بطور کلی تستهای پذیرش کالا یا acceptance tests ژنراتور توسط IEEE standard 115-1995 SG به شرح زیر بیان شده است که می باید پس از تعمیرات، متناسب با عملیات تعمیر و ناحیه درگیر موضوع ، تستهای لازم انجام شود.
According to IEEE standard 115-1995 SG, acceptance tests are classified as follows:
• A1: insulation resistance testing
• A2: dielectric and partial discharge tests
• A3: resistance measurements
• A4: tests for short-circuited field turns
• A5: polarity test for field insulation
• A6: shaft current and bearing insulation
• A7: phase sequence
• A8: telephone-influence factor (TIF)
• A9: balanced telephone-influence factor
• A10: line to neutral telephone-influence factor
• A11: stator terminal voltage waveform deviation and distortion factors
• A12: overspeed tests
• A13: line charging capacity
• A14: acoustic noise
در خصوص آیتم مورد نظر شما به دلیل تعمیر روتور انجام تستهایی به شرح زیر ضروری حائز موضوعیت است.
A3: Resistance Measurements
DC stator and field-winding resistance measurement procedures are given in IEEE standard 118-1978.
The measured resistance Rtest at temperature ttest may be corrected to a specified temperature ts:
where k = 234.5 for pure copper (in °C).
The reference field-winding resistance may be DC measured either at standstill, with the rotor at ambient temperature, and the current applied through clamping rings, or from a running test at normal speed. The brush voltage drop has to be eliminated from voltage measurement.
If the same DC measurement is made at standstill, right after the SG running at rated field current, the result may be used to determine the field-winding temperature at rated conditions, provided the brush voltage drop is eliminated from the measurements.
A4–A5: Tests for Short-Circuited Field Turns and Polarity Test for
The purpose of these tests is to check for field-coil short-circuited turns, for number of turns/coil, or for short-circuit conductor size. Besides tests at standstill, a test at rated speed is required, as short-circuited turns may occur at various speeds. There are DC and alternating current (AC) voltage tests for the scope.
The DC or AC voltage drop across each field coil is measured. A more than +2% difference between the coil voltage drop indicates possible short-circuits in the respective coils. The method is adequate for salient-pole rotors. For cylindrical rotors, the DC field-winding resistance is measured and compared with values from previous tests. A smaller resistance indicates that short-circuited turns may be present.
Also, a short-circuited coil with a U-shaped core may be placed to bridge one coil slot. The U-shaped core coil is placed successively on all rotor slots. The field-winding voltage or the impedance of the winding voltage or the impedance of the exciting coil decreases in case there are some short-circuited turns in the respective field coil. Alternatively, a Hall flux probe may be moved in the air gap from pole to pole and measures the flux density value and polarity at standstill, with the field coil DC fed at 5 to10% of rated current value.
If the flux density amplitude is higher or smaller than that for the neighboring poles, some field coil turns are short-circuited (or the airgap is larger) for the corresponding rotor pole. If the flux density does not switch polarity regularly (after each pole), the field coil connections are not correct.
A6: Shaft Current and Bearing Insulation
Irregularities in the SG magnetic circuit lead to a small axial flux that links the shaft. A parasitic current occurs in the shaft, bearings, and machine frame, unless the bearings are insulated from stator core or from rotor shaft. The presence of pulse-width modulator (PWM) static converters in the stator (or rotor) of SG augments this phenomenon. The pertinent testing is performed with the machine at no load and rated voltage. The voltage between shaft ends is measured with a high impedance voltmeter. The same current flows through the bearing radially to the stator frame.
The presence of voltage across bearing oil film (in uninsulated bearings) is also an indication of the shaft voltage.
If insulated bearings are used, their effectiveness is checked by shorting the insulation and observing an increased shaft voltage. Shaft voltage above a few volts, with insulated bearings, is considered unacceptable due to bearing in-time damage. Generally, grounded brushes in shaft ends are necessary to prevent it.