On the Use of a Low Voltage Power Factor Controller in Deforming Regime

Gabriel Nicolae Popa Corina Maria Diniş

Dept. Electrical Engineering and Industrial Informatics Politehnica University of Timişoara

Hunedoara, Romania gabriel.popa@fih.upt.ro, corina.dinis@fih.upt.ro

Costel Paliciuc S.C. Chantrom S.R.L. Hunedoara, Romania

costel_paliciuc@yahoo.com

Abstract— The paper presents the analysis of a power factor with capacitors banks, without and with series coils, used for improving power factor for an inductive loads. These capacitors banks cause deforming regime growth by this current harmonics. In order to diminish deforming regime through proper sizing, it can use a mix of passive filter and power factor improvement.

Keywords— harmonics; passive filter; power factor correction; power quality

I. INTRODUCTION Reactive loads determine the phase shift between voltage

and current. This phase (inductive or capacitive) is a form of energy and it has a significant and measurable adverse effect, charged the electrical network. For example, after applying power factor improvement for an induction motor - with the help of the capacitors, the current through motor-capacitors load is less than before improving power factor, assuming the same level of mechanical load. This occurs due to the fact that part of the reactive component, is ensured by the capacitors banks. Although the current is lower, it will be deformed. The harmonics are a consequence of the nonlinear loads using deformed forms of voltage, and because of the movement of such currents occur deformations. Low-frequency harmonics with frequencies up to 2÷2.5 kHz are called higher harmonics and occur most frequently in the network [1,2]. The current facilities have a reactive compensation and are affected by the presence of harmonics. Most of the standards electricity companies recommended, and some even prescribe, as existing installations of reactive power compensation to be supplemented with coils on every capacitors bank. This means that these capacitors must be connected with coils in series, so the circuit to behave for the higher harmonics as an inductive element, and for the lower harmonics and fundamental frequency to remain as the capacitive element. It is formed a passive LC filter for higher harmonics, and, also, can be improve the power factor [3,4,5]. The shape of currents depends on the character and size of the load. That is the reason that the filter needs to be oversized. Compared to active filters, passive LC filters are

always in operation and are ready at all times, ensuring the absorption of harmonic for the value are dimensioned. Active filters can not be overloaded due to limitation through electronic control. Thus, when working of the filter capacity is exceeded, shall ensure a partial reduction in the level of distortion [6,7].

Power factor controller with capacitors banks are used often in electrical stations of facilities. In this way, the power factor will become higher than the neutral power factor, but the deforming (total harmonics distortion - THD) will be higher. Through the introduction of series coil with capacitors banks ensure avoiding phenomena of resonance and lessening the deforming operation [8].

II. POWER FACTOR CORRECTION IN INDUSTRY In the industry can be used a mix of improvement due to the power factor correction, fitted in electrical stations of facilities, which connects directly the capacitors banks, sized according to reactive power electric loads. In practice, the functions of reactive power compensation and filtering of deforming currents are often combined (fig. 1) [1,3].

It is common to use resonant frequency of the LC circuit at a frequency corresponding to the inter-harmonics, which does not correspond to a harmonic, to avoid overloading the power factor installation. Coil sizing is done normally as a percentage of reactive power of the capacitor.

Since a LC circuit is connected to the electrical network, harmonics caused by outside sources to the consumer can go through it at the same time as those of the internal sources for which it has been sized. In practice must be kept in mind that, while the filter must be oversized in case other consumers not to use the filter. At the same time oversized the filter can cause the operation on unanticipated overloads, and also increasing the quality factor of the filter. Ensure, in particular, a more precise separation of the desired frequency of unwanted ones, and losses in the circuit are diminished. The coil must be computed from the total value of the actual current (which has the fundamental and harmonics currents). In addition, the coil must be of sufficient linearity, so the frequency of resonance to be the same regardless of the load.

978-1-4799-2442-4/13/$31.00 ©2013 IEEE

Fig. 1. Filtering equipment and improving power factor with ESTA type capacitors banks.

Also, the electrical capacity of the capacitors must remain constant. Accordingly, it is recommended that the possibility of using a small number of capacitors banks.

III. THE BELUX BLR-CX CONTROLLER Digital electronic controller (fig.2) for power factor compensation, is an electronic power factor regulator type BELUX BLR-CX, from BELUK-CX, measuring the phase shift of the current (per phase) and voltage (line voltage on the other two phases) when passing through zero, and acts to maintain the impose power factor. The controller ensures the optimal closed number for each step. It is equipped with input filter, which allows the correct operation and display even in presence of harmonics. The controller is able to order 2 ÷ 6 capacitors banks (for version with 6 steps) [8].

Fig. 2. Belux BLR-CX power factor controller.

Mounting the controller, measuring current transducer and voltage measuring connectors on the other two phases, is done before the electrical loads as in fig.3.

Fig. 3. Connection scheme of the Belux BLR-CX controller. The current measured by the controller is between 10mA and 5 A. To current measurement on a phase (fig. 3) used a current transformer Metra TL 10 with ratio transformation 5/15 A, so that power can be amplify three times due to the low power of the load. It can mount up to 6 contactors who operate at 230 V AC. The contactors can connect three-phase capacitors banks.

IV. EXPERIMENTS IN LABORATORY The experiments used a three-phase induction motor with 0.55 kW power, 1450 rpm, 400 V AC which is mechanically connected to a DC generator G 0.45 kW power, 1680 rpm, 24 V DC, with excitation coil 24 V DC. The generator was loaded with 10 A through an adjustable power resistance 3.3Ω/12A. In experiments, the excitation coil voltage was 24 V and current excitation 1.25 A.

Fig. 4. The experimental setup. To measure electrical signals used a three phase power quality analyzer CA 8334 B, connected as in fig. 4 [9]. The currents were measured on the three phases with three current transducers CT1, CT2 and CT3 type MN 93A (5A) on the inputs C1, C2 and C3, and voltages were measured on the inputs V1, V2 and V3. There were made two groups of measurements: the first group of capacitors that were directly connected to the controller, and in the second case, it is used the series coils on each phase of the capacitors banks.

A. Experimentation of Power Factor Improving with Capacitors Banks without Series Coils

Each capacitors banks is made of 3 three-phase capacitors connected in series with the coils, in a triangle (D) or star (Y) connected as shown in fig. 5, the values of the capacitors from banks being presented in table I. In table I with B1, ..., B6 have represented the number of capacitors banks.

a. b. Fig. 5. Variants of connection of the capacitors banks with series coils: a. capacitors bank connected in D; b. capacitors bank connected in Y. At the first set of experiments were not used series coils (there are shunts on these coils) like in fig. 5.

TABLE I CAPACITORS BANKS USED AT FIRST EXPERIMENTS

B1 – D (μF)

B2 – D (μF)

B3 – Y (μF)

B4 – Y (μF)

B5 – Y (μF)

B6 – Y

(μF) 3x2.7 3x2.5 3x4 3x3.5 3x2 3x2

Because in the laboratory there are not electric loads with high power, for experiments with the compensation installation, capacitors have small capacities. For an inductive load, the capacity of a capacitor CY on a phase from a capacitors bank with Y connection is calculated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −−

−⋅

⋅⋅⋅=

2

22

1

21

2f

y coscos1

coscos1

Uf32PC

ϕϕ

ϕϕ

π (1)

where P is the power of the load, f is the network frequency (50 Hz), Uf is phase voltage (230 V), cos ϕ1 is the power factor compensation before, and cos ϕ2 is the neutral power factor (cos ϕ2 = 0.92). For the motor M connected to a generator G the capacity of capacitors calculated with (1) is CY=17 μF. If it is used D connection then the capacity of capacitors CD is:

3CC Y

D = (2)

At these experimentations the capacitors banks are connected directly to the controller (without series coils). In table II presented the steps used in the first experiment. In this table, the second column, i presented inductive character and c capacitive character of load.

TABLE II STAGES AT FIRST EXPERIMENT

Measuring stages cos ϕ (-) If (A)

1. Motor M connected 0.21 i 1.34 2. B4 connecting 0.26 i 1 3. B6 connecting 0.3 i 0.99 4. B2 connecting 0.55 i 0.56 5. B5 connecting 0.65 i 0.5 6. Motor M disconnecting 0.063 c 0.98 7. B4 disconnecting 0.06 c 0.73 8. B6 disconnecting 0.058 c 0.62 9. B2 disconnecting 0.01 c 0.3 10. B5 disconnecting - -

a. b.

Fig. 6. Connecting the motor M: a. The phase voltage and current at the phase R; b. The currents harmonic analysis on three phase.

a. b.

Fig. 7. Motor M connected and capacitors banks B4+B6+B2: a. The phase voltage and current at the phase R; b. The currents harmonic analysis.

a. b.

Fig. 8. Motor M connected and capacitors banks B4+B6+B2+B5: a. The phase voltage and current at the phase R; b. The currents harmonic analysis.

a. b.

Fig. 9. Motor M disconnected and capacitors banks B4+B6+B2+B5 connected: a. The phase voltage and current at the phase R; b. The currents harmonic analysis on three phase. The current network goes down along with putting new capacitors banks, but the current will be deformed. Harmonics occur, higher values of order 5,17,23,3,11,13, whose amplitudes are increased with the introduction of a greater number of capacitors banks. Along the stages of the first experiment were recording some electrical measures from figs. 10-13. THD for line voltage (UTHD) has been preserved relatively constant throughout the first experiment. THD for current (ITHD) has changed permanently, being increasingly higher (<70%) with introducing new capacitors banks.

Fig. 10. UTHD during the first experiment.

Fig. 11. ITHD during the first experiment.

a.

Fig. 12. a. The current fundamental evolution.

b.

c.

d.

e.

f.

g.

h.

i.

j.

Fig. 12. b-j. The evolution of harmonic currents (b-j, the odd harmonics 3-19) throughout the first experiment. The fundamental current (fig. 12.a) is the only one that goes down with putting new capacitors banks. Harmonic currents (figs. 12. b-j) have an inverse evolution toward the fundamental current, the biggest being the rank, 5,17,7,3,13.

a.

b.

Fig. 13. Power factor evolution: a. in deforming regime; b. for fundamentals – 50 Hz. Progressive capacitors banks connection, increase the value of both power factor in deforming PF (fig. 13.a) and power factor for the fundamentals DPF (fig. 13.b), that has values between 0.66 ÷ 0.73. The electric motor M is not charged with a great load and reactive power that could be inserted by the capacitors banks B1 and B3 may cause capacitive character of the load. A greater difference between the PF and DPF indicate a stronger deforming regime.

B. Experimentation of Power Factor Improving with Capacitors Banks with Series Coils

Each capacitors bank has connected three coils as in fig. 5. With IG1,..., IG6 have noted the six groups of coils that were series with coils. The values of these coils are given in table III. Resonance frequency for a group LC filter is calculated with (3). For capacitors banks Bi connected with coils groups IGi, i = 1 ...6, in table III frequencies were calculated for resonance filters used:

CL21f

⋅⋅⋅=

π (3)

TABLE III THE INDUCTANCE USED AT SECOND EXPERIMENTS

Type IG1 IG2 IG3 IG4 IG5 IG6 L (mH) 385 71.83 15.25 3.78 2.4 2.51 f (Hz) 90.12 216.83 644.4 1383 2296.3 2247.2

TABLE IV STAGES AT SECOND EXPERIMENT

Measuring stages cos ϕ (-) If (A)

1. Motor M connected 0.21 i 1.34 2. B4 connecting 0.45 i 1.1 3. B6 connecting 0.5 i 1.04 4. B2 connecting 0.84 i 0.8 5. B5 connecting 0.94 i 0.7 6. Disconnecting excitation coil of generator G 0.065 i 1.15 And from the second experiment, the current network decrease in the same time with the increasing of the number of capacitors banks. In table IV with i was noted the inductive character of the load.

a. b.

Fig. 14. Motor M connected and capacitors banks B4+B6+B2: a. The phase voltage and current at the phase R; b. The currents harmonic analysis on three phase.

a. b.

Fig. 15. Motor M connected and capacitors banks B4+B6+B2+B5: a. The phase voltage and current at the phase R; b. The currents harmonic analysis on three phase. Through the series coils with capacitors banks, inrush current from the network, has a similar shape with the case from subchapter A and also there are overlapping some strong oscillations. The actual value of the current is higher than the results obtained from the subchapter A.

a. b.

Fig. 16. Motor M disconnected and capacitors banks B4+B6+B2+B5 connected: a. The phase voltage and current at the phase R; b. The currents harmonic analysis on three phase. There were recording some electric measure during the second experiment in figs. 17-20. UTHD has a linear trend for all three phases (fig. 17). The same, can not be said about the total coefficient measured for current harmonic distortion (ITHD), where the maximum values ranging between 70-150% when the controller has connected maximum number of capacitor banks to put power factor, in the range of 0.92 ÷ 1.

Fig. 17. UTHD during the second experiment.

Fig. 18. ITHD during the second experiment.

The current fundamental analysis indicates a maximum of 3.5 A at disconnection of the load, and a minimum value of 0.2A, when all capacitors banks are connected. Fundamental current diminishes with the introduction of an increasingly number of capacitors banks.

a.

Fig.19. a. The current fundamental evolution.

b.

c.

d.

e.

f.

g.

h.

i.

j.

Fig.19. b-j. The evolution of harmonic currents (b-j, the odd harmonics 3-19) throughout the second experiment. Current harmonics (figs. 19. b-j) have an inverse evolution towards fundamental current, harmonics with the biggest amplitudes are 5,7,13,19,9,3.

a.

b.

Fig. 20. Power factor evolution: a. in deforming regime; b. for fundamentals – 50 Hz.

Power factor measured in deforming (fig.20.a), has a maximum values ranging between 0.76÷0.8, when are the maximum number of capacitors banks, and the power factor for fundamental is in the range 0.92÷0.98.

V. CONCLUSION The power factor is an important parameter in electrical

power engineering. Increasing the power factor value of the power factor over neutral value is one of the aims pursued by the industrial facilities. Most of them have electrical loads that amplify the deforming regime, especially when using capacitors banks for improving power factor. Usually, capacitors banks are control using power factor controller and are connected in the power stations of the facilities.

By using power factor correction controller can conclude: - higher values of capacitors increasingly the deforming regime; - operation with small load or idle of the motor due the intensification of deforming regime; - a big difference between the power factor in deforming regime and power factor of fundamentals indicate a higher deforming regime; - if the capacitors banks are connected with series coils, the deforming is diminished if it uses filter with lower frequency (< 2 KHz).

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[8] *** - Operating and Commissioning Instruction for BLR-CX, Belux BLR-CX, Beluk Gmbh, Germany, 2009.

[9] ***, User’s Guide. Three Phase Power Quality Analyzer CA 8334B, Chauvin-Arnoux, France, 2007.