Processing method for single-phase ground fault of motor
Single-phase grounding FireWire (refers to any one phase electric) without direct loadand the ground connection, in 380/220 power supply system or other grounding system, due to the neutral line transformer is grounded, and the grounding resistance is very small, the line of fire (one phase electric) without load directly and ground wireis switched on the moment, will produce very big current, burning off the wire, power distribution equipment or trip, so the single-phase grounding fault is a serious accident, is the power system as far as possible to avoid.
In the power system, there are many places with no grounding system of power supply, such as in the serious dust, flammable and explosive and other special venues, all 6 - 10000 V 35000 V power supply system of our country, etc., are used inneutral point ungrounded or power supply system by the high resistance grounding,this kind of system single-phase grounding, with no loops or not produce large currentloop, no grounding current or no large grounding current, so does not affect the normal operation of the system. Although it doesn't affect the normal operation of the system, but the single-phase grounding is a fault, in order to prevent the ground is extended to two phase to ground or make grounding device further damage,regulation occurs after the single phase to ground fault, in 2 hours to find out the reason, to make a deal, 2 hours for no reason or could not be found processing, be out of power before the power supply.
The single-phase grounding fault locating method Daquan
For small current grounding system, how to quickly find the single-phase groundingfault, I give you some simple and feasible method.
1, the use of earthing device and fault indicator to find
Substation are generally installed grounding line selection device, although sometimes not, but can provide technical reference for the manual brake. Then install some grounding fault indicator in the line (or short circuit to ground fault indicator,thus indicating the combo) ground fault way. Grounding fault detection method is more reliable is the use of signal source method, more sensitive ground fault detection method is to use the first half wave method or the DC transient analysis method. Recommend the use of two methods of ground fault indicators are combined to find the grounding fault is better, to signal source based method, in the first half wave method or the DC transient analysis method.
2, the use of feeder automation method to search
If the user is rich, recommended the use of feeder automation method to find theground fault. By using the method of intelligent switch (electric load switch,sectionalizer, circuit breakers, recloser +FTU) artificial search method to replace the traditional logic function, and can automatically realize the fault isolation and supplyrestoration and transfer. Suppose a dual power hand in hand line is divided into 6 sections, namely 5 sets of intelligent switch (bilateral with three-phase five columnsignal PT or PT capacitive), the middle stage and to make contact between thegrounding fault point in the first station and a second station intelligent switch as an example, the concrete implementation steps are as follows:
(1) the substation grounding wire pull brake line outage, each segment of the intelligent switch automatic gate.
(2) substation switch on power, zero sequence voltage station alarm, the section to resume transmission success; the first intelligent switch FTU detected line voltage, butdid not detect zero sequence voltage, delay for a period of time after the automatic closing, as close to the ground fault and detected zero sequence voltage, then immediately brake and "locking"; second sets of intelligent switch also detects zero sequence voltage, the switch does not move and "locking", the abolition of the "electric time-delay automatic closing function.
(3) the middle contact switch to detect the unilateral loss of electricity, for a period of time after the automatic closing, due to the fault point is not in this section does not detect the zero sequence voltage, the power supply section transfer success.
(4) contact switch electric transmission, second sets of intelligent switch to detect theline voltage, did not detect zero sequence voltage, but there are "locked in" in the former, the abolition of the "electric time-delay automatic closing" function, the switch remains in the quantile.
(5) thus, the ground fault section has been separated from the other non fault sectionhave been restored or transfer of power supply.
3, change the neutral point grounding mode to find
Distribution system with neutral point ungrounded or through the arc suppression coilgrounding mode, there are also more favorable. Aiming at the fault finding difficult"defects" and thus to bring some of the personal and property safety problem, the user also do their own further consideration, there are two main thought out plan:
(1) the neutral point into small resistance + circuit breaker or contactor mode + high pressure resistance. The circuit breaker or contactor is usually divided into a high pressure, only when the detected system zero sequence voltage elevation to delay closing, short-term change into small resistance or resistance to ground, and then to find fault by detecting method with low resistance grounding mode. In addition, due tothe neutral point resistance off can be controlled flexibly, can be in after the arc suppression coil action in certain combination of timing to control resistance on-off, so that protection device or to ground fault indicator for identifying the signal and indicate the ground current path.
(2) will be changed to the neutral point grounding via low resistance. After transformation, the use of outlet circuit breaker of the zero sequence two section protection function and short circuit fault indicator, basically can solve 70% problemsof the grounding fault finding, but
About 30% of resistance and high resistance grounding fault is not good search, may also exist protection and line fuse coordination problem. According to this system,good solution is the use of digital fault indicator, the zero sequence current (cable),the total current line (overhead), insulation voltage to ground (overhead)measurement data indicator through wireless communication network sends to thescheduling system, through comprehensive analysis of substation real-time and historical information, can determine the answer location.
4, artificial search
If not installed in the substation grounding line selection device, line and also did not install the grounding fault indicator or short circuit to ground combo fault indicator, is also not very good grounding fault detector, it can only use the stupid way of manual search. The search procedure is as follows:
(1) by artificial (or scheduling, the same below) in turn pull gate, can know which lineof substation grounding, by scheduling know which grounding.
(2) then there are two ways to find the point of failure: one is to be piecewise line step by step, or will often have the fault line opened, with 2.5kV shaking table testgrounding relatively insulation, insulation resistance small one for fault section, in order to reduce searching range (of course, in a line of substation side must do hang the ground safety protection measures such as); two is the line as far as possible,segmented, and then step by step to try all the power supply, the interactivecoordination and scheduling, a zero sequence voltage alarm when the period for thefault section.
Artificial searching method of operation is very troublesome, if line length, multiple branches, switch segment and less, it is not operating properly, and the color of the sky and weather, the more not good treatment. Recommendations or to use someless equipment investment technical means to cooperate with the artificial search, can get twice the result with half the effort, not only provides the power supply reliability and social benefits, but also create economic benefits.
