Short Circuit And Earth Fault Indicator The Basis For Judging The Fault Location
The fault indicator discussed today mainly refers to cable fault indicators, which typically have three phase sensors (mounted on A, B, C phases, respectively), a zero sequence sensor (wrapped in three-phase cables), and a host Called display unit). When the distribution network short circuit failure occurs, the power side to the point of failure indicators are fault alarm, and the fault point after the indicator does not alarm,Short Circuit And Earth Fault Indicator which can determine the location of the fault point interval to help people find the point of failure. According to the basis of fault diagnosis, the fault indicator can be divided into two kinds: fault indicator with overcurrent principle and fault indicator with current mutation principle. As for the use of other principles such as the first half wave method, the fifth harmonic method, injection method, fault current direction method to determine the basis of the fault indicator, due to the existence of a variety of problems, the application of less.
1. Fault indicator with overcurrent principle
Line Short Circuit And Earth Fault Indicator, the fault current in the line will increase, when the current increases over a certain set value, the use of over-current fault indicator will alarm display. Such indicators need to set a Short Circuit And Earth Fault Indicator alarm threshold in advance, short circuit in general 400A-1200A, ground generally in the 5-60A, adjustable range.
2. Fault indicator with current mutation principle
When the line Short Circuit And Earth Fault Indicator, the line will occur more significant instantaneous current changes, when the protection device action trip, the line steady current current will be zero. Detection of the current value of this mutation, but also to determine the Short Circuit And Earth Fault Indicator. Because this type of indicator does not need to set the alarm threshold in advance, its scope of application is more extensive. But because of the need for real-time monitoring of line current, product power consumption, shorter service life. There are currently Snyder FLAIR series and some domestic manufacturers of products using such principles.
First of all, according to the fault phenomenon to determine the fault is broken, and then may occur according to the location of the fault to determine the scope of the fault and short circuit circuit, and then use the detection tool to find short-circuit point. 11311 voltage method: the circuit is broken, the circuit does not have the current through the circuit in a variety of buck components are no longer a voltage drop, all the power supply voltage drop at both ends of the circuit. And thus can be determined by measuring the voltage of the circuit breaker fault point. Figure 1 shows a simple circuit, the power supply voltage is 100V DC, through the normally open contact QF1 and normally closed contacts QF2, QF3, QF4, the control of the electromagnetic coil Y. Detection instrument for the universal multimeter, select the DC voltage 250V gear (greater than or equal to 100V range can be). Assume that the circuit has a fault point at A, and when the normally open contact QF1 is closed (or shorted by a wire), the solenoid Y still does not work. Will be multimeter red pen and power "+" pole connected, black pen and power "-" very connected, multimeter instructions should be 100V, and then move the black table pen, followed by the end of 1,2,3,4,5,6,7 , 8 connected, if the multimeter instructions are also 100V, then these points to the power "-" pole circuit without fault. When the black table pen moves to endpoint 9, the multimeter indicates zero, the fault is between 8-9. At this time, if the measurement of the voltage between 8-9, and the power supply voltage will be equal, and then can determine the circuit only A at the end of a fault point.
The short-circuit fault has the following characteristics: short-circuit point (ie, short-circuit at both ends) of the resistance (or impedance) is zero or close to zero; short circuit has a great destructive, in the event of a short circuit, generally not And then direct power check, and the fault is different. After the short-circuit fault occurs, the protection elements of the circuit (such as fuses, circuit breakers, etc.), and the protection of the components may control the composition of multiple circuits, and thus find electrical short-circuit fault,Short Circuit And Earth Fault Indicator you must first identify the fault area from the fault loop, and then Find a short-circuit fault point in the faulty loop. Short circuit fault circuit to find: multimeter method - multimeter method is in the circuit after the power, with a multimeter Ohm block (block) to determine the short circuit loop resistance method.