Discussion on voltage ratio, polarity and group test method of power transformer
There is a polarity relationship between the primary and two sides of the power transformer coil. If a few coils or several transformers are combined, it is necessary to know its polarity before it can be used properly. Two for transformer coil, if the potential at any moment in the induction have the same direction, is called polarity or minus polarity, otherwise with polarity. Transformer connection group is one of the important parameters of transformer. It is an important condition for parallel operation of transformer, and it needs measurement in many cases.
First, the purpose and significance of transformer polarity group and voltage ratio test
In the condition of no-load operation of transformer, the ratio of voltage of high voltage winding to voltage of low voltage winding is called transformer to change ratio:
Voltage is generally calculated by line voltage, it is an important performance index of transformer, and the purpose of measuring transformer ratio is:
(1) the voltage of each winding is guaranteed to be within the allowable range of the technique;
(2) check the accuracy of winding turns;
(3) determine whether the lead wires and tap switches of the windings are connected properly.
Two transformer polarity group and voltage ratio test method
1. The polarity of the transformer is determined by the DC method
The methods of measuring the polarity of transformer windings are direct current method and alternating current method.
DC: a battery connected with a high voltage transformer terminals, in the two side of the transformer is connected with a milliammeter or microammeter, observe the swing direction when the battery switch is closed when the experiment, can determine the polarity.
2, DC method to determine the transformer group;
3 、 measure transformer ratio with HSXBBC-II transformer ratio tester.
Three, attention and result analysis
(1) to determine the polarity of the DC method, test process should be repeated several times to avoid because of hand quickly and make the wrong conclusion swing.
(2) in the measurement group, the ratio of the transformer transformer should choose high voltage and small range DC voltmeter, ammeter or multimeter; the voltage transformer ratio small selection of low and wide range of the voltmeter, ammeter or multimeter.
(3) the transformer voltage ratio should be at each tap for measuring, when more than one coil with a tap, can be measured in each coil all turn under the tap position, while the opposite with coil is connected in rated tapping.
(4) with load regulating device, it must be switched by electric actuator.
(5) the entire measurement process should pay special attention to the transformer, A and a can not be switched, otherwise the high voltage will enter the bridge.
(6) when the test voltage is gradually increased, when the voltmeter rises rapidly to full level, the power shall be switched off for inspection.
(7) the voltage corresponding to the corresponding voltage shall be the same as that of the nameplate on the measured results; the allowable tap voltage ratio is allowed to be deviation, and the deviation of other tap shall be within the impedance value of the transformer, but not exceeding the allowable value.