DMF Relay Executive Summary


The DMF equipment has two basic component capabilities, 1) a fast and secure SSR generator protection relay, and 2) a high speed Digital Fault Recorder.


The DMF protection has two trip function, 1) steady state SSR detection and trip, and 2) fast transient resonant protection. The protection function measures the torsional velocity of the generator, and the generator voltages and currents.


The steady state protection uses digital methods to isolate the torsional responses of the turbine-generator. This protection detects unstable velocity response and has trip times coordinated with turbine-generator shaft fatigue capability, in the form of a time over-torque relay characteristic.


The fast transient protection is a new invention to provide very fast trip featuring both secure and dependable operation. This protection uses both velocity and acceleration measurements and uses the turbine-generator itself as the means to detect response without delay. Each mode is armed to trip based on exceeding a certain level of velocity. Trip is delivered based on a time over-acceleration function. Trip output from the DMF relay is typically available within one cycle of torsional frequency for worst cases. Lower responding acceleration events trip in correspondingly longer times. The trip is issued well before the peak transient response has been achieved, therefore limiting damage to the turbine-generator.


The Oscillograph DFR function is provided to allow quick evaluation of the SSR events for SSR severity and trip-point relative to local time and relative to event inception. The DFR provides event triggering based on relay targets, and based on conventional triggers for over and under voltage and current, and rate-of-change of response.


The DFR and DMF human interface is provided through a Windows 2000® computer equipped for Ethernet communication for enterprise-wide data access.



Cubicle Format DMF Module Front Panel


Cubicle Format DMF Module - Inside Front Panel View



Cubicle Format DMF Module - Rear Panel

Low Profile Panel Format, DMF Front Panel View - New Configuration Available 3Q 2004


Low Profile Panel Format, DMF Rear Panel View - New Configuration Available 3Q 2004

Maximum Capacity Configuration Shown

Detailed Specification


Analog Input Signals - up to 32 channels


Type                             - Differential

Isolation                       - 5000 volts

Bandwidth                   - 100 KHz

PT Secondary Voltage - 240v, short term 2 times rated max

CT Secondary Current - 5 amp, short term 20 times rated max

Other Analog Signals  - 10v nominal


Digital Inputs - up to 32 channels


            Type      – Single Ended

            Isolation – 250 volts


Digital Outputs – up to 8 relay outputs


            Type ‘C’ Form (NO/NC)


Analog to Digital Conversion


Bit resolution – 18 bits (14 bit converter, 4 bit AGC)

Sample Rate – 7200 Hz (120/144 samples per cycle at 60/50 Hz)

Anti-Aliasing Filter – 8 Pole, Linear Phase, Sample rate adjustable


Time Input Options


            NTP – TCP/IP three sources


            Satellite GPS Receiver


Host Computer


Operating Environment -Win2K

Processor - Pentium III 850 MHz

Memory - 256 M byte RAM

Storage - 16 G byte hard disk

Communications -10/100 Mb/s Ethernet

Enclosure - 4U 19” Rack Mounting

Local Human Interface – 6” diagonal LCD 800 by 600


Input Power


            AC 120/240 V AC 50/60 Hz

            DC 125V – 150 Watt




Operating Temperature Range - 0oC to 55oC

Non-Condensing Atmosphere


Applicable Standards


IEEE Standard C37.90.1, “ SWC requirements for fast transient immunity.”


IEEE Standard C37.90-1989 Section 8, “Requirements for dielectric withstand.”


IRIG Standard 200-95, “IRIG Standard Time Formats.” Telecommunications Working Group, Inter-Range Instrumentation Group, Range Commanders Council.


IEEE Standard C37.111-1999, “IEEE Standard Common Format for Transient Data Exchange (COMTRADE) for Power Systems.


IEEE Standard 1344-1995, “IEEE Standard for Synchrophasors for Power Systems.”


IEEE Standard C57.13-1993, “Standard Requirement for Instrument Transformers.”