Statistically on T&D facilities the most serious accidents such as flashovers between phase to phase and phase to earth, are caused by electrical issues such as local heat, floating and metallic particles. Furthermore, it is well known phenomena that Partial Discharge (PD) occurs as a symptom of those accidents. Therefore, it is very important to diagnose PD periodically to prevent the serious accidents in advance. This PD diagnosis service is available for T&D facilities(GCB, GIS and transformer) to detect insulating degradation without power outage. It is helpful for the early detection of failure and prevention of serious accidents.
This service adopts the ultra high frequency (UHF) method. By selecting the special frequency band of PD, we can distinguish the real PD produced inside of T&D facilities from outside noises existing in atmosphere such as mobile phone etc. with high sensitivity and reliability.
It uses a neural network that is capable of automatically identifying defective parts to perform real time determination of causes of insulating degradation.
It can locate the starting position of real PD in GIS judging from two point measurement.
![[image]Diagnosis system](/en/service/field/td/discharge/image/ph03_01.png)
![[image]Example of UHF sensors installed](/en/service/field/td/discharge/image/ph03_02.png)
| System configuration |
|
|---|---|
| Dimensions (excluding sensor) | 360 mm (L) × 450 mm (W) × 154 mm (H) |
| Mass (excluding sensor) | Approx. 12 kg |
A1. The AE method uses supersonic waves, while the UHF method uses electromagnetic waves in a UHF band for measurement.
The UHF method we adopt is a measurement and testing technology using electromagnetic waves in a UHF band. Because this method employs electromagnetic waves in a UHF band of 0.5 GHz to 1.5 GHz, higher than the frequencies of air noises, which are 0.5 GHz and lower. This means that the UHF method is less susceptible to disturbance than the AE method and ensures smooth testing.
A2. The computer in the diagnosis system automatically determines the causes. Nothing other than the system we prepare is required.
The computer in the diagnosis system automatically determines the causes by the frequency components and the phase pattern of electronic waves in the UHF band. Customers do not need to arrange any device.
A3. The rating is determined according to the risk assessment that is required by the Guidelines for Comprehensive Safety Standards of Machinery specified by the Ministry of Health, Labour and Welfare.
The Ministry of Health, Labour and Welfare specifies procedures and key points of risk assessment on mechanical facilities in the Guidelines for Comprehensive Safety Standards of Machinery, and we formulate rating standards accordingly.
The rating is thus calculated by the level of signals of partial discharge, its causes and the state of operation of the gas insulated switchgear.
It is generally thought that the power outage and inspection are immediately required after the detection of partial discharge signals.
However, this risk assessment announces a period of delay until the next inspection or the need for continuous monitoring, which helps develop a systematic inspection schedule.
