Method for manually screening the inter-turn test results of motor windings by using curve state
The motor manufacturers that regulate the production will carry out the diurnal test on the windings, but in the course of the test, they often encounter the fact that they are suspected of being difficult to determine directly. When testing with the double winding comparison method, if both windings are normal, the two curves will completely coincide, that is, only one attenuated sine wave curve is seen on the diurnal meter screen. If the two curves do not completely coincide, there may be a difference in the inter-turn short circuit or magnetic circuit parameters between the two windings of the test, or it may be a fault in the instrument and wiring. Ms. Participate today to organize and share several typical cases.
Several typical situation analysis
Due to different specifications or different manufacturers, the response of the daytime instrument to the same fault of the winding will be different; in addition, for the three-phase winding, different wiring methods will also have different reactions, so it is difficult to give a universal judgement standard. The tester should continually pass the test to sum up the experience and draw his own effective judgment criteria.
●The two curves are very stable, but there are small differences
(1) Compared with the total number of turns, a small amount of turns are completely short-circuited;
(2) If this phenomenon exists in the specification of the motor to be tested, it is likely to be caused by uneven magnetic circuit, such as uneven groove pitch and uneven air gap between stator and rotor (for the whole product) The magnetic permeability of the core is inconsistent in all directions, and the test is performed after the rotor is removed. If the curve becomes normal, it is not a problem of the stator winding;
(3) For windings with more turns, it may be that the number of turns of one phase winding is slightly more or slightly less than the normal value;
(4) For a multi-stranded coil, when the wire is connected, some of the wire strands are not connected or the node contact resistance is large, and the DC resistance of the two windings may also have a certain difference;
(5) The three-phase windings fluctuate due to the operation of the wire material and the coil, the end shaping, etc., resulting in a small difference in resistance or reactance;
(6) The diurnal instrument consisting of two thyristors will cause output due to changes in parameters of two thyratrons or related circuit components (such as capacitor capacitance and leakage current value) after a long period of use. The voltages are different, so that the two discharge curves produce a small difference. At this time, the same reaction will be performed for each test (such as three tests of the three-phase motor), but it should be noted that the reaction is comparable to the capacity. Large motors will be larger, and may not be obvious for smaller capacity motors;
(7) The instrument is not adjusted well, so that the two curves do not coincide when no voltage is applied.
●The two curves are very stable, but the difference is large
(1) The two windings have a large number of turns or one of the windings is far apart (in theory, the distance is zero, but the actual space distance is zero). The two sides or faces are completely short-circuited. There will be some difference in resistance;
(2) The number of windings of the two windings is the same, but there is a phenomenon in which the individual coils in one winding have a head-to-tail reverse connection. The DC resistance of the two windings will be identical or substantially the same.
● One curve is stable and normal, and the other curve has a messy spike
(1) There is a short-circuit between the windings in the winding where the chaotic sharp wave appears. Under the action of high voltage, the short-circuit point generates an electric spark. If it occurs at the end of the winding, it may see a blue spark. And can hear the sound of "啪啪".
(2) The instrument wiring is loose or virtual.
●The two curves are cluttered with sharp waves
(1) There are interturn short circuit faults in the two sets of windings tested;
(2) When the iron core is placed in a grounding manner, the grounding point is loose.