- in high-voltage circuit breaker contacts,
- in disconnecting switches, separators, and short-circuiters,
- in packaged switchgears,
- in contact couplings,
- in weld seams, etc.
One of the problems faced when measuring the transient resistances with permissible error is availability of oxide films between contact surfaces.
According to International standard IEC 60694 "General Specifications for High-Voltage Switch Gears" (International Electrotechnical Commission), for controlling this type of error, amperage of the test current during testing the electric resistance in the main circuit of a HV circuit breaker shall be between 50A and its rated value.
Current amperage in the passport data of many foreign circuit breakers is most often limited by specific values: 100A and 200A.
Amperage in the MIKO-21 can be set in several ways:
Only SKB EP microohmmeters measure transient resistances (R transient) of minimum-oil and bulk-oil circuit breakers using separate automatic modes optimized for those circuit breakers. Current transformers (CT) of bulk-oil circuit breakers form a prolonged transition process when the test current is applied. For this reason the time of measurement is determined by CT parameters, by their number, amperage and, for example, for U-220-2000-25U1 circuit breaker it may be as high as 30 seconds. Special algorithms with automatic stop of measurements allow avoidance of subjective mistakes and increase the number of measurements per one battery charge.
There are four methods programmed in the instrument for resistance measurement start-up:
Company's archive of passport values of resistances (R transient) of circuit breaker contacts ensures automatic comparison between measured and passport values subject to circuit breaker grade indication;
Archive of the instrument contains passports of HV circuit breakers with indication of maximum and/or minimum permissible transient resistances of contacts, and passports for rejected resistors with indication of permissible values of the upper and lower thresholds of resistances.
The user can also add the required template.
Availability of an in-built archive of passport values of eclectic resistances (main circuit of HV circuit breakers) facilitates automatic detection, and the device beeps if the results of measurements go beyond the permissible limits.
Color graphic display of high brightness ensures easy reading on a sunny day, whereas intuitively understandable interface with a sensor display facilitates the instrument use.
The Instrument can be manipulated either from the film keyboard or from the sensor display, as suits.
Communication with PC via USB or a flash card facilitates data transfer from the Instrument to the Company's data base.
The instrument can be built-in into testing systems under control of software complexes of diagnosis laboratories and equipment manufacturers.
For convenience the standard kit includes only one type of a test package (Kit 3 includes two test cables with crocodile clips for high-voltage circuit breakers up to 110 kV).
Suitable cable or a set of cables can be selected from a large range of additional accessories:
One set with spring-loaded contacts for measurements in busbars or in arc extinguish chambers. Two other kits with crocodile clips (with current and potential wires) for circuit breakers of up to 10 kV, circuit breakers of up to 110 kV, and a part for circuit breakers of up to 220kV.
Three kits that include cables with crocodile clips (with current and potential wires), a cable with a G-clamp (with current and potential wires). They differ in length and purpose, namely: for HV circuit breakers of up to 220kV, for HV circuit breakers of up to 330kV, some for 500kV, and for HV circuit breakers of up to 750kV.
|Range of resistance measurements, Ohm||0.1 µΩ ÷ 2 Ω|
|Range of test current amperage, A||1 ÷ 200|
|Error of measurements, %||±0.05|
|Time of measurement in Mode 1, sec||not more than 2.0|
|Time of measurement in Mode 2 on a bulk-oil circuit breaker, sec||10 ÷ 30|
|Time of measurement in Mode 3 on a bulk-oil circuit breaker with battery charge saving||5 ÷ 15|
|Period of continuous operation (in normal conditions), hrs, no less than||8|
|Number of tests (in normal conditions), no less than||500|
|Display of the instrument||Sensor, color, graphic, 480x272 dots|
|Types of data transfer channels||USB/USB Flash|
|Consumed power does not exceed, V||60|
|Operating temperature range, ºС||-20 ÷ +50|
|IP for transportation||IP64|
|IP rating in operating state||IP40|
|Weight of the test block, kg, not more than||3.1|
|User manuals language||English|
|Calibration period, year||3|
|Test block of MIKO-21 СКБ139.00.00.000||Instrument and covering documents: calibration certificate, Operations Manual, and a log book.|
|Set #2 СКБ039.27.00.000||Includes: Test cable with crocodile clips (up to 50 mm jaw capacity) for circuit breakers of up to 10kV. Current and potential wires (2 m, 0.56 kg, 2 pcs. per set).|
|Main cable СКБ018.09.00.000||For instrument connection to the main network and for the battery charging via an in-built charger (2 m long).|
|Earth wire СКБ010.01.00.000||For earthing the instrument casing. Terminated with a G-clamp and a lug for a screw. Rated current is 50A (Length: 1.75m).|
|Shunt 75 ShSM M3 75A-0.5||Shunt for checking the MIKO-21 operability.|
|Safety devices VP2B-1V-21 (ВП2Б-1В-2А) (2 pcs.).||For the power source protection.|
|Tool bag СКБ126.06.00.000||Robust, convenient, wear proof bag for transportation of cables, documentation and other accessories to the MIKO-21 instrument.|
|Includes: Test cable with spring-loaded needle-type contacts for measurements in busbars or in arc extinguish chambers. Current and potential wires (1.5 m, 0.5 kg, 2 pcs. per set).|
|Set #3 СКБ039.25.00.000||Includes: Test cable with a G-cramp (up to 80 mm jaw capacity) for all the circuit breakers of up to 35kV, and for some circuit breakers of up to 110kV. Current and potential wires (4.5 m, 1.86 kg, 2 pcs.).|
|Set #4 СКБ039.26.00.000||Includes: Test cable with a G-cramp (up to 80 mm jaw capacity) for all the circuit breakers of up to 110kV and some circuit breakers of up to 220kV. Current and potential wires (6 m, 2.83 kg, 2 pcs. per set).|
For precision measurements and for measurements on the sections of the circuit to the end points of which the yest current is applied.
It icludes: crocodile clips A25C (2 pcs.) and a probe (2 pcs.).
A test kit consists of two cables for circuit breakers of up to 220kV:
A test kit consists of two cables for circuit breakers of up to 330kV, and some for up to 500kV:
A test kit consists of two cables for circuit breakers of up to 750kV:
|Potential spring-loaded contact (2 pcs.) СКБ023.21.00.000||Together with test cables for avoiding high transient resistances between an input pin and a cramp of the device. To be used together with Sets ##3-7.|
|Potential pin contact (2 pcs.) СКБ023.22.00.000||Together with test cables for avoiding high transient resistances between an input pin and a cramp of the device. To be used together with Sets ##3-7.|
The rod is designed to ensure convenient connection to contacts of a high-voltage item.
The rod is completed with a clamp with current and potential contacts connected by wires with the measurement platform. Test cables are connected to the measurement platform from the ground.
In 2016, following the request of OJC MVZ named after M.L. Mil, SKB EP, LLC developed a new line of MIKO-21 microohmmeter specifically for solving the tasks of our Company.
Using MIKO-21, OJSC MVZ named after M.L. Mil performs measurements of transient resistances of:
Test operation of MIKO-21 in 2016 revealed certain drawbacks in the device’s design and software that were completely eliminated by the Manufacturer.
Since 2017 the MIKO-21 of special complement has been regularly used by JSC MVZ named after M.L. Mil and proved to be an instrument reliable and convenient in operation that fully replaces similar obsolete devices.
The main merit of MIKO-21 microohmmeter is its simple and understandable interface, sensor display, small size and low weight, options of being powered from 220V, 50 Hz networks and from an in-built battery.
There were no failures during the period of its operation.
In the first quarter of 2017, ELMASH (UETM), LLC (Yekaterinburg City), a research and testing division of BBA Production Complex performed pilot operation of MIKO-21 microohmmeter manufactured by SKB EP, LLC.
The microohmmeter was used for measuring the transient resistance of the main circuits of high-voltage column-type and bulk-oil circuit breakers of ВГБ-УЭТМ®-35, ВГТ-УЭТМ®-110, ВЭБ-УЭТМ®-220 types.
We should like to note the following merits of the microohmmeter: simple and user-friendly interface, touch display, small size and light weight, availability of the option of connecting the device to PC. Microohmmeter can be powered both from the 230V network and from an in-built battery that is a big advantage since devices are often used far from the available power sources.
The device’s kit allows a large variety of options. During pilot operation the microohmmeter proved to be a reliable and convenient device. There were no failures observed.
On July 1-2 Dimitrovgradsky metallurgical plant, LLC was testing the MIKO-21 microohmmeter. The instrument was used for measuring the electric resistance of copper items.
MIKO-21 is a convenient multi-functional instrument with user-friendly menu. One of its merits is a large range of manually set values of test current and an option of data downloading to PC. Touch color display, an archive of passport values of tested equipment, independent power supply and small size are also worth mentioning. The instrument demonstrated proper operation, there were no failures.
That PAO FSK EES Branch operates the following instruments: MIKO-1 (16 pcs.), PKV/M7 (6 pcs.), PKV/M6 (4 pcs.), PKV/U3.1 (1 pcs.), MIKO-21 (1 pcs.).
First instruments were procured in 2010. The instruments were used for monitoring and diagnosis of electric equipment at 220 and 500 kV substations.
MIKO-1 device is rather convenient in use as it is powered from an in-built battery; it has small weight and size. It can be easily connected to any measured equipment owing to cable with clamps of two types. The process is easily controlled, measurements are of high accuracy; capacity of the in-built battery is sufficient for a large number of measurement sessions.
We used PKV/M6 and PKV/M7 instruments for recording the time and speed characteristics of circuit breakers U-110, MKP-110, U-220, VMT-110, VMT-220, MKP-35, C-35, and of 6-10kV oil circuit breakers. The process of connection and diagnosis is rather simple.
We recommend PKV/M6 and PKV/M7 instruments to all the companies dealing with maintenance and operation of electric equipment and to electric network companies.