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Multilin 745

The 745 Transformer Protection System is a full featured transformer protection relay, suitable for application on small, medium, and large power transformers. The 745 can be applied on two-winding and three-winding transformers. Uses multiple current and voltage inputs to provide primary protection and back-up protection of transformers, including differential, ground differential phase, neutral, and ground overcurrent, over-fluxing, and on-load tap changer.


Key Benefits

  • Easy to use Transformer Protection supported by industry leading suite of software tools

  • Improved security for transformer energization

  • Accurate built-in metering functions

  • Advanced FlexLogic automation capabilities

  • Fast, flexible and reliable communications

  • IRIG-B time synchronization, event reports, waveform capture, data logger

  • Built in simulation features for setpoint verification

  • Modbus and DNP 3.0 Level 2 protocols through embedded Ethernet, standard RS232, RS485 & RS422 serial ports.

  • Optional conformal coating for chemically corrosive and humid environments

  • Security Audit Trail provides detailed traceability for system configuration changes

  • Minimize maintenance time with draw-out capability


  • Primary and back-up protection and management of small, medium and larger power transformers, autotransformers and reactors

  • Transformer asset monitoring using Hottest Spot, Loss-of-Life and Aging Factor

  • Stand-alone or component in automated substation control system Protection and Control

Protection and Control

Key Features

  • Variable dual-slope percent differential protection

  • Magnetizing inrush and overexcitation blocking

  • Phase & ground overcurrent elements

  • Overcurrent using Adaptive time FlexCurves elements

  • Underfrequency/Overfrequency Protection

  • Frequency rate-of-change Detection

  • Overexcitation (V/Hz) Protection

  • Restricted Ground Fault Protection

  • Transformer overload protection

Protection and Control
The 745 Transformer Protection System is a full featured transformer protection relay, suitable for application on small, medium, and large power transformers. The 745 can be applied on two-winding and three-winding transformers, and can be applied on transformers with breaker-and-a-half source terminals. Multiple current and voltage inputs are used to provide primary protection, control and back-up protection of transformers, including current differential, Restricted Ground Fault neutral, and ground overcurrent, over-fluxing, and on-load tap changer. The 745 also has specific features for industrial environments, including a drawout case to limit downtime during maintenance and conformal coating for harsh environments. The 745 also includes analog inputs and outputs, while incorporating advanced features such as transformer loss of life monitoring.

Monitoring & Metering

Key Features 


  • Metering - current, voltage, sequence components per winding, power, energy, voltage

  • THD and harmonics up to the 21st

  • Expanded (doubled) sequence of event recorder and waveform capture (256 time stamped events and up to 128 cycles of oscillography data at a sampling rate of 64 samples per power cycle)

  • Tap position up to 50 tap positions

  • Ambient temperature /analog transducer input

  • Analog transducer input

  • Oscillography & Data Logger - 10 records up to 32 power cycles

  • Simulation mode and playback capability.

  • Monitoring & Metering 


Monitoring & Metering
The 745 features advanced metering functions including:


All current inputs feature harmonic level detectors. A sampling rate of 64 times the power cycle allows recovery up to the 21st harmonic. Total Harmonic Distortion (IEEE.519-1986) or Harmonic Derating Factor (as per ANSI/IEEE C57.110-1986) are calculated for each winding and compared against user-adjustable setpoints.

Asset Monitoring

745 can monitor, calculate and log hottest-spot temperature, aging factor and lost of life data over a long period. These data combined with economic analysis, allows criteria to be developed regarding the best time at which to replace a power transformer due to load growth, i.e. to minimize the cost without significantly increasing the risk.


Event Recording

The last 128 events are captured and stored, recording the time, date, cause, and system parameters of each event. This information is easily accessible by computer via communication port or the front panel display.

Tap Position, Ambient Temperature, Analog Transducer-Input
The 745 monitors and displays tap position and ambient temperature. An optional general purpose transducer input allows a user-defined quantity to be monitored and used as part of the protection as defined by FlexLogic™.


Simulation Mode
Simulation Mode allows testing the functionality of the relay by simply feeding arbitrary waveform data into the relays simulation buffer for playback as sampled current input signals.

Fault Recording
System input signals are sampled at a rate of 64 times the power cycle. Because all the signals are sampled at the same instant in time the magnitude and phase relationship of each can be compared. 
A combination of 16 pre and post-trigger cycles can be saved.


Advanced Automation

The 745 incorporates advanced automation features including powerful FlexLogic™ programmable logic, communication, and SCADA capabilities that far surpass what is found in the average line relay. The 745 integrates seamlessly with other relays for complete system protection.


Key Features

  • Networking interfaces - 10Mbps Ethernet, RS232, RS485 and RS422 ports

  • Ethernet port, 10Mbps

  • Multiple protocols - ModBus™ RTU, ModBus™ RTU TCP/IP, DNP 3.0 Level 2

  • Fast, flexible and reliable communications - Embedded 10BaseT Ethernet capability provides faster data transfer thus improves system performance


Advanced Communications      
The 745 is equipped with three standard serial communications ports, one RS232 located in the front panel, and two RS485/RS422 in the rear of the relay. One optional Ethernet port is available at the rear of the relay. The front panel port allows easy local computer access. The rear ports provide remote communications or connection to a DCS, SCADA, or PLC. The baud rate of all the ports is variable from 300 to 19,200 bps. The optional Ethernet port can be used to connect the 745 to 10 Mbps Ethernet networks. The 745 supports ModBus® RTU, DNP3.0 Level 2, and ModBus® RTU TCP/IP protocols.

The three serial ports support ModBus® RTU protocol, while either of the two rear ports can be configured to support DNP 3.0 Level 2. The optional Ethernet port supports ModBus® RTU via TCP/IP protocol. The communication system of the 745 is designed to allow simultaneous communication via all ports.

Using Ethernet as the physical media to integrate the 745 to Local or Wide Area Networks, replaces a multidrop-wired network (e.g., serial Modbus®), and eliminates expensive leased or dial-up connections, reducing monthly operating costs.
User Interface      
Various user interfaces facilitate operation of the 745.

A 40 character display allows access to setpoints, actual values, and diagnostic messages generated by a trip or alarm condition. The45 can display 30 user-selected messages during keypad inactivity.

Twenty LEDs indicate relay status, system status, and trip and alarm conditions.

IRIG-B Input
This feature provides time synchronization via standard GPS clock inputs.



EnerVista Software

The EnerVista™ Suite is an industry-leading set of software programs that simplifies every aspect of using the 745 relay. The EnerVista™ suite provides all the tools to monitor the status of the transformer, maintain the relay, and integrate information measured by the 745 into DCS or SCADA monitoring systems. Convenient COMTRADE and Sequence of Events viewers are an integral part of the745 Setup software included with every 745 relay, to carry out post-mortem event analysis to ensure proper protection system operation. 


Multilin 845 Brochure

Multilin 845 Manual

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