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IEEE Std. 1459 power quantities ratio approaches for simplified harmonic emissions assessment Antonio Cataliotti, Member IEEE, Valentina Cosentino

Dario Di Cara, Member IEEE, Giovanni Tinè, Member IEEE,

Department of Energy, Information Engineering and Mathematic Models (DEIM), Università di Palermo, Palermo, Italy email: [email protected], [email protected]

National Research Council (CNR), Institute of Intelligent System for Automation (ISSIA) Palermo, Italy e-mail: [email protected], [email protected]

Abstract — The paper investigates the suitability of using power ratio parameters for harmonic emissions assessment at the point of common coupling (PCC). The study is carried out starting from the IEEE Std. 1459-2010 apparent power decomposition, where power factors are defined for evaluating line utilization and harmonic pollution levels. In addition, the study investigates the behavior of new parameters, which are expressed in terms of ratio between IEEE Std. 1459-2010 power quantities. The study is carried out for both single-phase and three-phase case, also considering the presence of capacitors. Index Terms -- power measurement, harmonic distortion, power definitions, power quality, IEEE Std. 1459-2010, harmonic sources.

I. INTRODUCTION The assessment of harmonic emissions levels is a very important issue for modern electricity distribution grids, where distortion levels are progressively increasing because of the presence of non linear loads (equipped with power electronic devices) or even distributed generation from renewable energy resources (equipped with inverter-interface for grid connection) [1]. The definition of an effective methodology for harmonic emissions assessment has been deeply debated in literature and it is an essential issue for ensuring normal power quality levels, promoting regulation for harmonic mitigation, sharing responsibility between customers and utilities for power systems disturbances [2]-[9]. Some of them allow to separate customers and utilities contribution to harmonic distortion, allowing also to investigate the impact of single harmonic components. The limitation of such approaches is that they are difficult to be implemented in practical measurement instruments. On the contrary, some proposed solutions are able to provide less information, giving only indication on the prevailing source of disturbance or on the presence of a disturbing load. The advantage is that such methods can be easily implemented on smart meters or other measuring instruments diffused over the whole network. Current international Standards on power quality and harmonics [13]-[19] set limits for networks and loads harmonic distortion levels; they define also

measurement methods for harmonic distortion evaluation (in terms of THD or single harmonics amplitudes) and electric power quantities for quantifying flow of electrical energy, as in IEEE Std. 1459-2010 [20]. This last Standard provides a set of power definitions (active, nonactive, apparent) and related line utilization, harmonic pollution and load unbalance factors, which can be used for revenue purposes, determination of major harmonic polluters and so on. As regards the line utilization, some power factor definitions are introduced. In sinusoidal conditions, power factor is an important index for power quality evaluation and it is a very suitable parameter, which is effective for power transmission efficiency improvement and it is also simple to be measured (almost all measuring instrumentation for power systems applications can easily implement its measurement). Power factor is well defined in sinusoidal situations, while different definitions exist in nonsinusoidal conditions, for example as those reported in [20]. As regards this, the IEEE Std. 1459 is based on the separation of the fundamental components from the harmonic content of voltage and current. This approach allows to measure the traditional quantities (active, reactive and apparent powers and energies, and related power factor), and to introduce some other quantities for harmonic pollution assessment. Starting from the approach of the IEEE Std. 1459 and the common concept of power factor correction, in this paper a study is presented, aimed at investigating the possibility of using power factor concepts or other power ratio parameters for harmonic emission assessment. The advantage of such solution, in comparison with more complex methods and algorithms is that, even if only qualitatively, it can be easily integrated in common field measurement instruments (smart meters, power quality analyzers, and so on) II.

BACKGROUND

A. IEEE Std. 1459-2010 and the apparent power resolution IEEE Std. 1459 [20] apparent power terms are defined starting from the separation of fundamental components of voltages and currents (at power system frequency) from the harmonics. The apparent power decomposition schemes are summarized in TABLE I. and TABLE II. for single-phase and

978-1-5386-0517-2/18/$31.00 ©2018 IEEE

three-phase systems, respectively. In both tables powers are divided into three basic groups: apparent, active, and nonactive; each group includes combined, fundamental and nonfundamental powers. The last rows report some combined indices for line utilization (power factors) and harmonic pollution assessment (as well as for load unbalance amount, in the three-phase case).

harmonic components, phase angles between harmonic voltage and current components or measurement uncertainties can affect the information correctness [9]. On the other hand impedance methods are quite complex to be implemented due to the practical challenge of the evaluation of utility and customer harmonic impedances. Various research works have been conducted to establish methods that can measure these impedances. Unfortunately, impedance measurement is a very difficult problem and research progress has been slow, i.e. independent component analysis method – ICA [10]. Also the authors have dealt with this issue, focusing the attention on the analysis of non-active powers [11]; in very brief the proposed strategy was based on the comparison of three different nonactive power quantities, which were derived form the IEEE Std. 1459 approach and measured at the same metering section. Such method was tested in several situations (both in simulation and experimentally), providing satisfactory results for the detection of the prevailing disturbance source (upstream of downstream the metering section) [12]. However, some difficulties arose in defining the thresholds for comparison, which can depend from different elements, such as the dependence of the power quantities values on the influence of other loads connected to the same PCC, the harmonic state of the system or the presence of capacitors for power factor correction [13].

In the single phase case, fundamental active, reactive and apparent powers, represent the apparent power components in the ideal case of a purely sinusoidal system; all the other apparent power terms provide a basis for harmonic assessment. Fundamental power factor (PF1) is often referred to as the displacement power factor and it is the most popular parameter to evaluate fundamental power flow condition and to adjust reactive power flow by means of capacitor banks (power factor correction). In nonsinusoidal conditions, power factor PF can be interpreted as the ratio between the energy transmitted to the load and the maximum energy that could be transmitted (with the same line losses), thus it is a line utilization factor, where the maximum utilization is gained when P = S, i.e. PF = 1 (for given values of apparent power S and rms voltage V, and even with harmonics). The overall amount of harmonic pollution is evaluated with the ratio SN/S1, that is equal to zero in purely sinusoidal conditions. Similar considerations can be made for the three-phase case, where the fundamental power factor PF1+ allows evaluating the positive-sequence power flow conditions, while PF, SeN/Se1 and SU1/S1+ factors allow evaluating line utilization, harmonic III. PROPOSED APPROACH AND SIMULATION RESULTS pollution and load unbalance amounts. In the absence of + In order to investigate the possibility to overcome the unbalance, SU1/S1 = 0, and the effective apparent power aforesaid problems, a simplified approach could be used, in decomposition becomes analogous to that of the single-phase accordance with that commonly used for PF correction. This case. would allow the following advantages: B. Summary of harmonic emission assessment techniques  assessing the global harmonic emissions, by means of the comparison with a tolerable threshold for The most popular indices for evaluating the harmonic harmonics; distortion level at a given metering section are the total harmonic distortion factors (THDV and THDI for voltages  providing a simplified tool for billing purposes, and currents, respectively. Such parameters are considered regulatory frameworks, incentives for mitigating also in IEEE Std. 1459; generally speaking, they can measure harmonics on power systems; the amount of the voltage and current distortion, but they  implementing the corresponding measurement in don’t allow assessing the disturbance source. As regards this simple and practical measuring instruments (even the last aspect, several methods have been proposed in literature existing meters, with few modifications). for harmonic sources detection have been presented, based To this aim, in this paper a preliminary simulation study is on both single-point and multi-point approaches. Some of carried out, with respect to line utilization and harmonic them allow quantifying the emission level, providing basis pollution factors of IEEE Std. 1459. The study is carried out for sharing responsibility between customers and utilities for for both the single-phase and the three-phase case (see tests power system harmonics; however they require the use of systems of Figure 1. and Figure 2. respectively). The complex algorithms, making use also of distributed behaviour of such indicators is investigated in different measurements infrastructure, thus the are not very suitable for operating conditions. Furthermore, the feasibility is also diffused and simple practical measuring instruments. On the studied of some other simplified new indicators, which are other hand, simpler solutions have been proposed, which can always derived from the IEEE Std. 1459 apparent power be able to reveal if a given load is producing harmonics or resolution. not, supporting the harmonic source detection, upstream or More in detail, apart from the defined PF1, PF and SN/S1, downstream the metering section. Examples of such the behaviour of the following new power ratio parameters is approaches are those based on harmonic active power flow investigated: P1/S, S1/S, Q1/N. As regards the first parameter, direction [3][4]or on a circuital approach based on impedance P1/S, it can allow evaluating the total amount of line measurements [5][6][7][8]. Active power flow direction utilization, considering not only the fundamental power flow method can provide misleading information, depending on condition, but also the presence of harmonics (which are the operating conditions. Compensating effects among

included in S); in purely sinusoidal case, P1/S = PF1, thus the indicator behaves as a power factor indicator (whose maximum achievable value is equal to PF1). As regards the second parameter, S1/S, it can allow evaluating the whole harmonic emission level, with respect to both active and reactive power components; in purely sinusoidal conditions, S1/S = 1, thus the indicator behaves as a power factor indicator (whose maximum achievable value is equal to 1). As regards the last parameter, Q1/N, in previous papers [11] the authors showed that the reactive powers behavior depends on the load nature (linear or nonlinear); in a given distorted working condition, Q1 is a minimum reference value, since it is the only nonactive power component in the sinusoidal condition; N is a maximum reference value since it groups all the nonactive components of the apparent power [11]; thus Q1 d N . In sinusoidal condition the two quantities are equal. When the load is linear, the amount of current distortion is low and it is due only to the distortion of the supply voltage; TABLE I. Quantity

Combined

Apparent [VA]

S=VI

Active [W]

P

n

¦V I

h h

IEEE STD 1459-2010 APPARENT POWER RESOLUTION – SINGLE-PHASE CASE Apparent power Fundamental Nonfundamental resolution scheme

cos T h

S P 2

SH = VH IH

P1 V1 I1 cosT1

N

Ph

¦V I h z1

h h

cos T h

P  P1

DI,= V1 IH DV = VH I1

Q1 V1 I1 sin T1

2

S 2  S12

Sn

S1 = V1 I1

h 1

Nonactive [VAR]

in this case the difference between Q1 and N is small. If the load is non linear the amount of current distortion is higher, Q1 > N. Thus, the comparison between Q1 and N, calculated in the same metering section and in the same working condition, can give a piece of information on the presence of disturbing loads. A. Single-phase study A preliminary validation of the proposed approach was carried out on a simple single-phase test system, which represents a simplified situation, in which both the supply and the load can be responsible for the harmonic distortion [11]. A scheme of the test system is reported in Figure 1. The system consists on: a supply voltage E1 = 230 V at the fundamental power supply frequency (50 Hz), with a phase angle D1 = 0°; a line impedance Z_Line with RL = 0,1172 : and LL = 3,934˜10-4 H; a resistive-inductive load Z_Load with capacitor C for power factor correction (In = 5 A, cosM = 0,95).

S H2  PH2

DH

Line PF=P/S PF1 =P1 /S1 – Utilization Harmonic – – SN /S1 pollution Vh and Ih are the rms values of the harmonic components of voltage and current, Th is their displacement and h is the harmonic order. TABLE II. Quantity

Combined

Apparent [VA]

Se = 3 Ve Ie

Active [W]

Nonactive [VAR]

IEEE STD 1459-2010 EFFECTIVE APPARENT POWER RESOLUTION – THREE-PHASE CASE Effective apparent power Fundamental Nonfundamental resolution scheme Se1= 3 Ve1 Ie1, S1+ =3 V1+ I1+ S eN S e2  S e21

SU 1 P

n

¦¦V I

h h

cos T h

a ,b , c h 1

N

S e2  P 2

S e21  S1

2

PH

P1+ =3 V1+ I1+ cosT1+

Q1 =3 V1 I1 sinT1 +

+

+

SeH = 3 VeH IeH, n

¦ ¦V I

h h

cos T h

a ,b,c h 2

P  P1 +

DeI = 3 Ve1 IeH DeV = 3 VeH Ie1

DeH

2 S eH  PH2

Line PF=P/Se PF1+=P1+ /S1+ – utilization Harmonic – – SeN /Se1 pollution Load – SU1 /S1+ – Unbalance Ve, Ve1, VeH, are the rms values of effective voltages; Ie, Ie1, I eH, are the rms values of effective currents (total, fundamental, harmonic)

Different harmonics can be added on both the supply voltage and the load current, by means of voltage and current generators (represented in the figure with Eh and Ih).; thus, it is possible to simulate the presence of a source of distortion on the supply side and/or the load side. Several simulations were carried out in different working conditions, which were obtained by introducing various harmonics on voltage and current. Voltage and current were measured at the load terminals (as represented by the voltage and current meters of Figure 1. As an example, the first simulation was carried out by introducing a fifth harmonic on the supply voltage, with rms value E5 = 0,1 E1; no harmonics were injected by the load. The measured quantities are reported in TABLE III. As shown in the table, the values of PF1, PF, P1/S, S1/S and Q1/N are between 0.94 and 1, in accordance with the linear load simulated conditions (SN/S1 is small, as the distortion amount is low). Further simulations were carried out by introducing the fifth harmonic on both the supply voltage and the load current, with E5 = 0,1 E1 and phase angle D5 = 0 and I5 = 0,4 I1 and phase angle E5,variable, from 0° to 360°. Thus, in this case the simulated load is nonlinear. The obtained results are synthesized in Figure 3. In all cases the values of PF, P1/S, Q1/N and S1/S are lower than PF1 and SN/S1 is higher than the previous simulated case, because of the harmonic injected by the load and depending on the phase angle E5,value. B. Three-phase study Further simulations were carried out on a simple threephase test system which is able to simulate different working conditions, with both sinusoidal or distorted supply and linear (RL) or non linear (N.L.) loads [11]. A linear load with capacitor bank for power factor correction (RLC) has been also added at PCC, in order to take under consideration the presence of capacitor banks. A block diagram of the developed system, with its main characteristics, is shown in Figure 2. Simulations were carried out for different working conditions. Some of the obtained results are summarized in Figure 4. They are referred to the following load conditions, all balanced and with nonsinusoidal supply voltage (switch 1 open, switch 2 closed): Test A. linear load, RL (switches: 3 closed; 4 and 5 open); Test B. linear load with capacitors, RLC (switches: 5 closed; 3 and 4 open);

Test D. RL and RLC loads (switches: 3, 5 closed; 4 open); Test E. N.L. and RL loads (switches: 3, 4 closed; 5 open); Test F. N.L. and RLC loads (switches: 4, 5 closed; 3 open); Test G. All loads (switches: 3, 4, 5 closed). It can be observed that the obtained values for linear load are similar to those obtained in the single phase test of TABLE III. In fact, the values of PF1, PF, P1/S, Q1/N and S1/S are high (between 0.94 and 1), while SN/S1 is small, as the load harmonic emission is nil. On the contrary, values for non linear load are similar to those obtained in the singlephase test with load harmonic injection. In fact the values of PF, P1/S, Q1/N and S1/S are lower than PF1 and SN/S1 is higher than that obtained for the linear load, because of the harmonics injected by the non linear load. As regards the behaviour of the load with capacitors bank (RLC), it can be observed that, when the RLC load is the only one load at PCC or it is connected together with the linear RL load, the values of PF, P1/S and S1/S are similar to PF1 while the most significant difference is obtained for SN/S1 and Q1/N because the capacitors amplify the distortion from the nonsinusoidal supply voltage. On the contrary, when both RLC and N.L. loads are connected to the PCC, the values of PF, P1/S and S1/S and Q1/N are lower than PF1 because the capacitors amplify the distortion injected both by the N.L. load and the supply; thus the RLC load behaves quite similarly to the non linear load, as expected. Z_Line

PCC

A

E1 V

C

Z_Load

Ih_Load

Eh

Figure 1. Single-phase test system. TABLE III.

SINGLE -PHASE TEST– MEASUREMENTS WITH E5 = 0,1 E1.

PF1

PF

SN/S1

P1/S

Q1/N

S1/S

0.95

0.95

0.11

0.94

0.96

0.99

Test C. non linear load, N.L. (switches: 4 closed; 3 and 5 open); 3 Sinusoidal Supply (230 V, 50 Hz)

1 Line impedance (R = 0,1172 :, L = 3.934 mH; Rn = 2R, Ln = 2L)

Non Sinusoidal Supply (V1 = 230 V, 50 Hz, THD = 6,9%)

Linear load (RL) (P = 5716 W, QL = 1281 var)

4

Nonlinear load (diode bridge rect. + DC load; P1 = 5716 W, Q1 = 1281 var)

2 PCC

Figure 2. Three-phase test system

5

Linear load (RL) + capacitor bank (C) (P = 5716 W, QL = 3542 var, Qc = 2261 var)

(a)

(b) Figure 3. Simulation results. Single-phase case. (a) IEEE 1459 line utilization and harmonic pollution factors; (b) new power ratio parameters 1,00 0,90 0,80 0,70 0,60 0,50 0,40 0,30 0,20 0,10 Linear load (RL)

Linear load + Cap. bank (RLC)

Nonlinear load (N.L.)

RL and RLC RL and RLC - values for - values for RL RLC -

PF1

0,98

0,98

0,97

0,98

PF

0,97

0,96

0,86

0,97

Sn/S1

0,09

0,16

0,55

0,09

NL and RL -values for RL -

N.L. and RL - values for N.L. -

NL and RLC N.L. and RLC -values for - values for RLC N.L. -

0,98

0,98

0,97

0,98

0,96

0,97

0,86

0,86

0,16

0,09

0,55

0,53

All loads - values for RL -

All loads - values for RLC -

All loads - values for N.L. -

0,97

0,98

0,98

0,97

0,87

0,97

0,89

0,87

0,53

0,11

0,46

0,53

(a) 1,00 0,90 0,80 0,70 0,60 0,50 0,40 0,30 0,20 0,10 Linear load (RL)

Linear load + Cap. bank (RLC)

Nonlinear load (N.L.)

RL and RLC RL and RLC - values for - values for RL RLC -

P1/S

0,97

0,96

0,85

0,97

Q1/N

0,98

0,82

0,44

0,97

S1/S

1,00

0,99

0,88

1,00

NL and RL -values for RL -

N.L. and RL - values for N.L. -

NL and RLC N.L. and RLC -values for - values for RLC N.L. -

0,96

0,97

0,85

0,86

0,82

0,98

0,43

0,38

0,99

1,00

0,88

0,88

All loads - values for RL -

All loads - values for RLC -

All loads - values for N.L. -

0,86

0,97

0,89

0,86

0,40

0,96

0,43

0,41

0,88

0,99

0,91

0,88

(b) Figure 4. Simulation results. Three-phase case. (a) IEEE 1459 line utilization and harmonic pollution factors; (b) new power ratio parameters

IV. CONCLUSIONS The paper has investigated the suitability of using power factors and the other new power ratio parameters for harmonic emissions assessment at the point of common coupling (PCC). The most sensitive power ratio parameter to harmonic emission is Q1/N while PF1 could be considered as reference value. The study has been carried out starting from the IEEE Std. 1459-2010 apparent power decomposition, by using only quantities derived from the IEEE Std. 1459 apparent power resolution. The study has been carried out for both single-phase and three-phase case, also considering the presence of capacitor banks. The obtained results show that the proposed approach allow obtaining a qualitative information on the presence of disturbing loads connected at PCC. The employed power ratio parameters are very easy to be measured, thus they could be easily implemented in common instrumentation for power system measurements. REFERENCES [1]

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