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China MR Series Current Transformer - Leading Suppliers & Factory for Power Monitoring and Protection Systems
Product Overview
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A Current Transformer (CT) uses electromagnetic induction with two windings — a main winding connected in series to a high-current circuit and a secondary winding connected to safety or measurement devices. The secondary winding is typically rated at 5A or 1A for most industrial applications.
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Key requirement: CTs require sufficient insulation to support high voltage between windings, linearity to reduce measurement errors, and high precision for energy metering. Never leave the secondary winding open circuit — an open circuit can generate extremely high voltages that may damage electrical equipment.
Current transformers are critical to the dependability, efficacy, and safety of contemporary electrical systems because they allow for more exact current monitoring and issue detection.
Technical Parameters
📋 General Specifications
| Parameter | Value |
|---|---|
| Primary Current | 30–5000A |
| Secondary Current | 5A, 1A |
| Standard Approval | BS7626, IEC185 |
| Maximum Voltage | 0.72 KV |
| Frequency | 50 / 60 Hz |
| Rated Load | 5VA – 15VA |
| Class | 1.0, 3.0 |
| Short-time Thermal Current | Ith = 60 × Ih |
| Rated Security Coefficient | FS < 5 |
📐 Model Dimensions & Rated Current
| Type | Rated Current (A) | ID (mm) | OD (mm) | HT (mm) |
|---|---|---|---|---|
| MR-28 | 30/5A – 100/5A | 28 | 70 | 40 |
| MR-42 | 100/5A – 250/5A | 42 | 80 | 30 |
| MR-45 | 300/5A | 45 | 80 | 30 |
| MR-60 | 400/5A | 60 | 100 | 30 |
| MR-60 | 500/5A – 600/5A | 60 | 100 | 30 |
| MR-85 | 800/5A – 1600/5A | 85 | 120 | 20 |
| MR-125 | 2000/5A – 5000/5A | 125 | 165 | 20 |
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Note: For measuring current transformers, the accuracy class is designated by the highest permissible percentage current (ratio) error at the rated current prescribed for the accuracy class concerned.
Frequently Asked Questions (FAQ)
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What is a Current Transformer (CT) and how does it work?
A Current Transformer (CT) operates on the principle of electromagnetic induction. It consists of a primary winding connected in series with a high-current circuit and a secondary winding connected to measurement or protection devices. The CT steps down large primary currents to a safe, measurable level — typically 5A or 1A — for use with metering and relay equipment.
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Why should the secondary winding of a CT never be left open circuit?
Leaving the secondary winding of a CT open circuit is extremely dangerous. Without a connected load, the transformer core becomes saturated and generates extremely high voltages across the secondary terminals, which can damage connected equipment, destroy the transformer insulation, and pose a serious safety hazard to personnel.
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What accuracy classes are available for these current transformers?
These current transformers are available in accuracy Class 1.0 and Class 3.0. The accuracy class is defined by the highest permissible percentage current (ratio) error at the rated current. Class 1.0 offers higher precision and is suitable for energy metering, while Class 3.0 is used in applications where a wider tolerance is acceptable.
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What standards do these CTs comply with?
These current transformers are manufactured in compliance with BS7626 (British Standard) and IEC185 (International Electrotechnical Commission standard for current transformers). These standards ensure consistent performance, safety, and interoperability with industrial metering and protection systems worldwide.
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How do I select the correct CT model for my application?
Selecting the right CT model depends on your primary current range, the physical dimensions of the conductor (ID/OD), and your required accuracy class. For example, if your primary current is 400A, the MR-60 model with an inner diameter of 60mm and outer diameter of 100mm would be appropriate. Always ensure the rated current matches your system's operating current range.
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What is the rated security coefficient (FS) and why does it matter?
The rated security coefficient (FS) indicates the instrument security factor of the CT. An FS value of less than 5 (FS < 5) means that the CT will saturate at 5 times the rated current, thereby protecting connected measuring instruments from damage during fault conditions or overcurrent events. This is an important safety feature for metering-class current transformers.