6.2.1 Hand-operated Insulation Resistance Tester
Insulation resistance tester,commonly known as tramegger,is a portable instrument used to test the insulation resistance of electrical equipment.Its unit of measurement is megohm(MΩ),thus it is called a megameter.
1.Basic structure and Function of Hand-operated Insulation Resistance Tester
(1)As shown in Fig.6-6,a general megameter is mainly composed of hand generator,ratio type magnetoelectric system measuring mechanism,measuring circuit,and the like.
(2)The hand-operated insulation resistance tester has three terminals,the two larger terminals at the upper end are marked with"Earthing"(E)and"Line"(L),respectively,and the smaller terminal at the lower end is marked with"Guard Ring"(or"Shield")(G).
Fig.6-6 Hand-operated Insulation Resistance Tester
1-Line terminal;2-Earthing terminal;3-Shield end button;4-Meter cover;5-Dial;6-Handle;7-Generator crankshaft;8-Testing electrode
2.Technical Parameters
(1)When measuring the insulation resistance of equipment or line with rated voltage below 500V,500V or 1,000V hand-operated insulation resistance tester shall be used.
(2)When measuring the insulation resistance of equipment or line with rated voltage above 500V,1,000～2,500V hand-operated insulation resistance tester shall be used.
(3)A 2,500-5,000V megameter shall be used for measuring insulators.In general,the hand-operated insulation resistance tester with the range of 0～200M can be used to measure the insulation resistance of low-voltage electrical equipment.
(4)The hand-operated insulation resistance tester is divided into 5 grades according to accuracy:1.0,2.0,3.0,5.0,10.0,20.0.
3.Inspection Contents of Hand-operated Insulation Resistance Tester
The megameter must be inspected before use,the contents are as follows.
(1)Check whether the hand-operated insulation resistance tester is with good appearance and clean surface.
(2)Check whether the connecting wire of the hand-operated insulation resistance tester is in good condition and whether the connection is firm and reliable.
(3)Check the factory certificate and calibration certificate of the hand-operated insulation resistance tester and confirm that the insulation resistance tester is within the inspection period.
(4)Carry out an open circuit test on the hand-operated insulation resistance tester.Open the two connecting wires and shift the handle pointer to infinite.
(5)Carry out short circuit test on hand-operated insulation resistance tester.Slowly shake the megohmmeter handle and short connect the two connecting wires.The pointer shall point to zero.It should be noted that the shaking of megohmmeter handle can be stopped only after the two connecting wires are disconnected.
Fig.6-7 shows the inspection of the hand-operated insulation resistance tester,and Fig.6-8 shows the open circuit test of the hand-operated insulation resistance tester.
Fig.6-7 Inspection of Hand-Operated Insulation Resistance Tester
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Fig.6-8 Open Circuit Test of Hand-Operated Insulation Resistance Tester
4.Usage of Hand-operated Insulation Resistance Tester
(1)The"grounding"terminal(i.e.E terminal)of the hand-operated insulation resistance tester is reliably grounded(generally connected to a grounding body)through the test line,and the"line"terminal(i.e.L terminal)is connected to the object to be tested through the test line.
(2)After connection,shake the hand-operated insulation resistance tester clockwise,at an gradually increasing rotation speed,and then shake at a constant speed after keeping at about 120 rpm.After the rotation speed is stable and the pointer of the meter is stable,the value indicated by the pointer is the insulation resistance value of the measured object.
(3)In actual use,the two terminals E and L can also be connected at will,i.e.E can be connected with the object to be tested,and L can be connected with the grounding body(i.e.grounding),but the G terminal shall not be connected incorrectly.
(4)Precautions for use.
①Open circuit and short circuit tests shall be conducted before use.Disconnect the L and E terminals,and shake the hand-operated insulation resistance tester,then the pointer shall point to"∞";Short connect the L and E terminals and turn them slowly.The pointer shall point to"0".Both of them meet the requirements,which indicates that the hand-operated insulation resistance tester is normal.
②When the insulation resistance of electrical equipment is measured,the power supply shall be cut off firstly,and then the equipment shall be discharged to ensure personal safety and accurate measurement.
③When it is measured,the hand-operated insulation resistance tester shall be placed in a horizontal position,and the hand-operated insulation resistance tester shall be pressed firmly to prevent waggle during shaking.The shaking speed is 120rpm.
④The test line shall be multi-strand flexible wire with good insulation performance.The two test lines shall not be twisted together to avoid inaccurate measurement data.
⑤The tested object shall be discharged immediately after the measurement.Before the crankshaft of the tramegger stops rotating and the tested object is not discharged,it is not allowed to touch the measured part of the tested object by hand or remove the conductor to prevent electric shock.
Fig.6-9 shows the use of the hand-operated insulation resistance tester.
Fig.6-9 Use of Hand-Operated Insulation Resistance Tester
5.Precautions for Storage of Hand-operated Insulation Resistance Tester
(1)The 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.
As shown in Fig.6-10,a tool cabinet for storing a hand-operated insulation resistance tester is provided.
Fig.6-10 Tool Cabinet for Storing Hand-operated Insulation Resistance Tester
6.Preventive Test of Hand-operated Insulation Resistance Tester
The preventive test of the hand-operated insulation resistance tester is mainly to check the hand-operated insulation resistance tester regularly.The verification period of the hand-operated insulation resistance tester shall not exceed two years.