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1、FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION Subject 2520 (1004-4) July 24, 2007 SUMMARY OF TOPICS The following changes in requirements are being proposed: 1) For Preliminary Review Only: The proposed fi rst edition of UL 1004-4, Electric Generators. There are no new technical chan
2、ges being proposed, just the separation of electric generator requirements into a separate standard. COMMENTS DUE: SEPTEMBER 14, 2007 The proposed fi rst edition of UL 1004-4 is being provided for review and comment prior to being balloted by the Standards Technical Panel for Motors (STP 1004). Comm
3、ents were received during the July 28, 2006 preliminary review and the January 10 L is the coils inductance; and di/dt is the time derivative of the applied current pulse. A1.2 The terminal voltage V at the leads of the coil is actually a summation of the induced voltage created between individual l
4、oops in the coil. If the insulation separating adjacent coils is weak and if the induced voltage is higher than the dielectric strength of the weak insulation, an arc will form between the coils. Surge testing equipment is designed to create the induced voltage between adjacent coils and detect the
5、arcing indicative of weak or failing insulation. in which: Fi(1) is a point in the time series of the fi rst waveform; Fj(2)is the corresponding point in the time series of the second waveform; Npts is the number of points in the time series sampled at each “jth” point; and EAR1-2is the Error Area R
6、atio of the test Fj(2)waveform with respect to the reference Fi(1)waveform. JULY 24, 2007SUBJECT 2520-7- Copyright Underwriters Laboratories Inc. Provided by IHS under license with ULLicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networ
7、king permitted without license from IHS -,-,- FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION A1.3 Figure A1.1 shows a block diagram typical of todays instrumentation. The internal capacitor is charged to a known voltage by the power supply. At a specifi c time, a high voltage switch c
8、loses which transfers the charge from the capacitor through the windings of the coil. If the resistances and loss of the entire circuit are such that the system is under damped, charge will be able to fl ow through the inductor and on to the other side of the capacitor resulting in an oscillation Th
9、is process of ringing will repeat until the resistances and losses in the circuit completely absorb all of the energy that was originally on the capacitor. The measurement of the terminal voltage of the coil vs. time gives the surge waveform, which shows the damped oscillation. This is generated tex
10、t for fi gtxt. A1.4 The ringing frequency of the dampened sinusoidal waveform will be according to the following formula: Figure A1.1 Block diagram typical surge instrumentation JULY 24, 2007SUBJECT 2520-8- Copyright Underwriters Laboratories Inc. Provided by IHS under license with ULLicensee=IHS Em
11、ployees/1111111001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networking permitted without license from IHS -,-,- FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION in which: f = the ringing frequency of the resulting waveform L = the inductance of the ma
12、chine winding under test C = the capacitance of the internal charge capacitor R = the system resistance If the turn-turn insulation fails with an arcing short between two turns in the coil, a fraction of the inductance will be shorted out of the circuit. From the equation above, the ringing frequenc
13、y f will increase as the inductance decreases due to the short. An increase in the ringing frequency will show itself to be a jump to the left of the ringing pattern. To reiterate, it is this sudden increase in ringing frequency that is the indication of the arcing turn-turn fault. Depending on the
14、coil and the location of an arcing short, the magnitude of the surge waveform may also slightly decrease. Todays instrumentation will slowly increase the test voltage and “look” for the increase in ringing frequency. A2 Automatic Fault Detection Methods A2.1 The greatest advancement in surge testing
15、 has come about with use of high-speed analog and digital electronics and the application of computers to control the testing process. Algorithms programmed into the computer can detect small variations in the shape of the waveform that peoples eyes miss. An additional benefi t to having a computer
16、control the test is the immediate shutdown of the test after the insulation “fails” a single pulse. The detection algorithms include: a) Zero Crossing Shift b) Pulse-to-Pulse EAR c) Line-to-Line EAR A2.2 Pulse-to-Pulse EAR Where the computer has the advantage over the human is detecting slight chang
17、es of the waveform shape. The computer uses the Error Area Ratio (EAR) to get a quantitative measure of the difference in shape of two subsequent waveforms called the Pulse-to-Pulse EAR (ppEAR). Before describing the ppEAR, the EAR calculation will be introduced. The formula for the Error Area Ratio
18、 is: This is generated text for fi gtxt. JULY 24, 2007SUBJECT 2520-9- Copyright Underwriters Laboratories Inc. Provided by IHS under license with ULLicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networking permitted without license from
19、 IHS -,-,- FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION This simple formula is a fast calculation for a computer, yet it is very accurate at detecting a difference in the shape of the two waveforms. Two exactly identical waveforms will have an EAR of 0%. Two waveforms that look iden
20、tical to the eye can have EAR values in the 4-5% range. Two waveforms with a noticeable difference will have an EAR value in the range of 10% or higher. The application of this formula for the ppEAR is to compare the most recently acquired waveform to the previously acquired waveform as the test vol
21、tage is slowly increased. The two waveforms are expected to be different since one is at a slightly higher test voltage than the other. This difference is on the order of 4%. However, if the most recently acquired waveform is above the arcing voltage for the failed insulation, its shape will change.
22、 The change in shape will then be detected by the EAR algorithm. Figure A1.2 shows the ppEAR detecting an arcing turn-turn insulation failure. This is generated text for fi gtxt. in which: Fi(1) is a point in the time series of the fi rst waveform; Fj(2)is the corresponding point in the time series
23、of the second waveform; Npts is the number of points in the time series sampled at each “jth” point; and EAR1-2is the Error Area Ratio of the test Fj(2)waveform with respect to the reference Fi(1)waveform. JULY 24, 2007SUBJECT 2520-10- Copyright Underwriters Laboratories Inc. Provided by IHS under l
24、icense with ULLicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networking permitted without license from IHS -,-,- FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION Figure A1.2 shows two surge waveforms and a small ppEAR graph
25、 in the lower right corner of the display. The two waveforms represent the previous to fail and the failed waveform. The small graph shows the running ppEAR where the fi rst value plotted is for the two pulses at 800V and 810V. The ppEAR values for successive pulses, each 10 volts higher than the pr
26、evious pulse, are shown along the majority of the graph until a pulse is applied above the dielectric strength (2700V) for the weak insulation. The ppEAR for the failed pulse compared to the previous to fail pulse is shown completely off the scale on the graph. The dashed line along the top of the g
27、raph represents the user defi ned maximum allowable ppEAR for the test. Anything above this value will fail the test. In the fi gure above, the maximum allowable ppEAR was set to 5% and the “failed” ppEAR was 12%. The ability to perform such detection schemes as the ppEAR is a testament to the advan
28、cement of the surge testing instrumentation available today. The ability to precisely control the impulse voltage, to precisely trigger the impulse generator, and the ability to implement advanced signal processing algorithms during the testing process are key to being able to fi nd the very small c
29、hanges in surge waveforms that represent insulation failures. Copyright 2007 Underwriters Laboratories Inc. Figure A1.2 Example of coil failing pulse-to-pulse EAR JULY 24, 2007SUBJECT 2520-11- Copyright Underwriters Laboratories Inc. Provided by IHS under license with ULLicensee=IHS Employees/111111
30、1001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networking permitted without license from IHS -,-,- FOR INTERNAL UL OR CSDS USE ONLY NOT FOR OUTSIDE DISTRIBUTION JULY 24, 2007SUBJECT 2520-12- No Text on This Page Copyright Underwriters Laboratories Inc. Provided by IHS under license with ULLicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 08/07/2007 01:59:20 MDTNo reproduction or networking permitted without license from IHS -,-,-