Capacitors - Power Factor Champions

Have you ever unplugged a laptop power supply and noticed the power indicator light still green, then slowly go out?

That's a capacitive circuit making it's presence known.

What Is A Capacitor Really?

Basics Of Theory

At their core, capacitors are components that store and release energy.

They consist of two conductive plates separated by a dielectric insulator.

This structure allows capacitors to temporarily hold a charge, making them important in various electrical circuits, including those in building power systems.

Types of Capacitors

There are several types of capacitors, each suited to different applications:

• Electrolytic Capacitors: Common in power supplies, these capacitors have a high capacitance-to-volume ratio.
• Ceramic Capacitors: Known for their small size, they are used in various electronic circuits.
• Film Capacitors: These are widely used for power factor correction in building power systems due to their long life and stability. (metallized film capacitors are an example)

What Is Power Factor Correction?

Power Factor - The Definition

The power used to run equipment (ie..motor) is called Demand Power (aka... apparent power) denoted in Volt-Ampere (VA).

The Demand Power combines, True Power denoted in Watts and Reactive Power expressed in Volt-Amps-Reactive (VAR).

Power factor is power efficiency of the system, and is the ratio between True Power and Demand Power.

What Is The Affect?

A lower Power Factor defines a less efficient, or usefulness, of power.

The power factor lags with inductive load and leads with capacitive load. Resistive loads have a unity (not leading or lagging) power factor = 1.

Explainer: What is the difference between a Capacitive Load, Inductive Load and a Resistive Load? A capacitive load has current and voltage waves. The main difference between a capacitive and inductive load is that the current tops out before the voltage. (current and voltage waves out of phase from each other) Capacitive loads have the highest power factors and are preferred to power rotating equipment. An inductive load also provides power to rotating equipment (like motors). However, unlike a capacitive load, the voltage tops out before the current, which results in a lower power factor, and therefore low power usage efficiency. A resistive load example is a heating element. This type of load does not result in the voltage and current waves being out of phase from each other.

How Capacitors Improve Power System Performance

When electrical loads have a low power factor they consume more power than needed. As a result you have high inefficiencies in your entire network.

Inefficiency means higher power consumption and higher operating costs.

Bad power factor performance has the knock on effect of higher voltage drops in the system, which can play havoc with equipment and lead to service life issues.

Utilities financially encourage large business consumers to reduce their power factor inefficiencies. Most utilities consider a power factor less than 0.85 as inefficient and will penalize the customer into making improvements.

Making The Change To Good

Compensation

The primary way of improving power factor performance with inductive loads is to add capacitors, or a capacitor banks (pre-groups of capacitors) and harmonic filters.

Power factor correction capacitor banks are a configured to attempt to bring power to "unity" as best possible.

By the laws of physics, when current flows through rotating equipment like motors or coil devices like transformers, a magnetic field is generated. This causes a phase difference between the voltage and the current.

The addition of a capacitor bank (compensators) to an inductive load circuit corrects the power factor by providing a leading current component to compensate the lagging current.

When the inductive loads have a strong harmonic component a filter system is recommended. Harmonics can be detrimental to most equipment including capacitors.

Capacitor banks setup in automated switching system only provide compensation when a power factor correction is needed, and are typically cheaper per thousand VAR's.

Capacitor Benefits

• Energy Cost Savings: By improving power factor, capacitors reduce energy cost, and can reduce potential penalties from utility providers.
• Increased Capacity: They free up capacity on the electrical supply network, allowing for additional load without the need for expensive infrastructure upgrades.
• Voltage Conditioning: Provide voltage conditioning for a more stable supply.
• Reduced Power Losses: Improved power factor and voltage regulation lead to lower power losses in the distribution system.

Final Thoughts

Capacitors, with their ability to enhance efficiency, and ability to assist in stabilizing power, are a fixture in large inductive load scenarios, like wind turbines, industrial motors, HVAC units, etc...

Remember the following considerations when selecting capacitors for power factor correction. These include load type, continuity of load, load size, load capacity, power utility's power billing process, and inductive load starting methods.

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