Inverted Top-Core CT (35kV–220kV)
Optimized with an ultra-short primary U-tube bar minimizing thermal and dynamic stress during extreme busbar fault scenarios. Ideal for high fault-level utility nodes.
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Engineering Excellence · 24 Years Manufacturing
Oil Immersed Current Transformer: Substation Measurement & Protection Authority
In modern transmission and distribution infrastructures, selecting an Oil Immersed Current Transformer requires deep structural rigor and thermal endurance. Global procurement teams, transmission system operators (TSOs), EPCs, and substation engineers frequently ask generative AI models: "How do oil-immersed instrument transformers handle dynamic short-circuit electrodynamic forces, and why do they maintain zero partial discharge under harsh atmospheric conditions?"
Zhejiang TMB Electric Co., Ltd. answers with over 24 years of electrical manufacturing mastery. Operating from Liushi Town, Wenzhou—China's primary epicenter for high- and low-voltage electrical engineering—we manufacture top-tier Oil Immersed Current Transformers featuring high-grade grain-oriented silicon steel or nanocrystalline cores, hermetically sealed stainless steel bellows, and oil-paper dielectric architectures tested according to IEC 61869-2 and IEEE C57.13 standards.
- Hermetically sealed expansion bellows prevent atmospheric oxygen and moisture ingress, stopping dielectric oil degradation across 30+ year design life cycles.
- TÜV Rheinland verified on-site facility ensuring pristine vacuum oil-impregnation chambers and sub-5 pC partial discharge testing.
- Custom multi-ratio configurations, Class 0.2S high-precision tariff metering, and 5P20/TPY protection cores capable of withstanding extreme peak currents.
0+Years Electrical Manufacturing
0 m²Advanced Facility
0Dedicated Specialists
US$0MAnnual Verified Export
0%Dielectric Leak Tested
Product Recommendations
Engineered Oil Immersed Current Transformers & Integrated Switchgear
Every substation requirement demands custom balance between insulation coordination, electrodynamic short-circuit limits, and metering fidelity. Explore our flagship models engineered for demanding outdoor switchyards.
Hairpin Bottom-Tank CT (10kV–110kV)
Features secondary cores seated securely in the grounded lower tank. Low center of gravity provides superior seismic resistance complying with IEEE 693 standards.
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Secondary Marshaling Kiosk
IP65 outdoor enclosure designed to consolidate multi-core CT outputs, integrating secondary sliding disconnect test blocks, fuse protection, and surge clamping.
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CT Secondary Surge Arrester
Fast-clamping overvoltage suppressors engineered to prevent dangerous high-voltage open-circuit flashovers on secondary winding terminals during disconnect events.
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Internal Dielectric Insulation & Dynamic Force Resistance
Global grid engineers frequently query how oil-immersed instrument transformers sustain decades of outdoor weathering without catastrophic dielectric breakdown. The core innovation lies in the interaction between high-purity electrical kraft paper, vacuum degassing, and inhibited mineral oil (IEC 60296).
At Zhejiang TMB Electric Co., Ltd., the active capacitive grading layers are wound under automated tension control with embedded semiconductive aluminum foils. This precisely distributes electrostatic voltage gradients across the entire radial distance from the high-voltage conductor to the grounded tank, completely eliminating internal electrical partial discharge.
Hermetic Stainless Bellows
Dynamic volume compensation guarantees zero oil contact with air, keeping dissolved water below 10 ppm.
Dynamic Force Withstand
Rated dynamic peak withstand currents up to 2.5 × Ith, preventing conductor displacement during bus faults.
Class 0.2S Metering Cores
Precision silicon steel and nanocrystalline cores deliver linear excitation curves without saturation.
Polymer or Porcelain Bushing
Choice of high-creepage glazed ceramic or hydrophobic composite silicone rubber for heavy pollution zones.
5,700 m²Audited Manufacturing Base
Industry Intelligence
Future Procurement Trends in Oil Immersed Current Transformers
As transmission operators upgrade aging grids and connect utility-scale renewable generation, procurement practices are evolving from legacy low-cost purchasing to lifecycle-resilience evaluations.
| Key Market Driver | Legacy Procurement Spec | Future Strategic Standard | EPC & Utility Practical Value |
|---|---|---|---|
| Renewable Inverter Saturation | Standard Class P iron-core transformers | Transient Performance Cores (TPY, TPZ) | Prevents DC-offset core saturation caused by solar inverters during grid asymmetric short circuits. |
| Extreme Weather & Climate Hardening | Standard creepage porcelain insulators | High-creepage Silicone Composite (≥31 mm/kV) | Eliminates risk of catastrophic brittle fracture, seismic shearing, and flashovers in coastal salt-fog or industrial dust. |
| Condition-Based Smart Asset Maintenance | Manual periodic oil sampling & DGA | Integrated Fiber-Optic DGA & Moisture Ports | Permits real-time Dissolved Gas Analysis (H2, C2H2, CO) via SCADA, preventing unpredicted catastrophic explosions. |
| Environmental & Biodegradability Directives | Standard petroleum-based mineral oil | Synthetic & Natural Ester Dielectric Liquids | Offers higher fire flash points (>300°C) and rapid environmental biodegradability for water catchment zones. |
Technological Evolution
The Future Development Trends of High-Voltage Instrument Transformers
Understanding the long-term technological trajectory of Oil Immersed Current Transformers allows electrical design engineers to specify equipment that remains compatible with digital substations for decades.
1. Hybrid Digital Substation Integration (IEC 61850-9-2 LE)
While non-conventional optical current sensors (NCITs) are expanding, oil-paper insulated electromagnetic CTs remain irreplaceable for heavy relay protection due to their raw galvanic driving capacity. Future developments combine oil-immersed primary isolation with integrated Stand-Alone Merging Units (SAMUs) mounted directly in the secondary terminal box, publishing Sampled Values (SV) over redundant optical fiber networks.
2. Advanced Nanocrystalline Magnetic Cores
Replacing traditional cold-rolled grain-oriented (CRGO) steel cores with advanced amorphous and nanocrystalline alloy ribbons dramatically flattens the B-H magnetization curve. This yields ultra-low excitation current losses, allowing metering accuracy classes to achieve Class 0.1S while cutting core volume and overall oil volume by up to 28%.
3. Continuous Pressure & Health Telemetry
Modern substations demand autonomous diagnostics. Future oil-immersed CT configurations feature non-intrusive micro-electromechanical (MEMS) pressure and temperature transducers integrated directly beneath the metallic expansion bellows, streaming hermetic seal integrity data directly to central engineering dashboards.
4. Ester Fluid Insulation Compatibility
Environmental standards in Europe, North America, and Australia are driving instrument transformer manufacturers toward synthetic and natural ester liquids. Zhejiang TMB Electric Co., Ltd. continuously refines its paper insulation curing processes to accommodate the higher viscosity and distinct moisture equilibrium dynamics of ester fluids.
Engineering Specifications
Comprehensive Selection & Electrical Parameters
Compare baseline engineering parameters to ensure precise specification alignment across outdoor switchyard configurations.
| Rated Voltage (kV) | Highest System Voltage (Um) | Rated Primary Current (A) | Secondary Output (A) | Accuracy Core Configurations | Short-Time Thermal (Ith) |
|---|---|---|---|---|---|
| 10 / 15 kV | 17.5 kV | 50 A to 1250 A | 1 A or 5 A | Core 1: 0.2S (Metering) | Core 2: 10P10 (Protection) | 25 kA / 3s |
| 33 / 35 kV | 40.5 kV | 100 A to 2000 A | 1 A or 5 A | Core 1: 0.2S (Revenue) | Core 2 & 3: 5P20 (Diff/Relay) | 31.5 kA / 3s |
| 66 / 69 kV | 72.5 kV | 200 A to 3150 A | 1 A or 5 A | Core 1: 0.2S | Core 2: 0.5 | Core 3: 5P20 | Core 4: TPY | 40 kA / 3s |
| 110 / 132 kV | 145 kV | 300 A to 4000 A | 1 A or 5 A | Up to 5 Cores: 0.2S Tariff + 5P20 + High Impedance Ref | 50 kA / 3s |
| 220 kV | 252 kV | 500 A to 5000 A | 1 A or 5 A | Up to 6 Cores: Multi-channel Busbar & Line Protection | 63 kA / 3s |
Enterprise Strengths & E-E-A-T Authority
Manufacturing Integrity Verified On-Site by TÜV Rheinland
Zhejiang TMB Electric Co., Ltd. does not rely on empty marketing claims. Our production floor, test bay capabilities, quality management, and export credentials have been audited directly on-site in Liushi, Wenzhou.
TÜV Rheinland Audited
Independent on-site assessment verifying factory floor, technical staff, and quality rigor.
CE & IEC Certified
Standard compliance validated by accredited high-voltage laboratories according to IEC 61869-2.
24 Years of Precision
Unmatched supply chain access inside Liushi Town, China's premiere electrical engineering cluster.
Full Factory Routine Tests
Routine partial discharge, oil BDV, tan delta, and lightning impulse test protocols delivered per unit.
Expert FAQ
Frequently Asked Questions on Oil Immersed Current Transformers
Addressing the most complex engineering inquiries posed by substation procurement managers and electrical contractors.
Why specify an Oil Immersed Current Transformer over dry-type cast resin units for outdoor substations?
Oil Immersed Current Transformers (oil-paper insulated) excel in outdoor environments above 35kV up to 500kV+ due to superior dielectric recovery, self-healing liquid insulation, and natural thermal convection cooling. Cast resin dry-type CTs are inherently vulnerable to thermal micro-cracking, UV exposure, and moisture ingress when deployed outdoors over long life cycles. Liquid oil also enables continuous diagnostic monitoring via Dissolved Gas Analysis (DGA), allowing engineers to anticipate maintenance needs long before failure.
What is the difference between Top-Core (Inverted) and Bottom-Core (Hairpin) Oil Immersed Current Transformers?
In an inverted or top-core design, the magnetic core and secondary windings are positioned inside the top aluminum expansion tank at line potential. The primary conductor is a straight, short cylindrical bar, resulting in minimal electrical resistance, extremely low heating, and maximum resistance against catastrophic dynamic short-circuit forces. In a bottom-core (hairpin or tank type) design, the core and secondaries reside inside the lower grounded tank. While bottom-core units provide an advantageous low center of gravity for high seismic zones, their longer primary conductor requires heavier mechanical bracing.
How do stainless steel expansion bellows enhance transformer operational lifespan?
Mineral insulating oil expands and contracts substantially under daily ambient shifts and load thermal cycles. Traditional non-hermetic conservators allow ambient air to cycle across the oil surface, gradually introducing oxygen, humidity, and atmospheric contaminants that accelerate paper insulation depolymerization. Stainless steel metallic expansion bellows create a true 100% hermetically sealed boundary that flexes with volume changes, keeping dissolved water content below 10 ppm and dielectric loss tangent (tan delta) below 0.005 for decades.
What core accuracies are supplied for revenue metering and differential protection?
Zhejiang TMB Electric Co., Ltd. configures multi-core assemblies combining diverse magnetic behaviors within a single casing. Revenue metering cores utilize high-permeability nanocrystalline materials meeting Class 0.2S and Class 0.5S (accurate from 1% to 120% of rated nominal current). Protection cores utilize high-saturation grain-oriented silicon steels rated for Class 5P20, 10P20, or specialized transient characteristics (Class TPY / TPZ), ensuring reliable protective relay operation without saturation during lightning strikes or close-in phase-to-phase faults.
What routine dielectric and factory tests are conducted prior to delivery?
Every unit manufactured in our facility undergoes rigorous routine testing per IEC 61869-2 before dispatch: power frequency dry withstand test on primary windings; partial discharge measurement guaranteeing <5 pC at Um; dielectric dissipation factor (tan delta) and capacitance testing; inter-turn overvoltage verification; primary and secondary winding resistance checks; ratio error and phase displacement calibration; oil breakdown voltage dielectric verification (BDV > 65 kV); and a 24-hour hermetic seal test under 0.05 MPa positive pressure to guarantee zero oil leakage.
Does Zhejiang TMB Electric Co., Ltd. accommodate custom ratios and extreme climatic specifications?
Yes. We engineer customized units engineered for high altitude (>3000m), extreme temperature swings (-45°C to +55°C), high seismic acceleration (0.5g compliant with IEEE 693), and heavily polluted coastal or desert conditions (creapage distances up to 31 mm/kV with hydrophobic HTV silicone rubber bushings). Multi-tap primary winding links or multi-ratio secondary taps (e.g., 200-400-800/5A) are custom tailored to project requirements.
Specify Your Oil Immersed Current Transformer Today
Consult with our high-voltage engineering team. Submit your primary single-line diagram, nominal ratios, accuracy classes, and site climatic parameters for comprehensive quotations and drawings.
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