A Study on the Improvement of Power Factor for Distribution Substation.
Chapter 1 Introduction Chapter outlines •
Introduction
•
Objectives of the Project
•
Layout of the Report
1.1 Introduction: The electrical energy is almost exclusively generated, transmitted and distributed in the form of alternating current. Therefore, the question of power factor immediately comes into picture. In most industrial and commercial facilities, a majority of the electrical equipment is inductive loads such as AC induction motors, induction finances, transformers and ballast-type lighting. Problems of power quality in industrial plants are growing due to the increasing number of rectifier controlled motors and the overall increase of harmonics and interharmonics. These loads cause poor power factor in industrial plants. The low power factor is highly undesirable as it causes an increase in current, resulting in additional losses of active power in all the elements of power system from power station generator down to the utilization devices. Though correction of power factor is very old practice, we have considered the work done from 1983 to 2007, 25 years in our survey. Jones and Blackwell proposed a technique for maintaining a synchronous motor at unity power factor (or minimum line current) from no-load to full-load conditions, assuring peak efficiency. This concept stemmed from an adaptation of the Energy Saver Power Factor Controller for induction motors developed and patented by NASA Marshall Space Flight Center. The method constantly and automatically adjusted the DC field current of a 3-phase synchronous machine such that the AC line current would always operate at the minimal point of the well-known "V" curves. [4].
Sharkawi et al. proposed an adaptive power factor controller for three-phase induction generators. The controller sensed the reactive current drawn by the machine and accordingly provided the needed reactive power to improve the power factor to as close to unity as possible. The controller was a modular, low-cost, harmonic free device. It did not create any transients in line current. It was designed to eliminate the self-excitation problems associated with induction generators. The controller was tested on an induction generator. [5]. Nalbant proposed the calculations and measurements of power factor correction and distortion reduction using the peak current programmed boost topology. The topology and a regulator used a dedicated power factor controller were introduced. The input current wave shape was modeled mathematically and analytical expressions for the calculation of the power factor and total harmonic distortion were derived. Various measurement methods were described and actual data related to the high power regulator were presented, including pictures of the low-frequency spectrum of the input current. [6]. Mandal et al. proposed a laboratory model of a microcomputer-based power factor controller (PFC) for compensating the reactive power of rapidly varying loads by switching capacitors sized in a binary ratio, with the help of zero voltage static switches. [7]. Dallago et al. proposed about the Monolithic ICs that allowed the simple and cheap singlephase power factor correction (PFC) systems to be implemented. They contained an analog multiplier, the transfer characteristic of which may be nonlinear. In this delta-sigma (ΔΣ) modulation technique was applied to fully implement the algebraic operations of a PFC system's multiplier block. A ΔΣ multiplier prototype was bread boarded and inserted in a PFC control loop based on a commercial IC. [8]. Tinggren proposed a new integrated power quality device-power factor controller (PFC) for power distribution system and industrial power circuit applications. A PFC integrated breaker-switched capacitor banks into a compact design with low cost sensing elements and an intelligent control unit. The device provided more accurate voltage control and power factor correction than traditional shunt capacitor bank installations. [9]. Cereda et al. proposed a better understanding of power quality (PQ) problems and their mutual impact on the power system and on the end-users facilities can lead to building and operating a safer, more reliable and more profitable energy supply system. The privatization of utilities and deregulation of the electrical energy market was boosting the interest for the energy supply PQ, focusing on its economic value. [10]. Machmoum et al. proposed a three-phase switching converter, acted as a PWM rectifier (PWMR) and/or as an active power filter (APF). A resonant current controller (RCC) for a
sinusoidal input current was involved. Pulse modulation allowed an efficiently control of the converter maximum switching frequency which slightly dependent on the electrical load, input passive filter or mains parameters. The converter provided controllable DC link voltage and a high power factor [11]. Cacciato et al. proposed a new approach that aimed at improving the power factor of pulse width-modulation inverters that equip low-power electric motor drives for household appliances. The key feature of the proposed approach consists of exploiting the dc-bus current as a suitable dither generator by means of a high-frequency transformer [12]. Barsoum proposed the programming of PIC micro-controller for power factor correction that described the design and development of a three-phase power factor corrector using PIC (Programmable Interface Microcontroller) chip. This involved sensing and measuring the power factor value from the load using PIC and sensors, then using proper algorithm to determine and trigger sufficient switching capacitors in order to compensate excessive reactive components, thus withdraw PF near to unity [13]. 1.2 Objectives of the Project: The goals of this thesis work are given below: • • •
To study about different power factor improvement techniques. To design and developed 7.5 KVAR power factor improvement plant. To design a model of an active power factor correction circuit.
1.3 Layout of the Report: This report is separated in seven chapters. The chapter wise brief discussions are given below: In chapter two, types of load, definition of power factor, effects of low power factor, techniques of power factor improvement and benefits of power factor correction. In chapter three, a brief discussion is made about PFI plant and its important components. In chapter four, the principle of active power factor correction technique is discussed and the comparison between conventional and bridgeless boost converter is shown. Also an algorithm is developed for automatic power factor controller. In chapter five, study of 4000 kvar PFI plant in Bextex. In chapter six, the design procedure of a PFI plant is discussed and suitable ratings of different components for 7.5 KVAR PFI plant are proposed. In chapter seven, future work and conclusion of this thesis.
Chapter 2 Theory of Power Factor Chapter outlines • Types of load • Definition • Effects of Low Power Factor • Techniques of Power Factor Improvement • Benefits of Power Factor Correction 2.2 Definition: Power factor is a measure of how effectively the current is being converted into useful work output. It is a good indicator of the effect of the load current on the efficiency of the supply system. To understand power factor, we first have to know that power has three components: i. ii. iii.
Real Power Reactive Power Apparent Power
Real Power (P): Real power is the actual amount of power being used or dissipated in a circuit; measured in watts. It is a function of a circuits resistances R; P = I 2R. Reactive Power (Q): Reactive power is the amount of absorbed/returned power by the reactive loads; measured in (KVAR). It is a function of a circuit’s reactance X; Q = I 2X. Apparent Power (S): Apparent power is the combination of reactive power and true power; measured in (VA) It is a function of a circuit’s impedance Z; S = I2Z.
Fig 2.1: Power Triangle
Basic Concepts
2.3 Effects of Low Power Factor: The adverse effects of low power factor are as follows: kW kVA •
For given power to be supplied, the current is increased.
•
The current increased then in term causes increase in copper losses (P =I 2R) and decrease the efficiency of both apparatus and the supply system.
•
Generators, transformers, switches and transmission lines become over loaded.
•
Voltage regulation of generators transformers and transmission line increases.
•
Cost of generation, transmission and distribution increase.
12
2.4 Techniques of Power Factor Improvement: Generally there are three types of technique are used to control the power factor. These are:
I. Passive PFC: This is a simple way of correcting the nonlinearity of a load by using capacitor banks. It is not as effective as active PFC, switching the capacitors into or out of the circuit causes harmonics, which is why active PFC or a synchronous motor is preferred. II. Active PFC: An active power factor corrector (active PFC) is a power electronic system that controls the amount of power drawn by a load in order to obtain a power factor as close as possible to unity. In most applications, the active PFC controls the input current of the load so that the current waveform is proportional to the mains voltage waveform (a sine wave). Some types of active PFC are: Boost, Buck and Buck-boost. Active power factor correctors can be singlestage or multi-stage. Active PFC is the most effective and can produce a PFC of 0.99 (99%). III. Synchronous Motor: Synchronous motors can also be used for PFC. Shaft less motors is used, so that no load can be connected and run freely on the line at capacitive (leading) power factor for the purposes of PFC. 2.5 Benefits of Power Factor Correction: • Reduce electric bill: Power factor correction equipment reduces the amount of reactive power in an installation. As a result electricity bills drop in proportion. • Effective utilization of electrical power: An improved power factor means higher active power for the same apparent power. This makes an electrical system more economical. • Reduction of losses: Cables carry less reactive current when the power factor is improved. This reduces the conduction losses in a cable. • Optimum dimensioning of cables: The required cable size reduces with the improvement of power factor. In an existing application the same cable can be used to serve an additional load. • Reduction of transmission losses: Since the transmission and switchgear equipment carry reduced current, only the active current, electrical losses will be reduced.
Chapter 3 PFI Plant Chapter outlines •
Introduction
•
Principle
•
Block Diagram
•
Important Components Required for Designing PFI Plant
•
Description of the Components
3.1 Introduction: In this chapter capacitive power factor correction technique is discussed and a 7.5 KVAR PFI unit is designed for that purpose. Capacitive Power Factor correction is applied to circuits, which include induction motors as a means of reducing the inductive component of the current and thereby reduce the losses in the supply. There should be no effect on the operation of the motor itself. An induction motor draws current from the supply, which is made up of resistive components and inductive components. The resistive components are: Load current and Loss current; and the inductive components are: Leakage reactance and Magnetizing current. Figure 3.1 is showing relations between magnetizing current motor current and work current.
Fig 3.1: Showing relation among magnetizing current, motor current and work current. The current due to the leakage reactance is dependent on the total current drawn by the motor, but the magnetizing current is independent of the load on the motor. The magnetizing current will typically be between 20% and 60% of the rated full load current of the motor. The magnetizing current is the current that establishes the flux in the iron and is very necessary if the motor is going to operate. The magnetizing current does not actually contribute to the actual work output of the motor. It is catalyst that allows the motor to work properly. The magnetizing current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but
will contribute to the power dissipated in the supply and distribution system. For example a motor with a current draw of 100 Amps and a power factor of 0.75. The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) / (75 x 75) = 1.777 or a 78% increase in the supply losses. In the interest of reducing the losses in the distribution system, power factor correction is added to neutralize a portion of the magnetizing current of the motor. Typically, the corrected power factor will be 0.92 - 0.95. Some power retailers offer incentives for operating with a power factor of better than 0.9, while others penalize consumers with a poor power factor. There are many ways that this is metered, but the net result is that in order to reduce wasted energy in the distribution system, the consumer will be encouraged to apply power factor correction. 3.2 Principle: Power factor correction is achieved by the addition of capacitor banks in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel. The resulting capacitive current is leading current and is used to cancel the lagging inductive current flowing from the supply which is shown in fig. below.
Fig 3.2: Power factor improvement using capacitor. 3.3 Block Diagram: Voltage and current step down arrangement
Power factor correction relay
Switching system (Magnetic contact)
…………………….. Inductor (Current limiting reactor)
…………………….. Capacitor bank Fig 3.3: Block diagram of a PFI plant. 3.4 Important Components Required for Designing PFI Plant: The most important components used for PFI plant are: a. PFC Relay b. H.R.C. Fuse c. Inductor d. Magnetic Contactor e. Capacitor Bank 3.5 Description of the Components: 3.5.1 PFC Relay: The capacitors are controlled by a microprocessor based relay called power factor controller (PFC) relay which continuously monitors the reactive power demand on the supply. The relay connects and/or disconnects the capacitors to compensate for the reactive power of the total load. This reduces the overall demand on the supply. A typical power factor correction system would incorporate a number of capacitor sections (‘stages’) determined by the characteristics and the reactive power requirements of the installation under consideration. The switching sequence shall be coordinated with the logic control of the sub-station device and Voltage Control (VC) device, and these shall be selectable from manual selection facilities. The switching steps shall be programmable to achieve switching of capacitor sub-banks through stage controlled circuit breaker. The PFC relay shall have a range suitable for proper selection of switching In/Out of the Sub-banks to maintain the Target Power Factor (0.95). Some Manufacturers of PFC relay: 1. 2. 3. 4. 5.
MAKRO BELUK Estimate ® PFC CELEC Enterprises Conserve Systems Pvt. Ltd.
Standard Features of MAKRO Power Factor Controller:
• • • • • • • • • •
Automatic self adjustment to any capacitor step value Digital indication of power factor, preset parameters and specified installation data. No. volt release feature to immediately disconnect all capacitors in the event of power failure TTL interface Plug. in terminal connection Digital setting of individual parameters (i.e target power factor, switching time, step limit) Indication of number of switching operations per step Indication of capacitor size (value of capacitor size in proportion to kvar steps) Visual display of target power factor alarm Visual display of harmonic overload alarm
Fig 3.4: Power Factor Controller Relay-BLR CA (MIKRO)
3.5.2 H.R.C Fuse:
The HRC (High Rupturing Capacity) fuse-links are used to protect capacitor banks against short-circuits. They protect switchgears from thermal and electromagnetic effects of heavy short-circuit currents by limiting the peak current values (cut-off characteristic) and interrupting the currents in several milliseconds. The main advantages of HRC fuses are: a) It is a precision fuse whose operating characteristics are accurately known. b) It can interrupt a large magnitude of fault current. Construction:
Fig 3.6: Internal construction of an HRC fuse An HRC fuse is shown in fig 3.6. Its construction consists of: a) The fuse element is made from silver or alloy to improve fuse life and reduce the element resistance. Silver oxide is a good conductor of electricity. Hence, the fuse characteristics do not change appreciably over the installed life of the fuse. Also, the use of silver keeps element corrosion to a minimum. b) To improve reliability, the fuse element is not notched. This ensures that the element will melt through at least one notch (possibly more), to quickly and cleanly, open the current path. c) The body of the fuse is made from ceramic or fiberglass. This provides good mechanical strength, high temperature stability and good electrical isolation between the two endcaps. d) The space, between the fuse element and the fuse body, is completely filled with silica sand, for the following reasons: 1) It removes the air from inside. Hence, reduces oxidation of the element life. 2) Provides cooling to the element, during the normal functioning of the fuse. 3) Acts as an arc quencher by forming high resistance glass, when high heat is produced, during melting of the fuse element. Types:
i.
HRC Fuse Link Blade Contact DIN Type:
HRC Fuse Link (Blade Contact type) has a unique design that provides significant saving in time and power. The contact blades of the fuse link are made up of electrolytic copper and are silver plated. Technical Specifications: • Range : 6A to 630A • Available in : size 00, 01, 02, 03 Series "gG" •
Rated Voltage : 415V 50Hz
Fig 3.7: DIN Type HRC fuse i.
HRC Fuse Link Bolted Connection BS Type:
HRC Fuse Link (Bolted Connection - BS type) guarantees reliability even in severe ambient conditions. These links reduce thermal stress because of lower let through fault energy to eliminate mechanical damages. There is no emission of gas or flames during the operation. Technical Specifications: • Range : 2A to 630A • Available in: SGNS, SGTIA, SGTSS, SGTSD. SGTSDC, SGTSF, SGTSK, SGTSMF, SGTTS S SGTTM •
Rated Voltage: 415V, 50Hz
Fig 3.8: BS Type HRC fuses
ii.
HRC Fuse Link Cylindrical Cap RH Type:
HRC Fuse Link (Cap RH Type) with fuse-links having cylindrical contact caps are used as overload and short circuit protection device for various electrical equipments. The fuse links with the striker are used for protecting motors against phase-failure operation when fitted in fuse isolators. Technical Specifications: • Range 2A To 63A Rated Voltage 415V 50 HZ • Utilization category "gG"
Fig 3.9: Cylindrical Cap RH Type HRC Fuse The fuse requirements for the different size capacitors are: Capacitor Rating kvar / 415V 12.5 25 50
HRC Fuses (A) – class gl 32 A 63 A 125 A
3.5.3 Inductor: Especially the switching of capacitors in parallel to others of the bank, already energized, causes extremely high inrush current, up to 200 times the rated current, and limited only by
the ohmic resistance of the capacitor itself. Such a capacitor’s AC resistance is very low and thus contributes to high inrush current. To limit this high inrush current, reactors are connected in series with the capacitor banks.
Series reactors are used with capacitor banks for two main reasons: i. ii.
To dampen the effect of transients during capacitor switching. To control the natural frequency of the capacitor bank and system impedance to avoid resonance or to sink harmonic current.
Fig 3.10: Inrush current limiting reactor 3.5.4 Magnetic Contactor: A contactor is an electro-magnetic switching device used for remotely switching a power or control circuit. A contactor is activated by a control input which can be a lower or higher voltage/current than that which the contactor is switching. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker a contactor is not intended to interrupt a short circuit current. Contactors range from having a breaking current of several amps and 110 volts to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side. Contactors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.
Fig 3.11: Magnetic Contactor Operating Principle: A contactor is basically composed of three different items. The contact item/s are the current carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs. The electromagnet item provides the driving force to close the contacts. The enclosure item is a frame housing the contact and the electromagnet. When current passes through the electromagnet, a magnetic field is produced, which attracts ferrous objects, in this case the moving core of the contactor is attracted to the stationary core. The electromagnet coil draws more current initially, due to its inductance. The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is deenergized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts. For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency. Most motor control contactors at low voltages (600 volts and less) are air break contactors; i.e. ordinary air surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage motor controllers use vacuum contactors. Motor controls contactors can be fitted with short-circuit protection (fuses or circuit breakers), disconnecting means, overload relays and an enclosure to make a combination starter. Ratings:
Contactors are rated by designed load current per contact (pole), maximum fault withstand current, duty cycle, voltage, and coil voltage. Current rating of the contactor depends on utilization category. For example IEC Categories are described as: • •
AC1 - Non-inductive or slightly inductive rows AC2 - Starting of slip-ring motors
•
AC3 - Starting of squirrel-cage motors and switching off only after the motor is up to speed. (Make LRA, Break FLA)
•
AC4 - Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make and Break LRA)
•
AC11 - Auxiliary (control) circuits
3.5.6 Capacitor Bank: Shunt capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Shunt capacitor banks (SCB) are mainly installed to provide capacitive reactive compensation/ power factor correction. The use of SCBs has increased because they are relatively inexpensive, easy and quick to install and can be deployed virtually anywhere in the network. Its installation has other beneficial effects on the system such as: improvement of the voltage at the load, better voltage regulation (if they were adequately designed), reduction of losses and reduction or postponement of investments in transmission. The main disadvantage of SCB is that its reactive power output is proportional to the square of the voltage and consequently when the voltage is low and the system needs them most, they are the least efficient. Location of capacitor bank: Today, with so many different types of motors and circuits in the plant, it becomes very difficult to determine where to wire power factor capacitors. In the "old days", with just across-the-line starters, the capacitor was wired between the contact and the overload of the starter, and it was done. But today, with high-efficiency motors, non-linear loads, drives and such, wiring of the capacitor becomes a very different story. Consideration must be given to the application of the capacitor and its wiring in the system. System 1:
Fig 3.14: Between Overload & Contacts This is the simplest connection for the capacitor. When the motor is energized, the capacitor is energized. When the motor is de-energized, the capacitor is de-energized. System 2:
Fig 3.15: Between Overload & Motors When it is not possible to connect between the contacts and the overloads, then the capacitor may have to be connected between the overload and the motor. With the capacitor connected here, the overload will see less current. System 3:
Fig 3.16: Between Fuse & Contacts Sometimes it may not be possible to connect the capacitor between the starter contacts and the overload. The capacitor may have to be connected between the fuse and the starter contacts. This type of connection is called "floating" the capacitor motor fuse experience less inrush current and helps avoid nuisance fuse tripping on startup. System 4:
Fig 3.17: Routed through the Overload If the overload device is upstream of the capacitor connection, the leads of the capacitor should be routed through the overload. The overload device then recognizes the motor current and the capacitor current, so no reduction of the overload is required. The Capacitor Unit: The capacitor unit is the building block of a shunt capacitor bank. The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series connected groups, within a steel enclosure. The internal discharge device is a resistor that reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a variety of voltage ratings (240 V to 24940V) and sizes (2.5 KVAR to about 1000 KVAR).
Fig 3.18: The Capacitor Unit Capacitor Unit Capabilities: a) Capacitor units should be capable of continuous operation up to 110% of rated terminal rms voltage and a crest voltage not exceeding 1.2 x √2 of rated rms voltage, including harmonics but excluding transients. The capacitor should also be able to carry 135% of nominal current. b) Capacitors units should not give less than 100% nor more than 115% of rated reactive power at rated sinusoidal voltage and frequency. c) Capacitor units should be suitable for continuous operation at up to 135%of rated reactive power caused by the combined effects of: • Voltage in excess of the nameplate rating at fundamental frequency, but not over 110% of rated rms voltage. • Harmonic voltages superimposed on the fundamental frequency. • Reactive power manufacturing tolerance of up to 115% of rated reactive power. Capacitor Bank Design: i. Multiple units grounded single Way:
Fig 3.19: Multiple units grounded single Way Delta-connected Banks: Delta-connected banks are generally used only at distributions voltages and are configured with a single series group of capacitors rated at line-to-line voltage. With only one series group of units no overvoltage occurs across the remaining capacitor units from the isolation of a faulted capacitor unit. In the PFI plant we mainly use delta connected capacitor bank. The reason of using delta connected capacitor bank is shown below by a simple calculation. In the case of delta connection:
The capacitor is subjected to line voltage U N, phase to phase. Thus total KVAR compensation:
From the above equations it follows that for the desired Q KVAR:
Thus for the same amount of KVAR compensation a star connection requires the triple capacitance of a delta connection. On the other hand, for the same nominal voltage U N in delta connection a √3 thicker dielectric film is required to get similar values of electric field strength. Capacitor Bank Protection: The protection of SCB’s involves: a) Protection of the bank against faults occurring within the bank including those inside the capacitor unit. b) Protection of the bank against system disturbances and faults. Chapter 4 Active PFC Techniques Chapter outlines •
Introduction
•
Conventional Boost Converter
•
Bridgeless Boost Converter
•
Comparison
•
Automatic Power Factor Controller
4.1 Introduction: In recent years, there have been increasing demands for high power factor. Among power factor correction techniques, the analogy control method is now attractive in industry, but the digital control method is the trend in the future. With the stringent requirements of power quality, power-factor correction (PFC) has been an active research topic in power electronics, and significant efforts have been made on the developments of the PFC converters. In general, the continuous-conduction mode (CCM) boost topology has been widely used as a PFC converter because of its simplicity and high power capability. It can be used with the universal input voltage range. Recently, in an effort to improve the efficiency of the PFC rectifiers, bridgeless PFC circuit topologies are used. Generally, the bridgeless PFC topologies may reduce the conduction loss by reducing the number of semiconductor components in the line current path. So far, a number of bridgeless PFC boost rectifier implementations and their variations have been proposed. 4.2 Conventional Boost Converter: Diode rectifiers are the most commonly used circuits for applications where the input is the ac supply. The power factor diode rectifiers with a resistive load can be as high as 0.9 and it is lower with a reactive load. With aid of a modern control technique, the input current of the rectifiers can be made sinusoidal and in phase with the input voltage, thereby having an input power factor of approximate unity. A unity power factor circuit combines a full bridge rectifier and a boost converter. 4.3 Bridgeless Boost Converter: The boost inductor is split and located at the AC side to construct the boost structure. In this first half line cycle, MOSFET M1 and boost diode D1, together with the boost inductor construct a boost DC/DC converter. Meanwhile, MOSFET M2 is operating as a simple diode. The input current is controlled by the boost converter and following the input voltage. During the other half line cycle, circuit operation as the same way. Thus, in each half line cycle, one of the MOSFET operates as active switch and the other one operates as a diode: both the MOSFET’s can be driven by the same signal. The difference between the bridgeless PFC and conventional PFC is summarized. Comparing the conduction path of these two circuits at every moment, bridgeless PFC inductor current only goes through two semiconductor devices, but inductor current goes through three semiconductor devices for the conventional PFC circuit. 4.4 Comparison: PFC converter Conventional
Slow diode 4
Fast diode
MOSFET
Conduction path On/(Off)
1
1
2 slow diode, 1 MOSFET/
(2 slow diode, 1 fast diode) Bridgeless 0 2 2 1 body diode, 1 MOSFET/ (1 MOSFET body diode, 1diode) Table 4.1: Differences between conventional PFC and bridgeless PFC As shown in Table 4.1, the bridgeless PFC uses one MOSFET body diode to replace the two slow diodes of the conventional PFC. Since both the circuits operating as a boost DC/DC converter, the switching loss should be the same. Thus the efficiency improvement relies on the conduction loss difference between the two slow diodes and the body diode of the MOSFET. Besides, comparing with the conventional PFC, the bridgeless PFC not only reduces conduction loss, but also reduces the total components count. 4.5 Automatic Power Factor Controller: This can be achieved by using microcontroller based power factor controller .The main core of this work is to design power factor controller. This system will be able to control the power factor of both linear and nonlinear load system. The design aims to monitor phase angle continuously and in the event of phase angle deviation, a correction action is initialized to compensate for this difference by continuous changing variable capacitors value via switching process. The overall system requires only one chip, a few power electronic components and a bank of capacitors.
Fig 4.3: Block Diagram microcontroller based PFC 4.5.1 Algorithm for Control Scheme: Step 1- Set the user define lower and upper power factor (LPF & UPF). Step 2- Set the user define threshold value of current (TUC). Step 3- Determine power factor.
Step 4- determine value of current. Step 5- if value of current is less than TUC, take no action and go to step 3.
Step 6- if the value of power factor is between LPF and UPF take no action and go to step 3. Step 7- if the value of power factor is less than LPF switch on the next off capacitor and wait for 1.0 seconds. Go to step 3. Step 8- If the value of power factor is more than UPF or as leading, switch off the first on capacitor and wait for 1.0 second. Go to step 3. 4.5.2 Algorithm for Determining Power Factor: Step 1- Check for voltage cross zero from negative to positive. Step 2- Timer T1 starts (T1). Step 3- Timer T2 starts (T2). Step 4- Check for current cross zero from negative to positive. Step 5- Timer T2 stops. Step 6- Check again for voltage cross zero from negative to positive. Step 7- Timer T1 stops. Step 8- Phase φ = (T2 / T1) * 3600 .Step 9- Get cos φ from look up table. Step 10- If T2 > T1/4 report power factor is leading. Chapter 5 Study in Bextex Chapter outlines • Study on 4000 KVAR PFI Plant LOAD OF BEXTEX (PADMA-2) Back Process: SL NO
Quantity
Actual Load No Of M/C (KW)
Actual Load Connected (KW) Load (KW)
01
Blow Room ( C-1,2 )
60
60
1
02
Blow Room ( F-Line )
30
1
30
130.86
03
Blow Room ( Rieter )
13
1
13
27.29
04
A/C Plant ( Luwa )
36
1
36
48.74
05
A/C Plant – 1
264
1
264
319.39
06
Card DK-760
9
20
180
250.00
07
Card DK-903
10.5
2
21
39.42
08
Card C-51
7
6
42
80.40
09
Comber ( Toyota )
4.5
6
27
32.76
10
Comber ( Rieter )
5
6
30
39.60
11
Luwa ( Comber )
3.45
1
3.45
5.87
12
D/F Breaker
5
5
25
47.60
13
D/F Finisher
5
5
25
61.45
14
Lap Former
5
2
10
22.71
15
Simplex FL-16
6
8
48
120.12
16
Simplex FL-100
7.5
1
7.5
17.67
17
PC 1 & 2 (D/F)
5
2
10
26.00
18
A/C Plant-2
168
1
168
214.74
999.95
1484.62
Total Ring Section: SL NO
Quantity
Actual Load No Of M/C (KW)
Actual Load Connected (KW) Load (KW)
1
Ring Frame
17
100
1700
2490
2
Over Head Cleaner
2
50
100
110
3
A/C Plant-3,6
180
4
720
884
2,520
3484
Total Winding Section: SL NO
Quantity
Actual Load No Of M/C (KW)
Actual Load Connected (KW) Load (KW)
1
Machoner
22
11
242
338.8
2
Schlafhorst
20
4
80
118.52
3
A/C Plant-7
118
1
118
157.55
4
Tex Tool & R.J.K
6
3
18
22.95
5
Twist Frame
6
7
42
71.26
6
Doubling
2
1
Total
2
3.51
502
711.82
Others: SL NO
Quantity
Actual Load No Of M/C (KW)
Actual Load Connected (KW) Load (KW)
1
Compressor
40
6
240
222
2
Diare
2
4
8
5.2
3
Xorella ( Boiler )
100
1
100
165.75
4
Work Shop
6
1
6
6
5
Q.C.A
12
1
12
12
6
Paper Cone Factory
6
1
6
6
7
Packaging
36
1
36
36
Total for others
408
452.95
Total Lighting
300
300
Total Load of BEXTEX (Y-2): SL NO
Quantity
Actual Load (KW) (Inductive)
Connected (KW)
Load Connected (KW)
(Inductive)
(Resistive)
1
Back Process
999.95
1484.62
_
2
Ring Section
2520.00
3484.00
_
3
Winding Section
502.00
711.82
_
4
Others
408.00
452.95
_
5
Lighting
_
_
300.00
4429.95
6133.39
300.00
Total Calculation:
Total Load of BEXTEX (Y-2) =6433 KW Average Power Factor ( cos φ) of BEXTEX (Y-2) = 0.8 We know, Most economical power factor, cos φ2 = 1 − sin 2 φ2
= 1 −( y / x ) 2
X = Maximum demand charges (Tk per KVA per annum). = 110 Tk per KVA per annum (approximate). Y = Expenditure on power factor correction equipment (Tk per KVA per annum).
Load
= 150 Tk per KVA per annum. (Approximate). =150*0.1 =15 (The annual interest and depreciation is 10%) Maximum demand in KVA = Peak
∴ Maximum demand in
KVA =
KW cos φ1
6433 0.8
= 8041.25 KVA Most economical power factor, cos φ2 = 1 − sin 2 φ2 = 1 −( y / x ) 2 = 1 − (15 ÷110 )
2
= 0.99
We want to increase Factories power factor from 0.95 to 0.99 When new PF is 0.95: 6433KW
2099.20
θ1=36.8 7
2725.55 8041.25 KVA
Fig: P = 6433kw cos
θ= 0.8 1
∴ θ= 36.87 1
∴ sin θ = 0.6 1
4824.75KVAR
Real Power = 8041.25 KVA, (6433/0.8) Reactive Power = (8041.25 x 0.6), = 4824.75 KVAR If we have try unity power factor than we have need to 4824.75 KVAR capacitive loads. Again, cos θ = 0.95 2 ∴ θ =18.19 2
∴sin θ = 0.31 2
Real Power = 6771.58 KVA, (6433/0.95) Reactive Power = (6771.58 x 0.31), = 2099.20 KVAR
∴ Required KVAR = (4824.75 - 2099.20), = 2725.55 KVAR 1.
When new PF is 0.99: 6433KW θ3=909.71
θ1=36.87 7 3915.04 8041.25 KVA
Fig:
P = 6433kw cos
θ= 0. 8 1
∴ θ= 36.87 1
∴ sin θ = 0.6 1
4824.75KVAR
Real Power = 8041.25 KVA, (6433/0.8) Reactive Power = (8041.25 x 0.6), = 4824.75 KVAR If we have try unity power factor than we have to need 4824.75 KVAR capacitive loads. Again, cos θ =0.99 3 ∴ θ =8.11 3
∴ sin θ =0.14 3
Real Power = 6498.00 KVA, (6433/0.99) Reactive Power = (6498.00 x 0.14), = 909.71 KVAR
∴ Required KVAR = (4824.75 - 909.71), = 3915.04 KVAR Chapter 6 Design of a PFI Plant & Calculation Chapter outlines •
Design of a 7.5 KVAR PFI Plant
•
Single Line Diagram
•
PFI Pant
6.1 Design of a 7.5 KVAR PFI Plant:
P 2 1
S1
Q2
S2 Q1
QN
Here, P = Real power in KW Q1 = Reactive power in KVAR before addition of capacitor bank QN = Neutralized reactive power = 7.5 KVAR Q2 = Reactive power in KVAR after addition of capacitor bank S1 = Apparent power in KVA before addition of capacitor bank S2 = Apparent power in KVA after addition of capacitor bank Let, Present power factor 0.8 and target power factor 0.95. cos 1 = 0.8 thus
1
And cos 2 = 0.95 thus
= cos-10.8 = 36.87 2
= cos-10.95 = 18.19
Now, QN = Q 1 Q2 QN = P (tanθ1− tanθ2) P= P= P = 17.77 KW Thus we have total 17.77 KW inductions motor.
Again, S1 =
And S2 =
=
17.77 / cos 36.87 = 22.21 KVA
= = 18.70 KVA
If we use 6-stage PFC relay then in each stage there will be 50 KVAR capacitor bank. Let, the capacitor banks are subjected to 11 KV line voltages and total load current be I for power factor 0.8. Then, P = √3×V×I cosθ 17.77 = √3×11×I×0.8
ďƒ° I = 1.16 Amp
6.2: Single Line Diagram:
6.3: PFI PLANT If we construct 7.5 KVAR PFI unit then the pictorial view will be
Fig 6.3: Pictorial view of a PFI plant Sl. No.
Item
Quantity
Rating
1.
PFC relay (BLR-CA)
One pcs
12 stage
2.
HRC fuse
Twelve pcs
100 Amp
3.
Magnetic Contactor
Twelve pcs
100 Amp, 11 KV
4.
Capacitor Bank
Twelve pcs
50 KVAR
5.
Current limiting reactor
Twelve pcs
Approx. 0.6 ÎźH, 7 turns
6.
LT CT
One pcs
Table 6.3: Proposed rating for important parts of 7.5 KVAR PFI units 6.4: Data Table Date table 1: With PFI Date: 13.04.11 Sl. No.
Name
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
Result
Remarks
5.
(T1 +T2) Active Total Power: kwh
51.5
6.
T1 Active Total Power: kwh
7.
T2 Active Total Power: kwh
8.
(T1 +T2) Reactive Total Power: kVArh
9.
T1 Reactive Total Power: kVArh
10.
T2 Active Total Power: kVArh
11.
A Phase Instantaneous Voltage V
225
12.
B Phase Instantaneous Voltage V
225
13.
C Phase Instantaneous Voltage V
227
14.
A Phase Instantaneous Current A
5.4
15.
B Phase Instantaneous Current A
5.5
16.
C Phase Instantaneous Current A
5.6
17.
A Phase Instantaneous Power Kw
18.
B Phase Instantaneous Power Kw
19.
C Phase Instantaneous Power Kw
20.
(A+B+C) Phase Instantaneous Power
21.
A Phase Power Factor
0.99
22.
B Phase Power Factor
0.98
23.
C Phase Power Factor
0.97
24.
MD (MAX.DEMAND) Kw
10
Date table 2: With PFI Date: 14.04.11 Sl. No.
Name
Result
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
5.
(T1 +T2) Active Total Power: kwh
335.6
6.
T1 Active Total Power: kwh
41
7.
T2 Active Total Power: kwh
94
Remarks
8.
(T1 +T2) Reactive Total Power: kVArh
22
9.
T1 Reactive Total Power: kVArh
6.8
10.
T2 Active Total Power: kVArh
15
11.
A Phase Instantaneous Voltage V
227
12.
B Phase Instantaneous Voltage V
226
13.
C Phase Instantaneous Voltage V
228
14.
A Phase Instantaneous Current A
5.2
15.
B Phase Instantaneous Current A
5.9
16.
C Phase Instantaneous Current A
6
17.
A Phase Instantaneous Power Kw
1.1
18.
B Phase Instantaneous Power Kw
1.2
19.
C Phase Instantaneous Power Kw
1.3
20.
(A+B+C) Phase Instantaneous Power
3.6
21.
A Phase Power Factor
1.0
22.
B Phase Power Factor
0.99
23.
C Phase Power Factor
1.0
24.
MD (MAX.DEMAND) Kw
4.45
Date table 3: With PFI Date: 15.04.11 Sl. No.
Name
Result
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
5.
(T1 +T2) Active Total Power: kwh
229.3
6.
T1 Active Total Power: kwh
62
7.
T2 Active Total Power: kwh
167
8.
(T1 +T2) Reactive Total Power: kVArh
34.27
9.
T1 Reactive Total Power: kVArh
9.99
10.
T2 Active Total Power: kVArh
24.29
Remarks
11.
A Phase Instantaneous Voltage V
208
12.
B Phase Instantaneous Voltage V
208
13.
C Phase Instantaneous Voltage V
209
14.
A Phase Instantaneous Current A
7.5
15.
B Phase Instantaneous Current A
7.3
16.
C Phase Instantaneous Current A
7.7
17.
A Phase Instantaneous Power Kw
1.5
18.
B Phase Instantaneous Power Kw
1.5
19.
C Phase Instantaneous Power Kw
1.5
20.
(A+B+C) Phase Instantaneous Power
4.5
21.
A Phase Power Factor
1.0
22.
B Phase Power Factor
0.99
23.
C Phase Power Factor
0.99
24.
MD (MAX.DEMAND) Kw
4.55
Date table 4: With PFI Date: 18.04.11 Sl. No.
Name
Result
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
5.
(T1 +T2) Active Total Power: kwh
454
6.
T1 Active Total Power: kwh
123
7.
T2 Active Total Power: kwh
331
8.
(T1 +T2) Reactive Total Power: kVArh
66
9.
T1 Reactive Total Power: kVArh
20
10.
T2 Active Total Power: kVArh
46
11.
A Phase Instantaneous Voltage V
215
12.
B Phase Instantaneous Voltage V
216
13.
C Phase Instantaneous Voltage V
216
Remarks
14.
A Phase Instantaneous Current A
7.3
15.
B Phase Instantaneous Current A
7.9
16.
C Phase Instantaneous Current A
7.7
17.
A Phase Instantaneous Power Kw
1.5
18.
B Phase Instantaneous Power Kw
1.6
19.
C Phase Instantaneous Power Kw
1.6
20.
(A+B+C) Phase Instantaneous Power
4.8
21.
A Phase Power Factor
1.0
22.
B Phase Power Factor
0.99
23.
C Phase Power Factor
0.99
24.
MD (MAX.DEMAND) Kw
4.49
Date table 5: Without PFI Date: 19.04.11 Sl. No.
Name
Result
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
5.
(T1 +T2) Active Total Power: kwh
544
6.
T1 Active Total Power: kwh
144
7.
T2 Active Total Power: kwh
399
8.
(T1 +T2) Reactive Total Power: kVArh
182
9.
T1 Reactive Total Power: kVArh
53
10.
T2 Active Total Power: kVArh
129
11.
A Phase Instantaneous Voltage V
224
12.
B Phase Instantaneous Voltage V
225
13.
C Phase Instantaneous Voltage V
225
14.
A Phase Instantaneous Current A
9.6
15.
B Phase Instantaneous Current A
10.2
16.
C Phase Instantaneous Current A
10.3
Remarks
17.
A Phase Instantaneous Power Kw
1.4
18.
B Phase Instantaneous Power Kw
1.4
19.
C Phase Instantaneous Power Kw
1.5
20.
(A+B+C) Phase Instantaneous Power
4.5
21.
A Phase Power Factor
0.67
22.
B Phase Power Factor
0.66
23.
C Phase Power Factor
0.68
24.
MD (MAX.DEMAND) Kw
4.58
Date table 6: Without PFI Date: 21.04.11 Sl. No.
Name
Result
1.
Date
2.
Time
3.
Meter Address: before six digital
4.
Meter Number
5.
(T1 +T2) Active Total Power: kwh
703
6.
T1 Active Total Power: kwh
187
7.
T2 Active Total Power: kwh
516
8.
(T1 +T2) Reactive Total Power: kVArh
409
9.
T1 Reactive Total Power: kVArh
113
10.
T2 Active Total Power: kVArh
296
11.
A Phase Instantaneous Voltage V
224
12.
B Phase Instantaneous Voltage V
224
13.
C Phase Instantaneous Voltage V
224
14.
A Phase Instantaneous Current A
7.2
15.
B Phase Instantaneous Current A
7.6
16.
C Phase Instantaneous Current A
7.2
17.
A Phase Instantaneous Power Kw
0.17
18.
B Phase Instantaneous Power Kw
1.38
19.
C Phase Instantaneous Power Kw
1.3
Remarks
20.
(A+B+C) Phase Instantaneous Power
4
21.
A Phase Power Factor
0.62
22.
B Phase Power Factor
0.63
23.
C Phase Power Factor
0.65
24.
MD (MAX.DEMAND) Kw
4.6
Date table 7: Without PFI Chapter 7 Conclusion Chapter outlines • 7.1
Conclusion
Conclusion:
Installing capacitors for power factor improvement can be beneficial to both the utility and the electrical consumer. When properly designed and installed, capacitors can increase voltage, lower overall system loading, and reduce energy costs. Consideration must be given to capacitor ratings and the effects of installing them on an existing distribution system. By evaluating the impact of location, voltage rise, and harmonic resonance conditions, capacitors can be installed for safe operation within their ratings. A comprehensive study should be performed on the existing system to fully assess the effectiveness and likelihood of potential problems of installing capacitors for power factor improvement. References: [1] V.K. Mehta & Rohit Mehta, “Principles of Power System”, 3 rd edition, 2002. [2] Cutler Hammer, “Power Factor Correction: A Guide for The Plant Engineer”. [3] en.wikipedia.org/wiki/Power factor correction [4] Jones, L. D.; Blackwell, D. (1983) “Energy Saver Power Factor Controller for Synchronous Motors”, IEEE Transactions on Power Apparatus and Systems, Volume: 5, Issue: 5, Pages: 1391-1394. [5] El-Sharkawi, M.A.; Venkata S.S.; Williams T.J.; Butler N.G. (1985) “An Adaptive Power Factor Controller for Three-Phase Induction Generators”, IEEE Transactions on Power Apparatus and Systems, Volume: PAS- 104, Issue: 7, Pages: 1825–1831.
[6] Nalbant, M.K. (1990) “Power Factor Calculations and Measurements”, IEEE Conference on Applied Power Electronics, Pages: 543 – 552. [7] Rakendu Mandal; Sanjoy Kumar Basu; Asim Kar; Shyama Pada Chowdhury (1994) “A Microcomputer – Based Power Factor Controller”, IEEE Transactions on Industrial Electronics, Volume: 41, Issue: 3, Pages: 361– 371. [8] Dallago, E.; Sasone, G.; Storti, M.; Venchi, G. (1998) “Experimental Analysis and Comparison on a Power Factor Controller Including a Delta – Sigma Pressing Stage”, IEEE Transaction industrial electronics, Volume: 45, Issue: 4, Pages: 544–551. [9] Tinggren, R.; Yi Hu; Le Tang; Mathews, H.; Tyner, R. (1999) “Power Factor Controller- an Integrated Power Quality Device”, IEEE Conference on Transmission and Distribution, Volume: 2, Pages: 572-578. [10] Cereda, C.; Gemme, C.; Moratto, A.; Tinggren, R. (2000) “Innovative Solutions for Power Quality in a Deregulated Market”, IEEE Conference on Industry Applications, Volume: 2, Pages: 932 – 939. [11] Machmoum, M.; Coulibaly, P.; Abdelli, Y. (2002) “A Power Factor Controller for ThreePhase PWM Rectifiers and Shunt Active Power Filters”, IEEE Conference on Harmonics and Quality of Power, Volume: 2, Pages: 626-631. [12] Cacciato, M.; Consoli, A.; De Caro, S.; Testa, A. (2005) “Using the Dc-Bus Current to Improve the Power Factor in Low-Cost Electric Drives”, IEEE Transactions on Industry Applications, Volume: 41, Issue: 4, Pages: 1084-1090. [13] Barsoum, Nader (2007) “Programming of PIC Micro-Controller for Power Factor Correction” IEEE Conference on Modeling & Simulation, Pages: 19-25 [14] en.wikipedia.org/wiki/Power factor correction.