1. Reasons for the second open circuit

(1) The test terminal in the AC current loop, due to structural and quality defects, causes poor contact between the screw and the copper plate screw hole during operation, resulting in an open circuit.

(2) The test terminal pressure plate in the current loop, because the glue wood is too long, the rotating terminal metal piece is not pressed on the metal piece of the pressure plate, and is mistakenly pressed on the bakelite sleeve, causing an open circuit.

(3) Mistakes in the work of the repair personnel, such as forgetting to connect the internal connectors of the relay, and fail to find it during the acceptance.

(4) The secondary wire terminal fitting is not tightly pressed, and when the current in the circuit is large, the heat is blown or oxidized to cause an open circuit.

(5) The outdoor terminal box and junction box are damp, and the terminal bolts and gaskets are rusted too much, resulting in an open circuit.

2. The phenomenon of secondary open circuit

(1) The loop meter indicates an abnormal decrease or zero. If the current loop is used to measure the meter open circuit, the three-phase ammeter indication will be inconsistent, the power meter indication will be reduced, the meter will not turn or the speed will be slow. If the meter is sometimes not indicated, it may be in a semi-open state (poor contact). When the operator encounters this phenomenon, the relevant meters can be compared and analyzed carefully. If the original primary side load indication of the transformer differs a lot, the current meter indicates that the phase difference is too large (note the difference of the voltage, the voltage level is different, and it is suspected that there is an open circuit fault on the lower side).

(2) Listen carefully to the current transformer body for noise, vibration and other uneven sounds. This phenomenon is not obvious at low load. When an open circuit occurs, the magnetic flux density increases and the magnetic flux is non-sinusoidal. The vibration force of the sheet is increased, which will generate a large noise.

(3) Use the temperature-changing wax or infrared thermometer to monitor the current transformer body for serious heat, whether there is odor or discoloration, smoke, fuel injection, etc. This phenomenon is not obvious at low load. When the circuit is open, due to the serious magnetic saturation, the iron core is overheated, the temperature of the outer casing rises, the internal insulation is heated and smells bad, and when it is serious, the smoke is burned out.

(4) Check the secondary circuit terminals of the current transformer, the component wire head, etc. for discharge and sparking. This phenomenon can be found in the secondary circuit maintenance and inspection. When the circuit is open, because the current transformer generates a high voltage twice, it may cause the secondary terminal of the transformer, the secondary circuit component connector, the terminal and so on to discharge and ignite. Insulates insulation in severe cases.

(5) The relay protection has malfunctioned or refused to operate. This condition can be found and processed after checking for the cause after a false trip or after a leap trip accident. Electrician's house

3. Treatment after secondary open circuit

(1) When the current transformer is found to be open twice, it should first distinguish which group of current loops the fault belongs to, the phase difference of the open circuit, whether there is any influence on the protection, report scheduling, and relieve the protection of possible misoperation.

(2) Minimize the load current once. If the current transformer is seriously damaged, transfer the load and check the power failure. If there is a bypass, bypass power supply can be used to ensure the reliability of the power supply.

(3) Try to try to short-circuit the current transformer on the nearest test terminal, and then check the open circuit point. When short-circuiting, use the short-circuit special short wire. The short circuit should be properly and reliable. It is forbidden to use fuse or general wire winding. And according to the drawings.

(4) Pay attention to the phenomenon of short circuit. If there is spark when short circuited, the short circuit is valid. The fault point is in the circuit below the short contact point. It can be further searched. If there is no spark when short circuited, it may be short circuit. . The fault point may be in the loop before the short contact point, and the short contact point can be changed forward by point to narrow the range.

(5) In the fault range, the terminals and components that are prone to failure should be inspected, and the part where the circuit is touched during operation should be checked. For the detected faults, the faults that can be handled by themselves can be processed immediately, and then the protection that is withdrawn is put into operation. If the open circuit point is on the terminal block of the transformer body, the power should be cut off. If it is a fault that cannot be handled by itself or cannot be self-identified, it should be reported to the superior and sent to the person for inspection. At this point, the current transformer should be short-circuited twice, or the load should be transferred and the power should be cut off.

(6) When short circuit the secondary circuit, the staff must adhere to the operation of the monitoring system, one person operation, one person supervision. Maintain a proper safety distance with live equipment. Operators must wear insulated boots, insulated gloves and tools with insulated handles. Do not perform any work on the loop between the current transformer and the short circuit point.

However, when the current fault occurs in the current transformer, it should be reported to the superior immediately, and the power supply should be cut off before processing.

1 The inside emits odor, smoke, and fire. Electrician's house

2 There is a discharge phenomenon inside, abnormal sound or spark discharge between the lead and the outer casing.

3 The main insulation breaks down, causing a single-phase ground fault.

4 oil-filled current transformer leaks oil and leaks.