McGill Power Sales & Engineering, INC.

Transcription

1 1 McGill Power Sales & Engineering, INC.

2 Power Factor Correction Terry McGill President McGill Power Sales & Engineering Inc Eaton Corporation. All rights reserved.

3 Agenda What is power factor? What are the costs of low power factor? What are the solutions to low power factor? Power factor correction selection considerations Design considerations and pitfalls 3

4 Power factor definition Power factor is the ratio between the real power and the apparent power of an electrical system kva kw kvar Real power = working power = kw Apparent power = Volts x Amps = kva Reactive power = magnetizing power = kvar 4

5 Is the Glass Half Empty or Half Full? Foam/Fizz Capacity (KVAR) Liquid (KW) Full Capacity (KVA) 5

6 Utility must generate, transmit, and distribute active AND reactive power 6

7 If reactive power could come from another source utility can reduce 7

8 Demonstration Power Factor Demonstration Unit 2007 Eaton Corporation. All rights reserved.

9 Why Consider PFC? PF correction provides many benefits: Primary Benefit: Reduced electric utility bill if there is a penalty (a typical payback period is less than two years) Other Benefits: 9 Increased system capacity Improved voltage regulation Reduced losses in transformers and cables May reduce harmonics on the power system (with harmonic filters)

10 Where has all the money gone? Energy (kwh) Demand (kw) PF Charges + Taxes 10

11 Typical Uncorrected Power Factor Industry Percent Uncorrected PF Brewery Cement Chemical Coal Mine Clothing Electroplating Foundry Forge Hospital Machine manufacturing Low PF typically results from unloaded or lightly loaded motors Unloaded motor PF =.20 Loaded motor rated PF =.85 Metal working Office building Oil-field pumping Paint manufacturing Plastic Stamping Steelworks Textile 65-75

12 Typical Sources of Low Power Factor Reactive power is required by many loads to provide magnetizing current for: Motors Power transformers Welding machines Electric arc furnaces Inductors Lighting ballasts 12

13 Cost to end user or consumer- Utility fees and surcharges There is no free lunch!! Many utilities pass on the extra costs they incur through penalties, surcharges or other methods Methods of recovering these costs vary with each utility and can be confusing to customers 13

14 Where do PF charges appear on a bill? Explicit Power Factor Penalty Power Factor Adjustment Power Factor Multiplier Reactive Demand Charge Calculated Demand Billed Demand 14

15 Where do PF charges appear on a bill? Shift to Temp 624 Model 15

16 Price/KWH (cents) Escalation in Electrical Energy Cost Electrical Energy cost has increased nearly 50% over the last 10 years. The rate of increase has accelerated in the past few years. Currently the PF adjustment is being increased Industrial Electrical Energy Cost by Year Year Source Energy Information Administration 16

17 Cost savings due to increased capacity Correcting poor power factor can significantly reduce the load on transformers and conductors and allow for facility expansion Transformers are rated by kva and must be sized accordingly 17

18 kvar =300 Example increase capacity with new transformer Existing plant has a power factor of 0.80 or 80% PF Existing transformer is 500kVA Plant needs to add new production line of 75kW kva = 500 kw =

19 Example increase capacity with new transformer Cost to increase capacity to accommodate new production New transformer next standard size 750kVA Long lead-time Plant shut down to add new transformer days? Labor and materials to install new transformer Upsize conductors for 750kVA transformer Disposal of old transformer 19

20 kvar = 100 kvar = 100 Example increase capacity by adding PFCC Correct power factor from 80% PF to 97% PF by adding 200kVAR power factor correction capacitor Keep existing 500kVA Add 75kW of new load Existing 500kVA transformer actually runs cooler than before!!!! Power Factor Correction kva = 412 kw =400 Power Factor Correction and addition of 75kW kva = 485 kw =475 20

21 Example increase capacity by adding PFCC Cost to increase capacity to accommodate new production New power factor correction capacitor Minimal interruption to energize and start up new capacitor system 21

22 How to correct poor power factor 2007 Eaton Corporation. All rights reserved.

23 Capacitor Selection Capacitor selection issues (besides size) Utility penalties Installed cost, payback of equipment, and NPV Load variability Voltage regulation Load requirements (Speed of changing PF) Harmonic resonance 23

24 Effect of Location R 1 R 2 Resistive Load Motor Load Place here for utility PF penalty Place here for line loss reduction and voltage improvement Place here for utility PF penalty (utility owned transformer) or Place here to reduce losses in transformer or free capacity 24

25 LV Fixed Capacitor Banks Designed for industrial and commercial power systems Lowest installed cost var Range: 1 kvar to 400 kvar 208 Volts through 600 Volts AC Must be harmonic free environment 25

26 LV Switched (Automatic) PFC Capacitors Banks Automatically sense changes in load Automatic Controller Steps of 50 kvar standard Smaller wall mounted units are available, and can be a real cost savings! 26

27 LV Harmonic Filtering Equipment Provides similar PF correction (as caps) Avoid harmonic capacitor interaction problems Filter harmonics to reduce voltage and current distortion 27

28 MV Capacitors Pole Mounted These banks have exposed live parts and are typically supported on a wood power pole. Rack Mounted These banks have exposed live parts and are supported on a steel structure. These banks are usually located in fenced-in substations. Metal Enclosed or Pad Mounted These banks are typically enclosed in a steel enclosure and are usually located within a fenced-in substation or switchgear room. 28

29 Cost of Power Factor Correction TABLE 4 INSTALLED COST COMPARISON OF POWER FACTOR CORRECTION EQUIPMENT TYPE OF CORRECTION INSTALLED COST, $/KVAR Fixed (LV motor applied) $15 Fixed (LV) $25 Fixed (MV) $30 Switched (LV) $50 Switched (MV) $50 Static Switched (LV) $75 Switched Harmonic Filter (LV) $75 Switched Harmonic Filter (MV) $60 Active Harmonic Filter (LV) $150 29

30 Additional Application considerations Switching transients Potential resonance 30

31 Capacitor switching transients Capacitor energization (common event) Voltage difference between system and capacitor Capacitor voltage cannot change instantaneously System voltage pulled nearly to initial capacitor voltage Inrush current as capacitor charges Voltage overshoots and oscillation occurs 31

32 Harmonics Definition Steady state components of voltage and current at higher frequencies than 60 Hz (or fundamental frequency) Causes Nonlinear loads, normally electronic loads In industrial facility, predominately motor drives (AC or DC), also large UPSs, computer loads, rectifiers These electronic loads draw non-sinusoidal current All load current (particularly transformers and motors) has some amount of harmonic content 32

33 Expected Harmonics Source Typical Harmonics* 6 Pulse Drive/Rectifier 5, 7, 11, 13, 17, Pulse Drive /Rectifier 11, 13, 23, Pulse Drive 17, 19, 35, 37 Switch-Mode Power Supply 3, 5, 7, 9, 11, 13 Fluorescent Lights 3, 5, 7, 9, 11, 13 Arcing Devices 2, 3, 4, 5, 7... Transformer Energization 2, 3, 4 * Generally, magnitude decreases as harmonic order increases H = NP+/-1 i.e. 6 Pulse Drive - 5, 7, 11, 13, 17, 19, 33

34 Harmonic Resonance The Self Correcting Problem Blown Fuses Failed Capacitor If a capacitor exists on the power system AND Harmonic producing loads are in use You MUST check for harmonic resonance. (Series and Parallel) 34

35 Harmonic Resonance - Solutions 1. Change the method of kvar compensation (harmonic filter, active filter, etc.) 2. Change the size of the capacitor bank to overcompensate or under-compensate for the required kvar and live with the ramifications (i.e. overvoltage or PF penalty). Natural System frequency of oscillation typically at 5th to 13th harmonic 35

36 When is resonance a concern? Several factors must converge simultaneously for resonance to be a potential problem 1) P.F. correction kvar >25% of xfmr kva 2) Nonlinear load > 25% of xfmr kva 3) Larger, fixed capacitance Often, resonance effects exist to some degree, but is not severe enough to cause problems 36

37 When is resonance not a concern? Resonance not generally a concern when: Total kvar <15% system kva Total nonlinear load <25% of system kva Adding capacitors to individual motors 37

38 How to know for sure? Resonance will happen when: Ht = (Sqrt ((xfmer kva / z)/kvar)) Ht = (Sqrt((1000/.058)/300) Ht = (Sqrt(17,241/300)) Ht = (Sqrt (57.47)) Ht = 7.58 Record harmonic data. Determine resonance points. Compare to required kvar. 38

39 Questions? 39

40 Power Quality Experience Center and Lab Overview of Lab and Capabilities Purpose To demonstrate and Test PQ Problems and Solutions Power Quality solutions, especially harmonic solutions, are difficult to understand Demystify solutions mis-information and confusion regarding PQ and energy savings Equipment (Harmonic Related) 18 Pulse Drives HMT s Active Filters Broadband Filters Passive (Fixed) Filters Passive (Switched) Filters Active Rectifier (UPS) Reactors Link: ence/index.htm Simply search on Google for Eaton Experience Center 40

41 41 Thank You.