MIKO-12-50A three-phase milli-ohmmeter is designed to measure DC resistance in the range of 1 μΩ to 100 kΩ at a current up to 50 A in inductive and non-inductive power equipment.
MIKO-12-50A diagnostic objects:
Windings of high-power transformers;
Windings of instrument transformers and other high-inductive equipment;
Windings of electric motors, generators, and linear compensators;
Electromagnet windings;
Contacts of circuit breakers, busbars, resistors, and other non-inductive circuits;
Compensating, current-limiting, and other resistors of high-voltage circuit breakers;
Cables.
Test current within a range of up to 50 A can be set in two ways:
Selection from a set of fixed values;
Automatic test current setting.
In Auto mode, the device automatically determines the optimal test current and simultaneously calculates the resistance of the diagnostic object, ensuring high measurement accuracy and precision.
Winding resistance measurement in high power transformers involves a number of challenges due to their design and operating conditions. The main difficulties include the high inductance of the windings, prolonged setup time, and unstable signals during low-current measurements. As a result, testing time increases and the accuracy of the results may be reduced.
MIKO-12-50A generates a test current of 50 A at an output voltage of 50 V, which facilitates rapid magnetization of the magnetic circuit and maintains stable measurement conditions.
High output power of up to 400 W under load significantly reduces the impact of transient processes, shortens the time to reach steady state, and improves the accuracy of resistance measurements for high-voltage (HV) and low-voltage (LV) windings, even under challenging operating conditions.
Depending on the object type, special measurement modes can be selected. The user can select one of the followings:
Sequential mode – current of up to 25 A;
Single mode – current of up to 50 A;
Parallel mode – current 12.5 A.
Measurements can be started and stopped manually
(by pressing a button) or automatically when a set criterion is met.
Based on the windings connection diagram, the following measurement modes are available:
2 windings HV + LV. The test current flows through the high- and low-voltage windings connected in series, while the resistance of each is measured simultaneously. The measurement is started by pressing the “START” button. It stops automatically or manually.
3 windings sequentially. The device performs automatic sequentialmeasurement across three phases with automatic process stop. Operation is initiated by pressing the “START” button and stops automatically upon reaching the set criterion.
3 windings parallel.Simultaneous automaticmeasurements across three phases is a distinctive feature of MIKO-12-50A. The measurement is started by pressing the “START” button and stops automatically upon reaching the set criterion or manually. The use of a parallel circuit significantly reduces measurement time, especially when checking resistance at all tap positions of the OLTC/NLTC.
The device can automatically calculate the parameters specified in technical inspection regulations:
Calculation of the relative difference in winding resistance;
Conversion of measured resistance values to the nominal temperature;
Calculation of phase winding resistance based on the measured line resistances;
Automatic identification of phases with a relative resistance deviation exceeding 2%.
The device automatically compares the measured results with the nominal values.
Once the measurement is complete, the calculated results are displayed on the screen, allowing the user to quickly determine whether the equipment is suitable for further operation
The device is equipped with an automatic OLTC position switching function for use during the measurement process. Once a stable resistance is reached, a signal is sent to the OLTC drive to switch to the next tap position, allowing the measurement process to continue.
This feature eliminates the need for specialists to constantly monitor the instrument's readings and manually switch the OLTC. It significantly simplifies the measurement procedure and reduces the time required for diagnostics.
MIKO-12-50A is equipped with the demagnetization mode, which is necessary to conduct certain tests and eliminate remnant magnetism of the transformer magnetic core.
Demagnetization is performed automatically – the device sequentially applies an electric current to the corresponding winding in both forward and reverse directions. With each change in polarity, the current gradually decreases, ensuring effective removal of the remnant magnetism from the transformer magnetic core. Demagnetization stops automatically when the current reaches threshold value or upon the user’s command.
Current change is displayed on the device screen as a graph in real time to ensure accurate demagnetization control.
Non-intrusive testing of the OLTC allows the user to assess the state of the switching OLTC equipment with current limiting resistors without removing the contactor tank cover (DRM – Dynamic Resistance Measurement).
Method is based on measuring instant test current values during the switching process. Test current firstly passes through the transformer winding and then through OLTC contacts at switching from one tap to another. The DRM graph is built on the basis of measurement results and shows current change during tap changing. This graph enables to check tap changing time and general object state.
Analysis of the acquired graphs enables not only to sort out OLTC by fault-free/faulty criteria but also to define the nature of the defect eliminating the opening of fault-free OLTCs.
Milli-ohmmeter mode and DRM test complement each other and provide the user comprehensive information about the transformer state
MIKO-12-50A has a built-in archive of up to 1,000 measurements for viewing, copying or deleting data. The device’s relatively light weight (10 kg) and compact dimensions make it easy to move around the site.
The device is equipped with a color graphic touch screen display of high brightness and an intuitive interface that facilitates interaction.
Special PC software is currently under development. It will allow users to control the device and transfer measurement results via Bluetooth or USB.
Specifications
Value
Resistance range
1µΩ – 100 kΩ
Resolution
0.1 μΩ
Accuracy
±0.1%
Number of digits in the output of the measurement result
Instrument and additional documents: Calibration Certificate, User Manual, Log Book.
Test cable for power transformers
052.20.00.000К
Test cable for power transformers
052.20.00.000К
A set of cables 4 x 8.5 m with jaw up to 75 mm for connecting MIKO-12-250A measurement channels to the power transformer bushings of any rating.
Mains cable
018.09.00.000
Mains cable
018.09.00.000
Mains cable 1 x 2 m. For instrument connection to the to the mains.
Ground cable
010.01.00.000
Ground cable
010.01.00.000
Ground cable 1 x 2 m (0.07 kg) for instrument grounding. The cable is equipped with a C-clamp and a screw end cap. Rated current is 50 А.
Fuse VP2B-1V-2А
Fuse VP2B-1V-2А
For the power source protection.
USB Type-A, USB Type-C Cables 1.5 m 2A
USB Type-A, USB Type-C Cables 1.5 m 2A
USB cable 1.5 m for charging and connecting devices.
Tool bag
126.06.00.000
Tool bag
126.06.00.000
Convenient, robust, wear proof bag for transportation of cables, documentation and other accessories.
Additional complete set (on order)
Photo
Item, Index
Application
Test cable
052.22.00.000
Test cable
052.22.00.000
Test cable 2 x 4 m with jaw up to 20 mm for connecting MIKO-12-25A measurement channels to the current and voltage transformers terminals of any rating.
Test cable extension
031.20.00.000
Test cable extension
031.20.00.000
Recommended to be used together with test cables 052.22.00.000 and 052.20.00.000K.
Made of elastic silicone tube that is resistant to low and high temperatures and corrosive environments. Length: 6.5 m. Weight: 1.18 kg
OLTC drive control cable
052.25.00.000
OLTC drive control cable
052.25.00.000
For sending a signal from the MIKO-12-50A to move the OLTC to a new position, as well as to initiate measurements by the MIKO-12-50A when the OLTC is moved to a new position using its standard controls (for example, from the OLTC control panel). Length: 5 m.
HV and LV winding short-circuiting and connection cable
041.23.00.000
HV and LV winding short-circuiting and connection cable
041.23.00.000
Cables for working in DRM mode – non-intrusive testing of OLTC devices of power transformers.
Set of 4 cables of the same length of 4 m. Set weight – 6.180 kg (1.545 kg + 1.545 kg + 1.545 kg + 1.545 kg).
Both ends of the short-circuiting cable are terminated with crocodile clamps with a jaw 70 mm.
Shunt SV75-0075A-D-02
060.02.18.000
Shunt SV75-0075A-D-02
060.02.18.000
For checking the operability of the device. Value – 1 mΩ ± 0.5%. Manufactured by SKB EP.
Adapter for a reference coil
023.12.00. 000
Adapter for a reference coil
023.12.00. 000
For testing laboratories: inspection / calibration of the instrument (0.024 kg).
Recommended accessories:
Photo
Item, Index
Application
Manipulating rod
010.41.00.000К
Manipulating rod
010.41.00.000К
Manipulating rod is designed for test cables connection from the ground or from the tank cover to the bushings of high-voltage circuit breakers, and to the structural elements of high-voltage disconnecting switches and earthing devices, without the use of ladders or elevated platforms.
The manipulating rod is completed with special extension cables 3.3 m. There is a Kelvin clamp with current and potential contacts to connect to the object on one side, and a contact pad on the other side. The device test cable is connected to the contact pad from the ground or a tank cover.
Manipulating rod extension cable is made according to a four-wire (Kelvin) scheme with the test current capacity of 100 A in the presence of a good contact.
Manipulating rod - 2.2 (length 2.2 m / weight as an assembled set 3.4 kg);
Manipulating rod - 3.7 (length 3.7 m / weight as an assembled set 4.0 kg);
Manipulating rod - 5.1 (length 5.1 m / weight as an assembled set 4.6 kg).
Extension cable
010.41.08.000
Extension cable
010.41.08.000
An additional cable set for the manipulating rod's standard complete set, designed for simultaneous connection to 4 high-voltage object bushings.
Manipulating rod's extension cable (0.86 kg) is designed with the 4-wire scheme and has a test current capacity of 50 A.
Official reviews from customers based on the results of operating SKB EP instruments are available upon request. Please, fill out the form on the website.
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