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DRL-EP
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| COMPLEX DIGITAL CONTROLLER
FOR ARC-SUPPRESSION COIL AND EARTH FAULT CURRENT RISING |
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| The complex digital automatic controller for
arc-suppression coil and earth fault current rising of type DRL-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. |
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| Application field |
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The DRL-EP type Complex Digital Automatic
Controller For Arc-Suppression Coil (Petersen Coil) And Earth Fault Current
Raising is designed for medium voltage compensated networks and has two
main functions: tuning the arc-suppression coil and controlling the earth
fault current raising resistor by switching it parallel with the arc--suppression
coil.
An efficient method of protections against earth faults occurring in a medium
voltage compensated network is the earth fault compensation. It is made
by an inductive coil (arc-suppression coil, called Petersen coil) inserted
between a transformer star point and the earth to compensate the zero sequence
capacitance of the network; it helps arc extinction of a temporary earth
fault. The arc extinction coil is effective only, if its inductance value
matches the zero sequence capacity of the actual state of a network. In
an approximate resonating state the earth fault current is a very low value.
Consequently, the compensation tuning is correct if the natural zero sequence
voltage of a network (Uon) is near to the peak of "bell-shaped curve"
characteristic to the resonance state, Uon value is maximum. "Tuning"
of an arc-suppression coil is made by changing its air gap, by moving its
"dipping" core.
The DRL-EP type digital automatic controller is an up-to-date automatic
controller device which is able to evaluate the actual state of a network
and is suitable to determine the optimal arc-suppression coil value (core
position) and to give command for the tuning. The method of the algorithm
of the DRL-EP digital automatic controller is the current
injection method, which calculates the optimal core position, and controls
the coil in one step to the optimal state.
Beside the DRL-EP controller, the needed injection units are housed in an
additional relay case of DRLi-EP of the same size. These units are as follows:
- insulation transformer supplied by the substation auxiliary AC voltage,
which transforms the current value necessary for the injection
- reactor to set the current to be injected
- current limiter to limit the high current in case of earth faults
- two midget CB's for inner fault protection
For selective and reliable detection of the earth faults, earth fault current
raising resistor is frequently applied. In this case simple and reliable
zero sequence overcurrent relays can be used. The DRL-EP digital automatic
controller is designed to control the switching of resistor parallel to
the arc-suppression coil and to protect it. |
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| Main features |
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- modular, microprocessor-based design
- high sensitivity
- low driver load (it does not need core position changing of the arc
suppression coil during the measurement process)
- taking simultaneous effect of more arc-suppression coils into account
- handling by external PC or built-in man-machine interface
- setting the device (programming and parameter setting), checking,
reading the evaluated and binary events, displaying the messages, editing
PROTLOG equations with an external PC
- on-line screen of external PC to support commissioning and testing
- setting the parameters of the device, reading and checking the evaluated
event recorder, displaying text messages via built-in man-machine interface
- functional equations edited by the user with the help of PROTLOG system
with 14 output and 38 input signals
- 7 NO output contacts with fixed assignment, 8 NO contacts programmable
with PROTLOG equations, and 1 NC contact for the results ofself-checking
- external communication interfaces, RS 232 on the front plate, optical
fibre cable on the rear side,
- automatic self-test system, built-in monitoring functions
- numeric type relay with own A/D converter and separate main processor
- display of evaluated events
- digital event sequence recorder for recording 300 events with 1 ms
time resolution
- 25 opto-coupler inputs, 14 fixed and 11 free
- real time clock with battery supplied RAM, which can be synchronised
via optical fibre cable connected to an external PC or via optical coupler
input
- the device is of rack mounted type, it can be mounted into a standard
19" cabinet frame or to a relay panel with raised-hinged or flush
mounted form
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| Working principle |
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| The two main functions of the DRL-EP digital
automatic controller are to tune the arc-suppression (Petersen) coil and
to control the earth fault current raising.
Arc-Suppression Coil Tuning
The DRL-EP automatic controller determines the necessary inductance value
of an arc-suppression coil by measuring the actual state of the network.
The controller uses the current injection method to determine the resultant
reactance of the network and then calculates the necessary Petersen coil
tuning.
Regulation of an arc-suppression coil is necessary when the network operating
state changes, lines or other parts are tripped or closed by the operator
or by protections, and the network zero sequence capacity changes. The inductance
of the arc-suppression coil has to be tuned according to the changed state.
A change in the network state causes a change in the star point (zero sequence)
natural voltage. The device detects this voltage and if its changing is
higher than a pre-set tolerance limit for a certain period, the DRL-EP automatic
controller initiates a measuring cycle. Both the Uo voltage change initiating
a measuring cycle and the control start delay can be set with parameters.
The change can be Uo voltage increasing or decreasing as well.
If the automatic device detects a change in voltage, it initiates a measuring
cycle. The principle of the measuring is as follows. The device injects
current to the system through the auxiliary power part of the Petersen coil
for 1 s, then it injects current which is of opposite phase to the previously
injected current for 1 s. It determines the actual tuning state from the
two measured data and calculates the necessary core position of the arc-suppression
coil. Then it tunes the coil if necessary by up or down commands. The coil
position is determined by checking the potentiometer. After the first tuning
cycle, the device measures once more to increase regulating accuracy, and
corrects if necessary .The actual Uo value is measured and stored after
completing the regulating process. This stored Uo value
serves as the Uobase value for initiating the next measuring cycle. The
device enters into a continuous injection mode if Uo voltage stays under
a settable limit voltage for a certain period.
Principally it would be possible to make injection with only one polarity.
The advantage of two direction injections is that half of the current used
for one direction injection is enough to achieve the same sensitivity. So
the DRLi-EP injecting unit can be built up by parts of lower power requirement
and the unit has a smaller size.
Manual up and down tuning command may be also defined with the PROTLOG equations.
SW pushbuttons on the front plate can also be used for this purpose. The
controlling function is inhibited during and for a pre-set period after
earth faults.
Since the DRL-EP digital automatic controller has a serial optical fibre
cable connector, and as an option a control engineering connection is also
possible, the automatic controller is able to co-operate with more controllers
in an interconnected network. One active automatic controller shall be dedicated
to the network, and the others shall be inhibited. Disturbances caused by
opposite working of more controllers can be eliminated in this way.
| Legend |
| Designation |
Example |
Place-function |
| KA |
KA1, KA2 |
two midget CB's detecting and tripping parts in the DRLi-EP injecting
unit |
| KA signal |
KA1 i KA2 signal |
two midget CB's signal alarm contacts inthe DRLi-EP injecting unit |
| CT |
CT |
device for measuring the injected current |
| Ii> |
Ii> |
current limiter in the DRLi-EP injecting unit |
| K |
K1-K4 |
output contacts of the DRL-EP device for switching-on and polarity
change of injected current |
Control Of Earth Fault Current Raising
An earth fault current raising resistor is used for selective and reliable
earth fault detection. In this case, simple overcurrent protections can
be applied for detecting earth faults and their safe operation is easily
ensured. The DRL-EP digital automatic controller is able to control the
switch of earth fault current raising resistor, and to protect the resistor.
The DRL-EP digital automatic controller detects an earth fault by comparing
the Uo zero sequence voltage with the set value, and waits for expiring
a pre-set period (e.g. 2 s) to allow the arc-suppression coil (Petersen
Coil) to suppress the fault. If the earth fault does not disappear after
the delay, a switching-on command is given to the switch of the earth fault
current raising resistor parallel with the Petersen coil. Then the 3Io>
overcurrent protection will selectively trip the fault. The automatic controller
will switch off the resistor on earth fault disappearing after a pre-set
delay.
The device automatically checks the resistor thermal load, and in case of
overloading ( overheating), it inhibits a subsequent switching-on. |
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| Technical data |
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Rated secondary current, In
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1 A or 5 A |
| Rated secondary voltage (line), Un |
100 V |
| Rated secondary zero sequence voltage,
Uon |
100 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 |
| Injected current, Iinj |
± 2 A |
| Measuring range of the secondary neutral point voltage,
Uo |
0,03-150 V |
| Frequency range |
45-55 Hz |
Status signal inputs
type
connection
rated value
measuring current (depending on the resistance)
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Voltage divider
3 wires
0,2-2 kOhm
37,5-3,75 mA |
Output contacts, electrical
data:
type
number
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 |
potential-free
16
250 V
8 A
16 A
0,25 A
0,14 A |
Digital inputs (opto-coupler)
rated voltage
number
consumption |
220 V DC
24 + 1 clock synchroniser
1 mA |
Auxiliary DC voltage (the same supply unit)
voltage tolerance
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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 |
| Electromagnetic (radio-frequency) radiation |
IEC 801-3 |
| Burst test, (IEC 801-4) |
2 kV |
| External communication mode |
RS 232/fibre optical cable |
| Series communication speed (BaudRate) |
150 do 19200, step:2x |
| Optical fibre cable operation mode |
radial or loop |
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| Design, size |
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| Ureðaj je èlan familije EuroProt i dizajniran
je u dva oblika. Jedan je pogodan za ugradnju u standardni 19" rek,
a drugi se montira na komandnu ploèu. Velièina zavisi od izabranog dizajna. |
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Design
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Width
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Height
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Depth
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Rack mounting
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483 mm
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132,5 mm
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201 mm
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Panel mounting
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490 mm
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250 mm
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250 mm
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Weight 8 kg. |
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| Options |
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- digital disturbance recorder (see separate information sheet)
- SCADA connection (see EuroProt system information sheet)
- relay contacts with 4 A breaking capability
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| Information required with order |
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