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limitation as recommended in IEEE 519-1992, THD-i 11.76% ... 2014 IEEE International Conference on Electrical Engineering and Computer Science.

2014 IEEE International Conference on Electrical Engineering and Computer Science 24-25 November 2014, Bali, Indonesia

Harmonics Mitigation for Offshore Platform Using Active Filter and Line Reactor Methods F. Husnayain1, N. D. Purnomo2, R. Anwar2, I. Garniwa1, Department of Electrical Engineering, Universitas Indonesia, Depok Indonesia 2 Electrical Engineering Division, PT Pertamina PHE ONWJ, Jakarta, Indonesia Email: [email protected], [email protected], [email protected], [email protected] 1

Abstract— Propose of this study is to analyze power system profile especially harmonic at one of Offshore Platform in Indonesia. Field survey was conducted and found that total harmonic distortion (THD) both of voltage and current exceed limitation as recommended in IEEE 519-1992, THD-i 11.76% ZUA, 11.29% ZUD, 31.11% ZUG, and unbalance load exceed 5%. Analysis using ETAP 12.6 shows harmonic reduction could be achieved by installing multi-tuned passive harmonic filters. However, since the result of actual measurement shows unbalance power flow that reflect the dynamic impedance on the network system, therefore the passive filter would not effective to reduce harmonics. On the other case active filter type is not sensitive on dynamic impedance, due to its internal controller capable to compensate and cancel harmonic currents in any condition. Based on the above considerations, it is recommended to install a line reactor on each VFD and active harmonic filter on respective Point of Common Coupling (PCC) with sizing 60A and 4% in ZUA; 75A and 4% in ZUD and 120A and 3% impedance in ZUG for active filter and line reactor impedance respectively. The final THD-i in each NUI as follow 5.87%, 4.95% and 6.65%.

Fig. 1 ZU Flow Station

II.

A. Harmonics According to IEC 555 - 1982: "Harmonics is sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at the which the supply system is designed to operate-(50Hz or 60 Hz)" which is more or less clear that the harmonics are periodic distortion of the wave sine current, voltage, with a waveform whose frequency is a multiple of the number beyond which the fundamental frequency in the supply system is designed to operate at 50 Hz/60 Hz [1].

Keywords: Power Quality, Total Harmonic Distortion (THD), Point of Common Coupling (PCC), Active filter, Passive filter, ETAP, IEEE 519-1992, Unbalanced system

I.

LITERATURE REVIEW

INTRODUCTION

ZU Flow station is one of Offshore flow stations in Indonesia. It is developed to support and maintain production. ZU Field consists of ESP pump load with VFD as control driver which is generally known as harmonic distortion source. Harmonic distortion may degrade the power quality on ZU Flow Station especially when it is over the standard limit. In order to determine the power quality condition in ZU Field, it is necessary to measure the power quality parameter in some points (loads or feeder) in ZU FS. Since the power quality issues become crucial in ZU FS due to economic and safety reasons, the quality of power in ZU FS shall be improved to meet the standard limit of Power Quality. There are many options shall be studied for recommendations and solutions to improve power quality in ZU FS Systems. The ZU Field Map is shown in Fig 1.

While the definition of harmonic distortion that any change in the form of signals generally unintentional and unwanted presence on the system. Harmonics is one of the things that can cause distortion on the voltage waveform and the current fundamentals. This phenomenon arises due to the influence of non-linear load characteristics are modeled as a current source that injects harmonic currents into the power system. Fundamental frequency of a power system is 60 Hz (ANSI Standard). If there is a 2nd harmonic then the wave has a frequency of 120 Hz, the 3rd harmonic has a frequency of 180 Hz and so on so that it can be made a general equation as follows: fh = f1 ×n

978-1-4799-8478-7/14/$31.00 ©2014 IEEE 331

( 2.1 )

Where: fh = harmonics frequency; f1 = fundamental frequency, n = positive integer. Summation of harmonic wave and distorted wave is a wave that is continuous and periodic (the wave has a period T if f(t)= f (t + T) for all t). If f (t) is periodic, then the characteristic harmonics can be represented using Fourier series as follows: f (t ) =

∞ a0 + ∑ {ah . cos (hω0t ) + bh . sin (hω0t )} 2 h +1

( 2.2 )

where: a0 =

1 T

ah =

2 T

∫ f (t ). cos (h ω t )dt

( 2.4 )

bh =

2 T

∫ f (t ). sin (hω t )dt

( 2.5 )

( 2.3 )

T

∫ f (t )dt

Fig. 3 Harmonic Spectrum For Battery Charger

0

T

0

0

T

0

0



Static load is representative of lighting load which is consisting of lighting transformer and lighting loads. Lighting fluorescent is consider as non-linier load and also generate harmonic source. Assumed that lighting transformer in saturated condition then generate and contribute harmonic to the network. Since no data harmonic source for saturated transformer are taken from ETAP Library such as typical IEEE.

In addition, to determine the value of the amplitude of a harmonic wave can be found by the equation: 2

C h = a h + bh

whereas h ≥1

2

( 2.6 )

the value of C as a function of h are often portrayed in a bar chart called "harmonic spectrum".

C. Harmonics Mitigation • Line Reactors

B. Harmonics Source Harmonic source at the ZU Flow station area power distribution network are generate from VFD, Battery Charger and Saturated Transformer such as lighting transformer which is supplied to fluorescent load type. •

Static Load

Line Reactors are the simplest and lowest cost means of attenuating harmonics. They connect in series (Fig.4) with an individual non-linear load such as an ASD. By inserting series inductive reactance into the circuit, they attenuate harmonics as well as absorb voltage transients that may otherwise cause a voltage source ASD to trip on over-voltage. The magnitude of harmonic distortion and the actual spectrum of harmonics depend on the effective impedance that the reactor represents in relation to the load.

Variable Frequency Drive (VFD)

There are two VFD manufacturers installed in ZU Flow station areas, Schlumberger and Schneider.

Fig. 4 Line Reactor

Line reactors offer the advantage of low cost and they can achieve a significant reduction in harmonics when the appropriate percent impedance is utilized. For reasonable harmonic attenuation, a 5% impedance line reactor should be installed ahead of the motor drive or other 6-pulse non-linear load. •

A tuned harmonic filter is a device with two basic elements: inductive and capacitive. These reactive elements are connected in series to form a tuned LC circuit. The tuned harmonic filter is connected as a shunt device to the power system, as shown in Fig. 4. In many cases, tuned harmonic filters are applied on a facility wide basis at the service entrance, or at distribution transformers

Fig. 2 Harmonic Spectrum



Tuned Harmonic Filters

Battery Charger

Since no data and no result have stated in Site Survey Report, harmonic source for battery chargers are taken from ETAP’s Library typical IEEE.

332

with the total as stated in Site Survey Report during Normal operation. System parameters such as voltage will be looked at terminals of the power generation units, main switchgear busbars and the terminals of the loads to ensure that all loads are operating as presented total load in current condition.

The tuned harmonic filter is a resonant circuit at the tuning frequency so its impedance is very low for the tuned harmonic. Due to its low impedance at the tuned harmonic frequency, the tuned filter now becomes the source of the tuned frequency harmonic energy demanded by the loads, rather than the utility. The filter impedance below the tuning frequency resembles a capacitive behavior, while the impedance above the tuning frequency has an inductive behavior and at the tuning harmonic the filter behavior is like a resistor.



Short circuit analysis study should be carry out to verify short circuit withstand capability level for all switchgear busbars. The result to be taken to indicate ratio comparison between current circuit and nominal current operation as required per IEEE 519-1992 table 10.3. •

Harmonics Load Flow Analysis

This study is carried out to determine the level of harmonics being present in the electrical distribution network to determine and recommend harmonic filter size to be installed of ZU Platforms Area. The injected harmonic currents in turn would cause voltage harmonic in the system and these voltage harmonics have detrimental effect on electrical loads connected to the electrical power system. It might also cause critical equipment not to function at its optimum capacity or even equipment damage and burning.

Fig. 5 Tuned Harmonics Filter



Short Circuit Analysis

Active Filter

The newest technology available for mitigation of harmonics is the active filter. Active filtering techniques can be applied either as a standalone harmonic filter or by incorporating the technology into the rectifier stage of a drive, UPS or other power electronics equipment. The application of an active filter is illustrated in Fig. 6

III.

METHODOLOGY

The methodologies conducted in this study are: 1. Preparation and Preliminary Study 2. Desk Study: Review and evaluation from secondary data, references, technical documents and others. 3. Site Visit and Survey: Direct observation and measurement to obtain primary data or information from the real operation conditions. 4. Software Simulation and Analysis: This study simulation for ZU Flow Station is using ETAP Power Station version 12.6. 5. Conclusions and Recommendation: Base on the recommendation stated in this document is assurance to guidelines and basic to design of the equipment selection, drawing modification and specification and datasheet.

Fig. 6 Active Filter

Typically, active filters will monitor the load currents, filter out the fundamental frequency currents, analyze the frequency and magnitude content of the remainder, and then inject the appropriate inverse currents to cancel the individual harmonics. Active filters will normally cancel harmonics up to about the 50th harmonic and can achieve harmonic distortion levels as low as 5% THD-I or less. To apply active harmonic filters, determine the magnitude of harmonics (by measurement) that you wish to remove from the system, and select an active filter with suitable harmonic current cancellation capacity.

Since in ETAP Power Station not capable to simulate with active filter, therefore consider to conduct workshop with active filter’s manufacture to compare filter sizing between passive filter as recommended by ETAP Power Station and active filter. IV.

The Power Generation of ZU Flow Station is covered by single Gas Turbine Generator (GTG-A) rated 2.5 MW as Main Power Supply located in ZU Junction at Main Deck area and 2x1400kW (G-101A and G-101B) Diesel Engine Generator as back-up and emergency supply Cellar Deck area. The Diesel Engine Generators will automatically started when the main supply failure. The parallel or synchronizing operation between GTG-A, G-101A and G-101B are allowed for

D. Study Simulaiton with ETAP Power Station Study Simulation with ETAP Power Station has three scenario, there are: •

POWER SYSTEM OVERVIEW

Load Flow Analysis

Load flow analysis study provides information and as checking that total power flow to the network is nearing close

333

TABLE II.

temporary (short duration time) during start-up / black start / maintenance condition Main Distribution voltage level from generators are 4160V step-up to 13.8 kV MV switchgear at ZU Junction. The MV 13.8 kV power distributed to others platforms (NUI-ZUA, NUI-ZUB, NUI-ZUD, NUI-ZUE, NUI-ZUF, NUI-ZUG, ZUJ1, and ZULQ) via subsea cables. Low voltage level 480 V AC, 60 Hz to consume loads distributed derived from LV switchgear and MCC via stepped down transformer.

No

MAIN POWER TRANSFORMER DATA 2000KVA DESCRIPTION

1

Primary Voltage

UP

4.16 kV

2

Secondary Voltage

US

480 V

3

Apparent Power

S

2000 kVA

4

Percent Impedance (*)

%Z

5.75 %

5

X/R Ratio (*)

X/R

7.098

TABLE III. NO

EQUIPMENT

1 2 3 4 5

ZUA MCC-001 ZUD LV MCC ZUG LV MCC ZUJ1 LV MCC LQ LV MCC TABLE IV. NO

Fig. 7 ZU Overall Single Diagram Power Network Configurations

V.

RESULT AND DISCUSSION

Software simulation using ETAP 12.6 was conducted in this study to find the representative model of the filter needed in order to reduce the THD-I and THD-V. Based on measurement data from site visit and load list existing, load flow analysis were conducted.

NO

Result Measurement

Simulation

1248

1321

1

Total KW

2

Total kVAR

605

867

3

Total kVA

1382

1580

4

Power Factor (%)

90.65

83.60

5

Total Current (A)

190.81

219.3

kW 222 222 203 255 223

kVAR 134 131 119 153 156

RESULT kVA 259 258 235 297 272

I (A) 321.5 319 290.4 368.1 336.5

VD % 2.99 2.86 2.69 2.88 2.84

SHORT CIRCUIT SIMULATION RESULT

EQUIPMENT

Result (kA) 3 Phase

Line to Ground

1

ZUA MCC-001

14.658

16.859

2

ZUD LV MCC

15.149

17.306

3

ZUG LV MCC

14.908

17.087

4

ZUJ1 LV MCC

10.570

8.386

5

LQ LV MCC

11.169

10.195

However for the sizing criteria and assumption used during filter calculation the method used are as follow. The following criteria shall be strictly followed in harmonic filter calculation:

POWER FLOW PROFILE IN ZU FLOW STATION Power Flow

LOAD FLOW SIMULATION RESULT

Calculation were conducted in every single Point of Common Coupling (PCC). The calculation conducted consist of 4 steps, there are: Calculate the Short Circuit current level (Isc), Calculate IL/Isc, Calculate filter size based on harmonic spectrum data and Calculate THD-i level on the PCC after compensation.

The result of normal operation of load flow analysis were as tabulated below, the comparison of load total at PCC MV 4.16 kV between site visit measurement and ETAP Simulation are as follow: TABLE I.

RATING

1. Permissible THD-I shall be of maximum as in accordance with TABLE 10.3 of IEEE 519-1992 2. Permissible THD-V shall be of maximum 3% linier load and 5% for non linier load as in accordance with TABLE 11.1 of IEEE 519-1992 3. Type of harmonic filter to be proposed in the simulation are single tuned, band pass or high pass filter as listed in the ETAP Library and available in market.

Compare to measurement result, there are difference because of impedance used in the simulation (Generator, Transformer, Cables, Motor) are using typical data from ETAP Library. This condition different from existing impedance actual at field. Based on assumption used for impedance from typical IEEE standard in ETAP Library, the load flow analysis for ZU and Papa in ETAP simulation are as follow:

4. Harmonic filter shall be sized to reduce high THD as tabulated below (extracted from site survey report) to meet the above requirement. 5. Provision spare for future expansion in order for sizing filter is 20 % (applicable for active filter)

334

TABLE V. NO

EQUIPMENT

SIMULATION RESULT FOR ISC/IL I Profile Isc (kA)

IL(fund) (A)

Isc/IL(fund)

a. Passive Harmonic Filter Total rating = 94 kVAR, passive filter multi-tuned type with detail below: Harmonic order 2nd =27 kVAR, XL= 8.789 Ω and XC/R = 8 Harmonic order 5th =56.5kVAR, XL= 4.19Ω and XC/R = 7.5 Harmonic order 7th =10.5kVAR, XL= 0.887 Ω and XC/R = 23 b. Input Line Reactor VFD-ZUG-1=100A, impedance (z)= 0.55 Ω with X/R = 61 VFD-ZUG-3=100A, impedance (z)= 0.55 Ω with X/R = 61 VFD-ZUG-4=100A, impedance (z)= 1 Ω with X/R = 62 VFD-ZUG-8=100A, impedance (z)= 0.32 Ω with X/R = 52 VFD-ZUG-10=100A, impedance (z)= 1 Ω with X/R = 62 After the above equipment connected to the MCC,THD-i down to 6.65% and THD-V down to 3.15% respectively.

REMARK

1

ZUA MCC-001

14.658

320.6

45.72

2

ZUD LV MCC

15.149

319

47.49

3

ZUG LV MCC

14.908

290.4

51.34

4

ZUJ1 LV MCC

10.570

368.1

28.72

No VFD

5

LQ LV MCC

11.169

366.5

33.19

No VFD

Based on result of harmonics by ETAP simulation, and to reduce THD-i below than TDD max. 8% and THD-V max. 5%, harmonic filter and line reactors shall be connected to the MCC:

Improvement of THD-i and THD-v after installation of Passive Filter and Line reactor could be found in Table VIII. After filter installation, the THD-i and THD-v are below the standard IEEE 519-1992.

1. ZUA-Platform, high level of Total Harmonic Distortion at bus MCC ZUA-MCC-001 are contributed from VFD-ZUA-1, VFD-ZUA-2, VFD-ZUA-4 and VFD-ZUA-10. To reduce THD-i below than THD-i max 8% and THD-V max 5%, harmonic filter and line reactors shall be connected to the MCC with minimum size: TABLE VI. No

Harmonics Order

Component Capacity (kVAR)

2

XL (Ω)

3

XC/R

5th

7th

11th

13th

10.5

11.5

7.5

7

0.9417

0.4268

0.3087

0.0953

4

25

1

3

Total Capacity (kVAR) TABLE VII. No 1 2 3

Component Line Reactor Current (A) Impedance (Ω) X/R

PASSIVE FILTER RECOMMENDATION

PASSIVE HARMONIC FILTER PROFILE

Passive Harmonics Filter

1

TABLE VIII.

VI.

Based on the site survey measurement results, it could be concluded that the power quality in ZU is:

36.5

1. 2. 3.

LINE REACTOR IN ZU FLOW STATION Feeder Contains VFD ZUA-1

ZUA-2

ZUA-4

ZUA-10

100

100

100

100

0.65

0.65

0.55

0.35

60

60

61

52

CONCLUSION

Severe unbalance power flow, which is more than 5% Excessive THD-i ZU: 4 – 32% Excessive THD-v ZU: 4 – 5%

After installation of Passive Filter and Line Reactor, the THD-i for ZU FS is in range 4.95 – 6.65% and for THD-v for ZU is in range 2.35 – 3.15%. Since, the passive harmonic filter will only effective if the load in stable condition but the other type the harmonic active filter type will effective in both whether stable or fluctuate condition, and also refer to statement that typically “active filters will monitor the load currents, filter out the fundamental frequency currents, analyze the frequency and magnitude content of the remainder, and then inject the appropriate inverse currents to cancel the individual harmonics”, The final recommendation shall be applied to ZU is to install line reactors and active filters at PCC ZUA, ZUD, and ZUG, Platform with the following details in table IX. Line reactor equipment very potential generate high heat dissipation, it is recommended the Air Conditioned in respective room shall adequate to control temperature upon of respective additional increasing.

After the above equipment connected to the MCC,THD-i down to 5.87% and THD-V down to 2.47% respectively. 2. ZUD-Platform, harmonic passive filter and line reactors shall be connected to the MCC with minimum size of total rating 24.6 kVAR, with detail tuned as follow: Harmonic order 5th =11.5kVAR, XL= 0.8161 Ω and XC/R = 9 Harmonic order 7th =9.1kVAR, XL= 0.532 Ω and XC/R = 50 Harmonic order 11th =4kVAR, XL= 0.6356 Ω and XC/R = 5 b. Input Line Reactor VFD- ZUD-2=100A, impedance (z)= 0.7 Ω with X/R = 61 VFD- ZUD-5=200A, impedance (z)= 0.7 Ω with X/R = 61 VFD- ZUD-9=200A, impedance (z)= 0.7 Ω with X/R = 61 VFD-ZUD-11=200A, impedance (z)= 0.7 Ω with X/R = 61 After the above equipment connected to the MCC,THD-i down to 4.95% and THD-V down to 2.43% respectively. 3. ZUG-Platform, harmonic filter and line reactors shall be connected to the MCC with minimum size:

335

TABLE IX.

No 1 2 3

LINE REACTOR AND ACTIVE FILTER RECOMMENDATION

Location ZUA Platform ZUD Platform ZUG Platform

Line Reactor (%) A1 4 D2 4 G1 3

A2 4 D5 4 G3 3

A4 4 D9 4 G4 3

A10 4 D11 4 G8 G10 3 3

REFERENCES

Total Capacity Active Filter Proposed (A)

[1]. Ian C Evans ”The Price of Poor Power Quality”, the 2011 AADE National Technical Conference and Exhibition, Texas, April 2011 [2]. Tony Hoevenaars, Ian C Evans “New Marine Harmonics Standard” IEEE Industry Applications Magazine, Jan-Feb 2010

60

[3]. Surya Santoso “Fundamental of Power Systems Quality” December 2010.

75

[4]. American Bureau of Shipping (ABS) “Guidance Notes on Control of Harmonics in Electrical Power Systems”, May 2006.

120

[5]. DET NORSKE VERITAS (DNV) “Offshore Standard”, DNV-OS-D201, April 2011

.

336

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