Through Hole Current Transformer

Providing with quality and standard customer-made electronic and passive components through hole current transformer and solution products, Fullstar Electronics is a leading through hole current transformer manufacturer and supplier in China. welcome to wholesale electronics through hole current transformer from our factory.

A through-hole current transformer (also known as a window-type or through-type current transformer) is a type of current transformer (CT) designed with a central opening, allowing a primary conductor to pass directly through its core. It is a passive sensing component based on the principle of electromagnetic induction, primarily used to step down high currents to a lower, measurable level for metering and protection.

1. Core Structure & Working Principle

• Structure: Unlike traditional transformers, a through-hole CT typically lacks a fixed primary winding. The center hole (window) is designed for cables or copper busbars to pass through. The conductor passing through this hole acts as a single-turn primary winding ( N1=1N1​=1 ).
• Working Principle: When an alternating current flows through the central conductor, it generates a time-varying magnetic field. This field creates a main magnetic flux in the high-permeability core, which then induces an electromotive force in the multi-turn secondary winding wound on the same core. This achieves a linear proportional transformation from a high primary current to a low secondary current (typically 5A or 1A).

2. Key Advantages & Applications

• Easy Installation: Since there is no need to break the main circuit for primary wiring-simply threading the cable through the center-the installation process is highly flexible and time-efficient.
• Versatility: It can accommodate single cables, multiple parallel cables, or solid busbars depending on the window size.
• Wide Application: These transformers are extensively used in power metering, relay protection systems, smart low-voltage distribution cabinets, and industrial equipment monitoring.

• 3. Critical Parameters & Safety Precautions

• Window Size Matching: When selecting a CT, the inner diameter of the window must match the outer diameter of the busbar or cable being measured to ensure proper fit and accuracy.
• Turns Ratio & Ampere-Turns: The transformation ratio is determined by the number of secondary turns. If the actual operating current is smaller than the rated single-pass value, the primary conductor can be looped multiple times through the center to adjust the ratio and maintain measurement accuracy.
• ⚠️ Secondary Side Must Never Be Open-Circuited: During operation, the secondary circuit must always be connected to a low-impedance load (such as an ammeter, sampling resistor, or protective relay). If the secondary side is open-circuited while the primary is energized, the core will saturate deeply, inducing a dangerously high voltage spike (up to thousands of volts) across the secondary terminals. This poses severe risks of electric shock, insulation breakdown, and permanent equipment damage.

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