Cause analysis and search processing of secondary open circuit of current transformer-Solutions

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

SMD aluminum electrolytic capacitor

inductance

If the current transformer is opened twice, the primary current will be used for excitation, which will seriously saturate the core. The alternating magnetic flux will induce a very high voltage on the secondary coil, and its peak value can reach several thousand volts or even tens of thousands of volts. Such a high voltage acts on the secondary coil and the secondary circuit, which will seriously threaten personal safety and The safety of the equipment, even if the coil insulation is burned out due to overheating, the protection may not reflect the fault due to no current. For differential protection and zero-sequence current protection, the unbalanced current may cause malfunction due to open circuit. Therefore, the "Safety Regulations" stipulate that the current transformer is strictly prohibited to open during operation. So what are the reasons for the secondary open circuit of the current transformer? (1) Due to defects in the structure and quality of the test terminals in the AC current loop, the screw and the copper plate screw hole are in poor contact during operation, resulting in an open circuit. (2) Since the rubber of the test terminal clamp in the current loop is too long, the metal piece of the rotary terminal is not pressed against the metal piece of the pressure plate, and is accidentally pressed on the bakelite sleeve, causing an open circuit. (3) Mistakes in the work of the test personnel, such as forgetting to connect the internal connectors of the relay and fail to find it during acceptance. (4) When the secondary wire terminal fitting is not crimped tightly, 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 screws and gaskets are rusted too much, resulting in an open circuit. When the current transformer opens twice, it is often accompanied by some phenomena: (1) The circuit meter indicates an abnormal decrease or zero. If the current loop is open for the meter, the three-phase ammeter indication will be inconsistent, the power meter indication will be reduced, the meter will not rotate 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 and secondary load indications of the transformer differ greatly, 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 fault on the low side. (2) Listen carefully to the current transformer body for noise, vibration, etc., which is not obvious when the load is small. When an open circuit occurs, due to the increase in magnetic flux density and the non-sinusoidal nature of the magnetic flux, the vibration force of the silicon steel sheet is increased, and a large noise is generated. (3) Use the temperature-changing wax or ultraviolet thermometer to monitor the current transformer body for serious heat, odor, smoke, fuel injection, etc. This phenomenon is not obvious at the 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 in severe cases, the smoke burns out. (4) Check the current transformer secondary circuit terminals, component wire ends, etc. for discharge and sparking. This phenomenon can be found in the secondary circuit maintenance and inspection. When the circuit is open, due to the secondary voltage generated by the current transformer, the secondary terminal of the transformer, the secondary circuit component connector, the terminal block, etc. may be discharged and ignited. Breaking the insulation in severe cases. (5) If the relay protection malfunctions or refuses to operate, this condition can be found and processed when the cause is checked after a false trip or a step-by-step trip accident. (6) Smoke from the meter, electric energy meter, relay, etc. This situation can be discovered in time. The above-mentioned meter burnout can make the current transformer open twice, and the relay of the power meter and the remote device of the electric energy meter and the relay of the protection device burn out, not only make the current transformer open twice, but also The voltage transformer is short-circuited twice. In this case, remove the AC voltage terminal from the terminal block and wrap the insulation. When a secondary open circuit of the current transformer occurs, the operation and maintenance personnel should not panic. The nature of the fault should be recorded in time, reported to the dispatcher or the competent department, and wait for processing. (1) When the secondary open circuit of the current transformer is found, it should first distinguish which group of current loops, the phase difference of the open circuit, whether there is any influence on the protection, report the dispatch, 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 short-circuit the current transformer on the nearest test terminal, and then check the open circuit point. When short-circuiting, use short-circuit wire or special short wire. Short circuit should be proper and reliable. Fuse or general wire is prohibited. Winding. (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, which can be further searched. If there is no spark when short circuited, it may be short circuited. The fault point may be in the loop before the short contact point, and the short contact point may be changed forward by point to narrow the range. (5) In the fault range, check the terminals and components that are prone to failure, and check whether the circuit has touched the part when it is working. 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 of the transformer body, the power should be cut off. If it is a fault that cannot be handled by itself or a fault that cannot be self-identified, it should be reported to the superior and sent to the person for inspection and treatment. At this time, the current transformer should be short-circuited twice, or the load should be transferred and the power should be cut off. (6) When short-circuiting 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) Internally emits odor, smoke, or fire; (2) Internal discharge phenomenon, abnormal sound or spark discharge between the lead and the outer casing; (3) Breakdown of the main insulation, causing single-phase grounding failure; (4) The oil-filled current transformer leaks oil and leaks.