Power Quality
Innovation in Harmonic Filtering
Abstract:
Power quality has become a great concern for both energy suppliers and their customers because the increasing use of sensitive devices and the significant consequences of a poor power quality for the competitiveness of the companies.
The increasing developments need increasing use of electricity. While meeting this power demand, there causes a pollution in electrical system called Harmonics. The harmonics are integer multiples of fundamental currents/voltages. Substantial presence of harmonics results in excessive overheating of the equipments and other problems. Harmonics are created by non linear loads that draw current in abrupt pulses rather than in a smooth. Different problems due to harmonics have different solutions. In this paper we are going to present you the Basic concept of harmonics, their generation, problems created by them and HARMONIC FILTERATION as a solution for this problem of Harmonics.
Introduction:
“power quality” is defined as “the concept of powering and grounding electronic equipment in a manner that is suitable to the operation of the equipment ina manner that is suitable to the operation of that equipment and compatible with the premise wiring system and other connected equipment.
power quality has become a strategic issue for the following reasons:
- The economic necessity for businesses to increase their competitiveness.
- The widespread use of equipment which is sensitive to voltage disturbances and /or generates disturbances itself.
- The deregulation of the electricity market.
In this context, it is essential for the utility and the customers to prevent and detect power quality problems and to have solutions available to fix them.
The power quality correction and harmonic filtering system give solution to solve the problems of harmonic disturbances and voltage fluctuations.
Main power quality distrubences:
Power quality usually involves characterising low frequency conducted electromagnetic disturbances which can be ranked in different categories.
VOLTAGE SAG:-
Voltage sag is a sudden reduction (between 10% and 90%) of the voltage magnitude at a point in the electric
System and lasting from 0.5 cycles to few seconds. Either switching operations or any type of faults as well as fault clearing process can cause a voltage dip. Switching like those associated with a temporary disconnection of the supply or flow of heavy currents associated with the starting of large motor loads is the most common. These events maybe originated at the utility side or at the customer site.
VOLTAGE VARITIONS AND FLUCTUATIUONS:-
Voltage variations are variations in the rms value or the peak value with amplitude of less than 10% of the nominal voltage. Voltage variations are a series of voltage changes which are characterised by the frequency of variation and the magnitude.
Voltage variations are caused by a slow variation of loads
connected to the network and mainly due to rapidly varying industrial loads such as welding machines.
HARMONICS:-
Harmonics are currents or voltages with frequencies that are integer multiples of the
fundamental power frequency. The fundamental frequency itself is called as the first Harmonic. The second Harmonic as frequency twice that of the fundamental, the third Harmonic has frequency thrice that of the fundamental and so on. For example – if the fundamental frequency is 50Hz then the second Harmonic is 100 Hz, the third Harmonic is 150Hz etc.
Generation of Harmonics:-
Harmonics are created by non-linear loads that draw currents abrupt pulses rather than in a smooth sinusoidal manner. These pulses cause distorted current wave shapes, which in turn cause harmonic currents to flow, back into other parts of the power system.
Consumers Generating Harmonics:
Harmonics are not generated by power generators but are produced by Non-linear loads as under:
Loads that make use of semi conductor devices
like transistor, thyristor i.e., static rectifiers. (AC/DC conversion using SCRs), static frequency converters, static inverters like:
-Static Power converters (AC – DC conversion using SCRs)
-Static rectifiers
-Static frequency converter
-Static uninterrupted power supplies
-Static induction regulators.
i)Variable impedance loads, using electric arcs, are furnaces, welding units, Fluorescent tubes, discharge lamps, light control, brightness etc.,
ii)Loads using strong magnetizing currents, saturated Transformers, inductance, furnaces, reactors etc.,
Office automation equipment like computers, UPS, printers and fax machine etc.,
problems due to low power quality:
- Damaging of computer hardware and memory.
- Motors fail to start due to low voltages
- Setting and resetting of electronic equipments will be out of control .
- Industrial and domestic loads will get damaged.
Solution to Harmonic Distortion:
Harmonic Filtration:
Harmonics in AC & DC waveforms are minimized by following means:
- Use of DC smoothing reactor.
- Use of DC harmonic filters.
- Use of AC harmonic filters.
DC Smoothing Reactor: This is oil cooled, oil insulated reactor having high inductance (0.35H to 1H).It is connected in series on the DC side of the converter. It smoothen the ripple in the DC current. The DC reactor also helps in reducing the rate of rise of current surges appearing on the DC side of the converter due to sudden changes in DC power flow due to faults or load change.
AC Filters: These are shunt connected AC harmonic filters. They are connected between AC busbars and earth. They offer low impedance to harmonic frequencies and high impedance to power frequency. Thus, harmonic frequencies are passed to earth and are eliminated from the AC network.
AC shunt filters serve dual purpose on AC side:
- They divert harmonics to earth and reduce the harmonic contents in main AC network.
- They provide shunt compensation required on AC side for satisfactory converter operations.
CLASSIFICATIONS OF AC SHUNT FILTERS: -
Tuned AC shunt filters are used for suppressing lower order characteristic harmonics eg. Separate tuned branches for 5th, 7th, 11th, 13th harmonics. These branches may be either single tuned for each of the above characteristic frequency or each branch double tuned for two frequencies eg. 5th/7th, 11th/13th, 23rd/25th, 3rd/36th etc.,
Tuned AC shunt filters are classified into two types.
a)A Single frequency tuned Shunt filters is a single RLC series circuit connected between a phase and earth. The filter is tuned to one particular characteristic harmonic frequency. Separate branches are necessary for each lower characteristic harmonic frequency. The filter is tuned to the resonates frequency equal to the corresponding characteristic harmonic order.
b)A Double frequency tuned shunt filters has two resonant frequencies eg. 5th / 7th, 11th / 13th, 3rd /36th. A typical circuit of a double tuned AC shunt filter consists of a RLC series circuit in series with another L2, C2, & R3, L3 parallel circuit. The values are selected such that the total filter has two resonant frequencies (One given by CLL2C2 & other by CR3 L3).
1)High pass filter branches are arranged to suppress harmonics of higher order say 24th & above. With High pass AC shunt harmonic filter connected near AC Bus bars, all the higher harmonics are diverted to earth and are not allowed to proceed to the AC Network. At resonant frequencies, the circuit of the double tuned filter is equivalent to two parallel single tuned branches. A double frequency tuned filter has lowest impedance at two resonant frequencies. These filters are also called as Damped Filters.
DC Harmonic Filters
DC filters are designed to reduce DC harmonics to minimize the telephone interference in voice frequency range (100Hz to 5 KHz). In addition to the telephone interference criterion, the DC filter is designed with interior of avoiding the resonance between DC filters & DC line at lower order harmonics.
Conclusion:
Power quality has become a strategic issue for consumers. In this present economic context, the consequences of electrical disturbances become more and more serious.
Harmonic currents & voltage distortion are becoming the most severe and complex electrical challenge for the electrical industry. So by designing and giving complete solutions in the form of detuned and tuned harmonic filter systems, Active filters and other protection systems for industrial installation that can ensure the trouble free operation of electrical installation for industries.
By defining and implementing these solutions users will be provided with the right quality of power supply for their requirements .