DTD2-EP, DTD3-EP

 EuroProt familija
DIGITAL DIFFERENTIAL PROTECTION
 
The digital differential protection of type DTD2-EP, DTD3-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.
 
DTD2-EP
 
Application field
 
The three phase differential protection type DTD2-EP is used as a selective and fast protection against short circuits of two-windings transformers ("2" in the type sign means two legs), or three-windings transformers ("3" in the type sign means two legs), generators and generator-transformer blocks.
 
Main features
 
  • No external additional auxiliary C.T.'s neither to adjust the C.T. ratios, nor to set the vector rotation according to the transformer connection group
  • Its characteristic of three section points may be set arbitrary
  • Its bias is made by the average of the two side currents
  • Insensitive against transformer inrush current
  • Its failure signal has phase conformity
  • Also overcurrent relays are built into both sides
  • As an option, sensitive earth fault relay with independent time delaying
  • As an option, breaker failure protection on low side C.B
  • Consumer-friend modern digital interactive parametering (setting) method
  • Fast checking possibility of the protection setting data
  • Password protection against unauthorized setting action
  • Handling the protection easier and faster by an external PC
  • Fast inquiring possibility of actual current data and sum of protection working counters
  • 8 output contacts, programmable by software matrix
  • 8 digital inputs through optical couplers, programmable by software matrix
  • Real time clock handling synchronizable by external PC or by local area radio transmitter
  • RS 232 or optical fibre cable for external communication
  • Immediately appearing "messages" on occurring protection events
  • Automatic and manually started self monitoring system
  • Event log for 50 events and digital event sequence recorder for 300 events of 1 ms resolution with real date and time
  • Cancelling all events by hand may be made by external PC only
  • Operational time is about 20 to 30 ms, and 15 to 20 ms if high current differential stage operates
  • As an option, an independent disturbance recorder PCB of DIGIPROT disturbance recorder family may also be built into the device which can be registered the currents of the transformer at both side as analogue signs, and digital signs characterised the protection work, and it is able to store a period of 50, 100 or 150 s as a sum.
Working principle
 
The currents are connected through analogue current terminals, auxiliary C.T.'s and analogue low pass filters to the multiplexer, sampler and A/D converter.

Setting the current balance of the differential protection is very easy. The one and the other side main C.T. primer rated current in Amps, and related to them, the transformer rated current in per cent to one and to the other side are needed to be set. With these actions, the balance setting is ready.

A current angle rotating according to the transformer connection group (e.g.Yd11) may be set by a parameter "angle rotating code" (settable from 0 to 11 [12 groups]).

Separate sections of the tripping characteristics have meanings as follows.

f1% Setting of the first horizontal section of the characteristic. It determines the basic sensitivity of protection in per cent of the transformer rating current.

f2% Setting of second section gradient of the characteristic. It is necessary for compensating the regulating transformer range. This section is a line originated from the origin.

f3% Setting of the third section. It is necessary for compensating the C.T. saturation, hence its gradient is always tga=2, and originating on the vertical axis at [-f3%].

f2h Setting of the second harmonic blocking. It is necessary against false trip on inrush current. It blocks if the second harmonic content of the differential current in per cent is more then the set value.

Id>> Setting of a high current value. If the differential current is higher than the set one the protection trip without bias. In the present case, the operation time is 15 to 20 ms.

The overcurrent relay has one stage only at side 1, and two stages at side 2.
As an option, sensitive earth fault relay may be built into the relay.
As an option, additional timer is serve for breaker failure protection.
The protection has 8 output relays which may be programmed by software matrix.

The tripping characteristics of the digital transformer differential protection is shown in Figure 1.

Figure 1.
 
Technical data
 

Rated secondary current, In

 1 A or 5 A

Overload capacity, continuous
1 s

 4×In
100×In (if In = 1 A)
50×In (if In = 5 A)
Dynamic current limit 100×In
Accuracy of digital overcurrent relays (over 50 %) ± 2 %
Accuracy of digital timers 10 ms range:
1 s range		 ± 3 ms
± 12 ms
Resetting ratio of overcurrent relays 95%
Operational time
if high current differential stage operates 		25 to 30 ms
15 to 20 ms
Inputs through digital optical coupler 8 pcs
Output contact number 16 pcs print relays
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
250 V
8 A
16 A
0.25 A
0.14 A
Auxiliary d.c. voltage 220 V or 110 V (range: 88 to 310 V)
Permissible ambient temperature 0°C to 50°C
Insulation test (IEC 255) 2 kV, 50 Hz
5 kV, 1.2/50 ms
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:
Main C.T. on side 1, primer rated currents, AV1 50 to 1500 A, steps 25 A
Main C.T. on side 2, primer rated currents, AV2 50 to 2500 A, steps 25 A
Transformer rated currents, Ibe1, Ibe2 20 to 270 %, steps 2 %
Diff.protection, trip without bias, Id>> 800 to 2500 %, steps 50 %
Characteristic, basic sensitivity, f1 20 to 50 %, steps 2 %
Characteristic, 2nd section gradient, f2 20 to 50 %, steps 2 %
Characteristic, 3rd section gradient, f3 200 to 2000 %, steps 10 %
Inrush current second harmonic blocking, f2h 10 to 30 %, steps 2 %
Overcurrent relays, detecting value, 50 to 2500 %, steps 5 %
Timers 0 to 60000 ms, steps 10 ms
External communication RS 232 or optical fibre cable
Communication speed 150 to 19200 Baud, with 2x steps
No. of substations within a system 0 to 254
No. of devices within a substation 0 to 254
 
Design, size
 
The device is a member of the device family EuroProt which has two different designs. The one is a device for rack mounting to a 19" standard cabinet frame, the other is a flash mounting or raising mounting device to a panel. Its size depends, of course, on the design chosen.

Design
Width
Height
Depth
Rack mounting
483 mm
132,5 mm
201 mm
Panel mounting (DTD2-EP)
384 mm
250 mm
250 mm
Panel mounting (DTD3-EP)
490 mm
250 mm
250 mm
 
Options
 
  • Disturbance recorder
  • Interface to a SCADA system
  • Output contacts with 4 A DC breaking capability
  • Sensitive earth fault relay on the middle voltage side
 
Information required with order
 
  • Type of protection [DTD2-EP]
  • Rated C.T. current [1 A, 5 A, independently chosen for both side]
  • Auxiliary d.c. voltage [220 V, 110 V]
  • Options [if needed]