1.4.3 Electrical Test of Tools for Live Working
Insulating tools and instruments for live working shall be subject to predelivery test before delivery,and the test items and relevant indexes must meet requirements of national standards.Due to long-term overstocking and delivery transportation of products and some manufacturers only conducting random sampling test during predelivery test,acceptance test must be conducted when users receive the products.The test standards shall refer to relevant national standards.
After a period of use and storage,tools for live working may suffer a certain degree of damage or deterioration in electrical performance or mechanical performance,so in addition to the above two tests,regular tests,namely preventive test and inspection test,shall also be conducted.Content and standards of electrical tests of insulating tools and instruments are introduced as follows.
Electrical tests of insulating tools and instruments shall be conducted regularly:preventive test once a year and inspection test once a year,with an interval between the two tests being half a year and test contents including power frequency withstand voltage test and operation impulse test.Since the operation impulse withstand voltage test can only be conducted by a party with the test qualification,so here is only a briefly introduction to test methods and test conditions of the power frequency withstand voltage test.
Fig.1-17 is the power frequency withstand voltage and operation impulse withstand voltage wiring diagram.
Fig.1-17 Wiring Diagram of Power Frequency Withstand Voltage and Operation Impulse Withstand Voltage Test
1-high voltage lead;2-simulation conductor(φ＞30mm);3-uniform ball(D=200-300mm);4-test object(spacing between test objects d≥500);5-lower test electrode;6-grounding lead
1.Test Method
(1)Power frequency withstand voltage test of insulating bar.During the test,the metal head(or metal joint)part of the insulating bar,such as support bar,pull bar,suspender,etc.shall be hung on the high voltage terminal(generally,a metal rod with a length of not less than 2.5m and a diameter of 20mm shall be used as the high voltage terminal to simulate the conductor and hung in the air),and the ground wire shall be connected at the handle part and the boundary of effective insulating length(referring to the operating bar)or the original ground terminal(referring to the support bar,pull bar and suspender),and then voltage test shall be conducted for the whole section.
(2)Power frequency withstand voltage test of insulating ladder.Insulating ladders include vertical ladder,herringbone ladder,horizontal ladder and hanging ladder.During the test,a metal rod with a diameter of 20mm and a length of 2.5m shall be used as the high voltage terminal and hung horizontally to simulate the conductor.Then one end of the insulating ladder(generally the end of metal head)shall be hung on the high voltage terminal,the ground wire shall be connected to the shortest effective insulating length(wrapping the surface with tin foil and then bare copper wire for grounding),and finally the voltage test shall be conducted.
(3)Power frequency withstand voltage test of insulating rope and insulating rope ladder.In order to check the voltage withstand level of the whole insulating rope ladder or the whole insulating rope,they shall be wired according to the method shown in Fig.1-18 during the test.Two metal rods with a diameter of 20mm and a proper length shall be wound with insulating rope ladder or insulating rope.One of the metal rods shall be used as the high voltage terminal,which is horizontally suspended in the air through insulator,while the other metal rod is suspended in the air and grounded at the same time.The distance between the two metal rods shall be equal to the shortest effective insulating length under the highest service voltage.
Fig.1-18 Power Frequency Withstand Voltage Test of Insulating Rope
1-metal rod;2-insulating rope
Fig.1-19 Power Frequency Withstand Voltage Test of Insulating Shelter
1-support platform;2-foam plastic;3-power supply;4-connecting piece;5-tested item;6-tin foil
Fig.1-20 Power Frequency Withstand Voltage Test of Insulating Boots
1-test boots;2-metal plate;3-metal ball;4-metal sheet;5-sponge with water;6-insulating support(https://www.daowen.com)
(4)Power frequency withstand voltage test of insulating shelter.Insulating shelters include all kinds of insulating soft board,hard board,film,etc.During the withstand voltage test,as shown in Fig.1-19,the shelter shall be horizontally placed on the insulating support platform,and at the same time,both sides of the tested object shall be provided with aluminum foil as electrodes,and pressed with plastic connecting pieces at the upper and lower parts to ensure good contact.Then the upper pole plate shall be connected to the power supply and the lower pole plate to the ground.In addition,the tested object shall be reserved with edge width according to requirements of service voltage.
(5)Power frequency withstand voltage test of insulating boots.During the test,a piece of metal consistent with the size of the sample boots shall be covered with a piece of copper with a diameter of no more than 4mm and a height of no less than 15mm,and a piece of copper with a diameter of more than 4mm shall be connected externally and embedded in the metal ball.The outer electrode shall be a soggy sponge placed in the metal container,and the test circuit is shown in Fig.1-20.The voltage shall rise from zero to 75%of the specified voltage at a speed of 1kV/s,and then rise to the specified voltage at a speed of 100V/s.When the voltage rises to the specified voltage,keep it for 1min,and then record the current value of the milliammeter.If the current value is less than 10mA,the test is passed and the insulating boots are qualified.
(6)Power frequency withstand voltage test of insulating gloves.Insulating gloves are very important personal protective equipment in live working of distribution line,and there are many kinds of them.Its AC withstand voltage test is shown in Fig.1-21.The length of the exposed part of 10kV insulating gloves is 75mm.
Fig.1-21 AC Withstand Voltage Test of Insulating Gloves
1-disconnecter;2-fusible silk;3-power indicator;4-overload switch;5-voltage regulator;6-voltmeter;7-transformer;8-metal water container;9-test sample;10-electrode;11-milliammeter short circuit switch;12-milliammeter
Electrical tests of insulating gloves include AC withstand voltage test and DC withstand voltage test.When conducting AC withstand voltage test on insulating gloves,the voltage shall rise to the AC withstand voltage test value shown in Table 1-3 for 1min,after which if there's no corona,flashover,breakdown or obvious heating,the insulating gloves shall be deemed as qualified.
Table 1-3 AC Withstand Voltage Value of Insulating Gloves
When When DC withstand voltage test is conducted on insulating gloves,the voltage shall rise to the DC withstand voltage test value shown in Table 1-4 for 1min,after which if there's no flashover,breakdown or obvious heating,the insulating gloves shall be deemed as qualified.
Table 1-4 DC Withstand Voltage Value of Insulating Gloves
(7)Power frequency withstand voltage test of water washing tools.During power frequency withstand voltage test assembly,water washing tools shall be placed at an angle of 30°-45°with the ground.As shown in Fig.1-22,the simulated conductor shall be a metal rod with a diameter of 20mm and a length of 2.5m suspended in the air through insulator string.The distance between the hydraulic giant nozzle and the simulated conductor shall be determined by the voltage class applied on the hydraulic giant,and microammeters shall be provided for grounding at the handle of the flushing rod and 1.8m from the penstock to the nozzle to measure the leakage current.A grounding switch shall be connected in parallel on the microammeter.When voltage is applied and scale knob is switched,the grounding switch shall always be in the on-position state and shall only be opened in case of reading to prevent the high voltage from acting on the microammeter.In addition,after the voltage of simulated conductor is boosted,the hydraulic giant shall be aimed at the simulated conductor to spray(water resistance 10000Ω·m)for 1min,and then the microammeter shall be opened and read.
Fig.1-22 Power Frequency Withstand Voltage Test of Water Washing Tools
1-voltage metal bar;2-water spray direction;3-operating bar in rainy days;4-rain cover;5-shield wire for measuring;6-switch;7-diode;8-DC microammeter
Considering the combined insulation problem(water+insulating bar+aqueduct)of water washing tools,the test voltage shall be calculated and selected according to regulations.
2.Test Conditions
The insulating strength of insulating tools includes two parts:external insulation and internal insulation,and the main factors affecting the external insulation are air pressure,temperature,humidity,rain,pollution and the proximity effects of adjacent objects.Therefore,if the atmospheric state during the test is different from the standard atmospheric state,the discharge voltage shall be corrected to the standard atmospheric state.When the relative humidity is more than 80%,the discharge voltage will change,so in the rain test,only the relative air density shall be corrected,not the humidity.