DTRV-EP

 EuroProt familija
COMPLEX DIGITAL PROTECTION FOR 120 kV/MEDIUM VOLTAGE TRANSFORMERS
 
The complex digital protection for 120 kV/medium voltage transformers of type DTRV-EP is part of device family named EuroProt. This short description contains special data of this type. General and common features of EuroProt family can be found in the EuroProt system information sheet. Accordingly it is proposed to study both this short description and system information sheet too, in order to understand the device entirely.
 
DTRV-EP
 
Application field
 
The DTRV type of complex transformer protection is designed to protect 120 kV/medium voltage transformers, mostly of oil isolated types, used allover the generation, transmission and distribution field, and to perform automatic regulation and control tasks. All usual transformer protection functions (differential protection, phase and earth fault protection, overload protection, breaker failure protection and other backup protection) are realised, including all control functions and some regulation functions as well. The intelligent programmable tripping matrix scheme offers high level of flexibility for engineering and operation. The full or partially independent operation of its individual functions and the built-in multiple self-checking system increases reliability of the protection system. Because of the different voltage levels at the medium voltage side, combined different the neutral grounding practice of the medium voltage networks, and the structure of the transformers with secondary and tertiary windings, and additionally the many possible substation configurations and number of parallel transformers for one voltage level, there are many variations and combinations of the protection functions.
 
Main characteristics
 

The DTRV-EP digital generator and generator-transformer unit protection is a complex system, consisting several cooperating microprocessor-based units of the EuroProt product family.

  • The complex protection system contains all protection and control functions needed for transformers, except the 120 kV bus-bar and breaker failure protection, assigned to many power system elements, and the transformer event driven switch-over relay (called ETRA) These latter functions are realised with auxiliary protection
  • all elements are fully numeric type
  • it has distributed structure, which means for example, that a complex protection can contain four EuroProt units, independent, separately supplied and individually housed:
    • DTD-EP+ (DTRV-EPI) multi-function differential protection
    • DTRV-EP2 containing mostly the high voltage side protection functions
    • DTRV-EP3 for medium voltage side functions, and
    • DTSZ2-HA-EP type automatic voltage regulator
  • main functions ofDTD2-EP (DTRV-EP1) numerical differential protection are:
    • collection of trip signals from the mechanical type transformer protection
    • transformer differential protection
    • overcurrent protection for the 120 kV side
    • overcurrent protection for the medium voltage side
  • DTRV-EP2 digital device serves mainly the 120 kV side:
    • collection of trip signals from the mechanical type transformer protection
    • two stage definite time overcurrent protection for the 120 kV side
    • protection against breaker discrepancy
    • starting the 120 kV breaker failure protection
    • collection of trip signal from the auxiliary 120 kV bus-bar protection and breaker failure protection
    • collection of ON and OFF commands from auxiliary event driven switch-over relay (called ETRA)
    • collection of manual ON and OFF commands
    • overcurrent protection for the auxiliary neutral grounding transformer
    • self-checking functions, supervision of the 120 kV circuit breaker command circuits, current transformer circuits, 20 kV status signal errors, power supply errors, EEPROM failures, power supply disturbances, DSP errors
  • the functions ofDTRV-EP3 digital device serve mainly the 20 kV side:
    • two stage definite time overcurrent protection
    • logic type bus-bar protection
    • dead zone protection
    • breaker failure protection for the transformer
    • breaker failure protection for the circuit breakers in the bays
    • automatic reclosing function
    • two stage definite time zero sequence overcurrent protection, for the neutral resistor (called FANOE, which increases the ground fault current to a detectable level)
    • oil temperature protection for the FANOE neutral resistor, and its breaker failure protection
    • automatic controller for the neutral resistor switching ( called FAVA)
    • Uo> relay
    • possible mode of operation in case of live line working (called FAM) (loFAMI relay function)
    • comprehensive self-supervision and monitoring of CB operating circuit, 20 kV status signals current transformer circuit supervision for the 20 kV side, EEPROM failures, power supply disturbances, DSP errors
  • optionally for 10 kV secondary voltage level:
    • two stage definite time overcurrent protection
    • backup impedance protection with three zones in forward direction and one in reverse direction, individual timers for all stages
    • logic type bus-bar protection
    • dead zone protection
    • breaker failure protection for the transformer
    • breaker failure protection for the circuit breakers in the bays
    • automatic reclosing function
    • two stage zero sequence definite time overcurrent protection, supplied by the FANOE resistor (oil isolated resistor for increasing the ground fault current to a detectable level)
    • two phase overcurrent protection for the auxiliary neutral grounding transformer
    • Uo> relay
    • supervision of the circuit of logic bus-bar protection
    • comprehensive self-supervision and monitoring of CB operating circuit, 10 kV status signals, current transformer circuit supervision for the 10 kV side, EEPROM failures, power supply disturbances, DSP errors
  • Intelligent trip matrix in alI of the devices mentioned above. In this way all protection functions can be enabled or disabled, and the commands can be directed to the appropriate output relay
  • the rows of the trip matrix can be disabled individually
  • the signals received via opto-coupler inputs by the devices EP2 and EP3 can be enabled or disabled by bit parameters
  • the advantage of the distributed structure is, that in case of failure of one device the others may remain in operation
  • the distributed structure offers backup protection scheme
  • the distributed structure supports easy tests of the relay functions

Software characteristics:

  • built-in self check functions
  • digital event recorder for 50 event, event sequence recording with'I ms time resolution for max. 300 events
  • analog event recorder for short-circuit current and voltage data
  • intelligent digital function matrix

Hardware characteristics of individual devices:

  • fully numerical type, with individual A/D converters, digital signal processors (DSP) and separate main processor
  • opto-coupler inputs
  • output contacts
  • type of output contacts (NC, NO) can be selected at design time
  • design for 19" rack cabinets

Communication:

  • relay setting with 2xI6 character LCD display, suitable also for text messages and for event log display
  • on-line screen of auxiliary PC for support of commissioning
  • auxiliary communication connection selectable for RS 232 or fibre optic cable
  • optional SCADA connection with IEC 870 protocol
  • parameters can be saved and saved parameters can be downloaded again
  • real-time clock with battery-fed RAM, (which can be synchronised via fibre-optic connection by auxiliary PC, by the SCADA system, or via opto-coupler digital input)
Principle of operation
 

The simplified principle of operation of the units in a typical DTRV complex protection:

DTD2-EP (DTRV-EP1) digital differential protection

  • The differential protection for the transformer is performed by a DTD2-EP type digital transformer differential protection. The main characteristics of this differential protection is summarised in a separate description
  • The protection is immune to the inrush current of the transformer. The operating time is 25-30 ms, in case of starting the high-set current stage about 15-20 ms. The protection contains an intelligent trip matrix, so the trip command can be directed to the appropriate output relay
  • The DTD2 type transformer differential protection performs the protection functions needed for a transformer independent of the other units, so the racks of the cabinet can be considered as backup protection for each other
  • The protection collects the signals of the mechanical protection of the transformer. There is an overcurrent protection configured for the 120 kV and medium voltage side, which is single stage in DTD2-EP for 120 kV, and two stage for the medium voltage level. In this way the appropriate reserve backup protection is provided.

Operation of DTRV-EP2 complex digital transformer protection

  • The device contains a two stage definite time overcurrent protection for the 120 kV side
  • In case of transformers fed by a radial line, the phase selective protection and automatic reclosing function is included as well
  • The protection against breaker discrepancy protects against single or two-phase continuous operation in case of 120 kV circuit breakers operated individually in the phases
  • It starts the 120 kV breaker failure protection, and collects the trip signals form the 120 kV bus-bar protection and from the 120 kV breaker failure protection
  • With an independent contact it gives command to the auxiliary ETRA automatic controller
  • Collects the trip and closing command from ETRA, and if the preconditions are fulfilled, they are passed to the CB
  • Collects manual ON and OFF commands
  • The device contains the two-phase overcurrent protection function for the neutral grounding transformer (in phases R and T)
  • There is a large display at the left side of the front panel
  • This device collects the signals of the mechanical protection of the transformer as well (two Buchholz (gas) relay, oil temperature and winding temperature protection, over-pressure protection for the transformer tap changer, protection for the neutral grounding transformer, and for the Petersen coil)

Operation of DTRV-EP3 complex digital transformer protection in case of 20kV version

  • The first stage (I>>t) of the definite time overcurrent protection for the 20 kV side in the deviceprotects the bus-bar and the connected power elements
  • The logic bus-bar protection provides selective and quick protection for the individual bus-bar sections
  • In case of failures of the circuit breaker in the bays the breaker failure protection function in DTRV trips the CB supplying the short-circuit
  • The second, low set stage (I>t) of the definite time overcurrent protection for the 20 kV side provides remote backup protection for the bays
  • The dead zone protection function of the device for the 20 kV side gives trip command in case of faults between the current transformer and the CB
  • The 20 kV transformer breaker failure protection trips the 120 kV circuit breaker, in case the 20 kV CB fails to trip, because of the failure of the operating circuit or of the CB itself
  • The high set stage of the zero sequence definite time overcurrent protection connected to the current transformer of the resistor for increasing the earth-fault current (FANOE) has two time stages. The first stage serves as remote backup protection for the 20 kV bays, the second stage is the reserve protection for the transformer and the bus-bar
  • The second stage of the zero sequence low set overcurrent protection (FAMI 3Io>> of FANOE gives an enabling signal in case of live line working to the "FAM" circuit after the time delay
  • The zero sequence Uo> overvoltage function controls the operation of FAV A automatics, and in case of live line working it starts the tUo>FAM time measuring, and serves in all modes of operation as backup protection
  • This device contains the temperature logic for F ANOE and the breaker failure protection for FANOE
  • This device contains the automatic control function of the resistor for increasing the earth-fault current (FAVA)
  • This automation function is controlled by the zero sequence overvoltage function (Uo>>, supplied by the voltage transformer connected to the 20 kV side of the transformer
  • This device can give a starting command to the external ETRA with an independent dedicated contact
  • The operation of the 20 kV single shot reclosing controller is initiated by external or internal signals. According to the primary structure, the device can operate one or two circuit breakers
  • There is a large display at the left side of the front panel

Operation of DTRV-EP3 complex digital transformer protection in case of 10kV version

  • The first stage (I>>t) of the definite time overcurrent protection for the 10 kV side in the device protects the bus-bar and the connected power elements
  • The logic bus-bar protection controls the operation of the 10 kV underimpedance protection
  • This device contains the overcurrent function for the neutral grounding transfromer. This protection is connected to two phases (R, T)
  • The device contains a four stage underimpedance protection, with independent time setting for each stages.Three of them is directed forwards and one in reverse direction (toward the transformer)
  • The dead zone protection function of the device for the 10 kV side gives trip command in case of faults between the current transformer and the CB
  • The 10 kV transformer breaker failure protection trips the 120 kV circuit breaker, in case the 10 kV CB fails to trip, because of the failure of the operating circuit or of the CB itself
  • The two stage zero sequence definite time overcurrent protection connected to the current transformer of the resistor for increasing the earth-fault current (FANOE protects the 10 kV bus-bar as main protection in case of earth faults, and serves as backup earth fault protection for the bays
  • There is a zero sequence overvoltage function in the device for signalling earth faults, which calculates the zero sequence voltage based on the phase voltages of the 10 kV voltage transformers. This function has a signalling role only
  • The 10 kV breaker failure protection function of this device trips the circuit breaker supplying the short-circuit, if the 10 kV bay circuit breaker fails to trip
  • This device can also give a starting command to the external ETRA via a dedicated contact, similarly to DTD2-EP and DTRV-EP2. The output contact for starting ETRA is controlled by the appropriate column of the trip matrix. The trip and close command for ETRA is handled by DTRV-EP2 device, and passes it to the CB
  • The basic version of the single shot automatic 10 kV reclosing function can handle selectively both 10 kV CB-s connecting two independent bus-bar sections of the same voltage level
Technical data of individual devices
 
Rated secondary current, In
 1 A or 5 A
Rated secondary voltage (line-to-line), Un 100 V or 200 V
Rated frequency
 50 Hz or 60 Hz
Overload capacity, voltage circuit, thermal, continuous
current circuit, thermal, continuous
1s 		2xUn/Ö3
4xIn
100xIn (In=1 A), 50xIn (In=5 A)
Dynamic current limit 100xIn
Accuracy of digital impedance protection functions (above 50% In)
Accuracy of digital current protection functions (above 50% In)
Accuracy of timers
 ± 5%
± 2%
± 3 ms (steps 10 ms)
± 12 ms (steps 1 s)
Drop ratio of current relays 95%
Output relay contacts type
 as requested
Output contacts, electrical data:
rated switching voltage
continuous load current
making current
DC breaking capability at 220 V,
at pure conductive load
at load of L/R = 40 ms
Optionally, at load of L/R = 40 ms
250 V
8 A
16 A

0,25 A
0,14 A
4 A
Auxiliary DC voltage (the same supply unit)
voltage tolerance
 220 V or 110 V
88 V to 310 V
Permissible ambient temperature 0o to 50o C
Insulation test (IEC 255) 2 kV, 50 Hz
5 kV, 1.2/50 µs
Disturbance test (IEC 255) 2.5 kV, 1 MHz
Electrostatic discharge (ESD; IEC 801-2) 8 kV (IEC 801-2)
Burst test, (IEC 801-4) 2 kV (IEC 801-4)
External communication mode RS 232 or fibre optical cable
Series communication speed 150-19200 Baud, step 2x
Optical fibre cable operation mode radial or loop
 
Design, size
 
The DTRV-EP complex protection equipment is delivered in a steel-sheet cabinet with standard 19" hinged rack system and locked door, accessible from the front side. When selecting the cabinet type the manufacturer can consider the special requirements of the user. If not specified at ordering, the cabinet is of RITTAL PS type.
 
Options
 
  • digital disturbance recorder (see separate information sheet)
  • SCADA connection (see EuroProt system information sheet)
  • relay contacts with 4 A breaking capability
 
Ordering data
 
When ordering our experts are ready for consultation and for the necessary engineering activity.