Application of ground resistance testers in offshore platforms

Thread Content

Technical Application Article: In Case KL3-2, an electrician conducting a routine inspection detected an insulation alarm on Unit #1 UPS. He promptly notified the electrical engineer to handle the issue. Upon arriving at the site, the electrical engineer used a FLUKE 360 ground testing instrument to diagnose the problem, quickly identified the faulty circuit, and took action to resolve it, thereby preventing the UPS from operating in a faulty condition. II. Processing Process: The UPS on the KL3-2CEPA platform is a Protect 8.31 UPS 50KVA industrial UPS manufactured by the German company AEG. This UPS consists of 2 UPS units, 1 bypass cabinet, and 1 load distribution cabinet. To monitor the insulation level of the UPS load, the manufacturer equips it with an insulation monitor at the time of delivery; this monitor issues audible and visual alarms if there are problems with the insulation of the UPS load. After receiving the report from the electrician, the electrical technician used a FLUKE 360 ground testing instrument to measure the ground resistance of each circuit in the UPS load one by one. It was found that the leakage current at the outlet of circuit QF104 was 1.67A, indicating that this circuit had a proper ground connection. The QF104 circuit breaker supplies power to the control system; after investigation, it was found that there was a problem with the power supply for the water content analyzer, and the UPS returned to normal operation after the power was cut off. An on-site inspection of the water content analyzer revealed that the ground resistance of one phase of the power cable was zero. Currently, the water content analyzer is temporarily powered off; we have contacted Offshore Engineering to have the cable reconnected. III. New methods for detecting insulation faults Insulation monitors are currently commonly installed on offshore platforms; they issue audible and visual alarms when an insulation fault occurs. However, it is not possible to determine which circuit or device is causing the insulation issue, and electrical professionals need to be on site to confirm this. Traditional methods for detecting insulation faults: the insulation resistance method, which involves turning off the power to the equipment one by one and measuring the insulation resistance until the fault location is identified. The drawback of this method is obvious: a power-off measurement is required to confirm it. However, for some relatively important equipment such as the loads connected to UPS (control systems, communication devices, power supplies for various high/medium/low voltage panels, etc.), as well as equipment that affects the production process, it is certainly not possible to simply cut off the power in order to conduct measurements; this increases the difficulty for electrical engineers in identifying devices with insulation faults. The FLUKE 360 leakage current tester solves this problem effectively; by measuring the leakage current, it enables electrical technicians to locate insulation faults quickly and easily. Leakage current is essentially the current that flows through the insulated parts of an electrical circuit or device when there is no fault and no voltage is applied. Therefore, it is one of the important indicators for measuring the quality of electrical insulation. In circuits of electronic devices using low insulation resistance or bandpass filters, there may be high leakage currents. Leakage current can cause devices and systems to fail to function properly. Using a Fluke 360 leakage current tester to conduct comprehensive measurements across the entire system allows for the identification of the source of the leakage current. Compared to insulation testing, the main advantage of leakage current testing is that measurements can be taken during normal operation without having to turn off the power supply to the system and equipment. IV. Measurement principle and usage of the Fluke 360 ground tester: According to Kirchhoff’s law, the current flowing into a circuit is equal in magnitude to the current flowing out of it, but in opposite directions. As shown in Figures (1), (2), and (3), if there is a reading on the tester, it indicates that there is leakage current in the circuit or device; the higher the value, the worse the insulation of the circuit or device. V. Conclusion: In the past, for a platform operating under normal conditions, the insulation of the power system has always been a problematic issue. The system is large and consists of numerous complex devices; if an insulation alarm occurs, it is necessary to turn off the devices one by one in order to conduct insulation tests and identify the faulty point. Currently, using an insulation monitor to oversee the insulation of power systems, combined with a Fluke 360 ground tester to identify the circuits or devices with insulation faults, and an insulation resistance meter to measure insulation resistance, allows such problems to be resolved quickly and efficiently, saving both time and effort. Appendix: Performance features of the Fluke 360 ground fault tester
– The leakage current measurement range is 3 mA, with a resolution as high as 1 μA, enabling accurate detection of insulation degradation.
– A wide measurement range from 1 μA to 60 A meets the testing needs of various devices.
– Advanced shielding technology ensures accurate results even when measuring near other wires.
– The highly durable clip design allows for 50,000 operations; its reinforced construction extends the lifespan of the ground fault tester.
– It is a portable handheld device, with clip dimensions of 40 mm (1.5 in).
– A convenient “display hold button” enables reading leakage current values in hard-to-reach areas.
– It features an automatic power-off function and a warning buzzer, which helps save battery power and extend its lifetime.
– Compliant with IEC1010 and EMC standards, ensuring reliable testing results.
– Meets all application and performance requirements related to leakage current and differential current measurements for electrical equipment, as specified by VDE0404-4 and VDE0702 safety standards