Method of testing partial discharge of rotating electrical machine driven by inverter

1. A method of testing impulse partial discharges in a rotating electrical machine comprising the steps of:

placing electrodes on the surface of an insulation layer of a coil conductor series connection area of a coil of the rotating electrical machine, or to the surface of an insulation layer of a coil turn conductor of a coil of a winding of the rotating electrical machine;

measuring a waveform of grounding voltage of the coil turn conductor through the medium with an electrostatic capacitance (C x ) of the insulation layer of the coil conductor series connection area, or of the insulation layer of the coil turn conductor; and

measuring a partial discharge, while measuring a voltage developing in the coil or across a winding turn in the coil, from a change in a waveform of the grounding voltage,

wherein a capacitor is connected in series with ground and with the insulation layer of the coil conductor series connection area, or the capacitor is connected in series with ground and with the insulation layer of the coil turn conductor;

wherein a measurement is made of a grounding voltage waveform applied across the capacitor;

wherein the measured grounding voltage waveform is converted to a grounding voltage waveform applied to the winding, by using a voltage division ratio determined from a separately measured ratio (α x ) between the electrostatic capacitance (C x ) of insulation layer and the electrostatic capacitance (C x ′) of the capacitor; and

wherein a partial discharge is measured from a change in the converted grounding voltage waveform, while measuring a voltage applied to the coil and across a winding turn in the coil.

2. The method of testing impulse partial discharge in the rotating electrical machine according to claim 1 ,

wherein an electrostatic capacitance of each of a first set of capacitors (C 1 ′, C 2 ′ . . . or C n ′) has a constant ratio (α) to an electrostatic capacitance of a first respective insulation layer (C 1 , C 2 , . . . or C n ), each of which is an insulation layer of the coil conductor series connection area in the rotating electrical machine winding, and wherein each of the first set of capacitors is connected in series with ground and with an electrode applied to the surface of its first respective insulation layer;

wherein an electric capacitance each of a second set of capacitors (C 12 ′, C 13 ′ . . . or C 15 ′) has a constant ratio (α) to an electrostatic capacitance of a second respective insulation layer (C 12 , C 13 , . . . or C 15 ), which is an insulation layer of the coil turn conductor, and wherein each of the second set of capacitors is connected in series with ground and with an electrode applied to the surface of its second respective insulation layer;

wherein voltages generated in the coil and across a winding turn in the coil are determined from a difference between waveforms of grounding voltages generated in the electrostatic capacitance (C 1 ′, C 2 ′ . . . C n ′) and from the constant ratio (α); and

wherein a partial discharge is measured while measuring the difference between waveforms of grounding voltages.

3. The method of testing impulse partial discharge in the rotating electrical machine according to claim 1 ,

wherein an electrostatic capacitance (C 1 ′, C 2 ′ . . . or C n ′) of each of a first set of capacitors has a constant ratio (α) to an electrostatic capacitance (C 1 , C 2 , . . . or C n ) of a first respective insulation layer, which is an insulation layer of the coil conductor series connection area in the rotating electrical machine winding, and wherein each of the first set of capacitors is connected in series with ground and with an electrode applied to the surface of its first respective insulation layer;

wherein an electric capacitance (C 12 ′, C 13 ′ . . . or C 15 ′) of a capacitor has a constant ratio (α) to an electrostatic capacitance (C 12 , C 13 , . . . or C 15 ) of a second respective insulation layer, which is an insulation layer of the coil turn conductor, and wherein each of the second set of capacitors is connected in series with ground and with an electrode applied to the surface of its second respective insulation layer;

wherein voltages generated in the coil and across a winding turn in the coil are determined from a difference between waveforms of grounding voltages generated in the electrostatic capacitance (C 1 ′, C 2 ′, . . . C n ′); and

wherein a partial discharge is measured while measuring said voltages.

4. A method of testing impulse partial discharges in a rotating electrical machine comprising the steps of:

placing electrodes on the surface of an insulation layer of a coil conductor series connection area of a coil of the rotating electrical machine, or to the surface of an insulation layer of a coil turn conductor of a coil of a winding of the rotating electrical machine;

measuring a waveform of grounding voltage of the coil turn conductor through the medium with an electrostatic capacitance (C x ) of the insulation layer of the coil conductor series connection area, or of the insulation layer of the coil turn conductor; and

measuring a partial discharge, while measuring a voltage developing in the coil or across a winding turn in the coil, from a change in a waveform of the grounding voltage,

wherein on the basis of measurement results, a magnitude of an impulse test voltage corresponding to a voltage across a predetermined winding turn is determined to thereby measure a partial discharge,

wherein a capacitor is connected in series with ground and with the insulation layer of the coil conductor series connection area, or the capacitor is connected in series with ground and with the insulation layer of the coil turn conductor;

wherein a measurement is made of a grounding voltage waveform applied across the capacitor;

wherein the measured grounding voltage waveform is converted to a grounding voltage waveform applied to the winding, by using a voltage division ratio determined from a separately measured ratio (α x ) between the electrostatic capacitance (C x ) of insulation layer and the electrostatic capacitance (C x ′) of the capacitor; and

wherein a voltage applied to the coil and across a winding turn in the coil is measured from a change in the converted grounding voltage waveform, and on the basis of the results of the measurements, a magnitude of an impulse test voltage corresponding to a voltage across a predetermined winding turn is determined to thereby measure a partial discharge.

5. A method of testing impulse partial discharges in a rotating electrical machine comprising the steps of:

placing electrodes on the surface of an insulation layer of a coil conductor series connection area of a coil of the rotating electrical machine, or to the surface of an insulation layer of a coil turn conductor of a coil of a winding of the rotating electrical machine;

measuring a waveform of grounding voltage of the coil turn conductor through the medium with an electrostatic capacitance (C x ) of the insulation layer of the coil conductor series connection area, or of the insulation layer of the coil turn conductor; and

measuring a partial discharge, while measuring a voltage developing in the coil or across a winding turn in the coil, from a change in a waveform of the grounding voltage,

wherein an electrostatic capacitance (C 1 ′ . . . , or C 12 ′ . . . ) of the capacitor connected between ground and with a first respective insulation layer, which is an insulation layer of the coil conductor series connection area, or between ground and with a second respective insulation layer, which is an insulation layer of the coil turn conductor, is at least 10 times of a stray capacitance of a voltage measurement probe, and corresponds to (C x ′) of the following formula:

C x ′<(PDIV)· C x /( V imp −(PDIV));

wherein partial discharge initiation voltage (PDIV) represents when an electrode is applied to the surface of insulation layer of the coil conductor series connection area, or electrodes are applied to the surface of insulation layer of the coil turn conductor.