5.3.1 Shielding Clothes
1.Basic Structure and Functions of Shielding Clothes
(1)Basic structure characteristics
The complete set of shielding clothes shall include coats,pants,hats,socks,gloves,shoes and their corresponding connecting lines and connectors.
(2)Basic function
Shielding clothes for live working,also called equipotential voltage-sharing clothes,are made of uniform conductor material and fiber material.When wearing the shielding clothes,an equipotential shielding surface will be formed on all external parts of the human body in the high voltage electric field to protect the human body from damages of high voltage electric field and electromagnetic wave.
2.Classification and Technical Specifications of Shielding Clothes
(1)Classification
There are two types of shielding clothes.The shielding clothes for 110(66)kV～500kV AC,±500kV DC and below voltage class are Type I,and that for 750kV AC voltage class are Type II.Type II shielding clothes must be equipped with a mask,and the whole set of clothes shall be one-piece clothes,pants and hats.Type I shielding clothes are shown in Fig.5-26,while Type II shielding clothes are shown in Fig.5-27.
Fig.5-26 Type I Shielding Clothes
Fig.5-27 Type II Shielding Clothes
(2)Technical Parameters
①Shielding clothes shall be with good shielding performance,low resistance,proper flow capacity,certain flame retardancy and good wearability.Each part of shielding clothes shall be connected reliably through two detachable connectors.
②The resistance of the apparel fabric used for making the shielding clothes shall not be greater than 800m;the apparel fabric shall have certain spark resistance ability,meaning that when the high-frequency spark discharge generated by the charging capacitor,it will not be burnt away,with only carbonization and no open fire spread.After 2min of spark resistance test,the carbonized damage area of apparel fabric shall not be greater than 300mm2.
③The fusing current of the apparel fabric used for making the shielding clothes shall not be less than 5A.
④The apparel fabric must be able to prevent the spread of open fire when contacting with it.The carbon length of the sample shall not be greater than 300mm;the burnt-out area shall not be greater than 100mm2,and the burnt-out area shall not spread to the edge of the sample.
⑤After washing for many times,the electrical and flame resistance properties of the apparel fabric do not decrease obviously.
⑥The apparel fabric must be abrasion-resistant,so that the clothes has a certain durability value.After 500 friction tests,the resistance of apparel fabric shall not be greater than 1Ω.
⑦For conductive fiber apparel fabric,the radial breaking strength shall not be less than 343N,the latitude breaking strength shall not be less than 294N,and the longitude and latitude breaking elongation shall not be less than 10%;for conductive coating apparel fabric,the radial breaking strength shall not be less than 245N,the latitude breaking strength shall not be less than 245N,and the longitude and latitude breaking elongation shall not be less than 10%.
⑧The apparel fabric shall have a large permeation volume,so that wearers can feel comfortable.The air flow through the apparel fabric shall not be less than 35L/(m·2s).(https://www.daowen.com)
⑨After the whole set of shielding clothes are connected well,the resistance between any two farthest ends shall not be greater than 20Ω,the resistance between any two farthest ends of glove,sock,coat and pants shall not be greater than 15Ω,and the resistance of conductive shoes shall not be greater than 500Ω.
⑩Good electrical connection between the hat and coat must be ensured.The hat must pass the shielding effect test.The shielding effect test of the hat is conducted together with the shielding property test of the whole set of clothes.For Type I shielding clothes,the protective tongue and extended edge of the hat must ensure that the exposed parts of the human body(such as the face)do not feel uncomfortable,and that the surface field strength of the exposed parts of the human body shall not be greater than 240kV/m at the highest applied voltage;Type II shielding clothes for 750kV voltage class shall be equipped with a shielding mask which shall be braided with conductive materials and flame-retardant fibers and shall have good vision,with the shielding efficiency no less than 20db;after the shielding clothes are supplied with the specified power frequency current and has been thermally stabilized for a certain period of time,the temperature rise of any part of the shielding clothes shall not exceed 50°C.
3.Inspection Contents of Shielding Clothes
The shielding clothes must be carefully inspected for voids,scratches,breakage and other defects before use;all parts are connected well,firmly and reliably.When testing the shielding clothes with special instruments,the resistance between any two farthest ends shall not be greater than 20Ωafter the whole set of shielding clothes are connected well,the resistance between any two farthest ends of glove,sock,coat and pants shall not be greater than 15Ω,the resistance of conductive shoes shall not be greater than 500Ω,and the shielding efficiency of the shielding apparel fabric shall not be less than 40db.
4.Usage of Shielding Clothes
(1)When wearing,it is necessary to connect the multi-strand metal connecting wires of various parts like coat,hat,gloves,socks and shoes in accordance with the specified order.The flame-retardant underwear shall be worn inside the shielding clothes to avoid direct contact with skin,as shown in Fig.5-28.
(2)It is strictly prohibited to short connect the grounding current,idle circuit and capacitance current of the coupling capacitor through the shielding clothes.
(3)After using,shielding clothes must be stored properly,and kept away from moisture and contaminant to avoid damages and affecting electrical performance.
Fig.5-28 Use of Shielding Clothes
5.Precautions for Storage of Shielding Clothes
(1)The shielding clothes shall be kept in a dry and ventilated place.The shielding clothes shall be kept in a dry and well-ventilated tools and instruments warehouse as shown in Fig.5-29,and placed on a upper shelf in a special tools and instruments box.
(2)When the shielding clothes is not worn,it shall be hung or wrapped into a cylindrical shape in a special box to prevent the break of functional fibers.
(3)The shielding clothes shall not be placed with other chemicals.
Fig.5-29 Storage of Shielding Clothes
6.Test Contents of Shielding Clothes
The test contents of the shielding clothes are as follows.
(1)Efficiency test of apparel fabric.Including shielding efficiency test,resistance test of apparel fabric,fusing current test of apparel fabric,electrical spark resistance test,fire resistance test,wear resistance test,breaking strength and elongation test,finished product test.
(2)Test of finished shielding clothes.Including resistance test of coat and pants,resistance test of gloves and socks,resistance test of shoes,shielding effect test of hat,shielding efficiency test of shielding mask,resistance test of complete set of shielding clothes,internal electric field strength test of complete set of clothes,test of internal current through human body of complete set of clothes,test of current capacity through human body of complete set of clothes,etc.
(3)Preventive test of shielding clothes.Including the resistance test of ready-made clothes and the shielding efficiency test of the whole set of clothes,with the test period of half a year.