Malfunction of CTs or VTs will cause power supply stop and closedown. Therefore Monthly or Yearly maintenance or inspection are recommended lest the above troubles should happen.
The maintenance and inspection should be performed based on Guidelines for Meter Transformer Maintenance, published by the Japan Electrical Manufactures Association (JEMA) as follows.
It could lead to injury or electric shock.Maintenance and inspection should only be performed by an experienced electrician.
It could lead to electrical shock.If necessary to touch live part (including resin surface), disconnected the CTs or VTs from the circuit and make sure to be no voltage with grounding. |
Daily inspection items (once a month)
| No. | Items | Contents | Acceptance criterion | In case of failure | |
| Cause | Approach | ||||
| 1 | Operating condition | The value indicated by meter | No abnormal value | Malfunction and failure | Wire connection check Replacement |
| 2 | Noise and Vibration | Ckeck for the followings (1) Chatter vibration (2) Resonance noise (3) Discharge noise |
No abnormal noise or vibration | Screw loose Resonance Internal / External factor |
Retorquing Replacement |
| 3 | Odor | Whether there is abnormal odor or not | No abnormal odor | Failure or Blown fuse | Replacement |
| 4 | Appearance | Rust / Corrosion | No rust / No corrosion | Surroundings containing Gas or Salinity | Repainting Improvement of the surroundings |
| Localized overheat of terminal | No discolorment No overheat |
Corrosion on contact surface | Sanding Further check |
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| Change in shape / Break (Treminal or Attaching bracket) |
No change in shape No damage |
External factor (Impact or the like) |
Replacement | ||
| Cracks | No cracks | Age deterioration Improper usage |
Replacement | ||
| Defacement | No defacemant | Dust accumulation | Wipe up | ||
| Discharge trace | No discharge trace | Abnormal voltage | Replacement | ||
| Tracking trace | No tracking trace | ||||
| Short circuit caused by small animal | No entry of animal No trace of entry |
- | Further check | ||
Peripodic inspection items (once a year)
| No. | Items | Contents | Acceptance criterion | In case of failure | |
| Cause | Approach | ||||
| 1 | Insulation resistance ※1 |
Between HV winding / LV winding and Ground | 100MΩ or more Megger of 1000V |
Age deterioration Contamination of insulator |
Wipe up Replacement |
| Between LV winding and Ground | 2MΩ or more Megger of 500V |
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| Between LV windings | |||||
| 2 | Partial discharge ※2 |
Changes in the discharge amount | Less than that detected the year before | Age deterioration External surge and/or integrated factors |
Replacement |
| Discharge amount | Below standard value | ||||
| 3 | Mountings | Tightness of screw | Sufficiently tight | Screw loose | Retorquing |
| 4 | Connections | Tightness of screw | Sufficiently tight | Screw loose | Retorquing |
| 5 | Wipe up of resin cast surface | Wipe with dry duster | - | - | - |
| Discharge trace | Check for discharge traces | No discharge traces | Abnormal voltage | Replacement | |
| Cracks | Check for cracks | No cracks | Age deterioration Improper usage |
Replacement | |
| 6 | Fuse | Fuse blowing | No fuse blowing | Equipment failure Surge |
Further check |
※1：This inspection had better be performed on a fine day.
※2：Recommended to inspect once a year after 10 years from the installation.