Earth-Fault Compensation Controller EFC30 / EFC40

Transcription

1 Earth-Fault Compensation Controller EFC30 / EFC40

2 Application Control Algorithms In high impedance grounded power distribution networks the neutral point of the network is connected to earth by means of an inductance coil which is adjusted continuously or stepwise. If the resonance circuit formed by the adjustable inductance coil and the earth capacitance of the network is tuned to or close to resonance, the fault current is greatly reduced in case of a line-to-earth fault (earth fault). In most cases the arc caused by the fault current is extinguished with no need to switch off the faulty part of the network. As the Arc Suppression Coil (ASC) and the earth capacitance form a resonance circuit, the neutral-to-ground voltage of the network depends on the value of the inductance of the ASC and reaches a maximum when the ASC is tuned to resonance. This dependence of the neutral-to-ground voltage is utilized by the EFC30/EFC40 Earth-Fault Compensation Controller for automatic tuning of on-load adjustable ASCs. Minimal Coil Movement (EFC30) This method relies on a sufficient asymmetry of the network. Whether this method is applied or not, is determined by setting a threshold value of neutral to ground voltage. In case of a tuning operation the ASC is adjusted by a small amount. Using the known coil-position as well as the neutral-to-ground voltage measured before and after the adjustment operation, the controller computes the detuning value v, the asymmetry value k and the damping value d, which determine the resonance curve of the neutral-to-ground voltage. Taking into consideration the desired, software-adjustable under- or overcompensation, the controller calculates the necessary position and directly adjusts the ASC to the calculated value. Determining the Resonance Peak by Going beyond It (EFC30) This method may be used if the asymmetry of the network is small, which results in very low neutral-to-ground voltages. In this case, network reactions may cause fluctuations of the neutral-to-ground voltage. Therefore it is not possible to reliably compute the parameters of the network by means of slight detuning of the ASC. The controller therefore adjusts the ASC over a wider range, which must include the resonance peak. It stores the measured values and calculates a mediated resonance curve. Taking into consideration the desired underor overcompensation, it computes the necessary position and adjusts the ASC to that value. EFC40 Algorithm In case of very symmetric networks there is no reliable resonance-curve available for tuning. By means of a short (seconds) variation of the neutral-to-ground voltage using current injection the equivalent impedance of the resonance circuit can be computed. Without prior movement, the ASC is now positioned directly to the desired compensation. 2

3 Configuration of the EFC30 and the EFC 40 Hardware Hardware Options Software Microprocessor-controller 19 -rack-mounted (EFC30 3HU, EFC40 6HU) Simple operation by means of a film-type keyboard and a 640x200 pixel LCD graphic display located on the front panel (fig. 1) High EMC by means of: Serial Interface (3 x RS232) Terminal Strip (AKL) Protective housing Wall-Mounting Option Alternative Power Supply Voltages User-friendly, menu driven operation "Help"-texts for all essential menu options The factory-set parameters can be changed by the user galvanic separation and filtering of inputs and outputs AUTOMATIC (FW ) :48:11 U% (D:2)tuned U = % kv I = % fully chromised unit A Fix = 0.0 % high creepage distances on printed circuit cards and plugs software- and hardware-monitored program operation Fig. 1 Typical display (resonance curve) zero sequence voltage coil-position Ires = 55.6 % % Ik = 5.0 % k = 0.10 % v = d = 1.8 % EW = 0 parameters are stored in non-volatile memory Highly flexible due to adjustment by software of the analogue inputs and outputs; allows user selection of digital inputs and outputs for control, monitor etc. 3

4 The measured signals are shown digitally as well as in analogue form, both as a bar diagram and as a resonance curve. The operation status is displayed by message text. Fault conditions (e.g. no coil movement) are signalled by short text describing the fault condition. The wave shape and its spectral analysis (FFT) of the neutral-to-ground voltage can be displayed. Recording of various network conditions (e.g. transient earth-faults) and controller operation modes for statistical evaluations. Continuous recording of the measured signals with the possibility of displaying or downloading to a PC or SCADA system via the optional serial interface. Remote parameter changes with a PC connected via a modem to the optional serial interface. Password-protected parameters. Software Options (EFC30-mode) Control of an additional fixed coil (automatic switching on/off of the fixed coil) Control of a resistor, to increase the ohmic component of the fault current. Adjusting the ASC to a pre-defined value when the ASC is switched-off. Several controllers within the same network system (up to four controllers may work without disturbing each other, even if they are not connected to each other by means of SCADA.) Automatic switching of a damping resistor during the search operation if U exceeds Umax Time-synchronization by means of an impulse input line Special functions for extremely low/high neutral-to-ground voltages Interconnection to SCADA (SPAbus, IEC /VDEW 6) EFC40 The EFC40 offers the following features: EFC30 mode compensation even in case of very symmetric networks by controlling a device which provides variation of the neutral-toground voltage (e.g. current injection) computing the detuning without coil movement controlling of stepadjustable ASCs controlling of high speed continuously adjustable coils easy to upgrade to a complete earth fault detection system 4

5 Technical Data Electrical Data EFC 30 EFC 40 Calculation Algorithm detuning of the ASC current injection Controller CPU 32 bit Transputer (RISC Processor) with floating point unit memory 1 MB RAM 8 MB RAM display double supertwist LCD 640x200 pixels with background lighting keyboard film type power supply V AC, 50 Hz, 50W optional: 24, 48, 60 V DC Analogue inputs input ranges are adjustable by software V V AC reference voltage V0 3 mv V AC 3 mv V AC Ieci - 1 A, current injections ASC position [A] linear potentiometer 200 Ohm... 2 kohm or current source built into the ASC ma Digital inputs 4 potential free contacts, 16 inputs 24 V 250 V AC or DC 24 V DC/60 ma 2 impulse inputs 0,1 s... 2 s, V AC or DC Digital outputs 7 16 freely assignable contacts 250 V AC, 4 A, 1000 VA max resp. 250 V DC, 1 A, 100 W max Analogue outputs software programmable characteristics, potential free V ma selectable range, linear, bent or logarithmic ASC position ma selectable range, linear All in- and outputs are designed according to VDE 110 part 1 overvoltage class III, contamination level II, insulation class IIIa VDE 0435 part 303, 50Hz test voltage: 2000 V rms., 1 min class III impulse voltage test (1.2/50 µs): 5 kv HF interference test: 2.5 kv VDE 0160 W2 overvoltage withstand capability VDE 0843 ESD level 3: test voltage 8 kv, burst test (power supply): 4 kv, burst test (signal input lines): 2 kv Mechanical Data Climatic conditions operation temperature -5 C to +40 C storage temperature -25 C to +55 C transport temperature -25 C to +70 C humidity class G according to DIN Dimensions width/height/depth 483/132.5/252 mm 483/266/300 mm max. depth (incl. protective case): 350 mm 350 mm Weight approx. 8.2kg approx kg 5

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