solvent varnish

Use a Zahn Varnish Cup No. 2 or Demmler Varnish Cup No. 1 to measure varnish viscosity in accordance with NAVSEA 0900-LP-060-2010 Series, Chapter 11, paras. 11-1 through 11-15.

The viscosity of the varnish should be between 150 and 250 centipoise. Varnish with a viscosity over 250 centipoise will be thinned with xylene in accordance with NAVSEA 0900-LP-060-2010 Series, Chapter 11, paras. 11-16 through 11-17.

Caution.gif (1040 bytes)Do NOT thin solventless varnish.

• Solventless varnish

When environmental regulations prohibit use of solvent varnish, a solventless dip varnish must be used. Such a varnish (Esterlite 862M) is approved for use by all IMAs.

The varnishing and baking procedures presented in this lesson will not apply to solventless varnish. NAVSEA 0900-LP-060-2010 Series directs reference to the manufacturer's instructions when using this varnish.

Lift the stator with the varnish tank chainfall and position the stator over the center of the varnish tank.

 Click on image to enlarge.
Figure: Varnish Viscosity Chart, No. 2 Zahn Cup and No. 1 Demmler Cup

Varnish Viscosity Chart, No. 2 Zahn Cup and No. 1 Demmler Cup
First varnish dip and bake  arrowright_w.gif (314 bytes)

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