6.2.2 Electronic Insulation Resistance Tester
1.Basic Structure And Function of Electronic Insulation Resistance Tester
(1)Basic structure
The electronic insulation resistance tester is mainly composed of a ground terminal,a shielding terminal,a wiring terminal,an instrument dial,a luminous display tube,a zero adjusting device,a test key,a band switch and a test electrode,and the functions of each part are as follows.
①Earth terminal.Connect to the shell or ground of the tested equipment.
②Shielding end.Connect to the high-voltage guard ring of the tested equipment to eliminate the influence of surface leakage current.
③Line end.The high voltage output port is connected to the high voltage conductor of the tested equipment.
④Double-row tick marks.The upper gear is green-5000V/2GΩ-200GΩ,10000V/4gΩ-400GΩ.The lower gear is red-5000V/0-4000MΩ,10000V/0-8000MΩ.
⑤Green LED.Read the green gear(upper gear)when emitting light.
⑥Red LED.Read the red gear(lower gear)when emitting light.
⑦Mechanical zero adjustment.Adjust the position of the mechanical pointer to align with the∞tick mark.
⑧Test key.Press to start the test,and then rotate clockwise to lock this key.
⑨Band switch.It can realize output voltage selection,battery detection,power switch and other functions.
⑩Test electrode.One end is connected to the meter,and the other end is in contact with the measured object.
(2)Basic function
Insulation resistance tester can be used to measure insulation resistance of transformers,mutual inductors,generators,high voltage motors,power capacitors,power cables,arresters,etc.
The appearance of the electronic insulation resistance tester is shown in Fig.6-11.
Fig.6-11 Electronic Insulation Resistance Detector
1-Earth terminal;2-Line terminal;3-Shielding terminal;4-Double-row tick marks;5-Green LED;6-Red LED;7-Mechanical zero adjustment;8-Test key;9-Band switch;10-Test electrode
2.Technical Parameters of Electronic Insulation Resistance Tester
(1)Output voltage:500V,1000V,2500V,5000V.
(2)Insulation resistance:200GΩ.
(3)Accuracy:0.05.
3.Inspection contents of electronic insulation resistance tester
The electronic insulation resistance tester must be checked before use(as shown in Fig.6-12),as follows.
(1)Check whether the appearance of electronic insulation resistance tester is good.
(2)Check the factory certificate and calibration certificate of the electronic insulation resistance tester and confirm that the electronic insulation resistance tester is within the inspection period.(https://www.daowen.com)
(3)Check whether the pointer of the instrument is on infinite,otherwise,adjust the mechanical zero adjustment screw.
(4)Check whether the instrument battery is in good condition.
(5)Check whether the joints are in good condition.
Fig.6-12 Inspection of Insulation Resistance Tester
4.Usage of Electronic Insulation Resistance Tester
(1)Insert one end(red)of the high voltage test line into the LINE terminal,connect the other end to or use a hook to hang it on the high-voltage conductor of the tested equipment,insert one end of the green test line into the GUARD terminal,and connect the other end to the high-voltage guard ring of the tested equipment to eliminate the influence of surface leakage current.Insert another black test wire into the EARTH terminal and connect the other end to the shell or ground of the tested equipment.When wiring,pay special attention to the connection between LINE(red)and GUARD(green),and do not short circuit them.
(2)Turn the band switch BATT.CHECK,press the test key,and the meter starts to detect the battery capacity.
(3)Turn the band switch to select the required test voltage.
(4)Press or lock the test key to start the test.At this time,the high-voltage output indicator light above the test key will illuminate and the buzzer built in the meter will sound every 1 second,which means that there is high-voltage output at the LINE end.Note that during the test,it is strictly prohibited to touch the exposed part at the front end of the probe to avoid electric shock hazard.
(5)When the green LED is on,read the insulation resistance value of the outer ring(high range);when the red LED is on,read the insulation resistance value of the inner ring.After the test,release the test key,stop the test,wait for a few seconds,and do not remove the test electrode immediately.At this time,the meter will automatically release the remaining charge in the test circuit.Note:when the test is completed or repeated,the test object must be fully discharged to ground after short connection(the meter also has built-in automatic discharge function,but for a long time).
(6)If the second measurement is required continuously,the steps(3)to(5)can be performed.Note:If the test is not carried out for a long time,the battery in the battery compartment shall be taken out so as not to damage the instrument due to leakage of battery liquid.
(7)For two or more test pieces,such as lightning arresters and coupling capacitors,the wiring shown in Fig.6-13 can be used for measurement.In the figure,the shielding end is connected to a flange on the lightning arrester under test.In this way,the interference current caused by the high voltage line above is shielded by the shielding terminal without passing through the main circuit under test,thus avoiding the influence of interference current.For the arrester at the top section,the upper flange of the arrester can be connected to the EARTH of the instrument and then grounded,so that the interference current is directly connected to the earth.However,the latter cannot completely eliminate the interference.
As shown in Fig.6-14,the insulation resistance tester is used.
Fig.6-13 Wiring of More Than Two Tested Items
Fig.6-14 Use of Electronic Insulation Resistance Detector
5.Precautions for Storage of Electronic Insulation Resistance Tester
(1)The electronic insulation resistance tester shall be stored in a well-ventilated,dry and clean environment,and put on shelves.
(2)Properly maintain instruments and apparatus.
(3)Properly keep technical data and instructions of instruments and apparatus.
Fig.6-15 shows the storage tool cabinet of insulation resistance tester.
Fig.6-15 Storage Tool Cabinet for Insulation Resistance Detector
6.Preventive Test of Electronic Insulation Resistance Tester
The preventive test of the electronic insulation resistance tester is mainly to check the electronic insulation resistance tester regularly.The verification period of the electronic insulation resistance tester shall not exceed 2 years.