An ohmmeter is sufficient to check the generator set and troubleshoot. However, more accurate information about the winding units can be obtained using special devices that search for faults in the windings by comparing their parameters with a known good winding. They are suitable for troubleshooting both stator windings and excitation.
Necessary
Ohmmeter, PDO-1 device
Instructions
Step 1
Check the rotor winding. To do this, turn on the ohmmeter to measure the winding resistance, and bring its leads to the rotor rings. The resistance of a serviceable rotor at a voltage of 14 V is within the following limits: for generators that work with voltage regulators designed for a maximum current of 3, 5-4, 0 A - 3-5 Ohms, for those working with voltage regulators that are designed for amperage 5 A - 2.5-3 Ohm. If the device showed an infinitely high resistance, this means that the field winding circuit is broken. This usually occurs at the place where the winding leads are soldered to the rings, when the winding burns out or when the frame with the excitation winding is turned on the half-bushings of the pole halves. This is also indicated by the darkening, as well as the crumbling of its insulation, which can be detected visually. This malfunction leads to a turn-to-turn short circuit in the winding, which is accompanied by a decrease in the total resistance. To determine a partial turn-to-turn short circuit, when the resistance of the windings changes little, it is possible only with a special device, for example PDO-1. In this case, this winding is compared with a known good one. The excitation winding of contactless generators (GA2, 955.3701) is checked with an ohmmeter, the output ends of which are connected directly to the winding terminals. Then check for a short to ground. To do this, one lead of the ohmmeter should be brought to its beak, the other - to any rotor ring, and in contactless generators - to the inductor bushing and any winding lead. A working winding should show a break on the ohmmeter, i.e. infinitely great resistance.
Step 2
Check the stator windings. To do this, connect the ends of the ohmmeter to one of the terminals of the winding and the iron package, i.e. check for short to ground. The device with a working winding should show an open circuit. Check the turn-to-turn short circuit in the stator windings. To do this, measure the resistance of individual phases and compare the results with each other, the difference should not be more than 10%. The phase resistance is fractions of an Ohm, therefore, high-precision measuring instruments are required for this. Complete information about the condition of the generator windings can be provided by the PDO-1 device connected to the terminals of the three phases. When the phases are identical, then one oscillographic curve is observed on the screen, if not (due to turn-to-turn closure in the phase) then there are two curves. The measurement should be repeated, having previously reversed the phases. Thus, it is possible to find the unevenness of the phases, for example, a different number of turns in them, which can occur after rewinding the stator. Check phase failure with an ohmmeter, alternately connecting it to the zero point and to the output of each phase.
