DETECTION OF SERIAL ELECTRIC ARC IN LOW VOLTAGE ELECTRICAL INSTALLATIONS Zoran Radakovic, PhD EE Department of power converters and drives Faculty of electrical engineering University of Belgrade Bulevar Kralja Aleksandra 73, 11120 Beograd, Yugoslavia mailto: [email protected]
DETECTION OF SERIAL ELECTRIC ARC IN LOW VOLTAGE ELECTRICAL INSTALLATIONS
Zoran Radakovic, PhD EE
Department of power converters and drives
Faculty of electrical engineering
University of Belgrade
Bulevar Kralja Aleksandra 73, 11120 Beograd, Yugoslavia
mailto: [email protected]
Characteristics of parallel and serial arcs
the differential current appears
State of the art
Our idea and research done
System for fine tuning of electrode position
Results of experiments
Materials and arc characteristics
Spectral characteristics of the electric arc: resistive load
By effective current of 6.5 A the higher current components are
I3g = 1.95 A
I5g is our great sicret
I7g and I9g are about 3 times lower than I5g
Harmonics caused by non-linear consumers
Fluorescent lamps. By the fundamental harmonic current of 3.35 A,
the third harmonics was 0.60 A and the fifth 0.015 A.
Mono-phase motor with speed control. Simular existance of a high third harmonic was detected: by the fundamental current of 3 A, the third harmonic was 1.6 A.
1.Detection algorithm will be based on the fifth harmonic.
Criteria: detected fifth harmonic greater than I5g.
2.The idea was to have simple algorithm, easy and chip in hardware realisation and without adjustment by the installation.
3.That is why the objective application is in household. All circuits, first of all in industry, having consumers with highly distort currents can not be
protected against the arc using this simple algorithm.
4.There is the need to test other consumers appearing in households which could jeopardise the algorithm application.
Specific problems with the non-linear consumers
Influence of the voltage distortion
The fifth current harmonic can appear in the case of pure resistive load in the case when the network voltage is distorted.
Quantification of the phenomena (the worst case study):
U5max IEC = 0.06 x 230 = 13.8 V
Ifuse max = 16 A
Rconsumer 230 V / 16 A =14.38
Iconsumer 5max = 13.8 V / (230 V / 16 A) =0.96 A I5g
Structure of the consumers in household
Having in mind noticed minimal currant of stable arc and the power of real consumers in household, the critical ones are thermal (boilers, heaters, furnaces).
Central protection, in the supply of the whole flat is not suitable due to the quoted non-linear consumers.
It is explained that harmful effect of non-linear consumers to the efficacy and reliability can be avoided.
Realised prototype of the arc protective device
Concept of the commercial device
Separate circuits should be monitored using analogue multiplexer.
Analogue multiplexed signals would be secondary currents from current transformers or voltage signals from the shunts.
Uniform scanning cycle would be interrupted in the case of detecting the signal of electric arc on one of the channels. Than, the monitoring of this channel only would be undertaken the following 10 seconds.
For every circuit two diodes (the green, indicating normal operation and the red would be installed) in order to distinguish the protection due to the electric arc.
Further research: Extension of the algorithm and its elaboration to a more general, industry applicable case. The idea is to train the detector with the harmonic characteristic of the consumer every time at the specific place of its instalment.