Online monitoring of wind farm transformer box

Online monitoring of wind farm transformer box

1. Product Introduction

This system adopts ultrasonic and transient ground waves, as well as spatial ultra-high frequency partial discharge detection technology, which is suitable for real-time monitoring and abnormal alarm of partial discharge signals in ring main units and outdoor switch boxes. It has the characteristics of high sensitivity, strong anti-interference performance, and multiple communication methods.

The safe and reliable operation of switchgear determines the reliability and safety of power supply, and plays a crucial role in the power supply system. Due to the inevitable degradation of electrical performance, thermal performance, chemical performance, and insulation caused by abnormal conditions during long-term operation of electrical equipment, the electrical insulation strength is reduced, resulting in partial discharge and subsequent failure, which affects the service life of the switchgear.

This system aims to deploy intelligent 2-in-1 wireless partial discharge sensors (AE, TEV) and spatial ultra-high frequency (UHF) in conjunction with acquisition devices to monitor partial discharge signals during cabinet operation in real-time online. By setting certain testing thresholds, analyzing spectra, and displaying spectra, users can easily determine whether there is partial discharge in the equipment. Based on long-term trends, potential fault hazards can be detected earlier, transforming the previous passive detection method into active "defensive" monitoring, making switchgear products safer and more reliable to use, and adding new technological highlights to the products.

The partial discharge online monitoring device mainly consists of a front-end ultrasonic (AE) and transient earth wave (TEV) wireless sensor, a partial discharge acquisition device, a wireless intelligent gateway, and an online partial discharge analysis system software. The front-end wireless partial discharge signal acquisition sensor is installed inside the cabinet through magnetic attraction. The wireless intelligent sensor itself has signal filtering and amplification functions, which can filter, reduce noise, and amplify the sensor coupling signal to achieve the range of AD conversion. The partial discharge acquisition unit adopts a sampling rate of 125MS/s and a resolution of 14 bits to collect the transient earth wave discharge signal and ultrasonic discharge signal coupled by the sensor, and maintains consistency with the actual voltage phase through the wireless synchronization unit.

The power distribution partial discharge acquisition device (host) receives the spatial UHF signal through the copper shaft cable, and communicates with the partial discharge sensor data through LORA and other communication methods. The collected data is summarized by edge computing and sent to the distribution intelligent gateway. It has partial discharge edge computing function and data storage function. Moving the processing of partial discharge data to the edge enables data processing, reducing the transmission and processing pressure on the server. Local real-time processing improves on-site responsiveness. After disconnection, it can continue to work normally and perform partial discharge data monitoring, storage and calculation on site. After network recovery, the cached data can be synchronized to the cloud server to keep the information complete.

2. Product Features

1) Distributed layout with strong scalability: The monitoring terminal is networked, and when adding or removing terminals based on the original layout, the system does not require additional settings and automatically identifies and configures them.

2) Real time monitoring: The system records real-time data from each monitoring node, and the monitoring cycle can be flexibly set.

3) Timely warning: When a node detects abnormal local volume, it will quickly feedback to the monitoring server, and the server software will record necessary information and issue an alert.

4) Impact resistance: can withstand 600KV flashover impact, terminal equipment is not damaged, and data is not lost.

5) Anti interference: Equipped with time-domain and frequency-domain signal analysis techniques, it can effectively separate interference signals and partial discharge signals, and effectively avoid interference from the instrument power supply end.

6) Stable transmission: With the help of powerful mobile networks, data can be directly transmitted to servers, with reliable transmission performance and low network latency.

7) Good access security: The system's access does not affect the sealing and insulation performance of the switchgear, nor does it affect the safe operation of the equipment.

9) EMC rating

Electrostatic discharge immunity: Level 4

Electrical fast transient burst immunity: Level 4

Surge (impact) immunity: Level 4

Power frequency magnetic field immunity: Level 5

3. Measurement principleOnline monitoring of wind farm transformer box

When partial discharge (PD) occurs in high-voltage switchgear and its internal high-voltage equipment (such as PT, CT, busbar, cable joints, etc.) due to insulation failure, the PD process is often accompanied by physical or chemical phenomena such as pulse current, electromagnetic waves, ultrasonic waves, light, ozone, heat, and corresponding processes. We mainly use ultra-high frequency, ultrasonic waves, and TEV as the main detection indicators for testing.

Partial discharge monitoring techniques include ultra-high frequency method, ultrasonic method, and TEV method.

1) Ultra high frequency detection technology is a non-contact detection method based on the principle of "field". It receives ultra-high frequency electromagnetic waves radiated during partial discharge through partial discharge sensors, thereby achieving partial discharge detection.

2) The ultrasonic method uses ultrasonic sensors to receive ultrasonic signals emitted by partial discharge as the basis for partial discharge judgment, and the detection frequency band is usually 20kHz to 100kHz. The biggest advantage of the ultrasonic method is that it uses ultrasound as the monitoring signal, avoiding various electromagnetic interferences in partial discharge monitoring sites, and therefore has been widely used. The ultrasonic testing method originated in the 1940s, but it was not widely promoted due to the low sensitivity of sensors. With the advancement of acoustic emission technology, the sensitivity of ultrasonic transducers has been greatly improved, and thanks to the rapid development of integrated circuits and signal processing technology, ultrasonic methods have regained people's favor. Nowadays, ultrasound has become an important method for partial discharge testing.

3) TEV method is a new partial discharge detection method, which is more commonly used for partial discharge detection of high-voltage switchgear. When partial discharge occurs in a switchgear, the electromagnetic waves generated propagate from the discharge point to the surrounding area. Due to the discontinuous metal of the switchgear body, it cannot shield electromagnetic waves. These electromagnetic waves propagate outside the metal shielding shell of the switchgear through metal discontinuous parts such as gaps in the switchgear and cable insulation terminals. When electromagnetic waves reach the outer surface of the metal shell, a brief ground voltage is generated on the outer surface of the metal shell, called transient ground voltage. The transient ground voltage rise time is only a few nanoseconds and quickly disappears. In practical applications, place the TEV sensor on the inner wall of the switchgear and detect the frequency band within the range of 3MHz to 100MHz. The TEV method has high sensitivity to internal discharge.

The system adopts a modular design method, which detects transient partial discharge ground wave signals, ultrasonic signals, and ultra-high frequency signals in the switchgear body by installing ground wave sensors, ultrasonic sensors, and spatial ultra-high frequency sensors. The detection circuit filters, amplifies, and converts the analog signals of transient ground wave signals, ultrasonic signals, and ultra-high frequency signals into digital signals. After high-order digital filtering, the signals are transmitted wirelessly by the processor to the wireless data relay unit, and then transmitted to the background through various communication interfaces.

Each group of partial discharge data collected by the unit is labeled with corresponding time parameters based on whether it is a time scale signal or a phase signal input. After algorithm processing, the data is first stored locally and then sent to the server according to server-side software instructions. Ensure data systematicity, without missing characteristic signals such as partial discharge signals, and without causing communication congestion.

The unit calculates the peak and effective values of the partial discharge signal within each measurement cycle set by the system, adds timestamps, and transmits them to the server software.