Power Factor basic

 Power Factor Fundamentals

Most Industrial loads require both Real power and Reactive power to produce useful work

You pay for BOTH types of power

Capacitors can supply the REACTIVE power thus the utility doesn’t need to

Capacitors save you money!

Why Apply PFC’s?

Power Factor Correction Saves Money!

Reduces Power Bills

Reduces I2R losses in conductors

Reduces loading on transformers

Improves voltage drop

What is PF ?

Introduction:

Most plant loads are Inductive and require a magnetic field to operate:

- Motors

- Transformers

- Florescent lighting

The magnetic field is necessary, but produces no useful work

The utility must supply the power to produce the magnetic field and the power to produce the useful work: You pay for all of it!

These two types of current are the ACTIVE and REACTIVE components

The Basics:

The Power Triangle:

You pay for fuel for the VERTICAL portion of flight, as well as the fuel for the HORIZONTAL portion of flight

Similarly, motors require REACTIVE power to set up the magnetic field while the ACTIVE power produces the useful work (shaft horsepower). Total Power is the vector sum of the two & represents what you pay for:

The Power Triangle:

Power Factor is the ratio of Active Power to Total Power:

Power Factor = Active (Real) Power /Total Power

                      = kW / kVA

                      =  cos(φ)

 Power Factor is a measure of efficiency (Output/Input)

Why do we Install Capacitors?

Capacitors supply, for free, the reactive energy required by inductive loads.

You only have to pay for the capacitor !

Since the utility doesn’t supply it (kVAR), you don’t pay for it!

Utility Supplies Reactive Current

Capacitor Supplies Reactive Current

Other Benefits:

1- Released system capacity:

The effect of PF on current drawn is shown below:

Decreasing size of conductors required to carry the same 100kW load at P.F. ranging from 70% to 100%

2- Reduced Power Losses:

- As current flows through conductors, the conductors heat. This heating is power loss.

- Power loss is proportional to current squared (PLoss=I2 R).

- Current is proportional to P.F.

- Conductor loss can account for as much as 2-5% of total load

3- Capacitors can reduce losses by 1-2% of the total load

4- Voltage Improvement:

- When capacitors are added, voltage will increase

- Typically only a few percent

- Not a significant economic or system benefit

Severe over-correction (P.F.>1) will cause a voltage rise that can damage insulation & equipment; or result
in utility surcharges!

- Usually a result of large fixed capacitors at mains

Summary of Benefits:

1- Reduced Power Costs:

- Since Capacitors supply reactive power, you don’t pay the utility for it

- You can calculate the savings

2- Off-load transformers

- Defer buying a larger transformer when adding loads

3- Reduce voltage drop at loads

- Only if capacitors are applied at loads

- (minimal benefit at best)

What we learned : 

1- Most Industrial loads (i.e. motors)are Inductive and draw REACTIVE power

2- The Utility supplies this energy therefore you pay for it

3- Power Factor Capacitors supply REACTIVE energy thus the utility doesn’t need to

4- Power Factor Capacitors save money

5- There are other benefits to correcting power factor,

6- reduced heating in cables

7- reduced heating in transformer(s)

8- frees up system capacity

transmission lines

Classification of transmission lines

Transmission lines are classified as short, medium and long. When the length of the line is less than about 80Km the effect of shunt capacitance and conductance is neglected and the line is designated as a short transmission line. For these lines the operating voltage is less than 20KV.

For medium transmission lines the length of the line is in between 80km - 240km and the operating line voltage wil be in between 21KV-100KV.In this case the shunt capacitance can be assumed to be lumped at the middle of the line or half of the shunt capacitance may be considered to be lumped each end of the line.The two representations of medium length lines are termed as nominal-T and nominal- π respectively.

Lines more than 240Km long and line voltage above 100KV require calculations in terms of distributed parameters.Such lines are known as long transmission lines.This classification on the basis of length is more or less arbitrary and the real criterion is the degree of accuracy required.

Open Circuit and Short Circuit

Open Circuit :
An electric circuit that has been broken, so that there is no complete path for current flow. A condition in an electric circuit in which there is no path for current between two points; examples are a broken wire and a switch in the open, or off, position.

Open-circuit voltage is the potential difference between two points in a circuit when a branch (current path) between the points is open-circuited. Open-circuit voltage is measured by a voltmeter which has a very high resistance (theoretically infinite).

Short Circuit :
A low-resistance connection established by accident or intention between two points in an electric circuit. The current tends to flow through the area of low resistance, bypassing the rest of the circuit.

Common usage of the term implies an undesirable condition arising from failure of electrical insulation, from natural causes (lightning, wind, and so forth), or from human causes (accidents, intrusion, and so forth).

In circuit theory the short-circuit condition represents a basic condition that is used analytically to derive important information concerning the network behavior and operating capability. Thus, along with the open-circuit voltage, the short-circuit current provides important basic information about the network at a given point.

The short-circuit condition is also used in network theory to describe a general condition of zero voltage.

Properties of AC electrical signal

Properties of AC electrical signal :

An electrical signal is a voltage or current which conveys information, usually it means a voltage. The term can be used for any voltage or current in a circuit. 

The voltage-time graph on the right shows various properties of an electrical signal. In addition to the properties labelled on the graph, there is frequency which is the number of cycles per second.

The diagram shows a sine wave but these properties apply to any signal with a constant shape.

• Amplitude is the maximum voltage reached by the signal. It is measured in volts, V.
• Peak voltage is another name for amplitude.
• Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage.
• Time period is the time taken for the signal to complete one cycle. It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. 1ms = 0.001s and 1µs = 0.000001s.
• Frequency is the number of cycles per second. It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and 1MHz = 1000000Hz.