Generator/Motor Surge Protection Measures & Insulation Monitoring
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Install a surge protective device (SPD) : Install an SPD in the generator and motor circuits to block or limit abnormal voltage (surge) caused by lightning, switching, etc. from flowing into the equipment. The SPD diverts the surge current to ground or suppresses the surge voltage using various elements such as MOV (metal oxide varistor) and gas discharge tube.
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Strengthen lightning arresters and grounding systems : Strengthen grounding equipment such as lightning arresters, equipotential grounding, and grounding impedance reduction to protect against external lightning surges. The lower the grounding resistance, the higher the surge discharge effect.
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Apply shielding and complex protection circuits : For sensitive equipment, apply shielding (EMI blocking), insulation transformer, and complex protection circuits in parallel to minimize surge and noise inflow.
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Regular inspection and maintenance : Regularly inspect the performance of protective devices such as SPDs and lightning arresters for deterioration, and replace them if necessary. The lifespan of SPDs is generally 5 to 10 years, and additional inspection is required after a strong surge event.
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Surge monitoring is used to collect data on the surge inflow direction, surge size, inflow time, and leakage current status, and is used to analyze accident prevention, accident prediction, and accident causes.
Insulation monitoring method
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division |
Methods and Features |
Application examples |
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Insulation resistance measurement |
After powering off, measure the insulation resistance between the winding and ground with an insulation resistance meter (Megger). If it is less than 1MΩ, it is judged as insulation deterioration. Calculate the 1-minute/10-minute resistance ratio with the Polarization Index (PI) test (PI<1.0 indicates serious deterioration). |
Regular maintenance of motors and generators |
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Partial Discharge (PD) Monitoring |
Partial discharge signals generated in stator windings, etc. during operation are measured and analyzed in real time using sensors. Warning/alarm is issued when PD activity exceeds the threshold. Utilizes online monitoring systems (such as MONGEMO). |
Generator, large motor |
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Insulation Monitoring Device (IMD) |
Monitors insulation resistance in real time and immediately issues an alarm when an insulation failure (leakage current, etc.) occurs. Mainly applied to non-grounded (IT) systems, but is expanding to various electrical facilities. |
Battery, Generator, Motor |
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Rotor short circuit monitoring |
Real-time monitoring of short-circuits and insulation abnormalities in the generator rotor winding using a flux probe, etc. Utilized for RSO testing during stoppage and magnetic flux detection during operation. |
Large generator |
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Online Monitoring System : Recently, many systems have been introduced to continuously monitor the insulation status of generator/motor stator windings during operation (online). Representative examples include PD (partial discharge) monitoring, insulation monitoring devices (IMD), and rotor short-circuit monitoring sensors.
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Periodic insulation resistance measurement : During regular inspections of motors and generators, insulation resistance measurement and PI testing are performed in parallel to diagnose insulation deterioration at an early stage.
In general , the latest standard method is to protect generators and motors from surges using hardware measures such as SPDs, lightning arresters, grounding reinforcement, and shielding, and to monitor insulation using a continuous monitoring system such as insulation resistance measurement, partial discharge monitoring, and IMD.