Key Points for Current Transformer Grounding Inspection
Apr 01, 2026| I. Core Points of Grounding Inspection
1. The casing must be grounded.
The metal casing of the current transformer should be connected to the grounding grid via a dedicated grounding bolt. The grounding wire should be a yellow-green copper conductor with a cross-sectional area ≥ 4mm², and the connection should be secure and without looseness.
2. The secondary side can only be grounded at one point.
The secondary winding (usually the S2 terminal) has one and only one grounding point, generally located in the terminal block or terminal box of the protection panel in the control room.
Multiple grounding points will create ground loop currents, leading to malfunctions in protection or inaccurate measurements.
3. Reasonable selection of grounding point location.
For independent current transformer secondary circuits, grounding should preferably be done at the switchyard terminal box; for common current circuits of multiple CT combinations (such as bus differential protection), the grounding point should be located in the control room.
4. Grounding Connection Reliability Verification
Check that the grounding wire crimp joints are free of rust and oxidation; the overlapping surfaces should be treated with anti-oxidation measures.
Use a continuity tester to test the grounding path; the grounding resistance should be ≤0.5Ω (for conventional systems).
II. Prohibited Items (Absolutely Prohibited)
❌ Operating the secondary side without grounding is strictly prohibited: If high voltage enters from the primary side, it will endanger the safety of secondary equipment and personnel.
❌ Two-point or multi-point grounding is strictly prohibited: This will cause current shunting under the influence of the ground grid potential difference, interfering with the normal operation of protection devices.
❌ Connecting the shielding layer to the neutral (N) line or a non-dedicated grounding terminal is strictly prohibited: The N line potential is unstable, easily introducing interference and does not comply with safety regulations.
