IEEE Std C57.12.58 pdf free download

IEEE Std C57.12.58 pdf free download.Conducting a Transient Voltage Analysis of a Dry-Type Transformer Coil.
3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause.’ Standard transformer terminology, which is available in IEEE Std C57.12.80TM, shall apply.S basic lightning impulse insulation level (BIL): A specific insulation level expressed in kilovolts of the crest value of a standard lightning impulse.
4. General
4.1 Functional diagram Because the function of transient analysis is to determine the response of various parts of the coil to an impulse wave, the circuitry and instrumentation shall be designed with that goal in mind. From a functional point of view, the relationship between the test specimen, circuitry, and instrumentation may be seen best in the form of a block diagram, as shown in Figure 1.
4.2 Recurrent surge generator The voltage-generation and wave-shaping functions are performed by a device called a recurrent surge generator. This generator shall duplicate and repeat, at some voltage compatible with low-voltage instrumentation, the wave shapes seen at the output of an impulse generator. The surge generator, since it is operating at a low voltage, may generate the wave on a recurrent basis. In fact, observation of voltages on an oscilloscope face will be facilitated if the voltage wave is recurrent.
4.3 Voltage measurement The voltage is applied across the test coil at the line terminals. Voltages between various points within the coil are measured with a high- frequency oscilloscope or other device using a differential amplifier and probes at the input. It is highly desirable that there be synchronization between the generator and the recording instrumentation. This may be accomplished by either a delay in the signal or triggering in advance of the wave. This ensures the establishment of a zero reference point at the readout. Digital equipment may offer other synchronization methods.
5. Recurrent surge voltage generator circuitry
5.1 Description of the circuit The circuitry is shown in Figure 2 in its simplest form to provide the function of voltage generation and wave shaping. The voltage is obtained from an ac source and is transformed to a desired level through a variable auto transformer and isolation transformer. Only the isolation transformer is shown in Figure 2. The magnitude of the voltage is determined by the initial charging voltage, the number of capacitors in series at discharge, and the voltage efficiency of the circuit. The wave shape is determined largely by the constants of the impulse generator or IG and the impedance of the load. The most practical range is between 50 V and 150 V. Accuracy is best at higher voltages. The repetition rate of the wave may be at the ac power frequency.
The generator capacitor, C, is charged during the positive half-cycle through the diode, D. The diode shall be rated so that it will hold off twice the transformer output voltage during the negative half-cycle. The diode shall also be capable of carrying the maximum charging current. The actual pulse generation is performed by the capacitor, C, and the switch, SW. The switch is closed synchronously with the power frequency. This should occur during the negative half-cycle, when the diode, D is blocking. The switch may take different forms, such as a thyratron, ac-driven mercury-wetted switches, and a silicon controlled rectifier (SCR). It is important that there be no bounce or other closing transients in the switch that would distort the shape of the wave front. Resistors R and R2, along with capacitor C2, help shape the wave. In reality, the values of capacitor C and the inductance and capacitive values of the test coil also influence the wave shape. For this reason, wave shape adjustments should be made with the coil in the circuit.
IEEE Std C57.12.58 pdf download.