On the base of our knowledge and experience we produce equipment to perform diagnostic measurements of the transformer as well as to control its operation.


WP-EC indicators are devices designed to detect the position of the on-load tap changers (OLTC). Their modern design allow to use them in any type of OLTC as well as in many configurations.

The family of WP-EC devices covers:

– Mechanical contact matrix
– 7-wire BCD encoder MKEC-1
– 5-wire BCD encoder MKEC-2
– Universal encoder BCD/RS-485 MKEC-3
– Universal OLTC position transmitter NWP-EC 03
– Receiver WP-EC 01-2a supporting RS485 01-2
– Receiver WP-EC 01-4a operating in BCD code
– Receiver WP-EC 02 operating in BCD code


The NWP-EC transmitter is an electronic device based on a 10 bit digital optoelectronic encoder. This solution means that the device is not limited to discreet tap positions, constant maximum number of positions or division of angles between the positions. In the programming process NWP-EC 03 can be adapted to any number of tap positions as well as the direction of change or division of angles. NWP-EC 03 transmits the position of OLTC in the form of a BCD binary code and is also equipped with a two-direction RS-485 port.

OLTC position detectorOptoelectronic matrix ± 0,7º
Communication with external devicesBCD, RS485
Power+24V DC
Output parameters BCD230V AC/DC, 1A contact
Transmission parameters RS485 1200 b/s, 8 bit, 1 bit stopu, parity: none

RECEIVERS WP-EC 01-2a and WP-EC01-4a

The design of the receivers is based on single-chip industrial microcontroller providing wide opportunities to adapt the device via software, having high reliability in operation in the power network environment. Large microcontroller capabilities allow to obtain additional benefits related to the acquisition of data on the OLTC operation, which can be used e.g. for the analysis of faults. The device is equipped in data transmission protocols that facilitates communication with external systems via RS-485 port. DNP 3 transmission protocol enables the transmission of data using the EX system.

Additional functions:

  • Global switchovers counter “Cg” (indicates the total number of switchovers counted by the indicator and the date from which the counting was started)
  • Resettable switchovers counter “Cr” (indicates the number of switchovers since the last overhaul and date of last reset)
  • Date and Time
  • History of the last switchovers  (shows direction of the change, the tap number and the exact time of the operation)
  • Operation statistics (shows the percentage of the transformer operation time on individual taps during the last 24-hours)
  • Fully customizable protection against unjustified switching to the tap other than specified
  • Possible safety mode against under- and overvoltages
  • Voltage measurement with digital visualization (voltage measured on 100 V voltage-transformer)
  • OLTC drive protection against unjustified switching to a higher tap
OLTC position detectorNWP-EC 03 BCD/RS 485NWP-EC 03 BCD/RS 485
Switchover counterDigital with registry to FLASH
FLASH memory capacity128 kB/5000 occurrence
Communication with external deviceRS 485 / BCD connection circuit
Transmitter output power24V DC stabilized
Receiver power230V AC/DC +20% / - 30%


WP-EC 02 is a device decoding the OLTC position information received in BCD code and visualizing it in a digital form on the LED display. Due to the simple construction it is cheap and reliable in service. WP-EC 02 can be operated with a transmitter NWP-EC 03 as well as with any other suitable source of the BCD signal (diode matrix).

OLTC position detectorsNWP-EC 03 BCD/RS 485
Communication with external deviceBCD
Transmitter output power24V DC Stabilized
Receiver voltage230V AC/DC +20% / -30%


Encoders MK-EC are devices based on industrial microcontrollers immune to electromagnetic interferences allowing for reliable operation in conditions of electric power facilities. They are used to encode a signal from the contact matrix of the tap changer drive to BCD or RS485 code. Compared to traditional diode matrix it is supplemented with a RS485 serial communication module making it possible to reduce the number of cables for communication of transmitter and receiver.


The encoder of the OLTC tap position type MK-EC is designed to work with any OLTC drives containing contact disc mapping the tap number with wires leading from each contact. It is particularly suitable to drives with an untypical value of rotation angle of the contact disc per each tap and in the case of ambiguity in the mapping of tap numbers on contact disc (i.e. change of two contacts results in a change of one tap). The encoder MK-EC is designed to be installed inside the drive cabinet on the DIN rail.

OLTC position detectionDiode matrix BCD and RS485
Transmitter power supply+24V DC (from WP-EC 01); from +12 to +24V DC (from other sources)
Operating temperature range-15 ... 50°C
Storage temperature range-30 ... 55°C
Relative humidityUp to 80%


MT-3 with new technical solutions simplifies and speeds up the measurement process. The device contains relay matrix and 12-wire measurement cable for full automation of measurement for the most common transformers (there is no need to modify the measurement system – no reconnecting of cables). Selection from the control level the measurement of a certain parameter (e.g. winding resistance or ratio) switches to  proper connection setup and measurement conditions. The remote control of OLTC allows to automatically repeat the measuring procedure on all taps. An interesting feature of the MT-3 is a three-phase measurement of ratio and magnetizing currents, which significantly reduces the time of measurements.

MT-3 is equipped with a protection of measurement systems against surges caused by the circuit interruption during winding resistance measurements. The method used to connect the measuring cable to the transformer terminals and measuring box minimizes the risk of accidental circuit opening, and applied electronic protection eliminate the risk of damage!


The topology of MT-3 measuring systems is based on the circuits designed and manufactured by B&C Diagnostics specifically for use in the diagnostics of transformers. This has provided a significant increase in the measurements accuracy and elimination of an additional external source for measuring the resistance of windings (for measurement of a very small resistance, it is possible to use additional forced current up to 50 A).

MT-3 is operated with external computer equipped with dedicated control software and system for the acquisition, analysis and data visualization. This approach provides a significant reduction in size and weight of the device. Communication between the MT-3 measuring system and the PC is realized via LAN using TCP/IP or IPX protocols. As a result it is possible to use for the measurements any PC equipped with a network card and working under Windows 98/2000/XP/7.


On the basis of the rich experience gained during the operation of the previous sets of MT family we developed the software that allows for efficient measurements of individual parameters, their analysis and results evaluation. Among other things, there is automated process of calculating deviations and errors, converting temperatures and also the comparison of the measured values ​​with the test card or the results of previous measurements. It is possible to compare the registered characteristics when switching OLTC, which allows for determining its condition.

Functions of MT-3:

  • Graphical interpretation of results
  • The report of the measurements
  • Comparison of measurement results with values ​​from the database (test card, previous measurement)
  • Converting the results of the resistance measurements to any temperature
  • Calculating the average value when measuring the resistance and the calculation of the maximum deviation from the mean
  • Reporting application allowing for filling up the protocol with measurements performed with other devices (insulation resistance, dielectric losses coefficient tgδ)
  • Measurements file in Excel format
  • The database of transformers and test results
Measurement of motor drive inherent delay
Measurement of power switch time
Resolution measurement time 0,1 ms
Winding resistance measurement
Technical method in accordance
PN-81/E-04070.05 standard
Scope of measurement 0,001 Ω - 100 Ω
Resistance precision measurement 0,2%
Voltage and current precision measurement 0,1%
Measurement of transformer ratio in accordance
with PN-81/E-04070.06 standard
Measurement precision of transmission 0,2%
Magnetizing current measurementPrecision of current measurement 0,2%
Scope of operation temperature-15 ... 45ºC
Personal computerPC LAN (IPX or TCP/IP protocol)
Supply voltage230V AC +10% -20%
Weight8,5 kg