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High-Precision FK Series Current Transformer (CT) from China Suppliers and Factory for Reliable Power Monitoring
Product Overview
Unlike direct current measurement methods, which risk damaging sensitive devices or endangering personnel when exposed to high primary currents, the FK series CT provides galvanic isolation between primary and secondary circuits. This isolation eliminates direct electrical connectivity, mitigating overload risks and ensuring compliance with electrical safety standards for both equipment and operators.
Core Working Principle
The FK series CT operates on the mutual induction principle, leveraging a closed magnetic core (typically constructed from silicon steel or amorphous alloy for low magnetic loss) with two concentric winding sets:
- 1 Primary Winding: Consists of a small number of turns (or a single pass-through conductor for bar-type CTs) connected in series with the high-current primary circuit. The primary current (Iₚ) flowing through this winding generates a magnetic flux in the core.
- 2 Secondary Winding: Features a large number of precisely wound turns, connected to measuring instruments or protective relays. The magnetic flux induced by the primary winding generates a proportional secondary current (Iₛ) in this winding.
The CT adheres to the ampere-turn balance relationship:
Iₚ × Nₚ = Iₛ × Nₛ
Where:
● Nₚ = Number of primary winding turns
● Nₛ = Number of secondary winding turns
This relationship ensures the secondary current is a fixed, scaled fraction of the primary current. The FK series CT is standardized to common secondary output ratings of 1 A or 5 A AC—values compatible with virtually all industrial ammeters, power meters, and protective relays.
Key Application Scenarios
The FK series CT is indispensable in the following electrical system applications:
- Power System Monitoring: Paired with digital ammeters, power meters, and energy meters to measure primary currents ranging from tens to thousands of amps (e.g., generator output current, distribution feeder current, industrial motor load current).
- Protective Relaying: Integrated with overcurrent, short-circuit, and earth-fault relays to trigger fast, selective tripping of circuit breakers during fault conditions, preventing equipment damage and system downtime.
- Industrial Process Control: Used in motor control centers, switchgear, and automation systems to provide current feedback for load regulation, overload protection, and process optimization.
- Revenue Metering: Deployed in utility-grade metering systems to ensure accurate, traceable current measurement for energy billing purposes.
Critical Performance Characteristics
🎯
High Measurement Accuracy
Classified by accuracy grade (e.g., Class 0.2, Class 0.5, Class 1.0) to meet diverse application requirements—from precision revenue metering to general-purpose monitoring.
🔋
Low Magnetic Saturation
The core material is selected to resist magnetic saturation under normal and moderate overload conditions, ensuring linear current transformation and preventing secondary current distortion.
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Robust Isolation Rating
Designed to withstand high dielectric voltage between primary and secondary windings, complying with international safety standards (e.g., IEC 61869) for reliable operation in high-voltage environments.
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Versatile Installation Design
Available in multiple configurations (e.g., wound-type, bar-type, bushing-type) to suit different cabinet layouts, busbar sizes, and installation space constraints.
Technical Parameters
| Type | Main Loop Current | (mm) Outline Size | ||||||
|---|---|---|---|---|---|---|---|---|
| A | B | C | D | E | F | M | ||
| FK-1025 | < 100A | 162 | — | 28 | 155 | 100 | 25 | c5*7 |
| FK-1435 | < 250A | 202 | — | 28 | 195 | 140 | 35 | c5*7 |
| FK-1835 | < 400A | 242 | 82 | 28 | 235 | 180 | 35 | c5*7 |
| FK-2245 | < 630A | 282 | 92 | 28 | 275 | 220 | 45 | c5*7 |
| FK-3045 | < 1,250A | 363 | 92 | 28 | 355 | 300 | 45 | c5*7 |
| Rated Primary Current: IA | Rated Secondary Current: 0.5 mA | |||||||
Frequently Asked Questions (FAQ)
Q
What is the main advantage of using the FK series CT over direct current measurement methods?
The FK series CT provides galvanic isolation between the primary and secondary circuits, eliminating direct electrical connectivity. This significantly reduces the risk of overload damage to sensitive instruments and protects personnel from exposure to high primary currents, while ensuring compliance with international electrical safety standards such as IEC 61869.
Q
What secondary output ratings does the FK series CT support, and which devices are compatible?
The FK series CT is standardized to secondary output ratings of 1 A or 5 A AC. These values are universally compatible with industrial ammeters, power meters, energy meters, and protective relays used across a wide range of industrial and utility applications.
Q
What accuracy grades are available for the FK series CT, and how do I choose the right one?
The FK series CT is available in accuracy grades including Class 0.2, Class 0.5, and Class 1.0. Class 0.2 is recommended for precision revenue metering and utility billing applications, while Class 0.5 and Class 1.0 are suitable for general-purpose monitoring, protective relaying, and industrial process control.
Q
What installation configurations are available for the FK series CT?
The FK series CT is available in multiple installation configurations including wound-type, bar-type, and bushing-type. This versatility allows it to accommodate different cabinet layouts, busbar sizes, and space constraints in switchgear, motor control centers, and distribution panels.
Q
Which FK series model should I select for a 400A application?
For a main loop current of up to 400A, the FK-1835 model is the appropriate choice. It features outline dimensions of A=242mm, B=82mm, C=28mm, D=235mm, E=180mm, F=35mm, and M=c5*7, making it suitable for medium-current distribution and motor protection applications.
Q
How does the FK series CT prevent magnetic saturation and ensure measurement accuracy under overload conditions?
The FK series CT uses a high-quality closed magnetic core made from silicon steel or amorphous alloy, materials specifically chosen for their low magnetic loss and high saturation resistance. This ensures the CT maintains a linear current transformation ratio and delivers accurate secondary current output even under moderate overload conditions, preventing secondary current distortion and measurement errors.