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High-Precision FK Series Current Transformer (CT) | China Suppliers & Factory for Reliable Electrical 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:
- 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.
- 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.
- 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.
- 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: 0.5mA | |||||||
Frequently Asked Questions
What is the purpose of galvanic isolation in the FK series CT?
Galvanic isolation eliminates direct electrical connectivity between the primary high-current circuit and the secondary measurement circuit. This protects sensitive measuring instruments and operators from dangerous high voltages and overload conditions, while ensuring compliance with international electrical safety standards.
What secondary output ratings does the FK series CT support?
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 applications.
Which accuracy classes are available for the FK series CT?
The FK series CT is available in multiple accuracy grades including Class 0.2, Class 0.5, and Class 1.0. Class 0.2 is suited for precision revenue metering, while Class 0.5 and Class 1.0 are appropriate for general-purpose monitoring and protective relaying applications.
What is the maximum primary current supported by the FK series CT?
The FK series covers a wide range of primary currents. The largest model, FK-3045, supports primary currents up to 1,250A, while the smallest model, FK-1025, is designed for currents below 100A. This range makes the series suitable for applications from small distribution panels to large industrial feeders.
What installation configurations are available for the FK series CT?
The FK series CT is available in wound-type, bar-type, and bushing-type configurations. This variety allows flexible installation across different cabinet layouts, busbar sizes, and space-constrained environments in switchgear, motor control centers, and distribution panels.
Does the FK series CT comply with international safety standards?
Yes. The FK series CT is designed to comply with IEC 61869 and other relevant international electrical safety standards. It features robust dielectric isolation between primary and secondary windings, ensuring safe and reliable operation even in high-voltage industrial environments.