Ang mga low-voltage current transformers, bilang hindi maaaring walang mga pagsukat at mga pananggalang na aparato sa mga sistema ng kuryente, madalas nakakaranas ng iba't ibang mga pagkakamali kapag ginagamit ito kasama ang iba pang mga aparato ng kuryente dahil sa mga environmental factors, mga isyu sa pag-ugnay ng mga aparato, at hindi tamang pag-install at pag-maintain. Ang mga pagkakamali na ito ay hindi lamang nakakaapekto sa normal na operasyon ng mga aparato ng kuryente kundi maaari rin itong makapanganib sa personal na kaligtasan. Kaya naman, kinakailangang maunawaan nang lubusin ang mga uri ng pagkakamali, mga paraan ng paghuhusga, at mga paraan ng pag-iwas upang matiyak ang matatag at maasahang operasyon ng mga rural power grids at mga low-voltage distribution systems.
I. Mga Karaniwang Sitwasyon ng Pag-ugnay ng Low-voltage Current Transformers sa Iba Pang Mga Aparato ng Kuryente
Ang mga low-voltage current transformers ay karaniwang ginagamit sa pag-ugnay sa mga sumusunod na aparato sa mga sistema ng kuryente, na nagpapabuo ng iba't ibang mga application scenarios:
Mga sistema ng pagsukat ng enerhiya: Nakakonekta sa mga instrumento ng pagsukat tulad ng watt-hour meters at power meters upang tumpakin ang paggamit ng kuryente ng mga gumagamit. Sa mga rural power grids, madalas itong matatagpuan sa mga meter boxes ng mga magsasaka o sa low-voltage side ng mga distribution transformers, responsable sa pag-convert ng malaking kuryente sa standard na small current signals ng 5A o 1A para sa pagsukat.
Mga pananggalang na aparato: Nakakonekta sa mga pananggalang na aparato tulad ng circuit breakers, residual current protectors, at overload protectors upang bantayan ang status ng kuryente sa linya at ma-cut off ang fault currents nang maagang panahon. Sa mga rural distribution boxes, madalas itong ginagamit upang bantayan ang overload, short circuits, o leakage sa linya.
Mga sistema ng automation control: Nakakonekta sa mga aparato ng automation tulad ng PLCs at RTUs para sa remote monitoring at control ng operating status ng mga aparato ng kuryente. Madalas itong matatagpuan sa mga rural small processing plants, irrigation pumping stations, at iba pa.
Mga distribution transformers: Nakakonekta sa outgoing lines sa low-voltage side ng mga transformers upang bantayan ang operating status at load conditions ng mga transformers. Madalas itong matatagpuan sa outgoing lines sa low-voltage side ng mga rural distribution transformers.
II. Karaniwang Mga Pagkakamali Kapag Ginagamit ang Low-voltage Current Transformers Kasama ang Iba Pang Mga Aparato ng Kuryente
1. Open Circuit Fault sa Secondary Circuit
Ang open circuit sa secondary circuit ay isa sa pinaka-mapanganib na mga pagkakamali ng mga low-voltage current transformers, na may mga katangian na:
Phenomenal features: Ang indication ng ammeters at power meters bigla na lang naging zero o lumaki nang malaki; ang transformer body ay naglabas ng abnormal na "buzzing" sound o discharge sound; may visible na burnt marks sa terminal block; ang watt-hour meter ay tumigil o nag-rotate abnormally.
Mga sanhi ng pagkakamali: Maluwag na terminals sa secondary circuit; nabawas ang secondary wires sa panahon ng pag-install ng meter; accidental disconnection ng secondary circuit sa panahon ng maintenance; mahina ang contact dahil sa oxidation ng terminal block; mechanical damage sa secondary wires na nagdulot ng pag-bwisit.
Mga panganib ng pagkakamali: Kapag open-circuited, ang secondary side ay mag-generate ng mataas na kuryente na ilang libong volts, na nanganganib ang kaligtasan ng mga operator; severe saturation ng iron core na nagdudulot ng overheating, na maaaring masunog ang insulation materials; protection devices ay nag-malfunction o hindi gumana dahil sa pagkawala ng signal.
Typical rural scenario case: Sa isang village transformer area, ang secondary wires ng current transformer sa meter box ay naging maluwag sa terminals dahil sa long-term vibration. Kapag ginamit ng mga magsasaka ang high-power electrical appliances, ang open circuit sa secondary circuit ay nag-generate ng mataas na kuryente, na nagdulot ng pag-sunog ng meter at nag-create ng fire hazard.
2. Poor Contact Fault
Ang poor contact ay isa sa pinaka-karaniwang mga pagkakamali kapag ginagamit ang mga low-voltage current transformers kasama ang iba pang mga aparato:
Phenomenal features: Unstable ammeter indication, intermittent presence; abnormal temperature rise sa transformer terminals; frequent misoperation ng protection devices; increased metering errors; visible oxidation at blackening sa terminal block.
Mga sanhi ng pagkakamali: Maluwag na screws sa terminal block; insufficient contact area sa pagitan ng wires at terminals; oxidation o corrosion ng wires; aging ng terminal block materials; non-compliant bolt torque; increased contact resistance accelerated by a humid environment.
Mga panganib ng pagkakamali: Increased contact resistance leads to local overheating, accelerating insulation aging; increased measurement errors affect metering accuracy; protection devices malfunction or fail to operate due to abnormal signals; long-term poor contact may cause short circuits or fires.
Typical rural scenario data: Sa isang metering circuit na konektado sa 2.5mm² copper wires, kapag ang contact resistance ay lumampas sa 0.65mΩ, ang terminal temperature rise ay maaaring umabot sa higit sa 40℃; kapag ang contact resistance ay lumampas sa 1mΩ, ang temperature rise ay maaaring umabot sa higit sa 70℃, na lubhang lumampas sa safety limit.
3. Overload at Iron Core Saturation Faults
Overload at iron core saturation ay karaniwang mga uri ng pagkakamali sa mga rural power grids, na may mga katangian na:
Phenomenal features: Ammeter indication exceeds the rated value; the transformer body heats up significantly; protection devices malfunction or fail to operate; increased metering errors; abnormal noise from the iron core.
Causes of failure: Large fluctuations in rural grid loads (such as peak electricity consumption during the Spring Festival and multiple water pumps operating simultaneously during the irrigation season) cause the transformer to work in an overload state for a long time; improper selection of the accuracy limit factor of the transformer; short-circuit current exceeding the bearing capacity of the transformer; degradation of iron core material performance; reduced magnetic permeability due to temperature rise.
Hazards of failure: Iron core saturation leads to increased measurement errors, affecting metering accuracy; protection devices malfunction or fail to operate due to signal distortion; reduced insulation performance of the transformer; long-term overload may burn the transformer.
Typical rural scenario data: The current transformer on the low-voltage side of a rural distribution transformer reached 120% of the rated current during the summer irrigation period, causing iron core saturation, a measurement error of 8%, and a 3-fold increase in the number of misoperations of protection devices.
4. Insulation Performance Degradation Fault
Insulation faults are particularly prominent in rural power grids, mainly characterized by:
Phenomenal features: Reduced insulation resistance (should be ≥1000MΩ under normal conditions); partial discharge phenomenon; surface discharge marks; increased leakage current; dampness or water stains on the equipment surface.
Causes of failure: Humid rural environments and poor sealing of the 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 on the terminal block; insulation breakdown caused by lightning overvoltage.
Hazards of failure: Degraded insulation performance leads to leakage or short circuits; misoperation of protection devices; increased metering errors; and may even cause fires in severe cases.
Typical rural scenario data: In southern rural areas, the humidity is maintained above 80% all year round. The insulation resistance of transformers without moisture-proof measures may 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 of connected ammeters and power meters suddenly becomes zero or fluctuates significantly; whether the watt-hour meter stops rotating or rotates abnormally.
Sound identification method: Approach the transformer body and listen for abnormal "buzzing" or discharge sounds; the sound should be small and uniform during normal operation.
Temperature detection method: Use an infrared thermometer to detect the temperature of the 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 of the secondary circuit. The impedance angle is independent of frequency when connected normally; the impedance increases significantly (>10000Ω) when open-circuited.
Rural scenario judgment skill: In 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 of the 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 of the 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 and last for more than 10 seconds.
Load testing method: Connect a standard load to the secondary circuit of the transformer and observe whether the output current is stable; the current may fluctuate when there is poor contact.
Rural scenario judgment skill: In metering boxes after rural network centralized reading transformation, if it is found that the metering of a certain household's electric meter is abnormal while that of other households is normal, focus should be on checking the connection status of the secondary circuit of the current transformer for that household.
3. Judgment of Overload and Iron Core Saturation Faults
Current monitoring method: Check whether the actual load current on the primary side exceeds the rated value; special attention should be paid to peak electricity consumption periods in rural power grids, such as the Spring Festival and the irrigation season.
Error testing method: Use a transformer calibrator to test the ratio error and 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 and draw the excitation curve; the slope of the 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 and uniform during normal operation.
Rural scenario judgment skill: On the low-voltage side of 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 and secondary, secondary to ground, and primary to ground; it should be ≥1000MΩ under normal conditions.
Partial discharge testing method: Use a partial discharge tester to detect internal discharge in the transformer; the discharge amount will increase when insulation performance degrades.
Visual inspection method: Check whether there are water stains, dirt, or damage on the transformer surface; whether there is dust accumulation or signs of animal gnawing on the terminal block.
Humidity detection method: Use a hygrometer to detect the humidity of the transformer installation environment; a humid environment in rural areas may lead to degradation of insulation performance.
Rural scenario judgment skill: In southern rural areas, if it is found that the insulation resistance of the transformer has decreased significantly, focus should be on checking whether the sealing structure is intact and 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 at the terminals near the transformer; if there is a spark during short-circuiting, it indicates that the fault point is in the circuit below the short-circuit point; if there is no spark during short-circuiting, the fault point may be in the 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 of the secondary circuit.
Rural scenario handling suggestions: In 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 on terminals; apply conductive paste to terminal contact surfaces; inspect and replace aging or damaged terminal blocks.
Preventive measures: Install moisture-proof heaters at 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 and maintain terminal blocks.
Rural scenario handling suggestions: In 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 of the wires at the 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 and load conditions; 1A transformers are suitable for long-distance metering; in rural power grids, iron core materials with good anti-saturation performance (such as permalloy) can be selected.
Rural scenario handling suggestions: At the incoming lines of 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); on the low-voltage side of distribution transformers, reserve sufficient transformer capacity according to load conditions; adopt intelligent monitoring devices to monitor the operating status of transformers in real-time.
4. Handling of Insulation Performance Degradation Fault
Maintenance measures: Regularly check whether the sealing structure of the transformer is intact; use silicone rubber sealing rings to enhance sealing; install moisture-proof heaters in metering boxes; clean dirt on the transformer surface.
Preventive measures: Select metering boxes with IP65 protection level; use flame-retardant ABS materials for the shell; use moisture-proof wiring terminals at the terminal block; conduct regular insulation resistance tests.
Rural scenario handling suggestions: In southern rural areas, epoxy resin-cast transformers can be adopted; install temperature and humidity monitoring devices in metering boxes; regularly inspect and replace aging sealing materials; install lightning arresters in lightning-prone areas.
