KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 1 / 23 Review on Power Factor Young Seung LEE 04/26/2005 SEMINAR

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 2 / 23 Table of Contents Introduction Power and Power Factor by the type of Loads Power Factor Correction Methods of Correction Benefits of Increased Power Factor Summary Further Study References

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 3 / 23 Introduction Power Factor  The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power.ACreal powerapparent power  If φ is the phase angle between the current and voltage, then the power factor is then equal to, and:

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 4 / 23 Introduction Power Factor( continuous)  a circuit with a low power factor will have higher currents to transfer a given quantity of power than a circuit with a high power factor.  By definition, the power factor is a dimensionless number between 0 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load. Power factors are usually stated at "leading" or "lagging" to show the sign of the phase dimensionless number As the power factor drops the system becomes less efficient. A drop from 1.0 to 0.9 results in 15% more current being required for the same load. A power factor of 0.7 requires approximately 43% more current; and a power factor of 0.5 requires approximately 100% (twice as much) to handle the same load. The objective, therefore, should be to reduce the reactive power drawn from the supply by improving the power factor.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 5 / 23 Introduction Power Factor Correction – Cause of Low Power Factor Low power factor is caused mainly by induction motors, but also by inductive loads (such as transformers and magnetic lighting ballasts). – Correcting Power Factor Install capacitors in AC circuit to decrease the magnitude of reactive power. Capacitors draw leading reactive power. That means their current is 180 degrees out of phase with inductive loads, so they are storing energy when inductive loads are releasing it back to the line and vice versa.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 6 / 23 Power and Power Factor by the Type of Loads The power factor is determined by the type of loads connected to the power system. These can be: – Resistive – Inductive – Capacitive If a purely resistive load is connected to a power supply, current and voltage will change polarity in phase, the power factor will be unity (1), and the electrical energy flows in a single direction across the network in each cycle. Inductive loads such as transformers and motors (any type of wound coil) generate reactive power with current waveform lagging the voltage. Capacitive loads such as capacitor banks or buried cable generate reactive power with current phase leading the voltage. Both types of loads will absorb energy during part of the AC cycle, only to send this energy back to the source during the rest of the cycle.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 7 / 23 Power and Power Factor by the Type of Loads AC Resistor Circuits  If we were to plot the current and voltage for a very simple AC circuit consisting of a resistor, it would look something like this:  The waveform for the current is exactly in phase with the waveform for the voltage. Note that the power is never a negative value. When the current is positive (above the line), the voltage is also positive, resulting in a power (p=ie) of a positive value. Conversely, when the current is negative (below the line), the voltage is also negative, which results in a positive value for power (a negative number multiplied by a negative number equals a positive number). This consistent "polarity" of power tells us that the resistor is always dissipating power, taking it from the source and releasing it in the form of heat energy. Whether the current is positive or negative, a resistor still dissipates energy. AC resistor circuits

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 8 / 23 Power and Power Factor by the Type of Loads AC Capacitor Circuits  The relationship between the current "through" the capacitor and rate of voltage change across the capacitor is as such:  The current "leads" the voltage, and the voltage "lags" behind the current.  The 90 degree phase shift between voltage and current results in a power wave that alternates equally between positive and negative. This means that a capacitor does not dissipate power as it reacts against changes in voltage; it merely absorbs and releases power, alternately.  Capacitive reactance can be calculated using this formula: AC capacitor circuits

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 9 / 23 Power and Power Factor by the Type of Loads AC Inductor Circuits  The relationship between the voltage dropped across the inductor and rate of current change through the inductor is as such:  The voltage "leads" the current, and the current "lags" behind the voltage.  Negative power means that the inductor is releasing power back to the circuit, while a positive power means that it is absorbing power from the circuit.  Inductive reactance can be calculated using this formula: AC inductor circuits

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 10 / 23 Power Factor Correction It is often possible to adjust the power factor of a system to very near unity. This practice is known as power factor correction and is achieved by switching in or out banks of inductors or capacitors. For example the inductive effect of motor loads may be offset by locally connected capacitors.inductorscapacitors Energy losses in transmission lines increase with increasing current. Where a load has a power factor lower than 1, more current is required to deliver the same amount of useful energy. Power companies therefore require that customers, especially those with large loads, maintain the power factors of their respective loads within specified limits or be subject to additional charges. Energy losses in transmission lines increase with increasing current. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 11 / 23 Power Factor Correction

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 12 / 23 Methods of Correction Components −A typical PFC installation will comprise the following components: Cubicle – switchboard type protective enclosure adjacent or very near to a main switchboard Capacitors – these are essentially two charged plates separated by insulation and accommodated in a metal can with two terminals on the top; Controller – preferably a microprocessor used to control the number of capacitors brought on line and to raise remote alarms; Contactors and Protection– contactors switch capacitors in and out of service to suit the load while protection is provided by circuit breakers and fuses; and Harmonic Reactors – capacitors in PFC equipment can be subject to resonance arising from system inductive loads and harmonics. Damaging over-voltages and current surges can be damped out by including harmonic reactors in the PFC system.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 13 / 23 Methods of Correction It is best to install power factor correction capacitors at the motor terminals (Figure 5, ① ) since distribution circuit loading is reduced. When this is done, motor settings that are over current protection relays must be adjusted down accordingly.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 14 / 23 Methods of Correction The second arrangement (Figure 5, ② ) shows capacitor banks connected at the bus for each motor control centre. This compromise to the individual Method will reduce installation costs.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 15 / 23 Methods of Correction The least expensive method (Figure 5, ③ ) shows capacitor banks connected at the service entrance. However, the disadvantage is that higher feeder currents still flow from the service entrance to the end of line equipment.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 16 / 23 Benefits of Increased Power Factor Improved voltage  A low power factor results in a higher current flowing for a given load. As power factor decreases, line current increases, causing greater voltage drops in the conductors. Greater voltage drops result in poor voltage at equipment. With improved power factor, the voltage drops are reduced and the voltage at the equipment is improved.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 17 / 23 Benefits of Increased Power Factor Improved efficiency  The voltage drop in supply conductors is a resistive loss, and wastes power heating the conductors. A 5% drop in voltage means that 5% of your power is wasted as heat before it even reaches the motor. Improving the power factor, especially at the motor terminals, can improve your efficiency by reducing the line current and the line losses.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 18 / 23 Benefits of Increased Power Factor Released system capacity  When a system’s power factor is improved, the amount of reactive current flowing is lowered, thus reducing transformer and distribution circuit loads, and releasing system capacity. Figure 7 shows the amount of capacity released for various amounts of correction. For the example given previously, the dotted lines indicate the system capacity released is 0.13 times the kilowatt load, which in this case is 10.4 kVA.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 19 / 23 Benefits of Increased Power Factor Additional potential benefits include: -Reduction of heating losses in transformers and distribution equipment -Longer plant life -Stabilized voltage levels -Improved profitability

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 20 / 23 Summary The power factor is determined by the type of loads connected to the AC power system, and the type of loads usually is inductive. The correcting power factor install capacitors in AC circuits to decrease the magnitude of inductive reactance. Power factor correction benefits improved voltage, improved efficiency, and released system capacity.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 21 / 23 Further Study I will review ill effects of capacitor and examine whether power factor correction is applicable to domestic power system of nuclear power plant or not. If it applies to NPPs, I want to propose an optimal point of connecting capacitors.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 22 / 23 References Wikipedia encyclopedia. “Lessons In Electric Circuits, Volume Ⅱ -AC” by Tony R. Kuphaldt. “Energy Efficiency Guide” by NPC( National Project Consultants) BC Hydro. Guides to Energy Management (GEM) Series: Power Factor. Vancouver, “Reducing Power Factor Cost” EnergyIdeas Clearinghouse, February 2003.

KAIST NUCLEAR & QAUNTUM NICIEL SEMINAR 23 / 23 Vectors vs. AC Waveforms