DZR-EP, DZR2-EP

 EuroProt familija
DIGITAL IMPEDANCE PROTECTION
 
Digital impedance protection of type DZR-EP, DZR2-EP is a member of the 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 the system information sheet, in order to get a clear picture of this protection.
 
DZR-EP
 
Application field
 
The DZR-EP type digital three phase under-impedance protection can be used as short-circuit protection in not grounded (isolated or compensated) networks, and in grounded networks, if the minimal short-circuit current and the maximal load current are at the same level, and therefore the selective protection needs impedance measurement instead of overcurrent protection. The protection is provided with offset circle characteristics, which are suitable to solve special protection tasks as well.
The frequent applications of DZR-EP under-impedance protection are: the reserve protection for generators in case of short-circuits inside the zone of the differential protection, main protection of medium voltage bus-bars of 120 kV/medium voltage transformers, reserve protection for short-circuits inside the zone of transformer differential protection and for short-circuits at the first section of the feeders.
The application of this protection is not advised, if directionality is required, i.e. difference must me made between short-circuits in front of and behind the protection. For these location the DKTVA-EP type distance protection for medium voltage networks is developed.
 
Main features
 

Under-impedance function:

  • two stages of three phase under-impedance functions (Z<<, Z<) with individual time delay
  • the offset of the circle characteristics ( compaunding) can be set for both stages independently
  • 3 point measuring principle, not sensitive for current transformer saturation
  • shortest operating time: 25 ± 5 ms

Overcurrent function:

  • two stages of three phase overcurrent functions (I>>, I>) with individual time delay
  • for the overcurrent stages can individually be selected:
    • trip circuit supervision in each phases
    • always enabled
    • enabled only if the MCB-s in the voltage measuring trip, and the impedance stages are disabled

Software characteristics:

  • built-in self-supervision functions
  • event 1og storing 50 events, and digital event sequence recorder with 1 ms time resolution, recording maximum 300 events
  • analog event log with current and voltage data
  • intelligent digital function matrix
  • two additional timers (T1 and T2) for free application in connection with the matrix
  • the rows of the matrix (relay-functions) can be set for latching

Hardware characteristics:

  • numerical design, with own AID converter, digital signal processor (DSP) and separate main processor
  • 8 opto-coupler inputs
  • 16 output relays
  • the type of contacts (NO, NC) can be selected individually when ordering

Communication:

  • 2x16 character LCD display for setting, message display and display of recorded events
  • on line screen on external PC for easier commissioning
  • external communication connection can be set for RS 232 or fibre optic cable
  • optional interface modules for SCADA connection
  • the parameters can be saved and downloaded
  • real-time clock with battery-fed RAM, (can be synchronised from external PC via fibre optic cable, from the SCADA system or via opto-coupler input
Working principle
 
The DZR-EP protection is a microprocessor controlled system, so its functions and their variations are based on software.
The device contains several 87C196 type 16 bit micro-controller and a DSP performing digital signal processing. The program is stored in EPROM, the message text for the display is stored in EPROM as well. The parameter setting is loaded in EEPROM. Events are recorded in battery supplied RAM. The man-machine interface consists of a keyboard with six push-buttons, above it the two row, 2x16 character LCD display, seven LEDs and two SW pushbuttons. With auxiliary PC and with the handling program a device can easier be operated.
The analog current and voltage inputs are connected via inductive internal measuring transformers and low-pass filters to the multiplexer then to the AID converter, where all current and voltage signals are sampled in every 0,5 ms. The sampled values of the 16 bit AID converter are passed via high speed CAN bus to the digital signal processors (DSP), which perform arithmetic operation with high speed. The outputs of the DSP are the processed and evaluated measurements, as "started" signals of the relay functions, which are sent to the CPU. The timers and logic functions are performed here. The central processor communicates via parallel bus with the opto-coupler inputs and with the relay drivers.
The under-impedance protection function is in all three phases a two stage impedance relay, and there is additionally a two stage overcurrent relay as well. Each stages have individual timers. Each stage contains 3-3 parallel impedance functions. Their operations is enabled by overcurrent relays with 0,2xIn fix setting. The staring caused by the highest phase current enables the operation of both impedance stage in all three phases. The measurements is disabled by the trip of midget CB in the voltage transformer secondary circuit with selectable NO or NC contacts.
The two overcurrent functions contain RMS measurements. The delay of both stages can be set independently. It can be selected by parameter setting if it is always enabled or enabled only in case of tripping the midget CB, causing the disabling of the impedance functions.
In case of DZR designed for not solidly grounded networks the impedance measurements are performed according to the formula for the three phases URS/2IR, UST/2IS and UTR/2IT. The impedance setting is the positive sequence impedance of the line. In case of two-phase short-circuits the explanation is drawn on Fig. 1.



Figure 1.

In case of 3 phase short-circuits the impedance relays measure Ö3/2 times less values, they "over-reach" .The operating distance of the function in case of 3 phase short-circuit is 2/Ö3=1,15 times greater, than that of 2 phase short-circuits. For the explanation see Fig. 2.



Figure 2.

In the DZR2 version for solidly grounded networks in case of earth faults the phase voltage is divided by the phase current compounded with the zero sequence current, and they calculate the positive sequence impedance proportional to the distance.
The setting of the impedance function is made according to the characteristics shown in Fig. 3.



Figure 3.
Technical data
 
Rated secondary current, In
 1 A or 5 A
Rated secondary voltage (line), Un 100 V or 200 V
Rated frequency 50 Hz or 60 Hz
Overload capacity, voltage circuit thermal, continuous
current circuit thermal, continuous
1 s 		2xUn/Ö3
4xIn
100xIn (In=1 A), 50xIn (In=5 A)
Dynamic current limit 100xIn
Accuracy, impedance relays (above 50% In)
Accuracy, current relays (above 50% In)
Accuracy, timers
 ± 5%
± 2%
± 3 ms (steps 10 ms)
± 12 ms (steps 1 s)
Reset ratio, current relays 95%
Output relay contacts 12 pcs
Type of contacts (NC, NO) 1 NC, 11 NO (or 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 ofL/R = 40 ms
option 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
Burst test, (IEC 801-4) 2 kV
Setting ranges
Impedance function second stage
center of the characteristic (real axis),
Z<Ro(*10*Cu*Ci)		 0-10000 mOhm, step 10 mOhm
center of the characteristic (imaginary axis),
Z<Xo(*10*Cu*Ci)		 0-10000 mOhm, step 10 mOhm
radius of the characteristics,
Z<r(*10*Cu*Ci) 		0-10000 mOhm, step 10 mOhm
setting of the quarters, Z<RoXo position 1-4, step 1
Impedance function first stage
center of the characteristic (real axis),
Z<<Ro(*10*Cu*Ci)		 0-10000 mOhm, step 10 mOhm
center of the characteristic (imaginary axis),
Z<<Xo(*10*Cu*Ci)		 0-10000 mOhm, step 10 mOhm
radius of the characteristics,
Z<<r(*10*Cu*Ci) 		0-10000 mOhm, step 10 mOhm
setting of the quarters, Z<RoXo position 1-4, step 1
Remarks: The values of the constants in the formulas above:

Cu=1, Un=100 V Cu=2, Un=200 V
Ci=1, In=1 A Ci=1/5, In=5 A
so the value of the factor: (10*Cu*Ci)=Un/(10In)
Low set overcurrent stage I>/In(AV) 30-2500%, step 10%
High set overcurrent stage I>>/In(AV) 30-2500%, step 10%
CT primary rated current, In(AV) 50-2500 A, step 25 A
Delay of second impedance stage, t Z> 0-10000 ms, step 10 ms
Delay of first impedance stage, t Z>> 0-10000 ms, step 10 ms
Delay of low set overcurrent stage t I> 0-10000 ms, step 10 ms
Delay of high set overcurrent stage t I>> 0-10000 ms, step 10 ms
Delay of additional timer 1, t T1 0-10000 ms, step 10 ms
Delay of additional timer 2, t T2 0-10000 ms, step 10 ms
Healthy-to-work failure signal timer, t(fail) 2 s, fixed
External cummunication type RS 232/fibre optical cable
Serial communication speed (BaudRate) 150 do 19200, step:2x
Optical fibre cable operation mode radial or loop
Daily automatic self-check time 0-23 h 59 min, step 1 min
Automatic self-check block do 60 min
 
Design, size
 
An EuroProt is always rack mounted, it has two design forms. One of the form is suitable to be mounted into standard 19" cabinet frame, this form is also suitable to be mounted directly to a relay panel with flash mounted form. The other form is a relay panel mounted device with raised-hinged form. Its size depends on the chosen form.

Design
Width
Height
Depth
Rask mounting
483 mm
132,5 mm
201 mm
Panel mounting
490 mm
250 mm
250 mm

Weight 8 kg.
 
Options
 
  • digital disturbance recorder (see separate infonnation sheet)
  • SCADA connection (see EuroProt system infonnation sheet)
  • 8 additional opto-coupler inputs to PROTLOG operating equations
  • output relays with 4 A breaking capability
 
Information required with order
  • Protection type [DZR-EP]
  • Output relay contact type [NC or NO]
  • Protection case type
  • Rated current [1 A, 5 A]
  • Rated voltage [100 V, 200 V]
  • Needed trip circuit supervision
  • Options if needed