Overview
Plastic-cased current transformers (CTs) are passive sensors designed to measure alternating current while providing galvanic isolation between the primary circuit and measurement devices. They are encased in durable thermoplastics, making them lighter and more economical than traditional epoxy or metal-housed CTs. Commonly used in switchgear, panel meters, and protection relays, they adhere to standards like IEC 61869 and ANSI C57.13. Their modular design simplifies installation in tight spaces, and they are favored for applications requiring moderate accuracy (typically 0.5% to 3%). Unlike split-core models, solid-core plastic CTs offer higher precision but require disconnecting the conductor during installation.
Structure and Working Principle
A plastic-cased CT consists of a primary winding (often a single conductor), a laminated ferromagnetic core, and a secondary winding connected to measurement instruments. The core material (e.g., silicon steel or nanocrystalline alloys) minimizes hysteresis losses, ensuring accurate signal reproduction. When AC flows through the primary conductor, it induces a proportional current in the secondary winding via electromagnetic induction. The turns ratio determines the step-down effect (e.g., 100:5 for 100A primary to 5A secondary). The plastic housing provides insulation (typically rated for 600V–10kV) and mechanical protection against dust and moisture.
Key Features
1. **Lightweight and Compact**: Thermoplastic casings reduce weight by up to 40% compared to metal housings, easing handling in crowded panels. 2. **Cost-Effective**: Mass-production-friendly materials like ABS lower manufacturing costs without compromising performance for standard applications. 3. **High Insulation**: Withstand impulse voltages up to 6kV, suitable for low- and medium-voltage systems. 4. **Temperature Stability**: Operate reliably between -25°C to +70°C, with flame-retardant variants (UL94 V-0) available for hazardous environments. Drawbacks include limited mechanical strength versus metal CTs and reduced accuracy under high-frequency harmonics.
Application Areas
1. **Energy Metering**: Submetering in commercial buildings or factories, often paired with kWh meters (accuracy class 0.5s). 2. **Motor Protection**: Overcurrent detection in industrial motor control centers (MCCs). 3. **Renewable Energy**: Monitor inverter output currents in solar PV systems. 4. **HVAC Systems**: Integrate with building management systems for load profiling. For high-voltage applications (e.g., grid substations), epoxy-resin CTs are preferred due to superior dielectric strength.
Maintenance and Precautions
Plastic-cased CTs require minimal maintenance but demand careful handling: - **Avoid Open-Circuit Secondary**: An open circuit can induce dangerous voltages—always short-circuit unused secondaries. - **Thermal Monitoring**: Prolonged overloads (>120% rated current) may deform plastic housings; use thermal fuses in critical setups. - **Cleaning**: Use dry cloths to prevent static buildup; solvents may degrade thermoplastic surfaces. Calibration checks every 2–3 years are recommended for accuracy-critical applications like billing metering.
B2B Procurement Guide
1. **Specifications**: Confirm current ratio, burden (e.g., 2.5VA), and accuracy class (e.g., 0.5 for billing). 2. **Compliance**: Look for CE, UL, or RoHS marks to ensure regulatory adherence. 3. **Customization**: Some suppliers offer adjustable ratios or Rogowski coil integrations for harmonic-rich environments. 4. **MOQs**: Standard models often have minimum orders of 100–500 units; lead times vary from 2–8 weeks. For bulk purchases (1,000+ units), negotiate discounts of 10–20%. Verify supplier testing reports for consistency in phase angle error and ratio accuracy.
Related Manufacturers
- 主营：电流表、互感器、电压表、转速表、分流器
- 主营：阀门、电机、减速机、电流互感器、联轴器
- 主营：互感器、变压器、高压计量箱
- 主营：控制阀、电机、密封、Janitza互感器、阀门、传感器、弹簧、振动电机、气泡传感器、空气传感器、振动器
- 主营：减速机、联轴器、传动链、电流互感器、传动带、离合器、制动器、执行器、液压阀门、气动阀、轴承、气缸、传感器、电机
- 主营：ktr联轴器、temp模温机tt、amtec液压螺母、Janitza互感器、ktr弹性联轴器、ktr波纹管联轴器
- 主营：指示灯、LED灯、LED数码管、电流互感器、船型开关
- 主营：电能质量分析仪、多功能功率分析仪、接地故障保护继电器、剩余电流互感器、电流互感器、德国剩余电流互感器、插件式电流互感器、测量级电流互感器、插入式电流互感器、贯穿式电流互感器、开口式电缆电流互感器、开合式电缆电流互感器、KUW系列电流互感器、供应开合式电流互感器、开合式互感器、多通道电能分析仪、数字漏电保护继电器、电能质量监测仪、多功能测量设备、德国JANITZA、多功能电能质量分析仪、原装电能质量监测仪、德国捷尼查、德国捷尼查CTB系列、UMG800
- 主营：音频表、数显led、数码管、单相电流、直流电流表、交流电流表、智能led、稳压器、电力仪表、三相数显、数显表头、智能直流、直接接通、单相数显、led数显表、数字表头、功率因素表、电瓶测试仪、直流电压表、多功能电能、单相电压表、数显电压表、交流电压表、vumeterdbmetervu、仪器专用仪表
- 主营：同步表、报警仪、弹簧管、电流互感器BH、配电箱、密封圈、洞洞板、机车灯、缩弹簧、传感器、刀开关、保险管、转分表、配电柜、接线盒、电力表、照明灯、电能表、变送器、陶瓷座、陶瓷管、警示灯、金属壳、同期表、转速表、变压器
- 主营：变阻器、发电机、绳开关、电流表、检测器、抽风机、电磁阀、转速表、料位计、变压器、电压表、绝缘板、继电器、计米器、数显表、皮带机、检测环、螺丝固、控制器、线速表、熟铁片、保护器、接触器、时控器、变频器
- 主营：避雷器、断路器、熔断器、高压电流、互感器、电压互感器、10kv电缆、户外隔离、复合硅胶、隔离保险、低压陶瓷、中间接头、低压刀熔、ZW32真空断路器、负荷开关、六氟化硫负荷开关、ZW20真空断路器、ZN63-12真空断路器、隔离手车、冷缩电缆附件、欧式前后接头、电缆分接箱、梅花触头、计量箱、穿墙套管