I.Introduction
Partial discharge does not cause the electric discharge of a completely short-circuited electrode. Such discharge usually has a very small amplitude value, but it will certainly cause the continuous deterioration of the property of the insulation layer and finally cause electric equipment fault.
The non-intrusive partial discharge detection, as a convenient and simple method, is used for identifying the potential insulation faults which may cause power cutoff or personal injury.
The partial discharge emits energy in following manners:
Electromagnetic energy: radio wave, light and heat;
Sound energy: sound wave and ultrasonic wave;
Gas: ozone and nitric oxide.
The most practical non-intrusive detection technologies are all based on the detection of the high-frequency signals and the ultrasonic signals in the electromagnetic spectrum. The product is an instrument which has simple operation and is specially developed for detecting the activities of electromagnetic waves and ultrasonic waves.
II.Airborne ultrasonic discharge activity
The sound radiation in a partial discharge activity appears in the whole sound spectrum. It is possible to hear, but this depends on the hearing ability of the person involved.
The use of the instrument for detecting the ultrasonic wave in the sound spectrum has following advantages: compared with human ear, the instrument is more sensitive and irrelevant to the operators, and runs at the frequency above voice frequency, and also has stronger directivity.
The most sensitive detection method is to use the ultrasonic sensor with the center frequency of 40 ~200 kHz. By virtue of this method, partial discharge activities can be successfully detected.
III. Airborne high-frequency electromagnetic discharge activity
When occurring in the insulation layer of a high-voltage switching cabinet, the partial discharge activity can generate high-frequency electromagnetic wave which can leak from the switching cabinet to the external surface through the openings on the metal shell, and such openings can be the shell gaps or seal washers and the gaps around other insulation components.
When propagating to the outside of the switching cabinet, the electromagnetic wave will generate a transient voltage on the grounded metal shell. Such transient earth voltage (TEV) exists in a very short time in the range from several millivolts to several volts, and has a rise time of several nanoseconds.
The probe can be placed outside the switching cabinet through a non-intrusive mode to detect partial discharge activities.
IV.Technical Parameters
1. Applicable scope: the non-intrusive mode is adopted to detect and locate the partial discharge defects of the high-voltage electric equipment.
2. sensor configuration
Standard: UA, TEV
Optional: Sensor network for transformer, high frequency sensor for GIS, sensor for high-voltage cable,or other senors customized according to user's requirements.
3. Detection principle: UHF (Ultra High Frequency) method, UA (Ultrasonic Analysis) method and TEV (Transient Earth Voltage) method.
4. Detection frequency band:
UA: 40～200KHz
TEV: 3~100MHz
UHF: 300～2000MHz.
5. Measurement range:
UA: -90～80dB
TEV: -80～10dBm
UHF: -80～10dBm.
6. Sensitivity: the minimum sensitivity is 10pC (specifically determined by the distance between the sensor and the discharge source).
7. Sensor:
a) Ultrasonic sensor: 20～200(kHz);
b) EV (Transient Earth Voltage) sensor: 5 ~ 100MHz;
c) UHF sensor: 300～2000(MHz), with directional reception characteristic.
8. Embedded ultrasonic sensor and TEV & UA integrated sensor: such components as transformer dedicated sensor, GIS dedicated sensor and cable dedicated sensor can be selected;
9. Software function:
a) Continuously detect UHF, TEV and ultrasonic signals to judge whether there is any partial discharge;
b) Display the variation tendency of the detected signal in a real-time manner to intuitionally judge the development of the partial discharge signal;
c) Field data storage function;
10. Instrument characteristics:
a) Screen display: high-contrast 3.5”TFT color screen.
b) Data storage: 1000 groups of test data can be stored.
c) Working power supply: embedded 8.4V lithium battery for 8h’s continuous operation.
d) Power supply: input 100-240VAC, output 8.4V/3A, charging time 3～4h.
e) Boundary dimension: 220 * 100 * 40.
f) Instrument weight: 1.5kg.
g) Environment temperature: -25℃～45℃.
h) Storage temperature: -35℃～60℃.
11. Complete standard configuration: host machine, sensor, AC adapter, connecting cable and transport case.
IV. Structural Layout
1.Panel arrangement
The product, with portable structure and embedded signal receiving and data processing module, has multiple analysis modes and can conveniently measure the UHF signals and the ultrasonic signals generated by the partial discharge of the electric equipment. Compared with similar products, this product has convenient operation and strong function.
Keyboard layout of the product is as follows:
1) F1 key: during test, “F1” key can be pressed to store present measured data;
2) F2 key: the historical data stored in the host machine can be called through “F2” key;
3) F3 key: in the measuring interface, F3 key is used for switching sensor type; in the data management or setting interface, F3 key is used as an ESC key;
4) Direction key: Up and Down keys are used for gain adjustment in the range of 0～90dB during test, and for time adjustment during function setting, as well as for page turning in historical data browsing;
5) OK key: during test, this key can be pressed to enter the setting menu;
6) Power key: the key should be pressed for 3s to turn on or turn off the power supply of the instrument;
The input end of the product is located exactly at the front of the instrument.
Besides the embedded ultrasonic sensor, the host machine of the product is also configured with an external sensor interface for connecting UHF sensor, TEV sensor and external ultrasonic sensor thereto. The uniform interface is adopted for convenient and simple operation.
2. Sensor configuration
1）Headphone jack: such jack is an international industrial standard interface, and the headphone can be used for monitoring the sound spectrum signal of the partial discharge during test, and the headphone volume can be adjusted through Left and Right keys.
2）Charging interface: the host machine is charged through the power supply attached to the machine, and it usually takes 4~5h to fully charge the host machine.
3）Reset switch: when the instrument is abnormal, click this switch or "▇" button to reset the system without worrying about historical data loss.
0.1Hz VLF AC/DC Hipot tester
