Most HVAC equipment comes marked with a direct current (DC). An everyday example is the car battery, which has two terminals, one positive (+) and the other negative (-). The accepted convention is that current flows from the positive terminal to the external circuit and back to the negative terminal. In a 3-wire system, the standard voltages are 460 and 230 V.
There are three wires, one at 230 V positive (or + 230 volts potential), the second at 230 V negative (or — 230 volts potential) and the third, called “common” or “neutral”, at zero potential. The 230 V power supply comes from “external” (or positive) and common conductors, or from the “inside” (or negative) and common conductors. The power for the 480 V motors is taken from the outer and inner conductors. As the coil rotates one revolution, the tension follows the variation shown in Figure 3 (right).
When the coil is at right angles to the magnetic field, it is not cutting off the field and the voltage is zero. The maximum cutting speed occurs when the coil is in line with the magnetic field and there is a maximum voltage output. The number of voltage cycles in a second of time is called the power supply frequency and is called hertz (Hz). The standard frequency in Australia and most countries is 50 Hz.
Alternating current has an important advantage over direct current, since transformers can change the voltage to a high value for transmission over long distances and then reduce it at the customer's point of supply to a lower level suitable for operating lights, motors and other appliances. The first condition can not always be met, since you need conductors with a large cross-sectional area. Large conductors are expensive and their heavy weight would require strong and expensive supports. Therefore, when dealing with large amounts of power levels, it is general practice to use high transmission voltages and relatively small currents with correspondingly small voltage drops.
This condition is much more efficient than if a power level equivalent to low voltage and high current were transmitted with a relatively high voltage drop. Transformers are used to provide the high voltages necessary for the transmission of high levels of power over long distances. According to the voltage value of the transmission line used, it is necessary to insulate the conductors against ground leaks. The voltage between two active conductors is often referred to as “line voltage”.
Neutral voltage, often referred to as “phase voltage”, is the voltage between any active conductor and the neutral point or ground of the system. Figure 4 shows the line and phase voltages in a three-phase system. The neutral point is usually grounded at the power end (for safety and safety reasons) and each active conductor is then at a defined grounding potential. For example, in an 11 kV three-phase system, the voltage between two active conductors provides a line voltage of 11 kV, while the voltage between any living conductor and the neutral (or ground) provides a phase voltage of 6.35 kV.
This system is generally associated with the distribution of low power levels over relatively short distances. Single-phase systems are generally powered from a three-phase line. It is common to have the three-phase system connected to the ground (at the neutral point of the transformer . In this system there are two conductors, one generally solidly grounded inthe transformer and known as “neutral” , while< strong >the other is known as< strong >a “living” , active or phase conductor .< br / >The voltage between< strong >the phase and< strong >the neutral is nominally 240 V and , therefore ,< strong >the voltage of< strong >the phase or< strong >the active conductor to< strong >ground is also 240 V ( see< strong >figure ).
In certain rural areas , it is often cheaper to install< strong >a single - phase high - voltage line saving< strong >cost of< strong >third high - voltage phase and supplying load by switching from transformer to 3 - wire system. One conductor is grounded and known as neutral , while other conductors are both “active”. Voltage between any active & neutral is 240 V , while between two active conductors 480 V. Facilitates supply larger loads or loads at greater...
