Paghulagway sa kusgan kaayong mga kable nga walay paglihok

1. Paghulagway sa Pagsusay sa Konstante sa Linya sa Kable sa Mataas nga Voltaje

Ang pagsusay sa konstante sa linya sa kable sa mataas nga voltaje nagpasabot sa sistemang pagsumala, gamit ang espesyalisadong instrumento, sa mga elektrikal nga parametro sama sa resistensya, indyuktansiya, kapasidad, ug konduktansiya sa wala pa mapahimulos ang linya sa kable o human sa dako nga pag-uli. Ang layo mao ang makakuha og pundok nga datos nga nagsarakyan sa electromagnetical nga katungod sa kable, nga nagserbi isip usa ka mahimong bahin sa pagsusay nga naghatag og eksakto nga suporta sa mga parametro alang sa pagkalkula sa load flow sa sistema sa kuryente, pag-configure sa relay protection, pag-analisa sa short-circuit current, ug pag-evaluha sa status sa operasyon sa kable.

Ang iyang core value nahimutang sa duha ka aspeto: una, ang pagpatunay sa desbaryo tali sa design values ug aktwal nga gisumala nga values aron malikayan ang mga problema sa proteksyon o system stability tungod sa mismatch sa mga parametro; ikaduha, ang pag-establish og "baseline parameter database" alang sa linya sa kable, nga naghatag og reference aron mas identify ang sunod nga mga pagbag-o sa operasyon (tulad sa insulation aging o dili maayo nga contact sa joint). Sumala sa DL/T 596 "Preventive Test Regulations for Electrical Equipment" ug GB 50217 "Design Standard for Power Engineering Cables," kinahanglan nga matapos tanang constant tests alang sa 220 kV ug uban pa nga linya sa kable sa panahon sa commissioning, samtang ang 110 kV ug ubos pa nga linya mahimong mapilihon basehan sa importansya sa sistema.

2. Kompleto nga Proseso sa Pagsusay sa Konstante sa Linya sa Kable sa Mataas nga Voltaje

2.1 Pre-Test Preparation Phase

2.1.1 Collection of Technical Data and Site Survey
Kinahanglan nga makuhon ang komprehensibong mga design parameters sa linya sa kable, kasama ang voltage level (tulad sa 220 kV, 500 kV), modelo sa kable (tulad sa YJV22-220 kV-1×2500 mm²), paraan sa pag-install (direct burial, conduit, cable tray), length (accurate hangtod sa 0.1 km), material sa conductor (copper o aluminum), tipo sa insulation (XLPE, oil-impregnated paper), metallic shield structure (copper tape, copper wire), ug grounding method (direct grounding, cross-bonded grounding). Ang site survey kinahanglan nga ipatuman ang kondisyon sa komunikasyon sa main test site (kasagaran ang cable terminal station) ug auxiliary site (opposite substation), integridad sa grounding system, safe distance gikan sa nearby energized equipment (≥1.5 times the safety distance corresponding to the test voltage), ug paggamit og electrostatic voltmeter aron sukolon ang induced voltage (na mahimong makaabot sa tens of volts sa mga kable near energized lines, requiring anti-electrocution measures).

2.1.2 Test Plan Development and Equipment Selection

Batasan sa "Guidelines for Cable Line Parameter Testing," kinahanglan nga makuhon ang detalyado nga plano kasama ang mga test items (positive-sequence resistance, zero-sequence capacitance, etc.), modelo sa instrumento, wiring methods, ug safety measures. Core equipment includes:

• Line parameter tester (accuracy class 0.2, frequency range 45–65 Hz, output current ≥10 A);

• Three-phase voltage regulator (capacity ≥5 kVA, adjustable range 0–400 V);

• Isolation transformer (1:1 ratio to prevent grid interference);

• Auxiliary tools: thermometer/hygrometer (ambient temperature and humidity must be recorded for temperature correction of parameters), discharge rod (25 kV class, discharge time ≥5 min), shorting wires (cross-sectional area ≥25 mm² copper cable, length customized on-site), and insulating pole (3 m, insulation resistance ≥1000 MΩ).

2.1.3 Safety Measures Deployment

Kinahanglan nga ibulid ang test area ngadto sa safety barriers ug imarkahan sa "High Voltage Danger" warning signs. Ang main ug auxiliary test sites kinahanglan nga magpadayon sa walkie-talkies (communication range ≥1 km) ug emergency stop buttons. Tanang test personnel kinahanglan nga magdugang sa insulating gloves (35 kV class), insulating shoes (breakdown voltage ≥15 kV), ug double-hook safety harnesses when working at height. Ang distant end sa kable kinahanglan nga idisconnect gikan sa uban pang equipment ug gitag sa temporary grounding wires aron malikayan ang back-feeding.

2.2 On-Site Testing Implementation Phase

2.2.1Test Wiring and Phase Verification
Taking positive-sequence parameter testing as an example, the wiring procedure is as follows:
(1) Short-circuit and ground the three-phase conductors (A, B, C) at the far end; ground the metallic shield at one end only (for cross-bonded systems, disconnect the bonding links in the cross-bonding box and test each section separately);
(2) Apply AC voltage (typically 380 V) to phase A at the main test end via a voltage regulator and isolation transformer; leave phases B and C open; connect the voltage and current sampling leads of the line parameter tester.
Phase verification: Use a multimeter to measure the voltage phase of each phase to ensure correct same-name phase connections and avoid measurement errors due to incorrect phase sequence.

2.2.2Parameter Measurement Procedure
Positive-sequence resistance (R1) and reactance (X1): Apply test current (typically 5–10 A) to phase A, measure the magnitude and phase angle difference between voltage and current, and calculate using the formulas R1 = U/I·cosϕ and X1 = U/I·sinϕ. Repeat the test three times and take the average value, with at least a 1-minute interval between tests to prevent conductor heating from affecting resistance values.
Zero-sequence capacitance (C0): Short-circuit and connect phases A, B, and C to the high-voltage terminal of the tester, ground the metallic shield, apply 100 V, and measure capacitance using the Schering bridge principle. Linearity must be verified at different voltage levels (50 V, 100 V, 200 V), with deviations ≤2%.
Insulation resistance (Rins): Use a 2500 V megohmmeter to measure insulation resistance between conductor and shield. Record the reading after 1 minute of applied voltage and simultaneously record ambient temperature. Convert to the 20°C reference value using the formula R20 = Rt × 10^(0.004(t−20)) (where t is the measured temperature).

2.2.3Data Recording and Validity Assessment
Immediately after completing each parameter test, record the instrument reading, ambient temperature and humidity, test time, and any anomalies (e.g., voltage fluctuations, unusual noises). Data validity criteria include:

• Relative deviation of three repeated measurements of the same parameter ≤5%;

• Deviation of positive-sequence impedance from design value ≤10% (accounting for installation length error);

• Insulation resistance, after temperature correction, should be ≥1000 MΩ·km (standard for XLPE cables).

2.3 Post-Test Processing Phase

2.3.1 Safe Discharge and Wiring Removal
After testing, first disconnect the power supply to the voltage regulator. Then, use a discharge rod to perform "multiple discharges" on the cable conductor and shield (each discharge lasting ≥1 minute, with a 30-second interval). Only after confirming the residual voltage is ≤50 V should the shorting wires and test leads be removed. For cross-bonded systems, reconnect the bonding links in the cross-bonding box and measure continuity to ensure proper connection.

2.3.2 Data Correction and Report Preparation
According to GB/T 3048.4 "Methods for Electrical Testing of Electric Wires and Cables," measured parameters must be corrected for temperature and frequency:
Resistance temperature correction:
For copper conductors: R₂₀ = Rₜ / [1 + α(t − 20)] (where α = 0.00393/°C);
Capacitance frequency correction:
When the test frequency deviates from 50 Hz, correct using: C₅₀ = Cf × (1 + 0.002∣f − 50∣).
The test report must include the testing standard (e.g., DL/T 475), instrument calibration certificate number, a parameter comparison table (design values vs. measured values), and a conclusive assessment (e.g., "Pass", "Retest Recommended").