How to connect current transformer?

1. Single-Phase Circuit:

• Connection Mode: A single current transformer is connected in series with the live wire or neutral wire of the circuit.
• Application: This is used for measuring single-phase current, power, and providing protection against single-phase faults, such as ground faults or short circuits.
• Diagram:
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2. Incomplete Star (V Connection) for Two Current Transformers (Three-Phase Circuit):

• Connection Mode: Two current transformers are connected in a “V” configuration (incomplete star), where the primary windings are connected to two of the three-phase conductors. The secondary windings are then connected together to form a measuring point.
• Application: This connection is used to measure three-phase current, power, and to protect the system from phase-to-phase short-circuit faults. Although only two transformers are used, it provides sufficient information about the three-phase system for protection and measurement in a balanced system.
• Diagram:
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3. Two-Phase Current Difference Between Two Current Transformers (Phase Difference Protection):

• Connection Mode: Two current transformers are placed in two different phases (e.g., Phase A and Phase B), and their secondary windings are connected to each other to detect any current difference between these phases.
• Application: This configuration is used for measuring one-phase current and for protecting against phase-to-phase short-circuit faults. It is based on detecting differences in the phase currents, which indicates a fault between phases.
• Diagram:
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4. Star (Wye) Connection Mode for Three Current Transformers (Three-Phase Four-Wire System):

• Connection Mode: Three current transformers are connected in a star (wye) configuration. Each CT is placed on one phase of a three-phase system, and the secondary windings are connected to a common point (neutral).
• Application: This setup is suitable for measuring three-phase current, power, and protecting the system in a three-phase four-wire system. It can detect any form of fault, including ground faults, phase-to-phase faults, and phase-to-neutral faults.
• Diagram:
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