Strategie di Risoluzione di Problemi di Cable in Scenari di Applicazioni Sferenti
U metudu di posa di cable è l'ambiente di l'applicazione affettanu significativamente a difficultà di risolve i prublemi è a scelta di metudi.
Diagnosi di difetti di u cable interratu direttu: Sfide è Soluzioni
Sfida: U cable hè intarratu in terra è ùn hè micca visibile; L'umidità di a terra è e variazioni di cumpusizioni affettanu u campu elettricu è a propagazione di l'onda sonora. Pipelines adiacenti (tubi d'acqua, tubi di gas, altri cavi) pò generà signali di interferenza; L'infurmazione precisa di u caminu di u cable hè difficiule d'ottene.
Prucedure cunsigliatu:
Jugement préliminaire: Megohmmeter è multimeter sò usati per ghjudicà u tipu di difettu (cortu circuitu, circuitu apertu, colpa a terra, ecc.).
A cunferma di a strada: Aduprate un tracciatore di rotta di cable per seguità accuratamente è marcà a direzzione di u cable per evità deviazioni in u posizionamentu sussegwenti.
Pre-location: Selezziunà u metudu apprupriatu basatu annantu à u tipu di difettu.
Cortu circuitu / circuitu apertu à bassa impedenza: TDR hè preferitu.
Fallu di terra à alta impedenza: U Metudu Impulsu Secundariu (SI/ME) hè preferitu. Se u dispusitivu ùn sustene micca, pudete pruvà u metudu High Voltage Bridge (chì deve esse brusgiatu u puntu di difettu prima) o u metudu acustomagneticu dopu un impulsu d'alta tensione.
Situazione di u puntu di difettu (Pin-pointing): Posizionamentu precisu utilizendu u metudu di timing sincronu acustomagneticu in l'area indicata da i risultati di pre-situazione. Una alta tensione pulsata hè appiicata à u cable, è u sonu più forte hè situatu à sente u sonu di scaricamentu in terra. Per i difetti di terra chì ùn pruducenu micca un sonu di scaricamentu chjaru, u mètudu voltage step pò esse pruvatu.
Verificazione: Dopu chì u puntu di difettu suspettatu hè determinatu, una piccula zona pò esse scavata, o verification lucale acoustomagnetic e voltage mètudu pò esse realizatu di novu.
Affrontendu e sfide: Riduce l'errori di rotta attraversu tracciatori di rotta di alta qualità; Sceglite un ricevitore acustomagneticu cù una forte capacità anti-interferenza; Aghjustate l'energia d'impattu à alta pressione secondu e cundizioni di a terra; Una cumminazzioni di metudi corroborate i risultati cù l'altri.
Cable aereo isolatu (ABC) Risoluzione di prublemi: Cunsiglii di Locazione Rapida
Sfida: I punti di difettu sò spessu visibili, ma sò largamente distribuiti è implicanu u travagliu in altitudine alta, chì pò esse periculosu per uperà.
I difetti tipici: A strata isolante invechja è cracking, graffi di ramu, fulmini, danni d'uccelli è animali, prublemi di prucessu cumuni.
Prucessu di prova:
Ispezione visuale: Inspeccione cù cura a linea, usendu un telescopiu, per circà tracce evidenti di carbonizazione, segni di bruciatura, crepe, sovrapposizione di corpi stranieri, è altre tracce evidenti di a capa d'insulation. I camion di bucket o droni aumentanu l'efficienza è a sicurità.
Thermal Imaging: Camere termali sò aduprate per detectà l'aumentu anormali di a temperatura in u corpu di u cable, in particulare à i giunti è i terminali, quandu u cable hè operatu sottu carica. L'aumentu di a temperatura hè un signu impurtante di fallimentu precoce o sovraccarica.
Misurazione elettrica di basa: Dopu à una mancanza di energia, Aduprate un megohmmeter è un multimetru per pruvà a resistenza d'insulazione è a continuità per determinà u tipu di difettu.
Situazione di difettu: Mentre l'ispezione visuale pò revelà u puntu di difettu, TDR o acustomagneticu (se l'impulsu d'alta tensione pò esse applicatu) pò ancu esse usatu per localizà u puntu di difettu s'ellu ùn hè micca evidenti (P.e., rottura interna).
Cumpetenze: Aduprate carte di rotta è indicazione geografica per aiutà à u pusizziunamentu; Prestate attenzione à l'influenza di i fatturi climatichi nantu à a termografia infrared è l'ispezione visuale.
Diagnosi di difetti di cable in Tunnels/Cable Trenches: Impattu Ambientale è Metodi di Rilevazione
Sfida: L'ambiente hè chjusu, è ci pò esse risichi cum'è gasi dannusu, carenza di ossigenu, alta temperatura, è alta umidità; U spaziu hè strettu, è l'equipaggiu hè sconveniente per portà è operate; Ci sò parechji cables, è hè difficiule di identificà u cable di destinazione; U rumore ambientale pò interferisce cù a rilevazione acustica.
Prucedure cunsigliatu:
Valutazione di Sicurezza: A rilevazione di gas è a ventilazione deve esse realizatu prima di l'ingressu per assicurà a sicurità.
Identificazione di destinazione: Cunfirmà i cavi difettosi utilizendu tag d'identificazione di cavi è disegni di u sistema.
Ispezione visuale: Inspeccione cù cura longu u caminu di u cable, in particulare à i articuli è i supporti, for signs of insulation damage, ablation, deformation, ecc.
Infrared Thermal Imaging: Conducted during loading, to detect abnormal hot spots.
Pre-location: TDR (for low resistance/open circuit) or Dual Pulse Method (for high resistance).
Situazione di u puntu di difettu: Acoustomagnetic synchronous positioning in tunnels/trenches is generally easier than direct burial because the discharge sound propagation is more direct. Use a contact acoustic sensor (placed on the cable surface) or an air-coupled sensor in combination with a magnetic field sensor.
Scaricamentu Parziale (PD) Detezzione: Tunnels/trenches are a favorable environment for partial discharge detection, and the background noise is relatively stable. Online or offline PD inspections can be performed using TEV sensors (on metal brackets or trays), HFCT sensors (on grounding wires), or ultrasonic sensors (on the cable body surface or accessories) to detect early insulation defects.
Diagnosi di difetti di u cable sottumarinu: Requisiti Speciali è Tecnulugia
Sfida: L'ambiente hè estremu, esige un equipamentu prufessiunale impermeabile è resistente à a pressione; Hè necessaria una alta precisione di posizionamentu perchè u costu di riparazione hè estremamente altu; U travagliu di riparazione hè complicatu.
I difetti tipici: Ganci di ancora, graffi di rete di pesca, danni à l'ancora di a nave, terrimotu è tsunami, l'arburu internu di l'acqua / l'arburu elettricu.
Prucedure cunsigliatu:
Pre-location: Si basa principalmente nantu à l'equipaggiu TDR specificu per i sottumarini d'alta precisione, chì generalmente richiede l'usu di boe o misurazione di a pusizione di a superficia assistita da GPS. U metudu di ponte d'alta tensione pò ancu esse usatu, s'è pussibule.
Situazione precisa è rilevazione: Estremamente difficiule. A ricerca dettagliata pò esse dumandata in cunjunzione cù sonars, robots sottumarini dotati di sensori acustomagnetici, o sensori di flussu chì rilevanu cambiamenti in u campu magneticu causati da correnti di fuga.
Riparazione di difetti: E navi prufessiunali di posa di cavi sottumarini è di riparazione sò spessu richieste, è a riparazione hè fatta cù a tecnulugia di cunghjunzione umida o secca, chì hè costu.
Equipamentu speciale: Sonda TDR sottumarina, ricevitore sincronu acustomagneticu subacqueu, ROV (Veiculu operatu à distanza).
Cable di cumunicazione (Fibra / Copper) Risoluzione di prublemi: OTDR è altri strumenti
U diagnosticu di difetti di u cable di cumunicazione hè diversu da i cavi d'alimentazione, in particulare i cavi di fibra ottica.
Guasto di u cable di fibra ottica:
I difetti tipici: Fibre rotte, connettori sporchi/dannati, perdita eccessiva di splice, raggiu di curvatura eccessivu (macrobend/microbend).
Strumenta basica: Reflectometru otticu di u duminiu di u tempu (OTDR).
Principiu: Simile à TDR, l'OTDR trasmette impulsi luminosi in a fibra è analizà i segnali di riflessione Rayleigh è Fresnel longu u percorsu di a fibra.. By analyzing the shape and position of the reflection/scattering curve, it is possible to determine the length, attenuazione, splice loss, connector loss, and the location of the fiber break point.
Applicazioni: Accurately measure the loss distribution of fiber links, locate breaks, high-loss points, connector, or splice issues.
Other Tools:
Light Source and Power Meter: Used to measure the overall loss of the optical link and determine if there is a problem.
Visual Fault Locator (VFL): Shines a visible red light to detect fiber breaks, bends, or connector problems over short distances (the fiber jacket must be optically non-dense).
Fiber Microscope: Inspects connector end faces for cleanliness, scratches, or damage.
Copper Cable Fault:
I difetti tipici: Open circuit, cortu circuitu, wrong wiring, circuitu apertu, crosstalk, excessive return loss.
Basic Tools: Cable Certifier/Tester or TDR (for open circuits, short circuits).
Applicazioni: Measure pair length, schema di cablaggio (per determinà i cortu circuiti, apre, mis-fili, coppie incruciate), Near-End Crosstalk (NEXT), Crosstalk à l'extrême (FEXT), perdita di ritornu, perdita d'inserzione, è altri paràmetri per valutà u funziunamentu di u ramu è localizà i difetti. A funzione TDR hè spessu usata per indicà punti di circuitu apertu o di cortu.
Analisi approfondita di i casi tipici di difetti di cavi
Cumminendu a teoria è a pratica hè a chjave per maestru di a tecnulugia. Eccu alcuni casi tipici di diagnostichi di difetti di cable in diverse scenarii.
Casu 1: Guasto di terra monofase di un cable d'alimentazione d'alta tensione in una pianta chimica
Sfondate: In l'area di una grande pianta chimica, un alarme di guasto à terra monofase hè accadutu nantu à l'alimentatore in uscita di a 35Cavu d'alimentazione insulatu kV XLPE in funziunamentu, pruvucannu una mancanza di energia in l'area affettata.
Fenomenu di colpa: The system’s ground protection device operated, and the circuit breaker tripped. The operator tried to reclose, but the relay operated again.
Diagnostic Steps and Procedures:
Jugement préliminaire
After the power outage, use a 2500V megohmmeter to test the insulation resistance of the faulty cable. The insulation resistance of phases A and B is normal (> 2000 MΩ), and the insulation resistance between phase C and ground decreases significantly, to only 5 MΩ. It is preliminarily judged to be a ground fault on phase C, and the resistance at the fault point is medium-to-high resistance.
Pre-location
Since it is a high-impedance fault, using conventional TDR directly may not be effective. The operating team decided to use Ultra-Low Frequency AC Hipot (VLF) testing with Dielectric Loss (Allora Delta) and Partial Discharge (PD) detection for pre-location and to assess the cable condition at the same time. Connect the VLF tester between phase C and ground, and apply 0.1 Hz, 2U0 (approximately 40kV) AC voltage. During the test, it was found that the tanδ value of phase C rapidly increased with increasing voltage, and a continuous large-amplitude partial discharge signal was detected. By analyzing the signal propagation characteristics (such as time difference positioning), the fault point is estimated to be located about 1.2 km away from the substation.
Precise Positioning (Quadratic Impulse Method)
In order to pre-locate more accurately for subsequent pinpointing, the O&M team used a cable fault tester with a quadratic impulse function. Connect the high voltage impulse generator (set to 15kV) to phase C and ground, and set the cable tester to secondary impulse mode. After applying a high voltage impulse, a flashover occurs at the fault point, and the cable tester captures a clear arc reflection waveform. The waveform was analyzed, and the fault distance was calculated to be 1.22 km. The results of the two pre-locations were fundamentally consistent.
Fault Point Detection (Acoustomagnetic Method)
According to the pre-location result of 1.22 km, O&M personnel carried the acoustomagnetic synchronous receiver and listened to the sound on the ground in the area around 1.2 km along the direction indicated by the radiometer (route tracer). The cable route tracer confirmed the precise cable direction on the ground beforehand. The operator carefully listened to the ground while applying a 15kV high voltage impulse, and finally heard the loudest discharge sound at a distance of 1225 meters from the test end. Combined with the synchronous judgment of the magnetic field signal, the precise location of the fault point was determined.
Excavation and Verification
A small excavation area was made at the location determined by the acoustomagnetic method, and it was found that the cable had a joint with blackened traces on the outer insulation. Dissection of the joint revealed that the internal filling (P.e., silicone grease) had failed, and moisture intrusion had led to moisture deterioration of the insulation, forming electrical trees, which eventually broke down and discharged at high voltage. The fault point was exactly the same as the diagnostic result.
Solution: Replace the faulty joint and check other joints from the same batch, performing preventive replacement or hidden danger treatment.
Casu 2: Rapid Repair of Communication Cable Fiber Fault in a Data Center
Sfondate: A large data center expanded its capacity and laid a new batch of multimode cavi di fibra ottica. During the commissioning process, it was found that a fiber optic link connecting the two buildings could not communicate normally, and the optical signal loss was huge.
Fenomenu di colpa: Through optical power meter testing, it was found that the optical link loss was much higher than expected, close to infinity, and the fiber optic was suspected to be broken.
Diagnostic Steps and Procedures:
Jugement préliminaire
End-to-end tests were performed using a light source and optical power meter, and it was confirmed that the link was not open circuit and the loss was extremely high. Suspected broken or severely bent fiber.
Situazione di difettu (OTDR)
Connect the OTDR to one end in the equipment room and select the appropriate optical wavelength (P.e., 850nm or 1300nm, corresponding to multimode fiber). After the OTDR emitted a light pulse, a large Fresnel reflection peak was clearly displayed on the waveform graph, followed by no scattered or reflected signal. This indicates that the fiber was completely broken at that point. The OTDR automatically calculated that the break point was located 356 meters from the test end.
On-site Search and Verification
According to the distance of 356 metri, O&M personnel combined with the pipeline manhole and bridge wiring drawings to conduct a search. In a pipe manhole approximately 350 meters from the optical fiber outlet of the equipment room, it was found that the optical fiber might have been crushed or bent during the pipe threading process, causing the optical fiber to break. Visual inspection also confirmed the break.
Solution
Fiber optic splicing repair in a pipe manhole. Use a fiber cleaver to cut the broken ends, clean the fiber, and use a fusion splicer to precisely align and weld the ends. After splicing is completed, the link is re-tested with an OTDR to confirm that the splice loss is qualified (di solitu < 0.1 dB) and the signal at the end of the link is normal. The link restored communication.
Lesson Learned
Fiber break point location is one of the most classic applications of OTDR, which is fast and accurate. For communication cables, in addition to break points, OTDR can effectively diagnose faults such as high-loss splices, connector issues, and macrobends.
Casu 3: Comprehensive Diagnosis of High-Resistance Faults in Medium Voltage Cables in Industrial Parks
Sfondate: A 10kV ring main unit (RMU) outgoing cable (XLPE insulation) in an industrial park frequently experiences instantaneous single-phase ground faults, causing the RMU to trip, but most reclosures are successful. The fault phenomenon is intermittent.
Fenomenu di colpa: The system’s protection device operates instantaneously, and the record shows it is a single-phase ground fault, but the fault does not continue, and reclosing is successful. Megohmmeter test insulation resistance is within the normal range, but breakdown occurs when performing the VLF withstand voltage test.
Diagnostic Steps and Procedures:
Jugement préliminaire
Instantaneous, intermittent failure and normal megohmmeter test, high suspicion is a high-impedance fault or flashover fault, which may be related to voltage level and environmental changes. Megohmmeters are unable to detect such faults.
Insulation Assessment (VLF + Allora Delta + PD)
A 0.1 Hz, 1.5 U0 voltage boosting test is performed on the cable using VLF withstand voltage test equipment (lower than the standard withstand voltage value to avoid burning the fault point). In the process of boosting the voltage, it is found that the dielectric loss tanδ value increases significantly and non-linearly with increasing voltage, and a continuous partial discharge signal appears when a certain voltage is reached. Analyze the PD signal characteristics to determine whether the fault may exist in the cable body or at a joint. The location function indicates that the fault is roughly at a certain distance in the cable area.
Precise Positioning (Quadratic Impulse Method + Acoustomagnetic Method)
In order to pre-locate and precisely locate, it is necessary to “excite” the fault point to make it stable during high-voltage discharge or breakdown. Connect the cable to the cable fault test van (containing the high voltage impulse generator and the secondary impulse main unit). Primu, try to pre-locate using the quadratic impulse method, setting the voltage to be close to the peak operating voltage (P.e., 15kV). After several impulses (thumps), a distance estimation (P.e., 750 metri) is obtained. Allora, acoustomagnetic pinpointing is conducted on the cable path around 750 metri. A pulsed high voltage was applied, the ground sound was carefully listened to, the magnetic field signal was observed, and finally, the loudest discharge sound was heard at a distance of 755 meters from the test end.
Excavation and Verification
Excavation at this point revealed that the cable was located in an underground trench with a prefabricated joint at this location. Inspect the appearance of the joint and find that the sealing tape was slightly damaged, and moisture intrusion was suspected. After dissecting the joint, small electric discharge traces were found at the interface between the insulation stress cone and the cable body insulation layer, which proved that the defect here was the cause of the intermittent high-resistance flashover fault.
Solution
Replace the faulty connector (cunghjunta). Since the connector is prefabricated and has a long service life, other joints on the same cable section are tested for preventive testing (P.e., ultrasonic or TEV partial discharge testing) to assess their condition.
Lesson Learned
For intermittent high-impedance faults, basic megohmmeter tests are often ineffective and need to be combined with high voltage testing (VLF) and advanced diagnostic techniques (quadratic impulse method, acoustomagnetic method) to effectively diagnose and locate. Patience and meticulous on-site investigation are critical.
Building an Effective Cable Fault Prevention and Maintenance System
“Prevention is better than a cure”. Effective preventive maintenance can significantly reduce cable failure rates, extend cable life, reduce power outages, and lower O&M costs.
Periodic Preventive Testing and Inspection Programs
Establishing and strictly implementing a cable inspection program is the basis for preventing failures:
Annual/Term Items:
Insulation Resistance Test: Measure regularly to observe its changing trend. The continuous decrease in insulation resistance value is an important signal of insulation aging.
Scaricamentu Parziale (PD) Monitoring: Especially for critical lines and aging cables. Early insulation defects can be detected offline (P.e., in combination with VLF withstand voltage) or through online monitoring.
Tan Delta Test: Usually performed in conjunction with VLF withstand voltage, it evaluates the overall degree of moisture or general aging of the cable.
DC Withstand Voltage Leakage Current Test: While VLF is more recommended for XLPE cables, there are still applications for DC testing for oil-paper cables, ecc., focusing on the change of leakage current over time.
Quarterly/Inspection Items:
Connector/Termination Temperature Inspection: Use a thermal camera or infrared thermometer to regularly check the surface temperature of cable joints and terminal heads. Abnormally high temperatures may indicate poor connection, excessive contact resistance, or internal defects.
Operating Environment Inspection: Check whether the cable trench, tunnel, manhole cover, support, fire blocking, ecc., are in good condition, and whether there are issues such as standing water, miscellaneous items, corrosive gases, and animal infestation.
Appearance Inspection: Inspect and check whether the cable body, sheath, armor layer, and anti-corrosion layer have damage, deformation, bulging, and other abnormal phenomena.
Introducing Smart Online Monitoring Technology
With the development of technology, smart online monitoring systems can provide more continuous and comprehensive information on the operating status of cables, achieving the transformation from periodic maintenance to condition monitoring and predictive maintenance.
Distributed Temperature Sensing (DTS): The temperature distribution of the entire cable line is monitored in real time using optical fiber laid next to the cable. This is an effective means to prevent thermal aging and overload faults by being able to detect cable overloads, poor heat dissipation, or the influence of external heat sources in time.
Online Partial Discharge (PD) Monitoring System: HFCT, TEV, or ultrasonic sensors are installed at cable terminals and critical joints to monitor PD signals 24/7. Through data collection, analisi, and trend assessment, early insulation defects can be found in time.
Conditional Online Monitoring Platform: Integrate DTS, online PD, current, tensione, temperatura, umidità, and other sensor data, through big data analysis and artificial intelligence algorithms, comprehensively evaluate and predictively diagnose the health status of cables, and find hidden dangers in advance.
Optimizing Design, Construction, and Operation Management
Design Stage: Reasonable selection of cable type and cross-section, consideration of laying environment, load characteristics, and short-circuit capacity; Optimize routing to avoid corrosive areas and areas prone to external damage; Standardize the design of cable tunnels and channels to ensure good ventilation and heat dissipation.
Construction Stage: Strictly implement installation process regulations, control cable pulling tension and bending radius; Ensure the quality of cable heads and joints, use qualified materials, and ensure good sealing; Specification of backfill material and depth (for direct-buried cables); Do a good job of sealing the tube well and tunnel entrance to prevent animals and moisture from entering; Strict handover tests (P.e., VLF withstand voltage + tanδ test + PD test) are performed on newly laid cables.
Operation Management: Avoid long-term overload operation of cables; Strengthen trustee management of construction to prevent external force damage; Clean water and debris in the cable channel in time; Operational data is monitored and analyzed.
Improving Personnel Skills and Emergency Response Capabilities
Professional Training: Regularly train cable O&M personnel on fault diagnosis technology and safety operating procedures to ensure they are proficient in using advanced testing equipment and fault analysis capabilities.
Emergency Plan: Formulate a detailed emergency plan for cable failures, clarify the responsible person, disposal process, and material preparation for each link, and shorten the fault response time.
Tools: Equipped with comprehensive and reliable fault diagnosis equipment and safety protection equipment.
Cunclusioni: Towards a Smart and Predictive Future of Cable Operation and Maintenance
Cable faults are a significant challenge affecting the reliability of power, communication, and industrial systems. Mastering systematic fault identification and diagnosis technology is the key to reducing losses and ensuring safe operation. This guide sorts out common cable fault types and causes, introduces common and advanced detection technologies and equipment in detail, and provides practical troubleshooting strategies for different scenarios, supplemented with typical cases to help you understand.
Looking forward, with the deep integration of technologies such as the Internet of Things, grandi dati, and artificial intelligence, cable operation and maintenance are accelerating development towards intelligence and prediction. The smart diagnostic system based on online monitoring data can achieve continuous evaluation and early warning of cable status, so as to change from passive emergency repair to active maintenance, maximize the value of cable assets, and build a more reliable and resilient power transmission and information network.
We recommend that relevant industries continue to invest in advanced detection technologies and smart monitoring systems, strengthen personnel training, and continuously optimize operation and maintenance strategies to cope with the increasingly complex operating environment and growing reliability requirements
