Water-tree resistance evaluation method, insulation design method, and rotary electric machine

1. A water-tree resistance evaluation method for a water tree phenomenon of insulation material, comprising:

selecting a candidate insulation material as a candidate;

carrying out, after the selecting, a water tree test on a test piece that is a flat plate made of the candidate insulation material selected by the selecting and has electrode holes formed on a first surface; and

evaluating, after the water tree test, characteristics of the candidate insulation material, including progress and speed of a water tree, based on a result of test at the water tree test, wherein

the water tree test includes:

setting a test system so that the first surface of the test piece is immersed in a ground-side aqueous solution of a voltage application side while a flat second surface of the test piece, which is an opposite side from the first surface, is immersed in an application-side aqueous solution,

grounding, after the setting, a ground-side electrode that is immersed in the ground-side aqueous solution, while applying an AC voltage to an application-side electrode that is immersed in the application-side aqueous solution,

measuring, after the start of the grounding and the applying, progress of water tree inside the test piece at predetermined intervals, and

determining, after the measuring, whether a test period has exceeded a predetermined period, and for ending the water tree test if the test period has exceeded the predetermined period while repeating the grounding and the applying and the measuring if the test period has not exceeded the predetermined period;

obtaining attenuation characteristics of a progress speed of water tree by dividing a slope of the progress speed at each point in test time by the slope at an initial time in the progress of the water tree obtained at the measuring;

determining, after the attenuation characteristic evaluating, whether or not the attenuation characteristics satisfy attenuation determination conditions, and for rejecting the candidate insulation material if the attenuation determination conditions are not satisfied; and

multiplying an amount of the progress by a predetermined coefficient if the attenuation characteristics satisfy the attenuation determination conditions at the determining, and of determining whether or not a value thereof is smaller than a progress amount determination value, and for rejecting the candidate insulation material if the value is not smaller than the progress amount determination value.

2. The water-tree resistance evaluation method according to claim 1 , wherein

the electrode holes are made after polymer material is heated to a predetermined temperature and poured into a mold member on which protruding portions corresponding to the electrode holes are formed and is hardened as the material is kept at a predetermined temperature and left for a predetermined time.

3. The water-tree resistance evaluation method according to claim 2 , wherein

the attenuation characteristic evaluating includes comparing either: a ratio of a temporal variation rate of the progress at final measurement time to a temporal variation rate of the progress immediately after the start of the measurement, or a logarithmic value of the ratio, with an attenuation determination value.

4. The water-tree resistance evaluation method according to claim 1 , wherein

the attenuation characteristic evaluating includes comparing either: a ratio of a temporal variation rate of the progress at final measurement time to a temporal variation rate of the progress immediately after the start of the measurement, or a logarithmic value of the ratio, with an attenuation determination value.

5. An insulation design method for designing in terms of insulation for a rotary electric machine in which voltage is applied at each component under operation, the method comprising:

selecting a candidate insulation material as a candidate;

carrying out, after the selecting, a water tree test on a test piece that is a flat plate made of the candidate insulation material selected by the selecting and has electrode holes formed on a first surface;

evaluating, after the water tree test, characteristics of the candidate insulation material, including progress and speed of a water tree, based on a result of test at the water tree test; and

determining conditions for configuration of insulation of the rotary electric machine based on a result of evaluating characteristics of the candidate insulation material and the voltage to be applied, wherein

the water tree test includes:

setting a test system so that the first surface of the test piece is immersed in a ground-side aqueous solution of a voltage application side while a flat second surface of the test piece, which is an opposite side from the first surface, is immersed in an application-side aqueous solution,

grounding, after the setting, a ground-side electrode that is immersed in the ground-side aqueous solution, while applying an AC voltage to an application-side electrode that is immersed in the application-side aqueous solution,

measuring, after the start of the grounding and the applying, progress of water tree inside the test piece at predetermined intervals, and

determining, after the measuring, whether a test period has exceeded a predetermined period, and for ending the water tree test if the test period has exceeded the predetermined period while repeating the grounding and the applying and the measuring if the test period has not exceeded the predetermined period;

obtaining attenuation characteristics of a progress speed of water tree by dividing a slope of the progress speed at each point in test time by the slope at an initial time in the progress of the water tree obtained at the measuring;

determining, after the attenuation characteristic evaluating, whether or not the attenuation characteristics satisfy attenuation determination conditions, and for rejecting the candidate insulation material if the attenuation determination conditions are not satisfied; and

multiplying an amount of the progress by a predetermined coefficient if the attenuation characteristics satisfy the attenuation determination conditions at the determining, and of determining whether or not a value thereof is smaller than a progress amount determination value, and for rejecting the candidate insulation material if the value is not smaller than the progress amount determination value.