The analysis of the

loss angle leads to information on the content of branched [23-25] and gel-like moieties [25-27].

According to international and national Standards [1, 8, 9], when conducting periodic tests of the state of insulation of high-voltage bushings, the values of the following indicators are monitored: dielectric

loss angle tangent of main insulation (tg[[delta].sub.1]), main insulation capacitance ([C.sub.1]), dielectric

loss angle tangent of measuring capacitor (tg[[delta].sub.2]), capacitance of measuring capacitor ([C.sub.2]), and the insulation resistance of the output to measure (R).

Higher value for the

loss angle indicates a high deg- ree of contamination.

The complement of angle between voltage and current vectors is called dielectric loss of angle [delta] or dielectric

loss angle. The tangent of this angle [delta] provides an indication of losses in insulation and is known as Power factor or Dielectric Dissipation factor.

The phase angle [theta] is the angle between the Z vector and Z1 and the

loss angle [delta] is the angle between Z" and the Z vector, where the dielectric loss tangent tan 8 is given by the relation:

Tan delta, also called

loss angle or dissipation factor testing, is a diagnostic method of dielectrics to determine the quality of the insulation.

1A and 1B, respectively) as well as the capacitance of a capacitor with specimens representing its dielectric and the corresponding values of tangens of the

loss angle (Fig.

compound properties Properties on part Rubber compound properties Stiffness (deformation under stress) Modulus Damping at low frequency High

loss angle Low stiffening at high frequency Low

loss angle Fatigue life Tear strength Resistance to cut increase Adhesion to metal Adhesion to metal Durability Aging resistance ([O.sub.2], [O.sub.3]) Creep resistance Compression set Table 2--MRPRA EDS 12 formulation Natural rubber 100 Zinc oxide 3.5 Stearic acid 2 Carbon black 45 Processing oil 5 Antioxidant paraphenylene diamine 2 Wax Sulfur 2.5 Sulfenamide (CBS) 0.7 Table 3--MRPRA EDS 12 properties Hardness ISO 27 (IRHD) 60 Tensile strength (ASTM D 412-87) 25 MPa Elongation at break (ASTM D 412-87) 590% Compression set 22 h.

[Epsilon]' = Re{Epsilon.sub.r} [Epsilon]" = Im{Epsilon.sub.r} = [Epsilon]' tan [Delta] [Delta] = dielectric

loss angle [Epsilon]" = dielectric loss factor

where [U.sub.f] is the phase voltage, [omega] is the angular frequency, C--is the own capacitance of wire, tg [delta] is the tangent of the dielectric

loss angle of insulation.

The tangent of dielectric

loss angle can be evaluated using the relation given as,