MIL-DTL-917F(SH)
APPENDIX A
A.3 DEFINITIONS
A.3.1 Capacitance. The capacitance of an insulating structure is the ratio of the capacitance of the insulator to
the capacitance of the equivalent spacing in a vacuum.
A.3.2 Complete winding. A complete winding is an electric winding installed in the electric equipment with
which it is used and which requires no further processing. For the purpose of this specification, an AC stator
winding, a solenoid coil, a DC armature, a transformer, or a DC field coil assembly may be considered complete
windings.
A.3.3 Dielectric constant (K). The dielectric constant of an insulator is the ratio of the capacitance of the
insulator to the capacitance of the equivalent spacing in a vacuum.
A.3.4 Dissipation factor (DF or D). The dissipation factor of an insulation structure is the ratio of its parallel
reactance to its parallel resistance. It is also the tangent of the loss angle (also called the loss tangent) and the
cotangent of the phase angle.
A.3.5 Insulation resistance. The insulation resistance between two electrodes that are in contact with, or
embedded in, an insulating structure, is the ratio of the direct voltage applied to the electrodes, to the total current
between them. It is dependent upon both the volume and surface resistances of the insulation structure.
A.3.6 Loss angle (δ, delta). The dielectric loss angle is the difference between 90 electrical degrees (90°) and
the dielectric phase angle.
A.3.7 Partial winding. A partial winding is an electrical winding which requires further processing when
installed in the electrical equipment with which used. For the purpose of this specification, a preformed armature or
stator coil or a field coil may be considered partial windings.
A.3.8 Phase angle (θ, theta). The phase angle of an insulating structure is the angle by which the current in a
capacitor, in which the material is the dielectric, leads the voltage across it.
A.4 REQUIREMENTS
A.4.1 Reliability. Reliability of operation shall be considered of prime importance in the design and
manufacture of the equipment. In those instances where resistance to unusual environmental conditions is a
requirement, a criterion of acceptance for the insulation system on the equipment must be established.
A.5 TESTING
A.5.1 Insulation suitability tests.
A.5.1.1 Place of tests. The insulation suitability tests shall be conducted at a laboratory and under conditions
acceptable to NAVSEA.
A.5.1.2 Equipment to be tested. As it is not practical to test each design of electric equipment, only
representative designs, typical of the line manufactured for each manufacturer's facility, will be tested. Table A-I
lists equipment by specification and the form of sample to be tested.
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