IEEE 115-2019 pdf download
IEEE 115-2019 pdf download.IEEE Guide for Test Procedures for Synchronous Machines Including Acceptance and Performance Testing and Parameter Determination for Dynamic Analysis.
4.3.5 Field resistance for running temperature tests
To determine the field temperature under specified or desired load conditions, the field resistance should be measured by the drop-of-potential method after the machine has been operated at the required field current and as near as practicable to the required loading conditions long enough for a uniform temperature to be reached. The temperature of the field winding is then determined in accordance with 7.4.4. The resistance obtained from this test is called R, in Equation (59).
Including brush voltage drop in the measured field voltage may introduce a substantial error in the temperature determination; therefore, it is highly desirable to eliminate or reduce its effect in this test (see 4.3.6).
When measuring the resistance of the field with the machine loaded, the voltage regulator should be disconnected, and a number of armature voltage, power, and current readings should be taken simultaneously with field current and voltage readings to help ensure that the resistance is measured under uniform conditions.
4.3.6 Effect of brush voltage drop
To determine the field resistance of a running machine accurately, it is necessary to obtain the voltage drop across the field winding without including the voltage drop of the brushes supplying the field current. This step is especially important when the field current is very small, e.g., when determining the reference resistance value (see 4.3.4). For this purpose. it is desirable to measure the voltage drop directly across the collector rings, using special brushes that arc in contact with the collector rings only during voltage measurement. For this purpose, it is possible to use the following:
a) Special copper or bronze leaf brushes bearing directly on the collector rings.
b) Insulated brushes that have not developed a glazed surface.
c) Insulated special carbon or graphite brushes compounded with highly conducting materials to reduce their resistance.
Unless a very small voltage drop occurs across these measurement brushes, a significant error may be introduced.
When these special methods of voltage measurement are not available, the voltage measurement necessarily includes the voltage drop across the brushes. In such cases, efforts to reduce its effect should be made. Since the voltage drop across the brushes remains reasonably constant with varying current, the effective brush resistance is reduced by increasing the current density. This step may be accomplished by reducing the number or cross section of brushes used during the test, particularly for low field currents. When information is available regarding the expected voltage drop across the brushes, more accurate results can be obtained by subtracting the brush drop from the measured voltage before calculating the resistance, but the results thus obtained should be used with caution.
On machines whose collectors have high peripheral speed, care must be exercised to avoid damaging the surface condition of the collector by voltage-measuring devices.
4.4 Tests for short-circuited field turns
4.4.1 General
The object of these tests is to detect field coils that have short-circuited turns, an incorrect number of turns, or incorrect conductor size. Not all short-circuited field turns are apparent at standstill, and a test at rated speed may be required. Short-circuited field turns can be
1. Voltage drop, dc (see 4.4.2)
2. Voltage drop, ac (see 4.4.3)
3. DC resistance (see 4.4.4)
4. Exciting coil for cylindrical rotors (sec 4.4.5)
5. Rotor waveform detection for cylindrical rotors (see 4.4.6)
4.4.2 Method 1. Voltage drop, dc
This method can be used to detect short-circuited turns only when connections between coils are accessible. The test is made, with the rotor at standstill, by passing a constant dc through the entire field winding. The drop in voltage of each coil or pair of coils is measured by means of a voltmeter. If these readings vary more than ± 2% from the average, it is an indication that there may be short-circuited turns in the coil or that part of the winding may be wound with the wrong number of turns or size of conductor.
