Section I. Product Overview
JY STT-24/200 24kV 200A double-way casing joint (Double-pass casing connector) is a separable, dual-branch cable bushing accessory designed specifically for 24kV (20kV class) medium-voltage power distribution systems. It features a fully insulated, fully sealed, touchsafe construction and serves as a critical component for 24kV ring main units (RMUs), pad-mounted substations, cable branch boxes, and similar equipment. The connector provides insulated, parallel connections between equipment bushings and two cable accessory branches, and is compatible with elbow cable connectors, surge arresters, and grounding devices to form a “one-in, two-out” distribution interface. It combines ground fault protection, insulation isolation, and line branching functions, and is widely used in urban distribution networks, industrial power distribution, and renewable energy distribution applications.
Section II. Product Features
Electrical and Insulation Performance
The connector is integrally injection-molded from high-purity EPDM (ethylene propylene diene monomer) rubber, with no seams or air voids, delivering excellent insulation performance capable of withstanding the rated voltage and transient overvoltages of 24kV systems. It meets the maximum operating voltage requirement of 24kV, providing sufficient insulation margin.
An integrated electric field optimization structure and stress control layer ensure uniform electric field distribution, effectively suppressing partial discharge. The connector is free from electrical erosion and breakdown risk during long-term operation, with a partial discharge level of ≤10 pC (at 1.5U₀).
A built-in grounding lead provides reliable grounding, effectively dissipating fault currents and induced voltages. The connector is compatible with voltage presence indicators for visual monitoring of energized status, eliminating the risk of inadvertent operation.
Current-carrying contact areas are finished with tin-plated copper, providing excellent conductivity, low contact resistance, minimal heat generation during long-term operation, and strong resistance to corrosion and oxidation. The connector is capable of simultaneously carrying 200A on two independent paths with stable electrical performance.
Structural and Safety Features
The fully insulated, fully sealed, touchsafe construction provides high outer insulation strength. The housing may be safely touched during operation without risk of electric shock, ensuring the safety of operations and maintenance personnel.
The integrated dual-pass design is compatible with standard American/European 24kV equipment bushing interfaces and allows simultaneous connection of two cable accessories for line branching. The compact structure facilitates easy installation with no additional adapter components required.
Anti-misinsertion and anti-misconnection design ensures standardized interface dimensions that only mate with accessories of the correct rating, preventing cross-use of mismatched accessories. A built-in positioning and locking mechanism prevents loosening or disconnection after installation.
The grounding lead uses a dedicated yellow-green dual-color grounding cable with secure terminations for direct connection to the grounding grid, providing reliable grounding and enhancing overall system safety.
Environmental and Weather Resistance
Excellent weather resistance accommodates a wide operating temperature range of -40°C to +90°C, with no degradation of rubber elasticity or insulation performance at extreme temperatures and no risk of cracking or embrittlement. Suitable for both outdoor and indoor applications.
Rated IP67 for protection against moisture, water ingress, contamination, and salt spray, enabling stable long-term operation in harsh environments including direct burial, high-humidity, and high-dust conditions, with resistance to rainfall and condensation.
Anti-aging, UV-resistant, and ozone-resistant properties provide a service life in excess of 30 years with maintenance-free operation, reducing long-term operational and maintenance costs.
Mechanical and Compatibility Features
High mechanical strength with impact and vibration resistance enables the connector to withstand mechanical stresses during transportation, installation, and operation without deformation or damage. Seismic rating: Grade 8.
Compatible with standard 24kV 200A equipment bushing interfaces. Both output ports are interchangeable with elbow cable connectors, surge arresters, and grounding devices of the same rating, providing strong cross-compatibility.
Standardized interfaces conform to IEEE 386 and applicable domestic standards, compatible with bushing interfaces of mainstream 24kV RMUs, pad-mounted substations, and cable branch boxes to fulfill “one-in, two-out” line branching requirements.
Section III. Technical Parameters
| Parameter Category | Item | Specification |
| Rated Electrical Parameters | Rated Voltage (Ue) | 24kV (applicable to 20kV systems; maximum operating voltage 24kV) |
| | Rated Current (Ie) | 200A (per path); dual-path parallel operation | |
| | Rated Frequency (fn) | 50Hz / 60Hz | |
| | Power Frequency Withstand Voltage | 65kV / 5 min (dry test); 55kV / 5 min (wet test); no breakdown, no flashover | |
| | Lightning Impulse Withstand Voltage | 125kV (peak); no breakdown, no flashover | |
| | Partial Discharge Level | ≤10 pC (at 1.5U₀) | |
| | Rated Short-Circuit Withstand Current | 16kA / 2s (20kA / 2s optional, matched to system requirements) | |
| | Contact Resistance | ≤100 μΩ (per path) | |
| Structural and Material Parameters | Main Body Material | EPDM rubber (insulation layer); tin-plated copper (current-carrying contact components) |
| | Ingress Protection Rating | IP67 | |
| | Interface Standard | 1 input port (24kV American standard bushing interface); 2 output ports (24kV 200A standard accessory interface) | |
| | Grounding Method | Integrated yellow-green dual-color grounding lead for direct grounding connection | |
| Environmental Parameters | Applicable Altitude | ≤2000m (high-altitude versions available on request) |
| | Ambient Temperature | -40°C to +90°C (operating); -40°C to +70°C (storage) | |
| | Relative Humidity | ≤100% (non-condensing) | |
| | Seismic Rating | Grade 8 | |
| Applicable Standards | IEEE 386, GB/T 12706, DL/T 404, GB/T 11022 |
Section IV. Application Scope
Applicable voltage class: 20kV to 24kV AC medium-voltage power distribution systems; compatible with equipment bushing interfaces rated for a maximum operating voltage of 24kV.
Applicable equipment and scenarios:
Bushing interfaces of 24kV RMUs, pad-mounted substations, cable branch boxes, American-style pad-mounted transformers, and other distribution equipment, enabling “one-in, two-out” line branching;
Used in conjunction with elbow cable connectors, surge arresters, and grounding devices to form dual-path cable termination and dual-path surge arrester interfaces;
Urban distribution cable lines, industrial and mining enterprise power distribution systems, renewable energy (photovoltaic/wind power) step-up substation distribution interfaces;
Insulated bushing connections in indoor/outdoor distribution rooms, underground utility tunnels, cable tunnels, and other multi-scenario applications to meet line branching requirements.
Functional purpose: Provides insulated, sealed, parallel connections between equipment bushings and two cable accessories, incorporating ground fault protection, insulation isolation, and line branching functions. Delivers a safe and reliable “one-in, two-out” interface solution for distribution systems.
Section V. Service Conditions
Normal Service Conditions
Altitude: ≤2000m
Ambient temperature: -40°C to +90°C; equipment operating temperature in accordance with applicable standards
Relative humidity: ≤100% (non-condensing)
Environmental conditions: free from corrosive gases, flammable or explosive media, and severe vibration or shock
Installation method: compatible with standard equipment bushing interfaces; horizontal or vertical mounting permissible; installation space must accommodate the operational requirements of both accessory connections
Special Service Conditions (Customization Required)
Altitude exceeding 2000m
Ambient temperature outside the -40°C to +90°C range
Heavily polluted, salt-spray, or chemically corrosive environments
High vibration or high-shock operating conditions
Non-standard equipment bushing interface dimensions
Special grounding requirements or high pollution severity class applications
Section VI. Installation and Maintenance
Installation Requirements
Prior to installation, inspect the product for cracks, damage, or voids; verify the insulation surface is undamaged. Confirm the grounding lead is intact and free of corrosion, and that all accessories are present.
Clean the equipment bushing interface surface to remove grease, dust, and foreign matter; ensure the interface is dry and clean.
Apply a uniform coat of dedicated silicone grease lubricant to the inner wall of the connector input port to prevent damage to the insulation layer during installation.
Slowly push the connector onto the equipment bushing interface until fully seated, then engage the positioning lock. Connect the grounding lead to the grounding grid; grounding resistance shall be ≤4Ω.
Connect each of the two output ports to the corresponding elbow cable connectors, surge arresters, or other accessories of the correct rating; ensure all accessories are fully seated and anti-withdrawal devices are engaged.
Upon completion of installation, perform insulation resistance testing and power frequency withstand voltage testing; the unit may be energized only upon satisfactory test results.
Maintenance Requirements
Periodically inspect the connector for cracks, discharge marks, and accumulated contamination; verify the grounding lead and both accessory connections are secure and free of looseness.
Periodically test insulation resistance to confirm performance meets requirements and to detect latent faults promptly.
Clean the connector surface to remove dust and contamination; maintain a dry, clean insulation surface free from grease and chemical substances.
If the connector or associated accessories exhibit cracks, damage, discharge, overheating, or any other abnormality, immediately de-energize and replace; operation of defective equipment is strictly prohibited.
Insertion and withdrawal of associated accessories must be performed using dedicated insulated operating tools. Bare-hand operation of energized connectors is strictly prohibited. All operations must strictly comply with distribution safety regulations.
Section VII. Important Notices
Installation, commissioning, and maintenance must be performed by qualified electrical personnel holding medium-voltage distribution construction credentials. Operation by unqualified personnel is strictly prohibited.
The product must be used only with equipment bushings, elbow cable connectors, surge arresters, and other accessories of the corresponding rating. Use of mismatched interface ratings is strictly prohibited, as it will result in insulation failure and safety incidents.
The connector must not be disassembled or modified without authorization, as doing so will void the warranty and safety guarantees. Forcible installation or removal using non-dedicated tools is strictly prohibited.
The two output ports must not simultaneously connect accessories of different voltage classes or different current ratings; all accessories must be matched to system parameters.
Store the product in a dry, ventilated, cool environment away from direct sunlight, high temperatures, moisture, and compressive loads. Contact with sharp objects that could damage the insulation layer is strictly prohibited.
Live-line operation of associated accessories must strictly comply with distribution safety regulations with appropriate personal protective measures in place; non-compliant operations are strictly prohibited.
Section VIII. Model Designation
| Model Identifier | Meaning |
|---|---|
| JY | Product series code |
| STT | Double-pass bushing connector series code |
| 24 | Rated voltage class; compatible with 24kV systems at a maximum operating voltage of 24kV |
| 200 | Rated current class; rated for 200A per path |
| Double-pass casing connector | Dual-pass bushing connector; insulated “one-in, two-out” connection accessory for equipment bushing interfaces |
Section IX. Applicable Standards and Certifications
International standard: IEEE 386, Standard for Separable Insulated Connectors for Power Distribution Systems Above 600V
National standards: GB/T 12706, Rated Voltage 1kV (Um=1.2kV) to 35kV (Um=40.5kV) Extruded Insulated Power Cables and Accessories; GB/T 11022, Common Specifications for High-Voltage Switchgear and Controlgear Standards; DL/T 404, 3.6kV to 40.5kV AC Metal-Enclosed Switchgear and Controlgear
The product has passed type testing by the National High-Voltage Electrical Apparatus Quality Supervision and Inspection Center and conforms to national electrical safety standards.
Section X. After-Sales Service
Product warranty period: 18 months from the date of manufacture, or 12 months from the date of commissioning, whichever occurs first
Within the warranty period, products with quality defects will be repaired or replaced free of charge
Technical support, installation guidance, and customization services are available (special specifications and special operating condition adaptations)
Document Notice
The technical parameters in this manual are based on standard operating conditions. Special operating conditions require customization based on actual requirements. The product technical agreement and type test report shall prevail as the final reference.
Appendix: Product Outline Drawing
