Testing short circuit

This is a very useful nomogram to determine the performance of a motor with the help of only no-load and short-circuit test results. In slip-ring motors, it also helps to determine the external resistance required in the rotor circuit to control the speed of the motor and achieve the desired operating performance. Slip-ring motors are discussed in Chapter 5. The concept behind this nomogram is that the locus of the rotor and the stator currents is a circle. Consider the equivalent circuit of an induction motor as shown in Figure 1.15, where... 

From a short-circuit test draw the start-up current at an angle ( ). ... 

Figure 13.23 Oscillograms of an actual short-circuit test carried out on a power distribution panel (Courtesy ECS)...

To isolate the circuit after the lest is over and to also interrupt the test in between, in case the test piece fails. The breaker must possess an instantaneous capacity of more than the test current and the short-circuit MVA of the feeding generator. To achieve the desired voltage it must be suitable to perform the duties of repeated short-circuit tests. 

Figure 14.3 General arrangement of a power circuit to conduct a short-circuit test...

For a switching device (which has not been previously tested for a short-circuit test). This should be closed and held in the normal service position. The test voltage (that would generate the required level of fault current) may be applied on one set of terminals, the other terminals being shorted. The test may be continued until the short-circuit device operates to clear the fault, but in no case for less than 10 cycles. In LT assemblies the point where the short-circuit is created should be 2 0.4 m from the nearest point of supply. 

For more clarity we have reproduced in Figure 14.3 an actual test circuit and in Figure 14.4, the oscillograms of the test results of a short-circuit test successfully carried out on an LT power distribution panel (Figure 14.8) for a system fault level of 50 kAfor 1 second, at CPRI (Central Power Research Institute). From a study of these oscillograms (Figure 14.4), we can infer the following test results ... 

By the immediate first current zero it is assumed that the contacts have travelled sufficiently apart to achieve the required deionization and have built up adequate dielectric strength to withstand at least 0.95 V, . If the circuit does not interrupt at the immediate current zero at a which is so near to the point of chopping Vt , the interruption will take place only by the next current zero at point h and result in another 260 strikes by then. To study more accurate behaviour of an intenupter, with the number of restrikes and the formation of the actual transient voltage waveforms on current chopping, oscillograms similar to those during a short-circuit test may be obtained (Section 14.3.6). 

Where V and I refer to full-load current and rated voltage and IZ is the voltage measured at rated current during a short-circuit test transformer. In the case of a transformer... 

The simulated short-circuit test was developed to characterize the response of the separator to a short circuit without the complications of battery electrodes. The separator was spirally wound between lithium foils and placed in an AA-size can. To avoid lithium dendrite formation, an alternating voltage was applied to the cell. The cell current and can temperature were monitored. Figure 6 shows the behavior of Celgard membranes. 

Short-circuit tests with lithium-ion batteries have been reported recently [35]. This work shows that the separator provides shutdown when the battery is subjected to an external short circuit with the PTC bypassed. The large increase in impedance of the separator is attributed to the temperature rise in the battery. 

There are additional advantages with recombination batteries. For example, topping up with water is not necessary over the whole life of the battery, and the battery can be designed to survive a 30-day short-circuit test and, after recharge, have virtually the same capacity as before the test. Due to a marked reduction in water decomposition, there is only a small release of hydrogen gas and a low rate of self-discharge. Many studies of VRLA batteries have been published in recent years some examples are given as Refs. [2-14] (see also Chapter 1). 

Association of Short-circuit Testing Authorities. American Society for Testing and Materials. Automatic voltage regulator. 

Short circuit testing authority in The Netherlands. Kilogram. 

Figure 20.16 shows the typical nail penetration behavior of a Li-Ion cell with shutdown separator. Clearly, there was a voltage drop from 4.2 to 0.0 V, instantaneously, as the nail penetrates through (when internal short circuit occur) and temperature rose. When the heating rate is low, the cell stops heating when the temperature is close to separator shutdown temperature as shown in Fig. 20.16a. If the heating rate is very high, then the cell continues to heat and fails the nail penetration test as shown in Fig. 20.16b. In this case, the separator shutdown is not fast enough to stop the cell from thermal runaway. Thus a separator only helps to avoid delayed failures in case of internal short circnit as simulated by nail and bar crush tests. Separators with high-temperature melt integrity and good shutdown feature (to avoid delayed failures) are needed to pass internal short-circuit tests.

HGURE 17.3 External short circuit test on a single lithium-ion cell using a 50 m J load. 

FIGURE 17.5 Temperatures recorded during the 14-cell short circuit test on lithium-ion 18650 cells. 

An external short-circuit test was carried out on a 16P bank of cells with a load of 2 mQ [16]. No catastrophic failures were observed. The maximum temperature recorded was 89 °C and the total peak current observed was 361 A. The voltage dropped to 1.48 Vat short initiation, which then fell to approximately 0.41 V about 3 s into the shorting process and then decreased to less than 100 mV after 2 min into the whole process. The voltage then settled down to between 50 mV and 60 mV until the last cell was fully discharged. 

It is possible to quantify some of the important transformer parameters through testing. Two simple tests, the open-circuit and short-circuit tests, allow the user to identify the leakage inductance, the coil resistance, the core loss, and mutual inductance of the transformer. Since the characteristics of the transformer change with frequency, the tests should be done at the frequency (or frequencies) of interest. 

The short-circuit test is conducted by shorting one of the transformer s cods, and applying rated current to the other cod. Only a fraction of the rated voltage is needed to produce the rated current. The input current and power are then measured. Figure 10.10 shows a circuit diagram for this test. 

Open- and short-circuit tests were conducted on a 60-Hz, 500-W 120 6-V transformer. In the short-circuit test, the readings were 10 V, 4.16 A, and 24 W. The combined impedance of the coil resistance and the leakage inductance can be found using Eq. (10.35). The resistance and reactance of the transformer can then be found using Eq. (10.35). The resistance and reactance of the transformer can then be found using Eq. (10.36) and Eq. (10.37). 

Battery safety is so important for mobile and vehicle apphcations. Especially for vehicles, on the road, accident likely becomes heavy, and the crash accident should not bring more danger by release of the energy stored in the cells. And various tests are usually conducted. In ZEBRA battery case, test results were reported. Crash of an operative battery against a pole with 50 km/h, overcharge test, overdischarge test, short circuit test, vibration test, external fire test, and submersion of the battery in water have been specified and performed [6]. The ZEBRA battery did pass all these tests owing to its four-barrier safety concept [7, 8] chemical aspects, cell case, thermal structure, and battery controller. 

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