DEIF DU-2/MKIII 3-Phase Synchronizing Relay – Supports Dead Bus, Live Line & Island Mode Operation
Description
The DEIF DU-2/MKIII is a digital automatic synchronizing unit designed for precise and safe connection of generators to live busbars or other power sources in marine,industrial,and utility applications.As part of DEIF’s renowned Generator Control&Protection product line,the DU-2/MKIII(also known as the Synchronizing Module MKIII)ensures smooth,low-stress closure of circuit breakers by matching voltage magnitude,frequency,and phase angle between the incoming generator and the target system.
Unlike basic synchro-check relays,the DU-2/MKIII actively controls engine speed(via contact outputs to governor)and excitation(via AVR interface)to achieve synchronization automatically—eliminating manual operator error.It supports multiple operating modes:
Dead Bus Synchronization(black-start)
Live Line Synchronization(to grid or another generator)
Island Mode Detection(with vector shift protection)
The unit features a built-in digital synchroscope display,real-time LED indicators for“Fast/Slow”and“High/Low”conditions,and configurable closing windows(e.g.,±2°phase,±0.1 Hz frequency difference).Once synchronization criteria are met,it issues a breaker close command with predictive timing to minimize transient stress.
Certified to IEC 60255 and widely used in DNV-GL,ABS,and Bureau Veritas-classed vessels,the DU-2/MKIII also includes integrated protection functions such as over/under voltage,over/under frequency,and vector shift—making it a compact all-in-one solution for generator control panels.
Application Scenarios
On a North Sea offshore supply vessel,two 1.5 MW diesel generators must synchronize seamlessly during dynamic positioning operations.The DEIF DU-2/MKIII units continuously monitor both generators and the ship’s bus.During a sudden load surge,Generator#2 auto-synchronized within 8 seconds—matching phase within±0.5°—preventing blackout and maintaining thruster control.The crew reported zero mechanical shock on the coupling,extending engine life and reducing maintenance costs.
Parameter
Main Parameters Value/Description
Product Model DU-2/MKIII
Manufacturer DEIF A/S(Denmark)
Product Category Digital Automatic Synchronizing Unit/Generator Synchronizer
Application Generator synchronization to bus/grid in marine,industrial,and standby power systems
Input Voltage(Generator&Bus)3-phase AC,100–690 VAC(phase-to-phase),50/60 Hz
Frequency Range 40–70 Hz(configurable)
Voltage Measurement Accuracy±0.5%
Frequency Measurement Accuracy±0.005 Hz
Phase Angle Accuracy±0.2°
Synchronization Window(Configurable)
•Phase:±1°to±10°
•Frequency diff:±0.02 to±0.5 Hz
•Voltage diff:±1%to±10%
Output Contacts
•Speed Up/Speed Down(for governor)
•Raise/Lower Voltage(for AVR)
•Breaker Close Command
•Alarm/Trip Relays
Display Backlit LCD with digital synchroscope,voltage/frequency bars,and status icons
User Interface 4-button navigation+rotary encoder for setup
Communication MODBUS RTU(RS-485)–optional;standard on later firmware versions
Protection Functions
•Over/Under Voltage(ANSI 27/59)
•Over/Under Frequency(ANSI 81O/81U)
•Vector Shift(ANSI 78VS)
•Synchro Check(ANSI 25)
Enclosure Panel-mount,IP65 front protection(when installed)
Operating Temperature–25°C to+70°C
Power Supply 24–240 VAC/VDC(universal,auto-ranging)
Dimensions~144 mm(W)×144 mm(H)×170 mm(D)–fits standard 144×144 mm panel cutout
Weight~1.1 kg
Certifications IEC 60255,DNV-GL,ABS,Bureau Veritas,CE,RoHS
Technical Principles and Innovative Values
Innovation Point 1:Closed-Loop Synchronization–Actively adjusts generator output via discrete contacts,not just monitoring—enabling true“hands-off”sync.
Innovation Point 2:Predictive Breaker Closing–Compensates for breaker operating time to close at exact zero-phase crossing.
Innovation Point 3:Multi-Mode Flexibility–Seamlessly handles islanding,reconnection,and black-start scenarios.
Innovation Point 4:Built-In Protection–Eliminates need for separate relays,reducing panel complexity and cost.
Application Cases and Industry Value
In a Caribbean island microgrid,three DU-2/MKIII units manage diesel generators feeding a 11 kV distribution network.During daily cloud cover events that reduce solar output,the DEIF units auto-synchronize backup generators within 10 seconds—maintaining grid stability without customer outages.
Similarly,a U.S.data center uses DU-2/MKIII for N+1 UPS bypass testing.The precise phase matching prevents inrush currents that could trip upstream breakers—ensuring Tier IV availability.
Related Product Combination Solutions
DEIF AGC-4 or AGC-5:Automatic Generator Controllers–for full genset management
DEIF AVR(e.g.,AVR-150):Automatic Voltage Regulators–interfaced via raise/lower signals
Governor Actuators:e.g.,Woodward,ComAp–controlled via speed up/down contacts
Circuit Breakers:Air or vacuum breakers with<60 ms close time for optimal sync
Power Meters:e.g.,DEIF PPU-3/4–for load sharing and power monitoring
SCADA Systems:Via MODBUS RTU for remote sync status and alarms
Redundant Synchronizers:Dual DU-2/MKIII units for critical applications
Test Benches:e.g.,OMICRON CMC–for validating sync logic during commissioning
Installation,Maintenance,and Full-Cycle Support
Installation of the DEIF DU-2/MKIII:
Mount in standard 144×144 mm panel cutout
Connect generator and bus VT signals(3-phase each)
Wire governor and AVR control contacts
Connect breaker auxiliary feedback
Configure sync windows and protection settings via front panel
Optional:Enable MODBUS for SCADA integration
Maintenance features:
Self-diagnostics on startup
Event log(last 100 sync attempts)
Calibration-free solid-state design
Field-upgradable firmware(via service port)
We supply DEIF DU-2/MKIII units that are:
Genuine new from DEIF or professionally refurbished/tested
Fully validated with simulated generator/bus waveforms
Supplied with terminal blocks,gasket,and user manual
Backed by technical support from DEIF-certified engineers
With decades of experience in power generation control and global logistics,we ensure your synchronization system delivers reliability,precision,and compliance—every time the breaker closes.
Contact us for a turnkey solution—whether you’re building a new genset skid,upgrading a marine switchboard,or securing spares for your critical power infrastructure.
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