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[attachment=8667]
Automatic Power Factor Control
Objective of the Project Work
To Design a Control Panel Which Will Provide a Constant Power Factor When Plant Load is Constantly Changing, resulting in the need for varying amounts of reactive power.
Scope of Work
• Reduce Power Bill
• Reduce I^2 R Losses In Conductor
• Reduce Loading On Transformers
• Improves Voltage Drop
• Avoid Penalty For Low Power Factor
• Optimise the Capacity By Reducing the Maximum Demand
• Avail Incentives By Maintaining Higher Power Factor
Methodology
• An intelligent power factor correction scheme is presented for three phase low power factor loads.
• This new scheme is able to perform individual phase sensing of parameters by monitoring at all times to sense a change in system parameters and affects individual phase correction by applying the exact amount of reactive components needed for each phase, and can also reduce negative sequence current caused by the load to improve system balance. An optimization criterion is used for the proper calculation of reactive power steps in a power compensation installation of capacitor banks. The criterion is enabled by sampling measurements performed on the electrical plant examined within specific interval of time.
• The scheme involves the application of bank of capacitors controlled by a micro-controller to balance the phases and correct the power factor to higher values.
• Applying this scheme can improve the performance of many industrial plants since it is capable of blocking the negative sequence currents, thus it can eliminate phase unbalance and improve system voltage whilst, and at the same time the power factor can be improved up to desired values.
• Many power industries can benefit from this scheme because of its low cost.
Work Carried Out
• Interested to boost up=90% ,Power Factor2=90%
• Power Factor=KW / KVA
• Cosq = kW / kVA
• q = Cos-1 (PF1)
• q = Cos-1 (75%) =41.41
• The Reactive Power was about:
• tanq = kVAR / kW
• kVAR = kW x tanq
• kVAR = 110 kW x tan (41.41) = 97.01 kVAR
• If the Power Factor were increased to 90%, the Reactive Power would be about:
• Cosq = kW / kVA
• q = Cos-1 (PF2) Power Factor1=75%
• Actual Power=110 kw
• Interested to boost up=90% ,Power Factor2=90%
• Power Factor=KW / KVA
• Cosq = kW / kVA
• q = Cos-1 (PF1)
• q = Cos-1 (75%) =41.41
• q = Cos-1 (90%) = 25.84
• kVAR = kW x tanq
• kVAR = 110 kW x tan (25.84) = 53.27 kVAR
• Thus, the amount of capacitance required to boost power factor from 75% to 90% :
• 97.01 kVAR – 53.27 kVAR = 43.74 kVAR
• So I recommended 50 KVAR Capacitor Bank to Design the Control Panel.
Conclusion
→ By observing all aspects of the power factor it is clear that power factor is the most significant part for the utility Company as well as for the consumer. Utility company rid of from the power losses while the consumer free from low power factor penalty charges.
→ By installing suitably sized power capacitors into the circuit the Power Factor is improved and the value becomes nearer to 0.9 to 0.95 thus minimising line losses and improving the efficiency of a plant
Posts: 5,362
Threads: 2,998
Joined: Feb 2011
PREPARED BY
CHAUHAN NISHANT J
SURATI NIKHILESH N
PATEL PRATIK N
PATEL BRIJESH D
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INTRODUCTION
In view of constantly rising power tariff & penalties imposed by the State Electricity Boards / Utility companies, it is imperative for any HT & LT Industry / Consumer to install an automatic power factor controller system for curtailment of Power Factor penalty and also to Save Energy by consistently maintaining higher power factor. Low Power Factor leads to poor power efficiency, thereby increasing the apparent power drawn from the distribution network. These results in overloading of Transformer, Bus bars, Switch gears, Cables and other distribution devices within the Industry or consumer area. An APFC is the most accurate way to correct a system’s power factor. They are ideal for distribution. Which have fluctuating load and distribution with numerous motors and APFC centralized system solution, eliminating individual motor capacitors scattered throughout a facility and their associated costly maintenance.
POWER QUALITY
In the present Low voltage (LV) industrial distribution system the power factor maintenance and harmonics control are the most critical issues to ensure acceptable power quality, and hence demands at most concern at consumers end to maintain a stable power system.
POWER FACTOR
The cosine angle between voltage and current in AC circuit is known as “Power Factor”. In AC circuit, there is generally a phase difference ᵩ between voltage and current. The term cosᵩ is called the power factor of the circuit. If the circuit is inductive, the current lags behind voltage and power factor is referred to lagging. However in capacitor circuit, current leads the voltage and power factor is said to be leading. Most of the industrial loads e.g. motor and transformers are inductive in nature and the power factor will be in the lagging side. Adequate reactive compensation is required at the consumer end to improve the power factor and effectively utilize the allotted Maximum demand. In a highly volatile load environment the reactive requirement of the loads is of variable nature and needs a dynamic & reliable reactive power compensation system to maintain the power factor and to control the Real power (KVA). To maintain the power factor generally fixed capacitors are installed in industries at various load centers balanced to the connected load level. In the fixed compensation system the amount of capacitors (kVAR) connected in the system will be always constant irrespective of the load variations. In such conditions the power factor maintenance is highly difficult in the ambience of variable load pattern and the overall plant power factor will tend to be lagging or leading. The leading power factor (I.e. excessive capacitors than the requirement) in the system will result in an excessive rise in the transient voltage during switching of loads and leads to insulation failures in the equipment and generates harmonic oscillations.
how does an APFC work?
An APFCU / FAPFCU works by constantly monitoring the load on a facility and connecting or disconnecting capacitive kVAr in order to maintain a preset target power factor. The kVAr within an APFCU / FAPFCU is divided into groups, which are called steps. Each step includes capacitors, a contactor, HRC fuses, an inrush current limiter (in APFCU) or a filtering reactor (in APFC). The brain of an APFCU / FAPFCU is the controller. It receives the plant load information from a current transformer which is located on the main bus bar, determines if any changes are required to maintain the target power factor, then adjusts the number of steps connected accordingly.
TECHNICAL SPECIFICATION FOR 600V AUTOMATIC POWER FACTOR CORRECTION BANKS:
1) Equipment Size / Ratings :
System operating voltage (line-to-line): 600V, 3 phase, 60Hz. Capacitors shall be rated minimum 690V to protect against current and voltage overload due to harmonic distortion.
Total kVAr required at system voltage at present:
Total kVAr required at system voltage for future:
Total bank to be switched in kVAr steps.
2) Capacitors:
Individual capacitors shall be CSA and UL approved, 3 phases, gas or oil filled under vacuum, and of a self-healing design utilizing a low loss metallised polypropylene film dielectric system with a pressure sensitive circuit interrupter. Metallised paper is not acceptable. Capacitor casing shall be of a seamless aluminums design. Electrical losses shall be less than 0.25w/kVAr. Dielectric fluid shall be high flash point, biodegradable, non-toxic and contain no PCB’s. Capacitors shall include internal fusing for short circuit protection to 10kA, and include grounding / mounting stud at the bottom of the capacitor cell for easy replacement. Capacitors shall be rated for a minimum of 130% continuous current overload and 110% continuous voltage overload based on the 690 Volt rating of the capacitors. Individual capacitor cells shall not exceed 25 kVAr at the system voltage to keep replacement costs at a minimum. Capacitors shall be suitable for -40oC to +60oC ambient temperature. Dry type capacitors and / or capacitors without a pressure sensitive circuit interrupter are not acceptable.
3) Discharge Resistors :
Adequate discharge resistors shall be provided for each capacitor cell to reduce the voltage to 50 Volts or less in one minute after disconnection of supply voltage.
4) Inrush Current Limiters:
Inrush current limiters shall be included for each step in the capacitor bank assembly. Inrush current limiters shall be three phase iron core type. Inductance shall be a minimum of 8 H per phase. Contactors equipped with pre-charge coils are an acceptable alternate to three phase iron core inrush current limiters.
5) Harmonic Filtering Reactor:
Multiple tuning frequencies as required for meeting the guidelines are acceptable. Harmonic filtering reactors shall be three phase iron core complete with one “+” tap and one “-” tap per phase for field adjustment of inductance. Reactor insulation shall be rated at 220oC. The maximum temperature of the reactor at maximum continuous rms amperage shall be no higher than 145oC with a 45oC ambient. Reactor maximum continuous rms amperage shall be sized to match the maximum continuous RMS amperage of the capacitors. The minimum reactor Q factor shall be 90.
Reactors shall be equipped with snap action thermostats which trip at 145oC and are wired to a monitoring system which switches off and locks out the associated contactor for the overheated reactor. An LED shall indicate which step has the overheated reactor. A pushbutton reset located on the door shall reset the alarm. In no case shall the harmonic filtering reactor size exceed 75 kVAr at the system voltage to allow for ease of replacement. The successful manufacturer shall be prepared to provide documentation showing the minimum capacitor voltage required to avoid overload due to import and export harmonics. This information may be required immediately following receipt of an order.
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can u provide me with the circuit diagram of the controller circuit
Posts: 7,939
Threads: 421
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