Description

Resistance measurement in inductive and non-inductive circuits in the range of 1 μOhm ÷ 30 kOhm The MIKO-9A milliometer is developed to measure DC resistance in the range from 1 µOhm ÷ 30 kOhm for the current of up to 10А for: Windings of power and measurement transformers, windings of electric motors, generators, linear compensators and windings of other high-inductance equipment; Contacts of circuit breakers, resistors, buses and other inductance-free circuit Equalizing, current limiting and other resistors of high-voltage circuit bre­akers; Сables. The device provides a fully automated process of measuring the resistance of a high inductive load and compensation of thermoelectric power in the external circuit. MIKO-9 implements specialized measurement modes for various configurations of 10 objects (resistive object, inductive, voltage transformer, current transformer and power transformer, generator, motor, compensator, connection filter and magnet), taking into account their specific features. The device automatically takes into account the configuration of the object for setting measurement modes Automatic measurement of three-phase transformers Depending on the type of object, special measurement modes can be selected. For a resistive object, the modes are completely similar to the MIKO-8М(А), and for an inductive object, in addition to the two modes MANUAL and AUTO 1Ph, you can select AUTO 3Ph and 2 WINDINGS. AUTO 3Ph makes it possible to simultaneously connect to the three phases of the transformer and take measurements with automatic switching between them.This mode allows you to reduce the number of ascents and descents from the object. AUTO 1Ph and AUTO 3Ph modes have SKB EP patented automatic measurement method that guarantees results with the highest accuracy. It is achieved by setting the max current in the measure- ment circuit not on a staggered basis (depending on the value of the measured resistance), but continuously w/o fixed measurement ranges in a wide load range. This measurement mode provides high signal level in a complex electromagnetic environment of industrial production or substation. Moreover, in AUTO modes of the measurement process the instrument produces the highest current that enables guaranteed saturation of the transformer magnetic system. Simultaneous resistance measurement across 2 windings Depending on the type of object, special measurement modes can be selected. For a resistive object, the modes are completely similar to the MIKO-8М(А) device, and for an inductive object, in addition to the three modes MANUAL, AUTO 1Ph and AUTO 3Ph, you can choose - 2 WINDINGS. The resistance measurement mode simultaneously on two windings guarantees a quick and reliable measurement of the electrical resistance of heavy power transformers, in particular, with the connection of the secondary windings into a triangle, when using traditional methods does not give a stable result. The device indicates which phases should be connected to accelerate the measurement process, taking into account the distribution of magnetic fluxes in the magnetic circuit. In addition, the simultaneous measurement of two windings reduces the total number of measurements from 6 to 3. AUTO demagnetization mode Demagnetization mode is designed to eliminate the rem- nant magnetism of the transformer magnetic core. It is compulsory before open-circuit test, short-circuit loss measurement, transformation ratio measurement, etc. The instrument can be used for demagnetization of both single-phase and three-phase transformers. Magnetic core demagnetization requires alternating current applied to the corresponding winding bidirectionally. Demagnetization is performed automatically. Current decreases with each direction change. Each rod of a three-phase transformer is subjected to demagnetizntion. Current change is displayed at the same time in a graph form to control demagnetization accuracy. Demagnetization stops automatically when the current reaches threshold value or upon the User’s command Non-demountable estimation of the OLTC‘s (DRM test) OLTC in-place check mode allows the User to assess the state of the switching OLTC equipment with current limiting resistors without removing contactor tank cover. This mode involves measuring of instantaneous current drops. Test current firstly passes through the transformer winding and then through OLTC contacts at changing from one tap to another. The DRM graph is built on the basis of the 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 opening of fault-free OLTCs. Milliohmmeter mode and DRM test complement each other and provide the User comprehensive informa- tion about the transformer state. Heat run test The test is performed by continuous measurement and periodic result saving of the transformer winding R (recalculated to t°) during the cooling process of the winding. To receive the most reliable information about the max winding t° the User should connect the instrument to the winding and start the measurement immediately after the transformer heating is stopped. Berofe the start of the measurement process the User has to specify winding, phase, max measurement dura- tion, frequency of measurement results saving, winding R and t° under normal conditions. Correlation between the winding t° and the time can be represented in tabular or graphical form. The time is counted from the moment of the measurement start. Heat run test stops automatically on expiry of preset test duration or manually by the User. Various auto calculations and non-volatile memory MIKO-9A has a built-in archive of up to 200 measurements for viewing, copying or deleting data. And thanks to the possibility of choosing an object at the measurement stage, the results are presented more systematically. This facilitates interaction with the archive. The group of MIKO-7M(A), MIKO-8M(A) and MIKO-9(A) instruments has a number of automatic calculation functions: Auto δ calculation of Rphase between one another. Auto conversion of Rlinear to Rphase. Linear windings are Delta or Star / Wye (with no neutral) connected. Auto correction of R measured at t° to R at t°p. Auto δ calculation between Rcorrected and Rp. Auto calculation of t° by its R. High level of protection and safety conformity MIKO-9A has the safety certificate IEC 61010-1. The instrument also meets the requirements of electromagnetic compatibility that are applied to class A instruments according to IEC 61326-1. The instrument has a high degree of protection against: test cable or mains cable breakdown; excess of measuring current; emf of self-induction; overheat of the test block.. At disconnection of the measuring cable from transformer bushings or from the instrument as well as at disconnection of the mains cable from the mains in the course of measurement, emf of self-induction of up to several kV is generated in the disconnected circuit and the electric arc appears in the break point. MIKO-9A is characterized by the redundant protection against emf of self-induction in case of involuntary disconnection of the measuring cable or power cable protecting users from electric shock and the instrument from being damaged. Autonomy, touch display, remote control and bluetooth data transfer The instrument can be powered from the mains (110÷220, 330V) - model MIKO-9 - or from an built-in battery - MIKO-9A. 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. The instrument can be built into the testing systems under control of software complexes of test laboratories and equipment manufacturers. It is supported by Modbus RTU Protocol.
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