Home Products AutomationRTU 401tD3 Transformer condition monitoring and automatic voltage regulation

RTU 401tD3 Transformer condition monitoring and automatic voltage regulation

Transformer monitoring and control system RTU401D3 & RTB12


General information

Power transformer is basic equipment in the Transmission and Distribution Network objects and requires the application of powerful Monitoring and Control Systems (MCSs). The MCS is developed and intended for medium and large oil immersed Power Transformers. The set provides safe, reliable, easy to use and cost effective power transformer condition monitoring and automatic voltage regulation with the following basic features:

  • Electrical and technological parameters measuring, processing and monitoring;
  • Automatic Voltage Regulation (AVR) for Single/Parallel operating Power Transformers;
  • Smart cooling system control;

MCS offers a modern Decentralized architecture with Central unit (CU) of type RTU401D3 placed in the Control room and Local units (LUs) of type RTB12 and Merging units RTB20 (optional) both placed in a cabinet near the Power Transformer.

Two types of local level architecture are available:

  • RTB12 with DC inputs (PT100, ±20 mA, 4÷20 mA inputs, thermocouple), AC current/voltage inputs, BIs, BOs and FO communication with CU
  • RTB12 with DC inputs (PT100, ±20 mA, 4÷20 mA, thermocouple), AC current/voltage inputs, BIs, BOs, FO communication with CU and Merging unit (optional) with AC currents/voltage inputs from CTs and VTs and FO Ethernet Process bus communication with CU.

Monitoring and control

Temperature monitoring

  • Ambient temperature
  • Transformer top oil temperature
  • Transformer bottom oil temperature
  • Calculation (IEC 60076) and monitoring of the winding Hot spot temperature
  • Transformer loss of life calculation(IEC 60076) and monitoring
  • OLTC oil temperature monitoring
  • Transformer operating hours monitoring

Technological parameters monitoring

  • Transformer oil pressure
  • Dissolved Gases in the oil
  • Transformer oil level
  • OLTC oil level
  • Moisture in oil content

OLTC/Motor drive unit (MDU) monitoring

  • Current through the OLTC contacts
  • OLTC contacts loss of life
  • MDU torque
  • OLTC runtime

Cooling system monitoring and control

  • Pumps and fans on/off position and operating hours monitoring
  • Oil pumps smooth control
  • Fan groups smart control


  • Statistic
  • User defined logical equation for limits monitoring

Voltage regulation functions

  • Automatic/Manual OLTC control of a single transformer
  • Automatic/Manual OLTC control of parallel operating transformers

The current position of the OLTC is measured via RTB12 in diferent ways:

  • Digital signals via BCD code
  • Analogue signals
  • Resistance measurements in different ranges (0 … 200 Ω / 2 kΩ)


Disturbance (Fault) Recorder

  • Sampling rate – 1 kHz/4kHz
  • User defined trigger conditions and records duration
  • Recording mode -overwrite (ring buffer) or saturate
  • File format - COMTRADE

Data Logger

  • Sampling rate – 50 Hz / 10 Hz / 1 Hz
  • User defined trigger conditions and records duration
  • Recording mode - overwrite (ring buffer)
  • Type of records - each sample contains RMS values of all selected analog values
  • File format - COMTRADE

Event Recorder

  • Up to 1000 records
  • Event type - pick-up current/voltage, elapsed time and time stamp (year, month, day, hour, minute, second, millisecond)
  • Recording mode – overwrite (ring buffer)

CU communication protocols and time synchronization

  • SCADA communication protocols - IEC 61850, IEC 60870-5-103, IEC 60870-5-104, MODBUS
  • Time synchronization - PTP (IEEE 1588), NTP / SNTP, IRIG-B or PPS
  • File system access – FTP
  • Web-based interface - HTTP

Configuration, settings and administration


  • PC based configuration and setting tool - ROCON MMI program
  • Web server