WESTERN MINING ELECTRIC ASSOCIATION

Power Factor ConsiderationsAtOpen Pit Coal MinesNovember 16, 2006By:Electrical Systems Consultants, Inc.Jerry Hager, P.E.Mark Galey, P.E.

DEFINITION OF POWER FACTORDEFINITION OF POWER FACTOR

•• Power Factor = is the ratio of real Power Factor = is the ratio of real power (kW) to apparent powerpower (kW) to apparent power

cos θkVAkWFactorPower ==

BENEFITS OF POWER FACTOR CORRECTION

There are just two benefits from power factor improvement -

Reduced losses or reduced kVA loading (not both)Voltage support (reduced voltage drop)

REDUCED KVA LOADING

• Most facilities are amp or kVA limited• Increasing power factor reduces kVA

loading and increases voltage thus reducing amp loading or resistive losses.

RI 2

VOLTAGE DROP

% Voltage Drop =

2)kV(10)sinXcosR(kVA θ+θ

VOLTAGE DROP

• Note:• Voltage drop is caused by kW real power

flowing through the resistance to electric source (generator) and

• Reactive (lagging pf) load flowing through reactance back toward electric source.

VOLTAGE DROP

Per Unit Voltage Drop Through TransformerTransformers are almost all reactive.Thus voltage drop due to reactive load.

VOLTAGE DROP

• Percent drop through transformer =

• Where:• XL = %percent impedance of transformer• kVAR = reactive load• kV = line-to-line voltage

2L

)kV(10)X)(kVAR(

Transformer = 10 MVA at 6% Impedance

Load = 8 MW and 6 MVAR at 10 MVA

Voltage Drop = R x P + Q x XV

R = 0.06 / 11 = 0.00545 pu X = 0.06 x cos 85 o = 0.05229 pu

Voltage Drop = 0.00545 x 0.8 + 0.05229 x 0.6

= 0.00436 + 0.03137 pu

= 0.0357 or 3.157%

Transformer ExcitationTransformer Excitation

•• 2% to 4% of Transformer Rating2% to 4% of Transformer Rating•• HysteresisHysteresis and Eddy Currents and Eddy Currents –– CoreCore•• Core Loss (kW) ~0.6% of RatingCore Loss (kW) ~0.6% of Rating•• Magnetizing (Magnetizing (kVARkVAR) ~2% to 4%) ~2% to 4%•• 20% Magnetizing 320% Magnetizing 3rdrd HarmonicsHarmonics

Transformer Winding Loss

VIpu = 10,000 kVA

Ipu2 x Rpu = 0.0054 pu Ipu

2 x Xpu = 0.0523 pu

MW Loss = 54 kW MVAR Loss = 523 kVAR

Typical MineTypical MineTransformer Transformer kVARkVAR ConsumptionConsumption

12,000 kW Mine Load12,000 kW Mine Load52,000 52,000 kVAkVA Connected TransformersConnected Transformers

1,000 1,000 kVARkVAR Magnetizing Magnetizing kVARkVAR LossLoss1,200 1,200 kVARkVAR II22X LossX Loss

Typical Mine ITypical Mine I22R & IR & I22X X Line LossLine Loss

II22R Loss 3% to 5% of Total LoadR Loss 3% to 5% of Total LoadTypical Cost (12 MW Mine) $150,000 per Typical Cost (12 MW Mine) $150,000 per Year at $0.05/kWhYear at $0.05/kWhII22X Loss at 10X Loss at 10--15% of MW Load15% of MW LoadLine Charging ~ +1,000 Line Charging ~ +1,000 kVARkVAR

AC & DC DrivesAC & DC Drives

VFDVFD’’ss at 95% Lagging Power Factorat 95% Lagging Power FactorStatic DC Drives at 30Static DC Drives at 30--85% Lagging 85% Lagging Power FactorPower FactorDC Drives with Reactive Power DC Drives with Reactive Power Compensation (RPC) at 90% Lagging PF Compensation (RPC) at 90% Lagging PF with with SCRSCR’’ss ((ThyristersThyristers))Static AC Drives with PWM or CCI Static AC Drives with PWM or CCI inverters at 95% Lagging to Power Factorinverters at 95% Lagging to Power FactorWardWard--Leonard DC at 85Leonard DC at 85--94% Lagging PF94% Lagging PF

AC & DC DrivesAC & DC Drives

AC Drives with IGBT rectifier/inverter at AC Drives with IGBT rectifier/inverter at 80% Leading to Unity Power Factor80% Leading to Unity Power Factor

Variable Static CapacitorsVariable Static Capacitors

• Adaptive Var Compensator (AVC) $35/kVAR, $50/kVAR with Step-up Transformer and Breaker

• Static Var Compensator (SVC) up to 100 MVAR

Harmonic ProblemsHarmonic ProblemsAdding capacitors can result in resonanceAdding capacitors can result in resonance

Harmonic_Number_of_ResonanceShort_Circuit_MVA

Capacitor_kVAR:=

Typical MineTypical Mine

480480--volt 6volt 6thth Harmonic 15,000 AmpsHarmonic 15,000 Amps2.4/4.162.4/4.16--kV 18kV 18thth Harmonic 17,000 AmpsHarmonic 17,000 Amps4.16/7.24.16/7.2--kV 11kV 11thth Harmonic 3,500 AmpsHarmonic 3,500 Amps4.16/7.24.16/7.2--kV 14kV 14thth Harmonic 5,100 AmpsHarmonic 5,100 Amps

Typical 12 MW Mine Typical 12 MW Mine kVARkVARRequirementsRequirements

1,200 1,200 kVARkVAR, I, I22X Transformer LossX Transformer Loss1,000 1,000 kVARkVAR Transformer MagnetizingTransformer Magnetizing4,200 4,200 kVARkVAR, 7,000 hp Motors, 7,000 hp Motors-- 1,000 1,000 kVARkVAR Line Charging Line Charging --2,000 2,000 kVARkVAR Excavation EquipmentExcavation Equipment

Total = 3,400 Total = 3,400 kVARkVAR at 96% Power Factorat 96% Power Factor

Mining ShovelsMining Shovels

Induction or synchronous motors driving Induction or synchronous motors driving DC machines 88% Lagging Power FactorDC machines 88% Lagging Power FactorDC Drives with SCR rectifiers and RPCDC Drives with SCR rectifiers and RPC’’s for s for reactive control at 90% Lagging Power reactive control at 90% Lagging Power FactorFactorNew AC IGBT inverters used with induction New AC IGBT inverters used with induction motors 90% leading Power Factormotors 90% leading Power Factor

P&H 4100 Shovel VAR InputP&H 4100 MVAR OUTPUT

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

6:20:10 PM 6:23:02 PM 6:25:55 PM 6:28:48 PM 6:31:41 PM 6:34:34 PM 6:37:26 PM

Time

MVA

R

MVARRMS VARAve VAR155 per. Mov. Avg. (MVAR)

P&H 4100 XPB - One Minute516 Shovel P&H4100 XPB

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

0 10 20 30 40 50 60 70

Time (sec)

Load

90.0%

92.0%

94.0%

96.0%

98.0%

100.0%

102.0%

104.0%

106.0%

Vol

tage

PQVoltage

3.84 MW + j0.31 at Voltage = 98%

-0.54 - j0.24 at Voltage = 100.9%

-2.13 + j0.19 at Voltage = 100.8%

3.89 - j0.03 at Voltage =

-0.06 MW - j1.26 MVAR at Voltage = 104.2%

P&H 2300 at RMS PF 98.9% Lag

P&H2300 PF 98.9%

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

Time

MW

MvarMWRMS QRMS P

Large DraglinesLarge Draglines

DC Motor loops provide power for hoist, DC Motor loops provide power for hoist, drag and swingdrag and swingSynchronous motor/generator sets act as Synchronous motor/generator sets act as prime moversprime moversSynchronous machines usually set to hold Synchronous machines usually set to hold 93% leading power factor93% leading power factor

Marion 8200 DraglineMarion 8200 Dragline

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

0 20 40 60 80 100 120 140 160 180

Time

MW

90.0%

92.0%

94.0%

96.0%

98.0%

100.0%

102.0%

104.0%

106.0%

MWMVARRMS MWVolt

6.82 - j0.83 at Voltage = 95.8%

-2.75 + j2.11 at Voltage = 102.4%

Voltage Swing = 9.5%

BI 1570 Dragline at 95% PF Lagging and Leading

BI 1570 Dragline

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

8,000

10,000

12,000

0 10 20 30 40 50 60 70 80 90 100

Time

Pow

er (k

W)

98.50%

99.00%

99.50%

100.00%

100.50%

101.00%

101.50%

102.00%

kWkVARRMS PRMS QVolt

230kV-69kV Source & Mine 69kV Voltages at 69kV

230-kV & 69-kV Substation Loads

101.0%101.5%102.0%102.5%103.0%103.5%104.0%104.5%105.0%105.5%106.0%106.5%

0 5 10 15 20 25 30 35Time (1.0 sec)

MW

230_kV

Max_V

Min_V

69_kV

4.3% Voltage Swing 69-kV Mine Bus

3.4% Voltage Swing at 69 kV Source Bus Low of 230-kV)

230kV-69kV Source & Mine 69kV Voltages at 69kV

230-69kV Source Substation and 69kV Mine Substation Loads

-5

0

5

10

15

20

25

0 20 40 60 80 100 120

Time (1.0 sec)

MW

P 230-69

Q 230-69

Mine_P

Mine_Q

RMS 230 Q

Capacitance Varies with Square of Capacitance Varies with Square of VoltageVoltage

►► 600 600 kVARkVAR at 102% Voltage produces 624 at 102% Voltage produces 624 kVARkVAR►► 600 600 kVARkVAR at 105% Voltage produces 661 at 105% Voltage produces 661 kVARkVAR►► 600 600 kVARkVAR at 95% Voltage produces 542 at 95% Voltage produces 542 kVARkVAR►► 600 600 kVARkVAR at 90% Voltage produces 486 at 90% Voltage produces 486 kVARkVAR

Load Loss Loss Cost12,000 kW 480 kW 117,688$

Loss Savings Approximate

Mine Loss with Capacitors # CostPF kVAR Load Loss Cost Capacitors Added Capacitors99.0% 1,687 kVAR 313 kW 77,000$ 41,000$ 6,000 kVAR 20 64,000$ 98.0% 2,373 kVAR 320 kW 78,000$ 40,000$ 5,000 kVAR 17 54,000$ 95.0% 3,690 kVAR 340 kW 83,000$ 35,000$ 4,000 kVAR 13 42,000$ 90.0% 5,084 kVAR 379 kW 93,000$ 25,000$ 2,000 kVAR 7 22,000$ 85.0% 6,078 kVAR 425 kW 104,000$ 14,000$ 1,000 kVAR 3 10,000$

Capacitor Additions for 80% PF Mine Loss Savings

Annual SavingsWith Capacitor