EQUIPMENT FOR THE ELECTRICAL ENERGY MEASUREMENT STUDY AT DIFFERENT TYPES OF CONSUMERS

Transcription

1 International Journal of Arts & Sciences, CD-ROM. ISSN: :: 4(19):89 97 (2011) Copyright c 2011 by InternationalJournal.org EQUIPMENT FOR THE ELECTRICAL ENERGY MEASUREMENT STUDY AT DIFFERENT TYPES OF CONSUMERS Gabriela Rata 1, Mircea Cirdei 2, Valentin Popa 1, and Mihai Rata 1 1 University "Stefan cel Mare" of Suceava, Romania 2 EON Moldova Distribution, Romania Measurement of electrical energy has a fundamental role in its trading on the electricity market. Exchanges of electrical energy between electricity market participants are constantly monitored quantitatively and qualitatively. Also, electricity billing is based on a more precise measurement. This paper presents an equipment for electrical energy measurement. Because for an industrial customer is required to monitor both active and reactive energy, with this equipment we study the resistive, inductive and capacitive regimes, in which a consumer can operate. Also the equipment allows the analysis of various fault or installation errors that have serious consequences for accurate recording of electricity, with the final result, often, serious misunderstandings between the electrical energy suppliers and the electrical energy customers. These faults or wrong connections are identical to those within the power network. Their identification is very important for the correct measurement of electrical energy. It is studying how is changing the phasors diagram for all cases analyzed. The equipment allows the transfer of data recorded on a PC through an optical communication probe. Keywords: energy measurement, power factor, consumer, error analysis, phasors diagram. INTRODUCTION Decentralization and restructuring the energy sector has led to the electricity market. Through a gradual transition, the vertically integrated monopoly has been replaced with a new structure that allows for electricity transactions in competition and created the conditions to the occurrence of eligible customers, the main beneficiaries of these changes. A competitive electricity market can be a vehicle for pursuing the public interest, but only if the market structure addresses the particular characteristics of the electricity system [1]. Customers will be able to choose among multiple suppliers, bringing about a far more complex and interactive control and billing scheme than in the previous situation with vertically integrated electricity companies [2]. The energy exchange between the market participants are constantly monitored quantitatively and qualitatively. Also, billing electric energy sold or purchased is based on a more precise measurement, which requires appropriate measurement systems. The modern electrical energy measurement systems must comply with legislation, meet the technical requirements imposed by the place where are located and the specific requirements of the 89

2 90 Gabriela Rata, Mircea Cirdei, Valentin Popa and Mihai Rata category to which the participant belongs to the energy market. The electrical energy meter manufactures have focused their research effort towards the development of modem and more precise energy meters for large customer, where the added precision justifies the necessary investment [3]. In our country, the electricity law 13/2007 [4] establishes in Art. 27. (2) participants in the energy market: the producer, the transport and system operator, the distribution operator, the supplier, the customer eligible, the captive customer and the operator of centralized electricity market. A good collaboration between the energy market participants depend on the reliability, performances and maintenance of measurement equipment. This paper presents an equipment for electrical energy measurement. Because for an industrial customer is required to monitor both active and reactive energy, with this equipment we study the resistive, inductive and capacitive regimes, in which a consumer can operate. Also, the equipment allows the analysis of various fault or installation errors. These faults or wrong connections are identical to those within the power network. THE CHOICE OF ELEMENTS THAT PRODUCE THE LOAD REGIME Resistive load We opted for a relatively simple solution to the choice of resistive load: three receptors consisting of incandescent lamps. They offer the possibility of achieving an unbalanced state by installing lamps with different power on the phases R, S and T. Capacitive load Choice of three capacitors on the phases R, S and T is based on the calculations from power triangle according to figure 1. We considered an active power P = 100 W per each phase. Calculations are valid for all three phases. 32 P=R I 2 =100 W Q C =X C I 2 =62VAR S=Z I 2 =118VA Figure 1 Power triangle used for capacitive load determination. We propose a capacitive power factor of In this case, the phase shift between apparent and active power is 32.

3 Equipment for the Electrical Energy Measurement Study at Different Types of Consumers 91 Capacitive reactive power Q C is determined by the relationship: Apparent power now becomes: (1) (2) The value is identical to that calculated by the relationship: (3) Knowing that: (4) So, to get a power factor of 0.85 for a 100W active power we need a capacitor with a capacity of: We chose three capacitors for each phase of 3.75 µf. (5) Inductive load The choice of three coils for the phases R, S and T is also based on calculations from power triangle (figure 2). Figure 2 Power triangle used for inductive load determination. We opted for three small coils that, at a current of 0.37 A, have a power factor cos φ = Each coil has a power of 18 W. When the coil is coupled in series with an incandescent lamp, its resistance will help limit the current through the circuit.

4 92 Gabriela Rata, Mircea Cirdei, Valentin Popa and Mihai Rata EXPERIMENTAL DATA The figure 3 gives the electrical scheme of electrical energy measurement equipment proposed and the figure 4 shows the assembly based on the scheme. L T L S L R K 1 SF R s 1 s 2 SF S SF T K 2 R S T N P 1 P 2 s 1 s 2 P 1 P 2 s 1 s 2 P 1 P 2 K 4 R T R S R R K 3 C T C S C R Figure 3 Electrical scheme of electrical energy measurement equipment. Figure 4 The electrical energy measurement equipment.

5 Equipment for the Electrical Energy Measurement Study at Different Types of Consumers 93 As shown in figure 4, the measuring equipment has the following components: Alpha A1500 electronic three-phase meter from ELSTER [5]. The transfer of data recorded on a PC is done by an optical communication probe. The success of the alpha meter is based on DSP technology with digital measurement and high accuracy; current transformers on each phase R, S and T; receptors consisting of incandescent lamps. These receptors are used to modelate the resistive regime. By choosing different power incandescent lamps we can study the unbalanced load regime; coils on each phase, used to study the inductive load; capacitors on each phase, used to study the capacitive load. RESISTIVE REGIME For resistive regime, the receptors used are three 100 W incandescent lamps. By closing the switch K1 respectively K4, the incandescent lamps are supplied. The transfer of data recorded on a PC is done by an optical communication probe. On the PC we can see the phasor diagram and the data recorded like in figure 5. The phase voltages UL1, UL2 and UL3 are symmetrical and the currents IL1, IL2, IL3 are in phase with the associated voltages. In the table attached to phasor diagram are given: RMS volatages, RMS currents, active powers, recative powers, apparent powers on each phase and the system, frequencies, power factors on each phase and total power factor. Also, we can see the phase angle between the phase voltages, phase currents, respectively the phase angle between the voltages and currents on the same phase. Figure 5 Resistive regime parameters and phasor diagram.

6 94 Gabriela Rata, Mircea Cirdei, Valentin Popa and Mihai Rata Capacitive regime If K3 is closed, the load is capacitive. In figure 6 is presented the phase diagram when the K3 and K4 are closed. The phase voltages UL1, UL2 and UL3 are symmetrical and the currents IL1, IL2 and IL3 are also symmetrical. All three phase currents are shifted before phase voltages with an angle of 34, a situation confirmed by a minus sign before the angle between the current and the voltage on each phase. The power factor that corresponds to this angle is 0.85 capacitive. We obtained a value of power factor very close to the value obtained from the calculations. Inductive regime The load is inductive when the switch K2 is closed and K3 is open. In an inductive regime obtained and presented in figure 7 currents are shifted from the voltages with an angle of The inductive power factor is Reactive power compensation Reactive power compensation is achieved by coupling the capacitors, and closing the switch K3. From the phase diagram represented in figure 8 we can see that we obtained a power factor enough close to the ideal power factor, 1. Figure 6 Capacitive regime parameters and phasor diagram. The experimental study of montage errors The equipment allows the analysis of various fault or installation errors that have serious consequences for accurate recording of electricity, with the final result, often, serious misunderstandings between the electrical energy suppliers and the electrical energy customers. Two relatively simple examples are presented below.

7 Equipment for the Electrical Energy Measurement Study at Different Types of Consumers 95 Figure 7 Inductive regime parameters and phasor diagram. By a simple turn of the phase voltages at 120 degrees counterclockwise (in the same regime) the currents are shifted from the voltages. For experiment we chose the capacitive regime. We changed the phase voltages between them, the currents connections remain unchanged. In practice the error can occur at the terminals of energy meter, on the voltages busbar (semidirecte mountage) or at the voltage transformer terminals due to negligence on the executive staff. The phase diagram obtained is shown in the figure 9. Basically, the energy meter records inductive reactive energy instead of capacitive reactive energy, which is a serious anomaly. Effect of montage error is reflected on the reduction of active energy consumption to almost zero although the incandescent lamps operate normally. Figure 8 Reactive power compensation parameters and phasor diagram.

8 96 Gabriela Rata, Mircea Cirdei, Valentin Popa and Mihai Rata Figure 9 Montage errors in capacitive regime - parameters and phasor diagram. Wrong polarization of a current, two currents and even three currents are, also montage errors. The occurrence of these errors is due to negligence of executors but, also, by wrong marking of current transformers terminals. Experimentally, we inverted the direction of the current on phase R. The phase diagram obtained is shown in the figure 10. The current vector on the phase R was rotated with 180 from the voltage UL1 (on the same phase). This has the effect of changing the power in this phase. Again, the consequences are very serious. It is seen from the table that the total power is equal to only a third of the real power absorbed, because the calculation of total power is the algebraic sum of the powers on the three phases. Figure 10 Montage errors in resistive regime - parameters and phasor diagram.

9 Equipment for the Electrical Energy Measurement Study at Different Types of Consumers 97 ACKNOWLEDGMENT This paper was supported by the project "Progress and development through post-doctoral research and innovation in engineering and applied sciences PRiDE - Contract no. POSDRU/89/1.5/S/57083", project co-funded from European Social Fund through Sectorial Operational Program Human Resources CONCLUSIONS The energy market operates on a complex mechanism. A fair billing of the electrical energy traded between participants in the energy market is dependent on an adequate and accurate measurement. The modern technology provides advanced equipment for measuring electrical energy with a high level of accuracy. Optimal recovery of these modern measuring equipments is possible only if they are mounted correct and the collection, processing and interpretation of data is performed by properly trained personnel. In this paper it was presented an equipment for electrical energy measurement. The data recorded are transfered on a PC through an optical communication probe. With this equipment were studied the resistive, inductive and capacitive regimes, in which a consumer can operate. The phasors diagram for all cases are discussed and analyzed. Also, was made the experimental study for two montage errors, in different operating regimes of equipment. The consequences of these errors are very serious and are presented in the paper. REFERENCES [1] William W. Hogan, Electricity market restructuring: reforms of reforms, 20 th Annual Conference Center for Research in Regulated Industries, Rutgers University, May 23-25, 2001; [2] J. Driesen, G. Deconinck, J. Van Den Keybus, B. Bolsens, K. D. Brabandere, K. Vanthournout, R. Belmans Development of a Measurement System for Power Quantities in Electrical Energy Distribution Systems, IEEE Instrumentation and Measurement Technology Conference, Anchorage, AK, USA, May 2002; [3] P. A. V. Loss, M.M. Lamego, G.C.D. Soma and J.L.F. Vieira, A Single Phase Microcontroller Based Energy Meter, IEEE Instrumentation and Measurement Technology Conference, St. Paul, Minessota, USA, May 18-21, 1998; [4] Parlamentul României Legea nr.13 din 2007 legea energiei electrice, Bucureşti, 2007; [5]