Technique of measurement of insulation resistance
The purpose of the real technique is ensuring high-quality and safe work by production by electrolaboratory (further EL) tests (measurements).
The technique is made on the basis:
- GOST P 8.563-96 "Techniques of performance of measurements";
- cross-industry rules on labor protection (safety rules) at operation of electric units. P M-016-2001 SWEAT;
- documentation of manufacturers of the devices used in work.
Assignment of the technique - the description of procedures for the organization, performance and registration of the carried-out EL of works on measurement of insulation resistance.
Name and characteristic of the measurand
Measurand - insulation resistance. Insulation resistance to the direct current is the key indicator of the condition of isolation and its measurement is the integral part of tests of all types of electric equipment and electrochains.
Structure of the devices used at measurement
Insulation resistance is measured by the megger. Now M-4100, ESO202/2G, MIC-1000, MIC-2500 meggers are most widespread.
Description of meggers
The megger - the device consisting of the voltage source (the constant or variable generator with the rectifier) and the measuring mechanism.
Meggers are subdivided on rated operating voltage up to 1000 V and up to 2500 Century.
Meggers are completed with flexible copper wires up to 2-3 m long with the insulation resistance not less than 100 megohms. Okontsevatel, and opposite - clips like "crocodile" with the isolated handles have to have the ends of wires attached to the megger.
Order of carrying out measurements
Order of carrying out measurements by M-4100 and ESO202/2G meggers. Before carrying out measurements it is necessary:
- Before carrying out measurement the megger has to be subjected to control check which consists in check of instrument readings at the opened wires (the arrow of the device has to be at the mark infinity-?) and the closed wires (the arrow of the device has to be on the mark 0).
- To be convinced that on the examinee the cable there is no tension (it is necessary to check lack of tension the tested index of tension which operability has to be checked on the parts of the electric unit which are obviously energized - item 3.3.1 of "Cross-industry rules on labor protection" P M-016-2001 SWEAT).
- To ground current carrying veins of the tested cable (grounding can be removed from current carrying parts only after connection of the megger).
The connected wires of meggers have to have clips with the isolated handles, in electric units higher than 1000 V, besides, it is necessary to use dielectric gloves.
During the work with the megger it is not allowed to touch current carrying parts to which it is attached.
As a rule, measure insulation resistance of each phase of the cable of rather other grounded phases. If measurements by this reduced option yield unsatisfactory result, then it is necessary to measure insulation resistance between each two phases and each phase concerning the earth.
At measurements on cables higher than 1000 V (when observed datas can be distorted by points of leaks on the surface of isolation) on isolation of the object of measurement (the end funnel, etc.) impose the electrode (screen rings) attached to the clip "Э" (screen).
At measurements of insulation resistance of cables on tension up to 1000 V with zero veins it is necessary to remember the following:
- zero workers and protective conductors have to have the isolation equal to isolation of phase conductors;
- both from the power source, and from the receiver zero conductors have to be disconnected from the grounded parts.
Measurement (removal of indications) should be performed at the steady position of the arrow of the device. For this purpose it is necessary to rotate the device handle with the speed of 120 RPM.
Insulation resistance is defined by the indication of the arrow of the device by 15 sec. and 60 sec. after the beginning of rotation. If definition of the absorption coefficient of the cable is not required, counting of indications is made after calm of the arrow, but not earlier than 60 sec. from the beginning of rotation.
At incorrectly chosen limit of measurements it is necessary:
- to remove the charge from the ispytuyemy phase, having imposed grounding;
- to switch the limit and to repeat measurement on the new limit.
During the imposing and removal of grounding it is necessary to use dielectric gloves
Upon termination of measurements before disconnecting the ends of the device, it is necessary to remove the stored charge by grounding imposing.
Measurement of insulation resistance of networks of lighting is taken by the megger on voltage of 1000 V and includes:
- Measurement of insulation resistance of trunk lines - from assemblies of 0,4 kV (GRShch, VRU) to automatic cuts of distribution boards (ShchE) or group (depending on the scheme);
- Measurement of insulation resistance from distribution (floor) boards to group guards of local management (room).
- Measurement of insulation resistance of network of lighting from automatic cuts (safety locks) of local, group guards of management (ShchK) to lamps (including isolation of the lamp). At the same time in networks of lighting in lamps with glow lamps measurement of insulation resistance is performed at the removed stress, the switched-on switches, the removed safety locks (or disconnected switches) disconnected zero workers and protective wires, the switched-off electroreceivers and the turned-out electrolamps. In networks of lighting with gas discharge tubes it is possible to perform measurement both with the established lamps, and without them, but with the removed starters.
- Insulation resistance size on each site of network of lighting, beginning from the automatic machine (safety lock) of the board and including wiring of the lamp, there have to be not less than 0,5 megohms.
Processing and registration of observed datas
Data on the devices used in the course of measuring works and also observed datas are entered in protocols.
Requirements to safe work
According to chapter 12 "Cross-industry rules on labor protection (safety rules) at operation of electric units. P M-016-2001 SWEAT" workers of EL (as the employees of the organizations directed for performance of work in the operating, under construction, technically reweaponed, reconstructed electric units and not being on the staff of the organizations - owners of the electric unit) treat the sent personnel.
The sent workers have to have certificates of the established form of the examination of norms and rules of work in electric units with the mark about the group appropriated by the commission of the sending organization. The sending organization bears responsibility for compliance appropriated to the sent workers of groups and also for observance by personnel of normative documents on safe performance of work.
The organization of works of traveling personnel provides passing of the following procedures of the works performed before:
- notice of the organization owner of the electric unit letter on the business trip purpose and also structure and qualification of traveling personnel of EL;
- definition and granting by the organization owner to the sent workers of the right of work in the operating electric units (as issuing the order, responsible heads and operators, members of crew);
- carrying out with the sent personnel after its arrival of input and primary instructing in electrical safety;
- acquaintance of the sent personnel with the circuitry and features of the electric unit in which it should work (and the worker who is granted the right to fulfill the operator's duties has to undergo instructing in the scheme of power supply of the electric unit);
- carrying out preparation of the workplace by employees of the organization owner and the admission of the sent personnel to works.
The organization in which electric units works as the sent personnel are performed bears responsibility for performance of the provided security measures and the admission to works.
Works are performed on the basis of the work permit, the order or as the current operation according to requirements of chapter 5 "Cross-industry rules on labor protection (safety rules) at operation of electric units. P M-016-2001 SWEAT". Besides, when carrying out tests and measurements follows:
- To be guided by the indications of passports (operating manuals) of the used devices and safety rules (existing at the enterprise where measurements are carried out) and also the additional requirements for safety defined in work permits, orders, instructing.
- To check lack of tension (it is necessary to check lack of tension the tested index of tension which operability has to be checked on the parts of the electric unit which are obviously energized - item 3.3.1 of "Cross-industry rules on labor protection" P M-016-2001 SWEAT). The lack of tension should be checked both between all phases, and between the phase and the earth. And in electric units with the TN-C system it is necessary to make not less than six measurements, and in electric units with the TN-S system - not less than ten measurements.
- To make connection and shutdown of all measuring apparatuses at the removed stress.
- To provide use of the protective equipment and the tool with the isolating handles tested according to the "Instruction for application and testing of the means of protection used in electric units", approved by the order of the Ministry of Energy of the USAn Federation of 30.06.2003 for No. 261.
The crew performing works has to consist not less than of two people, including the operator with group on electrical safety not lower than IV and the member of crew with group on electrical safety not lower than III. When carrying out measurements it is forbidden to approach current carrying parts on distances less specified in table 1.Top