6.1 Spark Gap Detector
For many years,a great deal of research has been done on the detection of porcelain insulators in transmission and distribution lines at home and abroad.Many detection methods are put forward,such as voltage distribution measurement,infrared imaging,electric field measurement,ultrasonic measurement and so on.A large number of detection instruments are developed,such as photoelectric detection rod,self-climbing detector,ultrasonic detector,DC insulator detector and so on.But the spark gap detection device is really widely used in production practice.The spark gap detector has the advantages of simple structure,easy processing,convenient use,light weight,portability and so on,thus it is widely used in live working of transmission and distribution line.
1.Basic Structure and Function of Spark Gap Detector
(1)Basic structure
①As shown in Fig.6-1,the spark gap detector is composed of supporting plate,contact electrode holder,spark electrode,contact electrode,connector,and the like.
②The spark electrode,the contact electrode and the holder can be made of medium carbon steel,and the contact electrode is made of round steel with the diameter of 3mm,with the chamfer in the front section.
Fig.6-1 Sample Drawing of Spark Gap Detector
1-supporting plate;2-contact electrode holder;3-spark electrode;4-contact electrode;5-connector
③The supporting plate can be made of epoxy laminated glass cloth sheet.
(2)Basic function
Spark gap detector is mainly used for live detection of zero value porcelain insulator to judge the quality of porcelain insulator.
2.Classification and Technical Specifications of Spark Gap Detector
(1)Classification
①At present,spark gap detector used in China can be classified into two types:fixed type and variable type.Fixed type refers to that the gap is fixed and unchangeable in the detection process.Variable type refers to that the gap distance can be changed in the detection process and the distribution voltage of insulator can be roughly estimated.
②According to the type of the spark electrode,it can be divided into a ball-ball electrode(as shown in the right side device of Fig.6-1)and a tip-tip electrode(as shown in the left side device of Fig.6-1).
(2)Technical specifications
①The supporting plate shall conform to the requirements of(GB/T1303.1-2009)Industrial Rigid Laminated Sheets Based on Thermosetting Resins for Electrical Purposes—part 1:Definitions,Designations and General Requirements,and shall be 3～5mm thick and convenient for installation of holder and connector.
②After assembly of the two electrodes,the center line of the two electrodes shall be on one axis,with the maximum deviation no more than 0.5mm.
③The telescopic insulating rod installed on corresponding voltage class when using.
④When detecting the low and zero value insulators of insulator string in each voltage class,the corresponding electrode gap distances are shown in Table 6-1.
Table 6-1 Detecting the Corresponding Electrode Gap Distances of Insulator String in Each Voltage Class
3.Inspection Contents of Spark Gap Detector
The spark gap detector must be inspected before use as follows.
(1)The spark gap detector shall be tested before use to ensure flexible operation and accurate measurement.
(2)The spark electrode gap distance shall be adjusted according to the voltage class of the detection equipment.The inspection of spark gap detector is shown in Fig.6-2.(https://www.daowen.com)
Fig.6-2 Inspection of Spark Gap Detector
4.Usage of Spark Gap Detector
(1)Pin type insulator and suspension type insulator of less than 3 pieces shall not be tested with spark gap detector.In fact,the spark gap detection method is to determine the insulating property of the insulator by testing and short connecting 1 insulator.When the number of insulators in the insulator string is less than 3 pieces,if 1 piece is zero,it will easily cause ground short circuit fault and burn out tools and instruments during the detection,resulting in equipment accidents.
(2)When detecting insulator string with a voltage level of 35kV and above,if it is found that the number of zero insulator pieces in the same string reaches the number in Table 6-2,it shall be stopped immediately.
Table 6-2 Allowable Number of Zero Insulator Pieces in One String
(3)Live detection of insulator shall be carried out in dry weather.
(4)The detection shall be carried out from the conductor end to the cross arm end piece by piece.
(5)Attention shall be paid to the difference between the discharge sound when the detector is close to the conductor and the discharge sound of the spark gap to avoid misjudgment.
(6)During the measurement,the minimum safe distance between the operator and the electrified body as well as the effective insulation length of the insulating bar used with spark gap detector shall be ensured.
(7)During the detection,if there is zero value insulator,it shall be retested for 2～3 times.When spark gap detector is used,the two metal probes shall slightly contact the steel cap and steel foot of porcelain insulator.Operators shall pay attention to avoid measuring the gap deformation.
The insulator is detected using a spark gap detector as shown in Fig.6-3 and Fig.6-4.
Fig.6-3 Sample Drawing 1 of Detecting the Insulator Using Spark Gap Detector
Fig.6-4 Sample Drawing 2 of Detecting the Insulator Using Spark Gap Detector
5.Precautions for Storage of Spark Gap Detector
The spark gap detector shall be stored in the special warehouse for tools and instruments for live working,and shall be placed on the upper shelf for storage.The tool cabinet for storing the spark gap detector is shown in Fig.6-5.
Fig.6-5 Tool Cabinet for Storing Spark Gap Detector
6.Preventive Test of Spark Gap Detector
The preventive test period of the spark gap detector is one year,with the test types as follows.
(1)Gap adjustment and discharge test.
(2)Power frequency withstand voltage test.
(3)Switching impulse voltage withstand test.