Unsa ang mga rutinong pagsubay sa outdoor voltage transformers?

1. Pagpasilabot

Ang mga outdoor voltage transformers mao ang mga mahimong butang sa pagseguro sa kalambigitan sa electrical apparatus. Gikinahanglan og siyentipikong ug komprehensibong test analysis aron malihok ang mga hazard ug property losses gikan sa dili maayo nga operasyon. Ang test analysis makapugos sa pagbuhat og strategies ug precautions, siguraduhon ang stable nga operasyon sa equipment, ug makamit ang maximum nga economic ug social benefits.

2. Konsepto sa Outdoor Voltage Transformers

Ang outdoor voltage transformer mao ang usa ka outdoor step-down transformer, uban sa core function sa pag-isolate sa high-voltage electricity:

• Ibalhin ang high-voltage electricity ngadto sa secondary voltage nga 100V o mas baba nga proporsyonado aron mapasabot ang panginahanglan sa measuring instruments ug relay protection.

• Gigamit para sa line output control/supervision sa power plants ug substations, sama usab sa electricity settlement sa pagitan sa power grid ug users, ug sa pagitan sa power plants ug stations.
  Adunay mataas nga value ug applicability ug gikinahanglan og reasonable nga paggamit aron makamit ang maximum nga value.

2.1 Test Methods ug Working Principles

Ang reverse connection method kasagaran gigamit sa pagsusi sa outdoor voltage transformers. Ang reverse connection method madetekta ang tangent sa dielectric loss angle sa insulation sa sumala nga tatlo ka bahin:

• Insulation sa pagitan sa primary electrostatic screen (X terminal) ug secondary ug tertiary windings.

• Insulation sa pagitan sa primary winding ug ends sa secondary ug tertiary windings.

• Insulation sa pagitan sa insulating support ug ground.

2.2 Defect Analysis sa Reverse Connection Method

Ang reverse connection method adunay tres ka deficiencies:

• Measurement Limitation: Mainly reflects the tangent of the dielectric loss angle of the insulation between the primary electrostatic screen and the secondary and tertiary windings. Because the capacitance of this part reaches 1000pF, which is much larger than that of the other two parts (tens of picofarads), it is difficult to reflect the change of the dielectric loss angle of the latter two parts.

• Low Test Voltage: The insulation level of the grounding end of the high-voltage winding of the cascade voltage transformer is low. The test voltage designed by the manufacturer is 2000V, and usually only 1600V can be applied in preventive tests (some units have used 2500-3000V. Although it can detect water ingress and moisture, the overall voltage is relatively low, which affects the measurement sensitivity of the bridge).

• Pollution Interference: The pollution of the terminal board and small porcelain sleeve led out from the X terminal will increase the measurement error. Although the positive connection method can be used to reduce the impact (the positive connection method also measures the tangent of the dielectric loss angle between the primary electrostatic screen and the secondary and tertiary windings), the measurement error of the positive connection method itself is still large.

To be precise, voltage transformers and power transformers have roughly the same working principle. Their basic structure consists of three parts: the iron core, primary winding, and secondary winding. A power transformer’s main function is to transmit electrical energy, so it generally has a large capacity. A voltage transformer mainly functions to transform voltage, ensuring power supply for measuring instruments and relay protection devices, and measuring voltage, power, and electrical energy in circuits. It should be noted that voltage transformers can also analyze and monitor line faults. These factors determine that outdoor voltage transformers have relatively small capacities. Normally, outdoor voltage transformers operate under no-load conditions. The working principle analysis diagram of the voltage transformer is shown in Figure 1.

As seen from the diagram, the high-voltage winding of a voltage transformer is parallel to other relevant circuits in the primary circuit. The secondary voltage is proportional to the primary voltage and reflects its value. The ratio of the rated voltages of the primary and secondary windings is the rated transformation ratio, usually K_n = U₁/U₂. Also, the primary winding is parallel in the primary circuit, so the secondary side can’t be short-circuited — a short circuit would generate a strong current, damaging the transformer and even paralyzing the line in severe cases. Similarly, during outdoor voltage transformer tests, to avoid excessive high or low voltage, ground the secondary winding, iron core, and housing. This ensures the transformer and outdoor equipment stay safe even if accidents occur.

3. Classification sa Outdoor Voltage Transformers

• Classified by the working principle of voltage transformers: Electromagnetic voltage transformers and capacitive voltage transformers.

• Classified by the characteristics of specific outdoor working conditions: Conventional outdoor voltage transformers and special outdoor voltage transformers.

• Classified by the number of phases of voltage transformers: Single-phase type and three-phase type. Generally speaking, a single-phase voltage transformer refers to one that can be manufactured for any voltage level and can perform conversion as required under different conditions to ensure all needed changes; while a three-phase voltage transformer is limited to voltage levels of 10 kV and below.Although this type of voltage transformer has certain limitations to a large extent, it is relatively suitable for playing its value and role in specific situations.

• Classified by the number of windings of voltage transformers: Double-winding combined type and three-winding combined type.

• Classified by the insulation structure: Dry type, plastic-poured type, gas-filled type, and oil-immersed type. Of course, as for what type of outdoor voltage transformer to use, it is necessary to fully consider the working environment and actual characteristics of the entire voltage transformer for specific analysis.

4. Analysis sa Wiring Modes sa Outdoor Voltage Transformers sa Routine Tests

Sa tanang test sa outdoor voltage transformers, ang wiring mode mao ang usa ka key ug importanteng link sa buong voltage transformer, ug gikinahanglan nato'g analisis aron siguraduhon ang safety ug stability sa tanang test.

4.1 Single-wire Connection

Mao kini ang wiring mode nga gamiton ang single-phase voltage transformer aron sukidan ang voltage sa usa ka phase sa ground o ang voltage sa pagitan sa mga phase. Ang wiring method sa voltage transformer mao ang gamiton sa relatybong symmetrical nga three-phase circuits.

4.2 V-V Wiring Mode

Ang tinuod nga V-V wiring mode mao ang pagkonekta og duha ka single-phase transformers sa incomplete structure. Kini nga wiring mode makagamit sa pag sukidan sa voltage sa pagitan sa mga phase, pero adunay disadvantage, mao na dili makasukid sa voltage sa ground. Mas notable, giwasto kini sa mga power grids nga may voltage nga 20 kV o mas baba diin ang neutral point dili grounded o ang arc-suppression coil grounded.

4.3 Y0-Y0 Wiring

Kini nga wiring mode nagkonekta sa primary ug secondary sides sa single-phase transformer sa single voltage transformer sa Y0 type. Kini nga wiring mode adunay advantage, mao na makapaghatag sa meters ug relays nga gibutangan sa voltage ug sa insulation monitoring meters nga gibutangan sa phase voltage. Kasagaran, kini nga wiring mode gamiton sa systems nga 35 kV o mas baba.

5 Analysis sa Precautions Sa Routine Tests sa Outdoor Voltage Transformers

• Sa proseso sa test, sa wala pa sa formal test sa voltage transformer, gikinahanglan og scientific treatment ug testing sa polarity ug insulation resistance measurement sa voltage transformer. Aron siguraduhon nga ang voltage transformer dili magdawat og unnecessary losses gikan sa external factors sa panahon sa test.

• Ang wiring sa outdoor voltage transformer dapat correct. Particular, mahimo nga atiman nga ang primary winding ug ang circuit sa test kinahanglan iparalelo, ug ang secondary winding ug ang voltage coils sa connected measuring instruments ug relay protection devices kinahanglan iparalelo. Kinahanglan usab nga atiman ang correctness sa polarity.

• Sa panahon sa test, ang load sa secondary side sa voltage transformer dili dapat mogawas sa iyang specified rated capacity sa normal circumstances. Kon mogawas, mahimo nga magresulta og large data error sa buong transformer, ug dili makamit ang required normal values.

• Ang secondary side sa voltage transformer dili allowed mogawas sa short-circuit. Niini, ang internal impedance sa voltage transformer labi ka gamay. Kon short-circuit, mahimo nga mobuntog ang large current, mahimo nga makadaot sa buong voltage transformer equipment. Sa severe cases, mahimo nga mag-threaten sa personal safety sa test staff. Sa dugay, kon possible, certain protection ug monitoring equipment dapat igamit sa primary side aron siguraduhon ang stability sa buong test system ug iwasan ang unnecessary situations.

• Arong mas maayo nga atiman ang measurement sa related tests ug safety sa related experimental personnel, ang secondary winding kinahanglan ipakita sa usa ka point sa experiment. Ang advantage niini mao na kon mag-insulate damage, makamit ang property ug personal safety.

6 Conclusion

Sa test analysis sa outdoor voltage transformers, napormula ang complete ug scientific nga test methods ug precautions. Siguraduhon ang normal nga progress sa tanang test, protektahan ang safety sa equipment ug personnel, ug hatagan og reliable nga foundation sa application sa outdoor voltage transformers sa field sa power supply aron makamit ang maximum nga value.