Current Transformer Buyer's Guide: Types, Applications, and Working with Chinese Manufacturers
Current Transformer Buyer's Guide: Types, Applications, and Working with Chinese Manufacturers
A current transformer (CT) is an instrument transformer that steps down high primary currents to a standard, measurable secondary current for metering, monitoring, and protection. The right CT depends on the application, accuracy class, output signal, and physical installation constraints, not merely on the brand or price. This guide explains the main CT types, their specifications, how to select one, and how to qualify a Chinese manufacturer. HEYI ELECTRICAL (WENZHOU HEYI ELECTRICAL CO.,LTD.) is a Chinese manufacturer established in 2012 that produces a broad range of current transformers and current sensors. Its product families are used in this guide as concrete reference examples.
HEYI split-core current transformer (HK series)
The Challenge: Why CT Sourcing Is Harder Than It Looks
Buyers searching for "current transformer manufacturers Chinese" quickly discover that CTs are not universal parts. A current transformer must match the primary conductor size, handle the expected load current, provide the right secondary output, and maintain accuracy across the operating range. Common sourcing problems include specifying a split-core CT when a solid-core CT would be more accurate, choosing a general-purpose CT for revenue billing, or overlooking environmental requirements such as outdoor UV protection and waterproofing. In addition, overseas buyers need evidence that a Chinese supplier can maintain quality across batches, provide technical documentation, and support OEM customization.
Industry Background: Current Transformer Market at a Glance
The global current transformer market was estimated at USD 2.63 billion in 2024 and is projected to reach USD 3.90 billion by 2030, according to Grand View Research. Asia Pacific accounted for the largest regional share, with 40.15% of revenue in 2025 (Straits Research). Within the product landscape, split-core current transformers are the fastest-growing segment, driven by retrofit installations and smart grid upgrades (Fact.MR). The EV charging transformer market, including current monitoring components, is forecast to expand at a CAGR of 23.6% from 2025 to 2033 (Research Intelo). Although large global brands are active, the top five players (ABB, Siemens, GE, Schneider Electric, and Arteche) held approximately 40% of the market in 2024 (Global Market Insights). Specialized Chinese manufacturers therefore remain important sourcing partners for project-based and OEM supply.
Current Transformer Types and Real Product Families
Solid-Core Current Transformers
Solid-core CTs are permanently installed on cables or busbars. HEYI offers several solid-core families. The MSQ is a plastic-cased current transformer with a square window, classified as a solid-core low voltage CT and busbar-type measuring CT, with a measurement range up to 6000 A, accuracy options of 1.0, 0.5, 0.5S, 0.2, and 0.2S, and an inner diameter up to 125 mm. The SDH is a low voltage window-type CT, busbar-type measuring CT, and relay protection CT, with a measurement range up to 10000 A and an inner diameter up to 220x80 mm. The CP is a compact DIN-rail mounted, space-saving panel CT with an inner diameter up to 100x31 mm, intended for smart grid, switchgear panels, HVAC, smart buildings, and data centers. Core materials are silicon steel sheets or nanocrystalline materials, and the windings use pure copper enameled wire.
Split-Core Current Transformers
Split-core CTs open for installation around an existing conductor without disconnecting it, which makes them the fastest-growing CT category for retrofit and smart grid applications. HEYI's KCT is a split-core clamp-on CT with an inner diameter of 0 to 50 mm, a measurement range of 0 to 1000 A, and accuracy options of 3.0, 1.0, or 0.5.
Split-core clamp-on current transformer KCT-36
The DP/HK busbar split-core CT reaches 0 to 8000 A with a larger window of 0 to 80x160 mm. For outdoor environments, the OCT is an outdoor waterproof split-core CT rated IP65/IP67, designed for overhead line monitoring and municipal infrastructure.
Outdoor waterproof split-core current transformer OCT-45
For data-driven monitoring, the KCD smart split-core CT provides RS485/Modbus communication and 4-20 mA output, and is used in Beijing and Hangzhou metro lines. The KCT-L is a loop-powered True RMS current transmitter with 4-20 mA DC output for PLC/DCS and IoT systems.
Three-Phase Current Transformers
Three-phase CTs combine three measuring elements in one housing, saving space in panels and reducing installation time. The DASN is a compact three-phase integrated CT with DIN-rail mounting. It has a measurement range of 0 to 1000 A, accuracy class 1.0, secondary output of 5 A, and an inner diameter of 0 to 50 mm. It is intended for EPC solar/wind/storage projects, smart buildings, UPS systems, motor control centers, IDC and telecom applications, and main and branch circuit monitoring.
HEYI three-phase current transformer (DASN series)
Revenue-Grade and High-Accuracy CTs
Utility billing requires CTs with high accuracy and low saturation error. The RECT is a revenue-grade billing current transformer classified as an Extended Range Current Transformer (ERCT) and an IEEE C57.13 compliant revenue CT. It is a 0.15S high-accuracy, resin-insulated, anti-saturation CT with a measurement range of 0 to 1000 A, secondary output of 5 A or 1 A, an inner diameter of 0 to 78 mm, IP65 protection, and UV protection. It is intended for utility and substation billing, utility-scale solar and wind plants, and data center revenue sub-metering.
Outdoor Resin-Cast Current Transformers
For outdoor feeders and harsh industrial environments, the LMZW is an outdoor resin-cast current transformer and a 0.66 kV weatherproof solid-core CT. It uses hydrophobic epoxy resin, provides IP65 protection, and has an inner diameter of 0 to 80 mm. It is intended for ring main units, marine and offshore installations, and chemical and metallurgy facilities.
Flexible Rogowski Coils
For large or irregular conductors and high-current measurements, the FRC is a flexible Rogowski coil with an air-core, non-saturating design. It has an inner diameter of 245 mm, a measurement range of 100 to 10000 A, and millivolt output. The Rogowski coil with integrator (G1) is a lightweight flexible CT made of silicone and pure copper enameled wire, intended for lightning and transient current measurement, portable testing meters, data center power retrofit, and heavy industry and smelting applications.
Flexible Rogowski coil FRC-350-G1
Hall Effect Current Sensors
When DC current measurement is required, a Hall Effect sensor is needed. The C2/C3 is a split-core Hall Effect current transducer and DC current transmitter with a measurement range of 0 to 1000 A, output signal of 5 A, accuracy rating of 1.0/0.5, and an inner diameter of 125x35 mm. It is intended for PV string monitoring, VFD DC bus monitoring, railway traction, BMS/battery storage, renewable energy, and industrial automation.
Leakage Current Sensors for EV Charging and ESS
Leakage detection is a safety-critical function in EV charging and energy storage systems. The HYCA is a 6 mA DC leakage current sensor classified as a residual direct current protective device (RDC-PD). It has a differential current range of 0 to 300 mA with a measurement resolution of 0.2 mA, supports load currents up to 80 Arms in single-phase systems or 3x32 Arms in three-phase systems, and operates over a frequency range from DC to 2 kHz. It provides a switching output for 6 mA DC and 30 mA AC according to IEC 62752, and includes integrated self-monitoring and test functions. Variants with a pass-through opening or with integrated primary conductors are available.
HYCA leakage current sensor for EV charging infrastructure
DIN-Rail Mounted Current Transformers
For compact panels and high-vibration environments, the DX/DM is a DIN-rail mounted current transformer classified as a compact low voltage CT (0.66 kV). It has a plug-in terminal design with a hinged terminal cover, an inner diameter of 125x35 mm, and an accuracy class of 1.0/0.5. It is intended for EMU/high-speed rail, modular data centers, and other high-vibration applications.
How to Select a Current Transformer: Step-by-Step
- Define the measurement task: current range, system frequency (typically 50/60 Hz), and whether DC detection is needed.
- Measure the available space: conductor diameter or busbar cross-section, panel clearance, and mounting style (cable, busbar, DIN rail, or panel).
- Choose the core structure: solid-core for new installations, split-core for retrofit and existing conductors, flexible Rogowski for large or irregular conductors.
- Select the accuracy class: 1.0 or 0.5 for general monitoring, 0.5S for energy sub-metering, and 0.2S/0.2 or 0.15 for revenue-grade billing under ANSI C12.20 or IEC 61869-2.
- Match the output signal: 5 A or 1 A for conventional meters and relays, mA/mV for compact devices, 4-20 mA for PLC/DCS and transmitters, RS485/Modbus for smart monitoring networks.
- Check the environment: indoor vs outdoor, IP rating, UV exposure, humidity, and temperature range.
- Review applicable standards: IEC 61869-2 for instrument transformers, IEEE C57.13 for revenue CTs, IEC 62752 for EV charging residual current protection.
- Confirm customization and OEM support: housing material, color, terminal type, lead wire length and connector, logo printing, and packaging.
- Request samples and verify: ratio, polarity, phase angle error, insulation, and physical fit before bulk production.
Typical Applications and Use Cases
- Smart grid and distribution: split-core CTs such as KCT and OCT are used for distribution transformer monitoring and overhead line monitoring; KCD is a metro-grade smart CT used in Beijing and Hangzhou metro lines.
- EV charging infrastructure: HYCA detects 6 mA DC leakage current in charging piles, with 30 mA AC detection per IEC 62752 for residual current protection.
- Solar, wind, and energy storage: KCT, DASN, and C2/C3 support PV string monitoring, inverter monitoring, and ESS applications.
- Data centers and smart buildings: SDH, CP, MSQ, and DASN are used for branch metering, PDU monitoring, and HVAC power monitoring.
- Utility-scale renewable plants: RECT provides revenue-grade measurement for utility-scale solar and wind plant billing.
- Outdoor and industrial sites: LMZW and OCT handle RMU, marine/offshore, chemical/metallurgy, railway trackside, and municipal infrastructure monitoring.
Comparison Table: HEYI Current Transformer Family
| Model | Classification | Measurement Range | Accuracy | Output | Inner Diameter | Typical Application |
|---|---|---|---|---|---|---|
| MSQ | Plastic-cased solid-core / busbar-type measuring CT | 0-6000 A | 1.0 / 0.5 / 0.5S / 0.2 / 0.2S | 5 A / 1 A / mA / mV | Up to 125 mm | Smart grid, HVAC, smart buildings, data centers |
| SDH | Low voltage window-type / relay protection CT | 0-10000 A | 1.0 / 0.5 / 0.5S / 0.2 / 0.2S | 5 A / 1 A / mA / mV | Up to 220x80 mm | Large-scale industrial monitoring, smart grid |
| CP | Compact DIN-rail mounted panel CT | 0-6000 A | 1.0 / 0.5 / 0.5S / 0.2 / 0.2S | 5 A / 1 A / mA / mV | Up to 100x31 mm | Smart grid, HVAC, data centers |
| DX/DM | DIN-rail mounted compact low voltage CT (0.66 kV) | 0-6000 A | 1.0 / 0.5 | 5 A | 125x35 mm | EMU/high-speed rail, modular data centers |
| KCT | Split-core clamp-on CT | 0-1000 A | 3.0 / 1.0 / 0.5 | 5 A / 1 A / mA / mV / RS485 / 4-20 mA | 0-50 mm | EV charging, smart grid, solar/wind/ESS |
| DP/HK | Busbar split-core CT | 0-8000 A | 3.0 / 1.0 / 0.5 | 5 A / 1 A / mA / mV | 0-80x160 mm | Smart grid, EMS, smart pole/IoT, data centers |
| OCT | Outdoor waterproof split-core CT | 0-8000 A | 3.0 / 1.0 / 0.5 | 5 A / 1 A / mA / mV | 0-120 mm | Overhead line monitoring, outdoor solar/wind, railway trackside |
| DASN | Three-phase integrated CT | 0-1000 A | 1.0 | 5 A | 0-50 mm | EPC solar/wind/storage, UPS, MCC, IDC/telecom |
| RECT | Revenue-grade billing CT (IEEE C57.13) | 0-1000 A | 0.15S | 5 A / 1 A | 0-78 mm | Utility and substation billing, utility-scale solar/wind |
| FRC | Flexible Rogowski coil (air-core) | 100-10000 A | Non-saturating | mV (millivolt) | 245 mm | Heavy industry, power retrofit, portable testing |
| HYCA | 6 mA DC leakage current sensor (RDC-PD) | Differential 0-300 mA; load up to 80 Arms (1-ph) / 3x32 Arms (3-ph) | Resolution 0.2 mA | Switching output per IEC 62752 | Pass-through or integrated primary | EV charging infrastructure, solar/wind/ESS |
Frequently Asked Questions
What compliance standards should a Chinese current transformer manufacturer meet for export?
Current transformers for export should comply with IEC 61869-2, the core international standard for inductive current transformers, which defines accuracy classes such as 0.5 and 0.5S. Revenue-grade CTs used for utility billing are typically required to meet ANSI C12.20 or IEC 61869-2 accuracy classes such as 0.2 or 0.15, and models such as HEYI's RECT are designed to IEEE C57.13. For EV charging safety components, IEC 62752 defines the switching output levels (6 mA DC and 30 mA AC) for residual current protection. Buyers should ask for documented compliance against the standard relevant to their market.
What types of current transformers can a Chinese manufacturer like HEYI produce?
Chinese manufacturers can produce a wide range of current transformers and current sensors. For example, HEYI ELECTRICAL manufactures solid-core CTs (MSQ, SDH, CP), split-core CTs (KCT, DP/HK, OCT, KCD, KCT-L), three-phase CTs (DASN), DIN-rail mounted CTs (DX/DM), outdoor resin-cast CTs (LMZW), revenue-grade billing CTs (RECT), flexible Rogowski coils (FRC), Hall Effect current sensors (C2/C3), and leakage current sensors for EV charging (HYCA). This range covers applications from busbar metering and switchgear to smart grid, solar, EV charging infrastructure, and data centers.
How much should I budget for current transformers from China?
CT pricing depends on core material (silicon steel versus nanocrystalline), accuracy class, output type, environmental rating, and level of customization. General-purpose monitoring CTs with accuracy class 1.0 or 0.5 are typically more economical than revenue-grade CTs with 0.2S/0.2 or 0.15S accuracy. Split-core CTs usually cost more than equivalent solid-core CTs because of the mechanical complexity of the clamp-on design. Because prices depend on exact specifications, buyers should prepare a detailed specification sheet and request a quotation before finalizing the budget.
Can I request samples before placing a bulk order?
Sample testing is a standard part of current transformer procurement. Before mass production, buyers should verify the ratio, polarity, phase angle error, insulation, and physical fit of the CT in the actual panel. Chinese manufacturers such as HEYI typically support sample requests and OEM customization. The exact sample policy, cost, and lead time should be confirmed during the quotation stage.
What lead time should I expect for OEM current transformer orders?
Lead time for OEM current transformer orders depends on the complexity of customization, order quantity, and the manufacturer's production schedule. Custom housing, accuracy, output, lead wire type, and packaging extend lead time, while standard products can be delivered faster. When evaluating a Chinese manufacturer, confirm current capacity and lead time during the RFQ. HEYI operates a 10,000 m² facility with an annual production capacity of 356,000 units and an R&D team of 5 engineers, which provides a baseline for supply continuity. To get current lead times, a quotation, or the HEYI PDF brochure, contact bethy@heyiele.com or visit www.heyiele.com.
Conclusion: How to Start Sourcing from a Chinese CT Manufacturer
Selecting a current transformer requires matching the product to the application, the accuracy requirement, and the environment. Chinese manufacturers offer a wide technology base, from solid-core and split-core CTs to Rogowski coils and leakage current sensors, but buyers must verify standards compliance, sample quality, and customization capability. With a clear specification and a structured supplier qualification process, sourcing from China can deliver reliable CT supply for energy meters, EV chargers, solar inverters, smart grid systems, and power monitoring projects.
HEYI states that its engineering is trusted by global technology companies including Siemens, Schneider Electric, LG, Samsung, and SoftBank. The company exports to Southeast Asia, South Korea, Europe, South America, Australia, Africa, the Middle East, and North America, with export business accounting for 95% of total sales.
HEYI manufacturing facility in Wenzhou
Contact HEYI ELECTRICAL:
WENZHOU HEYI ELECTRICAL CO.,LTD.
Address: 5 Floor, Building 2, No.56 Nirong Middle Road, Kunpeng Street, Wenzhou Marine Economy Development Demonstration Zone, Wenzhou City, Zhejiang, China
Email: bethy@heyiele.com
Tel / WhatsApp: +86 13968747975
Website: www.heyiele.com