Devices that are connected to the power system are referred to as electrical loads. Toasters, refrigerators, bug zappers, and so on are considered electrical loads. There are three types of electrical loads. They vary according to their leading or lagging time relationship between voltage and current.
The three load types are resistive, inductive, and capacitive. Each type has specific characteristics that make them unique. Understanding the differences between these load types will help explain how power systems can operate efficiently. Power system engineers, system operators, maintenance personnel, and others try to maximize system efficiency on a continuous basis by having a good understanding of the three types of loads. They understand how having them work together can minimize system losses, provide additional equipment capacity, and maximize system reliability.
The three different types of load are summarized below.
1) RESISTIVE LOAD:
The resistance in a wire (i.e., conductor) causes friction and reduces the amount of current flow if the voltage remains constant. Byproducts of this electrical friction are heat and light. The units (measurement) of resistance are referred to as ohms. The units of electrical power associated with resistive load are watts. Lightbulbs, toasters, electric hot water heaters, and so on are resistive loads. |
| Resistive loads. |
2) INDUCTIVE LOAD:
Inductive loads require a magnetic field to operate. All electrical loads that have a coil of wire to produce the magnetic field are called inductive loads. Examples of inductive loads are hair dryers, fans, blenders, vacuum cleaners, and many other motorized devices. In essence, all motors are inductive loads.The unique difference between inductive loads and other load types is that the current in an inductive load lags the applied voltage. Inductive loads take time to develop their magnetic field when the voltage is applied, so the current is delayed. The units (measurement) of inductance are called Henrys.
Regarding electrical motors, a load placed on a spinning shaft to perform a work function draws what is referred to as real power (i.e., watts) from the electrical energy source. In addition to real power, what is referred to as reactive power is also drawn from the electrical energy source to produce the magnetic fields in the motor. The total power consumed by the motor is, therefore, the sum of both real and reactive power.
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| Inductive loads. |
3) CAPACITIVE LOAD:
A capacitor is a device made of two metal conductors separated by an insulator called a dielectric (i.e., air, paper, glass, and other non-conductive materials). These dielectric materials become charged when voltage is applied to the attached conductors. Capacitors can remain charged long after the voltage source has been removed. Examples of capacitor loads are TV picture tubes, long extension cords, and components used in electronic devices.Opposite to inductors, the current associated with capacitors leads (instead of lags) the voltage because of the time it takes for the dielectric material to charge up to full voltage from the charging current. Therefore, it is said that the current in a capacitor leads the voltage. The units (measurement) of capacitance are called farads.
Similar to inductors, the power associated with capacitors is also called reactive power, but has the opposite polarity. Thus, inductors have positive VARs and capacitors have negative VARs. Note, the negative VARs of inductors can be cancelled by the positive VARs of capacitors, to leading a net zero reactive power requirement.
As a general rule, capacitive loads are not items that people purchase at the store in massive quantities like they do resistive and inductive loads. For that reason, power companies must install capacitors on a regular basis to maintain a reactive power balance with the inductive demand.
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| Capacitive loads. |