Surge-testing

The impulse test is basically an in-house coil insulation withstand test for surge voltages and forms a part of the test requirement for HT machines with resin-rich formed coils of 2.4 kV and above. Once the machine is assembled, such a test is unnecessary, as it may not be able to reveal deficiencies, if any, in the insulation of the coils deep inside the slots. Moreover, if a failure is noticed on the assembled machine, there is no option but to scrap the whole winding. 

In practice, voltage surges can be of various shapes (Figure 17.2) and may even be so steep as to have a front time as low as 0.2 )as or less. For the purpose of the impulse test, however, only a standard lightning impulse, as defined by 1.2/50 (Section 17.6) can be considered. 

X time taken by the impulse to rise from 0% to 95% of its peak value For the sake of laboratory testing and analytical studies, these surges have been represented by standard impulse waveforms. According to lEC 60060-1 a 1.2/50 /is impulse is called a standard lightning impulse, and a 250/2500 /is impulse a standard switching impulse. 

On the load side, the interrupter is connected through a cable to the equivalent circuit, with the required quantities of lumped resistance and reactance, to represent the motor to be tested, under a locked rotor condition. The circuit would also represent an interruption immediately after a start, to check for the most onerous operating condition for the interrupter to generate the highest surges as discussed earlier. 

With these data, one can determine the dielectric curve the machine must have when switched with such an interrupting device. This can be compared with the actual dielectric curve of the machine (Figure 17.18) obtained from its manufacturer to decide the compatibility of the interrupting device for the machine or vice versa and the extent of surge protection, if necessary. For more details and results of similar simulation tests, see Central Board of Irrigation and Power (1995). 

For adequate protection of the machine it is essential to know the amplitude, F, and the rise time, /, of the severest voltage surge (FOW) that may occur on the system. It is recommended that the actual field tests be conducted for large installations according to the recommended simulation test circuits, noted above, to ascertain these surges. 

Accounting for reflections, the total time must be considered as 2 X 1400 or 2800 /ts. Accordingly, 2800, us is specified by lEC 60099-4 for the testing of the arrester under the worst conditions. The arrester must also have the capability to successfully discharge the prospective surge under such conditions. 

The power frequency voJiage lest refers to indoor units. The outdoor eapaciior units must be subjected to a wet test as in lEC 60060-1.. 3 The choice between list I and list 2 will depend upon the extent of exposure of the units to the internal and external vollage surges and... 

ANSI/IEEE C.37.90.1/1989 Guide for surge withstand capability tests, for protective relays and relay systems ... 

Whether surge is eaused by a deerease in flow veloeity or an inerease in rotational speeds, either the indueer or vaneless diffuser ean stall. Whieh stalls first is diffieult to determine, but eonsiderable testing has shown that for a low-pressure-ratio eompressor, the surge initiates in the diffuser seetion. For units with single-stage pressure ratios above 3 1, surge is probably initiated in the indueer. 

The author has a patent for a dynamic surge-detection system, using a boundary-layer probe, presently undergoing field tests. This system consists of specially mounted probes in the compressor to detect boundary-layer flow... 

The use of pressure transdueers and easing aeeelerometers in the exit piping has been instrumental in deteeting eompressor surge. It has been found that as the unit approaehes surge, the blade passing frequeney (number of blades times rpm) and its seeond and third harmonie beeome exeited. In a limited number of tests it has been noted that when the seeond harmonie... 

Performance maps These are performanee maps based on design or initial tests (base lines) of the various maehinery parameters. These maps, for example present how power output varies with ambient eonditions, or with properties of the fuel, or the eondition of the filtration system or how elose to the surge line a eompressor is operating. On these maps, the present value is displayed, thus allowing the operator to determine the degradation in performanee oeeur-ring in the units. 

Waste water rules sometimes require that water conform to the limitations at all times. Under such rules, surges of non-conforming sewage are not permitted. Tests run on composite samples over a 24-hour period, for example, will then not be acceptable. 

Hodgson TA, Shirlaw PJ, Challacombe SJ Skin testing after anaphylactoid reactions to dental local anesthetics. A comparison with controls. Oral Surg Oral Med Oral Pathol 1993 75 706-711. 20... 

In addition, a recent primate study reported that dietary consumption of soy infant formula reduced the neonatal testosterone surge and increased Leydig cell numbers in the testes of male marmosets. However, the longterm effects on the fertility of the animals has not been determined, and the health implications of these findings for humans are unclear (Sharpe et al,... 

ENA was recently used for remote on-line corrosion monitoring of carbon steel electrodes in a test loop of a surge water tank at a gas storage field. An experimental design and system for remote ENA and collection of electrochemical impedance spectroscopy (EIS) data (Fig. 13) have been presented elsewhere. In the gas storage field, noise measurements were compared with electrode weight loss measurements. Noise resistance (R ) was defined as... 

Abstract. The Milky Way harbours two disks that appear distinct concerning scale-heights, kinematics, and elemental abundance patterns. Recent years have seen a surge of studies of the elemental abundance trends in the disks using high resolution spectroscopy. Here I will review and discuss the currently available data. Special focus will also be put on how we define stars to be members of either disk, and how current models of galaxy formation favour that thick disks are formed from several accreted bodies. The ability for the stellar abundance trends to test such predictions are discussed. 

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