参考文献

In power plant and substation DC power supply as the main electrical equipment security, power and control signal power, is a very large multi branch power supply network. In general, a grounding does not affect the operation of DC system, but if they can not quickly find the grounding fault point and to be repaired, the other one point grounding fault, it may lead to the occurrence of major faults.

Method for DC system insulation detection are the main existing bridge balance principle and the principle of low frequency detection. According to the principle of bridge balance to achieve the insulation monitoring device is widely used, but it cannot detect the DC system of positive and negative insulation equal decrease; insulation monitoring device even if the alarm and can not be directly obtained on the size of the insulation resistance. With low frequency principle of detecting grounding fault is in recent years, we have adopted a new method, but it can detect the grounding resistance is controlled by the control of the distributed capacitance of the DC system, and low frequency AC signal is vulnerable to external interference, in addition to the injection of low frequency AC signal increased DC system voltage ripple coefficient. Therefore, the bridge balance principle and the principle of low frequency detection of all defects are difficult to overcome. A new detection method is proposed in this paper, main circuit with unbalanced bridge was used to detect the total insulation resistance, and branch to DC transformer testing in the end is what the insulation to reduce. At the same time using single chip to achieve the detection method. Measure the insulation resistance of the main loop

Traditional balancing bridge detection principle as shown in Figure 1, by detecting the voltage UJ and um, and given the resistor R to calculate R, R, but when the positive and negative insulation are reduced, test results will with the actual situation don't match.

In order to detect positive insulation decreased, following an unbalanced design method of measuring bridge. Using MCS 80C196KC microcontroller to achieve, as shown in figure -2. First, we first explain about electronic relay AQW214 usage. When the AQW214 1, pin 2 conduction, 7, 8 feet conductive; and the guide through the internal resistance is very small. Similarly, 3, 4, 5 foot turn-on, 6 foot is turned on. And AQW214 pressure value can reach 400V, namely when the 7, 8, 5 or 6 is not conductive, across them can withstand 400V voltage. So we can use P10 to control the level of control, 1, 2 feet of the conduction and can control the JK1 turn-on and turn off. Similarly, the level control P11 to control the JK2 turn-on and turn off. The first step, jk1, JK2 are disconnected, we by 80C196 microcontroller A / D port of Ac4 channel acquisition C4 at both ends of the voltage so as to measure the UM. The second step, jk1, JK2 is closed, the voltage through the A / D of AC5 channel acquisition across C2, which estimates UJ, remembering this measured voltage UJ Uj1. The third step, the closure of JK1, JK2, Uj on voltage measured at this time is Uj2. Uj1 and R+ is obvious, R-, Uj2 and R+, R-. So we can get a two yuan equation. Here, because the R and R3 and R and RW2 and is equal to, so R and R3 and called R, R and RW2 and also known as R. So we can get the formula of 1-1 and 1-2.

The above analysis, we obtain theoretical, but the real use of practical application, we need to pay attention to several issues. First, given in the circuit parameters are only suitable for 100V-300V DC voltage, less than 100V, is measuring accuracy decreased; higher than 300V, relays, electronic pressure enough. The DC voltage is very low. We can change the relative resistance value and the measurement precision is improved. But for the DC voltage higher than 300V, we want to re select the electronic relay or other relay. Secondly, the actual measurement, should first determine the