What precautions should be taken when installing current transformers?
Jun 01, 2026| 1. Polarity and Direction Must Be Correct: The primary side terminals are marked P1 and P2. Current should flow into P1 and out through P2.
P1 must face the power supply side (e.g., transformer or incoming line), and P2 must face the load side; otherwise, the energy meter will reverse and the protection system will malfunction.
On the secondary side, S1 is connected to the positive terminal of the measuring equipment, and S2 is connected to the negative terminal and reliably grounded.
2. Secondary Side Wiring and Safety Specifications:
Open circuit on the secondary side is strictly prohibited: An open circuit during operation will induce thousands of volts of high voltage, endangering personnel and equipment safety. Before maintenance, terminals S1-S2 must be short-circuited.
Use copper core wire with a cross-sectional area ≥ 2.5mm², and the length should not exceed 50m to reduce voltage drop.
S2 terminal must be grounded at one point: This prevents multiple grounding points from creating circulating currents that interfere with protection devices.
3. Primary Side Installation Requirements
For through-type CTs, ensure the conductors pass through vertically and centered to avoid eccentricity, which can lead to magnetic circuit asymmetry and measurement errors.
When multiple cables pass through the core, the three-phase connections should be symmetrical, especially in zero-sequence current measurements.
Open-type CTs must be securely closed after installation to prevent magnetic circuit leakage from affecting performance.
4. Environmental and Fixing Requirements
The installation location should be dry and well-ventilated, away from strong electromagnetic interference sources (such as transformers and high-power frequency converters).
Vertical installation tilt ≤ 1°, securely fixed to prevent vibration and loosening.
When installed inside a distribution box, leave ≥ 80mm of ventilation space at the top.
5. Turns Ratio and Load Matching
The turns ratio should be selected so that the operating current is within 60%~120% of the rated value to ensure measurement accuracy.
The total impedance of the instruments connected to the secondary side must not exceed the CT's rated load (e.g., 15VA), otherwise it will cause increased errors or saturation.
