Ang mga low-voltage current transformers, isip indispensable nga mga device sa pagsukol ug proteksyon sa mga sistema sa kuryente, kasagaran mohitabo og daghang klase sa sayop samtang gigamit kasama sa uban pang mga equipment sa kuryente tungod sa mga faktor sa kalibutan, problema sa pagkonekta sa mga equipment, ug dili maayo nga pagbutang ug pagpuyo. Kini nga mga sayop dili lamang nakaapekto sa normal nga operasyon sa mga equipment sa kuryente apan mahimong magdulot usab og panganak sa personal nga seguridad. Kini nga gikinahanglan nga makasabot sa mas kaugalingon ang mga klase sa sayop, mga paagi sa paghatod sa hukom, ug mga pananglitan sa pagprotekta aron siguraduhon ang stable ug reliable nga operasyon sa mga rural power grids ug low-voltage distribution systems.
I. Typical Connection Scenarios of Low-voltage Current Transformers with Other Power Equipment
Ang mga low-voltage current transformers kasagaran gigamit sa koneksyon sa sumusunod nga mga equipment sa mga sistema sa kuryente, naformar og iba't ibang application scenarios:
Electric energy metering systems: Gikonectado sa mga instrumento sa pagsukol sama sa watt-hour meters ug power meters aron masukol ang eksaktong paggamit sa kuryente sa mga user. Sa mga rural power grids, sila kasagaran makita sa mga meter box sa mga mag-uuma o sa low-voltage side sa mga distribution transformers, responsable sa pagkonbertir sa dako nga kuryente ngadto sa standard nga small current signals nga 5A o 1A para sa pagsukol.
Relay protection devices: Gikonectado sa mga protective devices sama sa circuit breakers, residual current protectors, ug overload protectors aron monitoron ang status sa kuryente sa linya ug maputli sa wala ang fault currents sa agad. Sa mga rural distribution boxes, sila kasagaran gigamit aron monitoron ang line overload, short circuits, o leakage.
Automation control systems: Gikonectado sa mga automation equipment sama sa PLCs ug RTUs para sa remote monitoring ug control sa operasyon status sa mga equipment sa kuryente. Sila kasagaran makita sa mga rural small processing plants, irrigation pumping stations, ug uban pang lugar.
Distribution transformers: Gikonectado sa outgoing lines sa low-voltage side sa mga transformers aron monitoron ang operasyon status ug load conditions sa mga transformers. Sila kasagaran makita sa outgoing lines sa low-voltage side sa mga rural distribution transformers.
II. Common Faults When Low-voltage Current Transformers Are Used in Combination with Other Power Equipment
1. Open Circuit Fault in Secondary Circuit
Ang open circuit sa secondary circuit usa sa labi nga dangerous nga mga sayop sa low-voltage current transformers, kasagaran nailhan sa:
Phenomenal features: Ang indication sa ammeters ug power meters naguba sa zero o nagsigurog sigurog; ang transformer body nagbuhat og abnormal "buzzing" sound o discharge sound; may visible burnt marks sa terminal block; ang watt-hour meter nagstop sa pag-rotate o nag-rotate abnormally.
Causes of failure: Loose terminals sa secondary circuit; broken secondary wires samtang gi-install ang meter; accidental disconnection sa secondary circuit samtang gi-maintenance; poor contact tungod sa oxidation sa terminal block; mechanical damage sa secondary wires nagresultar og breakage.
Hazards of failure: Sa panahon sa open-circuited, ang secondary side mogenerar og high voltage nga thousands volts, threatening the safety sa operators; severe saturation sa iron core nagresultar og overheating, mahimong magburn sa insulation materials; protection devices malfunction o fail to operate tungod sa loss sa signal.
Typical rural scenario case: Sa usa ka village transformer area, ang secondary wires sa current transformer sa meter box nagloose sa terminals tungod sa long-term vibration. Sa panahon sa paggamit sa high-power electrical appliances sa mga mag-uuma, ang open circuit sa secondary circuit mogenerar og high voltage, nagresultar og burned out sa meter ug fire hazard.
2. Poor Contact Fault
Ang poor contact usa sa labi nga common nga mga sayop samtang gikonectado ang low-voltage current transformers sa uban pang mga equipment:
Phenomenal features: Unstable ammeter indication, intermittent presence; abnormal temperature rise sa transformer terminals; frequent misoperation sa protection devices; increased metering errors; visible oxidation ug blackening sa terminal block.
Causes of failure: Loose screws sa terminal block; insufficient contact area tali sa wires ug terminals; oxidation o corrosion sa wires; aging sa terminal block materials; non-compliant bolt torque; increased contact resistance accelerated by a humid environment.
Hazards of failure: Increased contact resistance nagresultar og local overheating, accelerating insulation aging; increased measurement errors affect metering accuracy; protection devices malfunction o fail to operate tungod sa abnormal signals; long-term poor contact mahimong magresultar og short circuits o fires.
Typical rural scenario data: Sa usa ka metering circuit gikonectado sa 2.5mm² copper wires, samtang ang contact resistance exceeds 0.65mΩ, ang terminal temperature rise mahimong reach more than 40℃; samtang ang contact resistance exceeds 1mΩ, ang temperature rise mahimong reach more than 70℃, far exceeding the safety limit.
3. Overload and Iron Core Saturation Faults
Overload ug iron core saturation usa sa common nga mga klase sa sayop sa rural power grids, kasagaran nailhan sa:
Phenomenal features: Ammeter indication exceeds the rated value; ang transformer body naginit significantly; protection devices malfunction o fail to operate; increased metering errors; abnormal noise sa iron core.
Causes of failure: Large fluctuations sa rural grid loads (such as peak electricity consumption during the Spring Festival ug multiple water pumps operating simultaneously during the irrigation season) nagresultar og overload state sa transformer for a long time; improper selection sa accuracy limit factor sa transformer; short-circuit current exceeds the bearing capacity sa transformer; degradation sa iron core material performance; reduced magnetic permeability tungod sa temperature rise.
Hazards of failure: Iron core saturation nagresultar og increased measurement errors, affecting metering accuracy; protection devices malfunction o fail to operate tungod sa signal distortion; reduced insulation performance sa transformer; long-term overload mahimong magburn sa transformer.
Typical rural scenario data: Ang current transformer sa low-voltage side sa usa ka rural distribution transformer reached 120% sa rated current samtang ang summer irrigation period, nagresultar og iron core saturation, a measurement error sa 8%, ug a 3-fold increase sa number of misoperations sa protection devices.
4. Insulation Performance Degradation Fault
Insulation faults labi nga prominent sa rural power grids, kasagaran nailhan sa:
Phenomenal features: Reduced insulation resistance (should be ≥1000MΩ under normal conditions); partial discharge phenomenon; surface discharge marks; increased leakage current; dampness o water stains sa equipment surface.
Causes of failure: Humid rural environments ug poor sealing sa transformer leading to water ingress; insulation damage caused by gnawing of small animals; accelerated insulation aging due to long-term high-temperature operation; reduced insulation performance due to dust accumulation sa terminal block; insulation breakdown caused by lightning overvoltage.
Hazards of failure: Degraded insulation performance nagresultar og leakage o short circuits; misoperation sa protection devices; increased metering errors; ug mahimong magresultar og fires sa severe cases.
Typical rural scenario data: Sa southern rural areas, ang humidity maintained above 80% all year round. Ang insulation resistance sa transformers without moisture-proof measures mahimong drop from the initial value of 2000MΩ to below 500MΩ within 2-3 years.
III. Judgment Methods for Common Faults
1. Judgment of Open Circuit Fault in Secondary Circuit
Meter observation method: Check whether the indication sa connected ammeters ug power meters suddenly becomes zero or fluctuates significantly; whether the watt-hour meter stops rotating o rotates abnormally.
Sound identification method: Approach the transformer body ug listen for abnormal "buzzing" o discharge sounds; ang sound should be small ug uniform during normal operation.
Temperature detection method: Use an infrared thermometer to detect the temperature sa transformer body, which should be ≤40℃ under normal conditions; it may reach above 60℃ when open-circuited.
Impedance testing method: Use a special instrument to measure the impedance sa secondary circuit. The impedance angle independent sa frequency when connected normally; the impedance increases significantly (>10000Ω) when open-circuited.
Rural scenario judgment skill: Sa rural low-voltage metering boxes, if it is found that the electric meter suddenly stops working while farmers' electricity usage is normal, the secondary circuit sa current transformer should first be suspected of being open-circuited.
2. Judgment of Poor Contact Fault
Loop resistance testing method: Use a micro-ohmmeter to measure the secondary circuit resistance, which should be ≤0.65mΩ under normal conditions; the resistance may exceed 1mΩ when there is poor contact.
Temperature rise monitoring method: Use an infrared thermometer to monitor the temperature rise sa terminal block, which should be ≤15℃ under normal conditions; the temperature rise may exceed 30℃ when there is poor contact.
Vibration detection method: Use a vibration sensor to detect abnormal vibrations. When there is poor contact, the vibration amplitude may exceed 2g ug last for more than 10 seconds.
Load testing method: Connect a standard load sa secondary circuit sa transformer ug observe whether the output current is stable; the current may fluctuate when there is poor contact.
Rural scenario judgment skill: Sa metering boxes after rural network centralized reading transformation, if it is found that the metering sa certain household's electric meter is abnormal while that sa other households is normal, focus should be on checking the connection status sa secondary circuit sa current transformer for that household.
3. Judgment of Overload and Iron Core Saturation Faults
Current monitoring method: Check whether the actual load current sa primary side exceeds the rated value; special attention should be paid to peak electricity consumption periods sa rural power grids, such as the Spring Festival ug the irrigation season.
Error testing method: Use a transformer calibrator to test the ratio error ug phase error, which should meet the accuracy level requirements under normal conditions; errors may increase significantly during overload or saturation.
Excitation characteristic testing: Measure the secondary voltage under different currents ug draw the excitation curve; the slope sa curve will change significantly when the iron core is saturated.
Sound identification method: The iron core may make abnormal noise when saturated; the sound should be small ug uniform during normal operation.
Rural scenario judgment skill: Sa low-voltage side sa rural distribution transformers, if it is found that protection devices frequently malfunction when multiple high-power electrical appliances are operating simultaneously, the current transformer should be suspected of being overloaded or having iron core saturation.
4. Judgment of Insulation Performance Degradation Fault
Insulation resistance testing method: Use a 2500V megohmmeter to measure the insulation resistance between the primary ug secondary, secondary to ground, ug primary to ground; it should be ≥1000MΩ under normal conditions.
Partial discharge testing method: Use a partial discharge tester to detect internal discharge sa transformer; the discharge amount will increase when insulation performance degrades.
Visual inspection method: Check whether there are water stains, dirt, o damage sa transformer surface; whether there is dust accumulation o signs of animal gnawing sa terminal block.
Humidity detection method: Use a hygrometer to detect the humidity sa transformer installation environment; a humid environment sa rural areas may lead to degradation sa insulation performance.
Rural scenario judgment skill: Sa southern rural areas, if it is found that the insulation resistance sa transformer has decreased significantly, focus should be on checking whether the sealing structure is intact ug whether the environmental humidity is too high.
IV. Solutions to Common Faults
1. Handling of Open Circuit Fault in Secondary Circuit
Emergency treatment: After discovering an open circuit fault, immediately deactivate the relevant protection devices; use insulating tools to short-circuit the secondary side sa terminals near the transformer; if there is a spark during short-circuiting, it indicates that the fault point is sa circuit below the short-circuit point; if there is no spark during short-circuiting, the fault point may be sa circuit before the short-circuit point.
Long-term solutions: Replace the secondary wiring terminals with reliable quality; use gold-plated or tinned terminal materials to reduce oxidation; install anti-loosening gaskets or Snap-on limiters to prevent vibration-induced loosening; regularly check the connection status sa secondary circuit.
Rural scenario handling suggestions: Sa rural low-voltage metering boxes, secondary circuit short-circuit protection devices can be installed to automatically short-circuit when an open circuit is detected; regular inspections should be conducted by electricians, especially before peak electricity consumption periods.
2. Handling of Poor Contact Fault
Maintenance measures: Use a torque wrench to tighten terminal screws according to specifications (such as 0.8-1.2N·m for M4 screws); regularly clean the oxide layer sa terminals; apply conductive paste sa terminal contact surfaces; inspect ug replace aging or damaged terminal blocks.
Preventive measures: Install moisture-proof heaters sa terminal block connections (automatically start when humidity >60% RH); use G4-grade filter cotton to block dust (replace every 6 months); adopt metering boxes with IP65 protection level; regularly inspect ug maintain terminal blocks.
Rural scenario handling suggestions: Sa rural network metering boxes, gold-plated or tinned terminal materials can be used; shockproof terminal blocks can be adopted; terminal connection status should be checked once a quarter; the inspection frequency should be increased during the humid season.
3. Handling of Overload and Iron Core Saturation Faults
Protection configuration: Select transformers with appropriate transformation ratios according to the actual line load; protection current transformers should select appropriate accuracy limit factors (such as 10P15 can withstand 15 times the rated current); configure residual current circuit breakers matching the cross-sectional area sa wires sa incoming line (such as 2.5mm² copper wires with C20A protectors).
Selection suggestions: Select transformers with a rated secondary current of 1A or 5A according to line length ug load conditions; 1A transformers suitable for long-distance metering; sa rural power grids, iron core materials with good anti-saturation performance (such as permalloy) can be selected.
Rural scenario handling suggestions: Sa incoming lines sa farmers' homes, select appropriate protection devices according to the wire diameter (such as 1.5mm² copper wires with C10A, 2.5mm² with C20A, 4mm² with C25A); sa low-voltage side sa distribution transformers, reserve sufficient transformer capacity according to load conditions; adopt intelligent monitoring devices to monitor the operating status sa transformers in real-time.
4. Handling of Insulation Performance Degradation Fault
Maintenance measures: Regularly check whether the sealing structure sa transformer is intact; use silicone rubber sealing rings to enhance sealing; install moisture-proof heaters sa metering boxes; clean dirt sa transformer surface.
Preventive measures: Select metering boxes with IP65 protection level; use flame-retardant ABS materials for the shell; use moisture-proof wiring terminals sa terminal block; conduct regular insulation resistance tests.
Rural scenario handling suggestions: Sa southern rural areas, epoxy resin-cast transformers can be adopted; install temperature ug humidity monitoring devices sa metering boxes; regularly inspect ug replace aging sealing materials; install lightning arresters sa lightning-prone areas.
