In response to the evolving needs of smart grid development, Shandong Qixing has developed the Smart Dry-Type Condenser Bushing. Building upon our standard condenser bushing design, this innovative product integrates an embedded self-diagnostic online monitoring system. This system provides real-time monitoring of leakage current, three-phase current vector sum, dielectric loss and capacitance of the main insulation, as well as partial discharge within both the bushing and transformer insulation.

Furthermore, select models are equipped with smart terminals and an insulation status indicator, offering a highly convenient solution for real-time online insulation monitoring.

Smart Dry-Type Condenser Bushings are primarily categorized into the following two types based on their monitoring system implementation:

1. Integrated Self-Diagnostic System Type: Features a built-in, comprehensive online measurement unit.

2. Smart Terminal Interface Type: Provides standardized terminals for connecting external monitoring devices.

Features of the Integrated Self-Diagnostic Dry-Type Condenser Bushing System

Compared to commonly used online dielectric loss monitoring devices, this self-diagnostic system offers distinct advantages: simpler structure, easier installation, lower cost, and higher stability and reliability. Traditional online monitoring devices are susceptible to on-site strong electromagnetic interference, PT phase errors, and system intrinsic errors, resulting in poor data stability and low reliability. Consequently, many installed products offer limited practical utility.

The three-phase current vector sum measurement method employed by this system operates on the premise that "three-phase bushings will not fail simultaneously," enabling effective identification of insulation faults in individual bushings. Furthermore, the device possesses the following performance features:

1. Integrated Design, Enhanced Safety:The current measurement sensor is integrated into a specially designed tapping adaptor, significantly reducing the tapping lead length and fundamentally eliminating the risk of an open tapping circuit.

2. Effective Shielding, High Precision: The tapping adaptor provides excellent shielding for the current measurement sensor, significantly improving measurement accuracy.

3. Powerful Processing, Rich Functionality: The monitoring unit utilizes a high-speed digital signal processor (DSP) to measure and calculate the three-phase leakage currents and current vector sum in real-time with precision. The unit also offers multiple functions including local display, alarm, and remote data transmission.

Features of the Smart Terminal Interface Type Condenser Bushing System

1. Smart Device Does Not Compromise Bushing Safety

The smart device is connected in parallel with the internal voltage grading screen of the bushing. The capacitance of the grading screen is far greater than the main capacitance of the transformer bushing. Consequently, during operation, the voltage across the grading screen is extremely low, easily meeting insulation requirements. This means that any fault in the smart device—whether open circuit, short circuit, or even burnout—will not affect the safe operation of the bushing itself.

2. Strong Anti-Interference Capability

A voltage grading screen is incorporated within the main insulation of the smart bushing. Through this screen, the smart device can directly access the capacitive current at the milliampere (mA) level. This provides a strong signal source for the signal processing unit, greatly enhancing the device's immunity to interference.

3. Direct Capacitance Monitoring with Intuitive Warning

Operational experience shows that changes in the capacitance of a dry-type condenser transformer bushing directly reflect the operating condition and breakdown degree of its internal capacitive screens within the main insulation. By presetting a breakdown threshold in the smart chip, a connected warning light can provide a simple, timely, and efficient indication of insulation breakdown.

4. Future-Ready, Upgradable "Smart Terminal"

The "Smart Terminal" serves as a standard output interface for future system upgrades. As smart grids evolve, if users need to upgrade the insulation online monitoring system for an entire substation, they can easily connect to a device insulation information management platform via this interface. This enables real-time monitoring and early warning of insulation breakdown without major modifications to the bushing itself, effectively preventing serious incidents.

5. Convenient, Practical, and Compatible Design

The product is designed with user convenience in mind, ensuring excellent compatibility between the smart bushing and standard bushings for routine tests, commissioning tests, and preventive tests.

Principle and Structure of the Smart Bushing

1. Working Principle

As shown in Figure 1, the smart bushing operates on a dual-capacitance principle. HV is the high-voltage terminal connected to the grid. C1 represents the main insulation capacitance of the bushing, while C2 is a dedicated monitoring capacitance (its value is significantly larger than C1). Terminals a and b (Smart Terminals) are brought out from the two plates of C2 for connecting external devices like insulation monitors. C1 and C2 together form the insulation withstand voltage barrier.

2. Safety and Monitoring Design

The much larger capacitance of C2 ensures that any external device connected to terminals a/b cannot affect the main insulation (C1) under any condition, including short or open circuits. The value of C2 is also optimized considering external device impedance, ensuring the capacitive current through C1 is effectively shunted through the monitoring circuit.

The key advantage of this design is that it eliminates the need to use the critical tapping terminal for monitoring, thereby preserving the fundamental safety of the bushing.

3. Structural Description

The smart bushing is identical in overall structure and external dimensions to a standard FRP condenser transformer bushing, with the sole addition of a set of smart terminals (a, b). These terminals can connect to an insulation indicator light or an intelligent voltmeter. The light remains off during normal operation and emits a red glow upon internal capacitive screen breakdown, enabling immediate preventive action. This indicator requires no external power.

4. Important Safety and Usage Notes

(1) Terminal Identification: Terminal E (marked “Measurement Terminal”) is located on one flange side. Smart terminals a and b (marked “Smart Terminal”) are on the opposite side.

(2) Test Prohibition: AC withstand voltage tests are strictly prohibited between terminals E, a, and b.

(3) Operational Grounding: Terminal E must be reliably grounded during normal operation.

(4) Terminal Connection: Insulation online monitoring devices may be connected between terminals a and b.

(5) Voltage Warning: During operation, the open-circuit voltage between a and b is 20V–100V. CAUTION: Hazardous voltage is present.

Supply Scope for Smart Dry-Type Condenser Bushings

Smart versions are available for all our dry-type condenser bushings rated 12kV and above, including:

Oil-Air Transformer Bushings

Oil-SF₆ Transformer Bushings

Oil-Oil Transformer Bushings
SF₆-Air Transformer Bushings

Product Model Designation for Smart Dry-Type Condenser Bushings