湘西干式变压器：绕组直流电阻测定

绕组直流电阻测定 　　
通过本项目的测定，检查绕组内部引线与绕组的焊接质量绕组所用导线规格是否符合设计。分接湘西干式变压器，引线与套管等载流部分的接触是否良好；三相电阻是否平衡；并作为温升试验中的测试及判断电压比和湘西干式变压器故障诊断的辅助手段等。
在湘西干式变压器负载试验中，对于附加损耗较大的湘西干式变压器，要提供测量较准确的直流电阻，以便计算电阻损耗部分用。
在湘西干式变压器温升试验中，用电阻法侧量绕组的平均温度时，直流电阻的测量误差好不超过±0. 2，以便达到要求。而选择适当的方法和测量设备，是保证测量准确度的关健。
直流电阻的测定方法有电压降法和电桥法。

1.电压降法
它是根据欧姆定律R=U/I原理在被试电阻上通以直流电流，用多量程的毫伏-伏特表测量电阻上的电压降，然后算出电阻。为了减少接线所造成的测量误差，测量小电阻时，电路中电压表接在电流表之内；测量大电阻时，电流表接在电压表之内。测量时必须待电源电流稳定后，才接入电压表进行读数。而在断开电源前，一定要先断开电压表，以免因湘西干式变压器绕组的电感产生反电动势而损坏电表。
由于此方法存在准确度不高、需要换算等缺点，因此，很少采用，一般仅用于检查性试验。

2.电桥法
电桥法测量具有准确度高、灵敏度高、能直接读数等优点。
测量电桥有单臂电桥(惠司登电桥)和双臂电桥（凯文电桥)两种。通常使用0.05-0.2级电桥较好。以前常用的电桥有QJ-23 型和850型携带式单臂电桥；QJ-101型和QJ-103型携带式双臂电桥；QJ-5型双单臂(凯惠)两用电桥等等。一般湘西干式变压器采用QJ-101、QJ-103和850型电桥即可。对于2Ω以上的直流电阻，可采用单臂电桥测量；对于2Ω以下的直流电阻，一般应采用双臂电桥测量。

Winding resistance measurement

Through the project determination, check the internal winding lead wire and winding winding wires for welding quality meets the design specifications. Tap switch, leads and bushings, current-carrying parts contact is good; phase resistance is balanced; and as the temperature rise test and judge the voltage ratio and auxiliary means for transformer fault diagnosis.In the transformer load test, for the additional loss of large transformer, to provide more accurate DC resistance measurement, in order to calculate the resistance loss part.In the transformer temperature rise test, resistance method measuring winding DC resistance when the average temperature, the measurement error of no more than + 0.2, in order to meet the requirements. While selecting the appropriate method and measuring equipment, is the key to ensure measurement accuracy.DC resistance determination method of voltage drop method and bridge method.The 1 voltage drop methodIt is according to Ohm's law of R = U / I principle in subjects with resistance on DC current, with multiple range MV - volt meter measuring the voltage drop across the resistor, and then calculate the resistance. In order to reduce the wiring caused by measurement error, small resistance measurement, circuit voltage meter connected to the current meter; measuring resistance, voltage meter ammeter connected in. When measuring the supply current must be stable, to access voltage meter reading. In the disconnect the power supply before, must first disconnect voltage meter, so as to avoid the transformer windings inductance generated back EMF and damage to the meter.Because this method has low accuracy, conversion and other shortcomings, therefore, rarely used, generally only used to check test.2 bridge methodBridge measurement with high accuracy, high sensitivity, can direct reading etc..Measuring bridge a Wheatstone bridge (Hui Department of Wheatstone bridge ) and double arm bridge ( Kevin bridge ) two. Usually use a class 0.05-0.2 bridge well. Used before the bridge is of type QJ-23 and type 850 portable Wheatstone bridge; QJ-101 type and QJ-103 type portable arms bridge; QJ-5 type double arm ( Hui Kai ) dual purpose bridge etc.. General transformer using QJ-101, QJ-103 and type 850 bridge. For more than 2 ohm resistance by Wheatstone bridge, measuring about 2 ohm; following DC resistance measurement, in general should be used.

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