The Three Types of Electrical Loads

1) Resistive Load

2) Inductive Load

3) Capacitive Load

Resistive Load

The resistance in a wire 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. Light bulbs toasters electric hot water heaters and so on are resistive loads.

     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 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. The units of electrical power associated with reactive power are called positive VARs. The acronym VAR stands for volts-amps-reactive.

   Capacitive Load

A capacitor is a device made of two metal conductors separated by an insulator called a dielectric 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 requirements. How capacitors cancel out inductors in electrical circuits and improve system efficiency will be discussed later. 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.

3Phase Power Modern Electrical Engineering

Power engineering also called Power systems engineering is a sub field of that deals electrical engineering with the generation transmission distribution and utilization of electric power as well as the electrical devices connected to such systems including generators, motors and transformers. Although much of the field is concerned with the problems of three phase. AC power the standard for large scale power transmission and distribution across the modern world a significant fraction of the field is concerned with the conversion between AC and DC power as well as the development of specialized power systems such as those used in aircraft or for electric railway networks. It was a sub field of electrical engineering. In a three phase system three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at one third of a cycle from each other.

 

Taking one current as the reference, the other two currents are delayed in time by one third and two thirds of one cycle of the electric current. This delay between phases has the effect of giving constant power transfer over each cycle of the current and also makes it possible to produce a rotating magnetic field in an electric motor.
   

Generation and distribution:

At the power station an electrical generator converts mechanical power into a set of three AC electric currents one from each coil (or winding) of the generator. The windings are arranged such that the currents vary sinusoidal at the same frequency but with the peaks and through of their wave forms offset to provide three complementary currents with a phase separation of one third cycle (120° or ^2π⁄₃ radians). The generator frequency is typically 50 or 60 Hz varying by country. Main power systems at the power station transformers change the voltage from generators to a level suitable for transmission minimizing losses. After further voltage conversions in the transmission network the voltage is finally transformed to the standard utilization before power is supplied to customers. Most automotive alternators generate three phase AC and rectify it to DC with a diode bridge.

Three-phase loads:

An important class of three phase load is the electric motor. A three phase induction motor has a simple design inherently high starting torque and high efficiency. Such motors are applied in industry for many applications.

A three phase motor is more compact and less costly than a single phase motor of the same voltage class and rating and single phase AC motors above 10 HP (7.5 kW) are uncommon. Three phase motors also vibrate less and hence last longer than single phase motors of the same power used under the same conditions. Resistance heating loads such as electric boilers or space heating may be connected to three phase systems. Electric lighting may also be similarly connected.

 Rectifiers : 

May use a three phase source to produce a six pulse DC output. The output of such rectifiers is much smoother than rectified single phase and, unlike single phase does not drop to zero between pulses. Such rectifiers may be used for battery charging electrolysis processes such as aluminum production or for operation of DC motors. Zigzag transformers may make the equivalent of six-phase full-wave rectification twelve pulses per cycle, and this method is occasionally employed to reduce the cost of the filtering components, while improving the quality of the resulting DC.

   
Phase converters:   

Phase converters are used when three phase equipment needs to be operated on a single phase power source. They are used when three phase power is not available or cost is not justifiable. Such converters may also allow the frequency to be varied (re-synthesis) allowing speed control. Some railway locomotives use a single phase source to drive three phase motors fed through an electronic drive.