Power factor (PF) in the context of Programmable Logic Controllers (PLCs) isn't directly a PLC property or setting. Instead, power factor is a characteristic of the electrical load connected to and controlled by the PLC, and its impact is on the overall electrical system supplying power to the PLC and the equipment it controls.
Here's a breakdown:
-
Definition: Power factor is the ratio of real power (kW - kilowatts) to apparent power (kVA - kilovolt-amperes). It's a measure of how effectively electrical power is being used. A power factor of 1.0 (or 100%) indicates perfect efficiency, meaning all the supplied power is used to do useful work. A power factor less than 1.0 indicates that some of the supplied power is not being used to do useful work.
-
Why it Matters (Outside the PLC Itself): Low power factor increases current draw in the electrical system to deliver the same amount of real power. This can lead to:
- Increased energy costs: Utility companies may charge penalties for low power factor.
- Overheated equipment: Higher current can cause transformers, cables, and other electrical equipment to overheat, shortening their lifespan.
- Voltage drops: Increased current flow can cause voltage drops, which can negatively impact equipment performance.
- Reduced system capacity: Low power factor reduces the overall capacity of the electrical system.
-
Causes of Low Power Factor (In Equipment Controlled by PLCs):
-
Inductive Loads: The most common culprit is inductive loads, such as:
- Motors: AC induction motors (very common in industrial automation controlled by PLCs for pumps, conveyors, etc.) draw reactive power to establish a magnetic field, lowering the power factor.
- Transformers: Transformers themselves consume some reactive power.
- Solenoids: Used for valve actuation and other applications.
- Ballasts: Used in some lighting systems.
-
Non-Linear Loads: While less common in typical PLC controlled applications, non-linear loads (like variable frequency drives - VFDs - when improperly filtered) can also contribute to a poor power factor by generating harmonic currents.
-
-
PLC's Role (Indirect):
- PLCs control equipment that causes low power factor (e.g., motors).
- PLCs can be used to monitor power factor through power monitoring devices connected as inputs. The PLC can then trigger alarms or control power factor correction equipment.
- PLCs can control power factor correction equipment, such as capacitor banks, which are used to improve power factor. The PLC can switch capacitors in and out of the circuit as needed to maintain a target power factor.
-
Power Factor Correction: The most common way to improve power factor is to add capacitors to the electrical system. Capacitors supply reactive power, which offsets the reactive power consumed by inductive loads, bringing the power factor closer to 1.0.
In summary, while the PLC doesn't inherently have a power factor, it often controls the equipment responsible for power factor and can play a role in monitoring and correcting it. The focus is on the loads controlled by the PLC and their impact on the overall electrical system.
