To check the expected impact of the bushing insulation type on the values of diagnostic indicators, a two-factor dispersion analysis of the tangent of the dielectric loss angle of the main insulation for paper-oil-insulated bushings of type [GAMMA]MTA 110 kV and bushings of [GAMMA]TTA type 110 kV (the frame is wired with cable crepe paper and impregnated with epoxy compound) was performed.
The distribution of the average values of the tangent of the dielectric loss angle of the main insulation of high-voltage bushings by the levels of the influencing factors is shown in Fig.
To test the hypothesis of the type of bushing influence, we analyzed the values of the tangent of dielectric loss angle for hermetic bushings with paper-oil insulation of two types: [GAMMA]MTA and [GAMMA][??]MTY.
To assess the impact of the type of protection, a dispersion analysis of the values of the tangent of the dielectric loss angle of the main insulation for the sealed-type bushings of the TEMT type and the non-hermetic bushings of the EMT type with rated voltage of 110 kV was carried out.
3 curves 1-3 are constructed under the assumption: curve 1--with a constant value of tg[delta] of thermosetting composite insulation; 2 and 3--with the power law of change of the tangent of the dielectric loss angle of insulation: 2--at tg[delta] = tg[[delta].sub.0][([f.sub.0]/f).sup.0.2]; 3 - at tg[delta] = tg[[delta].sub.0][([f.sub.0]/f).sup.0.4], where the indices <<0>> correspond to the value at the frequency of 100 Hz.
Thus, when monitoring the capacitance and tangent of the dielectric loss angle tg[delta] of the hull insulation system at frequency of 10 kHz (above resonant), the readings of the immittance meter become negative: C = -2.8639 nF < 0.
At frequency of 10 kHz, the tangent of the dielectric loss angle of the entire insulation system of the windings changes by a factor of tens--hundreds which makes it possible to monitor the state of the composite insulation at this frequency.
Dynamics of changes in partial capacitances and tangent of the dielectric loss angle in the process of accelerated aging under conditions of high humidity and temperature
Table 1 Coefficients of mutual pair correlation between the capacitance in the initial state and the capacity after accelerated aging (rC), between the tangent of the dielectric loss angle in the initial state and after accelerated aging (rtgS) Frequency of Conditions of accelerated aging measurements 336 hours 1440 hours 206 hours 456 hours f, kHz under At normal of heat of heat conditions conditions aging at aging at of 100 % temperature temperature humidity 90[degrees]C 90[degrees]C [r.sub.c] 0.1 0.9998 0.9998 0.9999 0.9998 [r.sub.tg[delta]] 0.9001 0.8176 0.8578 0.7876 1 [r.sub.c] 1.0000 0.9999 0.9999 0.9999 [r.sub.tg[delta]] 0.9810 0.9909 0.9876 0.9622 10 [r.sub.c] 1.0000 1.0000 0.9999 0.9999 [r.sub.tg[delta]] 0.9111 0.9966 0.9942 0.9904