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1, the detection of no-load current of special transformer for medium frequency induction melting furnace
(1) Direct measurement method. Open all the secondary windings, place the multimeter in the appropriate gear of the AC current, and string it into the primary winding. When the primary winding of the transformer is connected to its rated voltage supply, the multimeter indicates the no-load current value. This value should not be greater than 10%-20% of the transformer's full load current. If it exceeds too much, the transformer has a short-circuit fault.
(2) Indirect measurement method. A 10Ω/5W resistor is placed in series in the primary winding of the transformer, and the secondary is still completely empty. Turn the multimeter to the AC voltage block. When the primary winding of the transformer is connected to its rated voltage supply, the voltage U across the resistor R is measured with two test leads, and then the no-load current I is calculated by Ohm's law, ie I=U/R.
2. Detection of no-load voltage of special transformer for medium frequency induction melting furnace,
When the primary winding of the transformer is connected to its rated voltage power supply, the idle voltage value of each winding (U21, U22, U23, U24) should be measured in sequence with the multimeter's AC voltage gear. The allowable error range is generally: high voltage winding. ≤±10%, low voltage winding ≤±5%, voltage difference between two sets of symmetrical windings with center tap ≤±2%.
3, the special transformer of the intermediate frequency induction melting furnace identifies the same name end of each winding of the transformer
When using a transformer, sometimes two or more secondary windings can be used in series in order to obtain the required secondary voltage. When the transformer is used in series, the same name of each winding participating in the series must be correctly connected, and it cannot be mistaken, otherwise the transformer will not work normally. The method of discriminating the same name of each winding of the transformer is as follows.
Anyone can find a set of winding coils connected to the 1.5-3V battery, and then connect the remaining winding coils to the positive and negative terminals of the DC millivoltmeter or DC mA meter. When the power is turned on, the pointer of the watch will swing quickly. If the pointer is deflected in the positive direction, the wire end of the battery positive terminal and the wire terminal of the positive terminal of the power meter are the same name; if the pointer is deflected in the reverse direction, the battery is positive. The wire end is the same name as the wire end of the negative terminal of the power meter. Pay attention to the following two points when testing:
(1) If the boosting winding of the transformer (that is, the winding with more turns) is connected to the battery, the meter should use the minimum range to make the pointer swing larger to facilitate observation; if the transformer's step-down winding (ie, the number of turns) If there are fewer windings to connect the battery, the meter should use a larger range to avoid damage to the meter.
(2) When the power is turned on, the pointer will deflect in a certain direction, but when the power is turned off, the pointer will deflect in the opposite direction due to the self-inductance. If the time interval between turning the power on and off is too short, it is very likely that only the direction of deflection of the pointer when disconnected is seen, and the measurement result is mistaken. Therefore, after turning on the power, wait a few seconds and then disconnect the power supply. You can also measure it several times to ensure the accuracy of the measurement.
4. Comprehensive detection and identification of transformers and transformers for medium frequency induction melting furnace
(1) Transformer short circuit fault detection. The main symptoms after a short-circuit fault in the transformer are severe heat generation and abnormal secondary winding output voltage. Generally, the more short-circuit points between turns in the coil, the greater the short-circuit current, and the more severe the transformer heats up. A simple way to detect if a transformer has a short-circuit fault is to measure the no-load current. A transformer with a short-circuit fault will have a no-load current that is much greater than 10% of the full-load current. When the short circuit is severe, the transformer will heat up quickly within a few tens of seconds after the no-load power-on, and the iron core will feel hot when touched by hand. At this time, it is not necessary to measure the no-load current to conclude that the transformer has a short-circuit point. Generally, the temperature rise of the transformer is 40~50C. If the quality of the insulating material used is good, the temperature rise can be increased.
(2) Insulation performance test. Use the multimeter ohmic block RxlOk block to measure the resistance between the core and the primary winding, the primary winding and the secondary winding, the iron core and the secondary winding, respectively, which should be infinite, otherwise the transformer insulation performance is poor.
(3) Measure the winding continuity. Use the multimeter Rx1 block to measure the resistance between the primary and secondary windings of the transformer. Generally, the resistance of the primary winding should be tens of ohms to several hundred ohms. The smaller the power of the transformer, the larger the resistance value; the resistance value of the secondary winding is generally For a few ohms to a few hundred ohms, if the resistance value of a certain group is infinite, the winding has an open circuit fault.
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