Phase Changer highlights the benefit of three phase power by comparing three phase power to single phase power. This comparison will help to make sense of how it relates to other fundamental sources such as the basic DC battery found in cars, toys and mobile phones.
Batteries have a designated positive and negative end. When applied to a DC motor, swapping these two connections will change the direction that the motor rotates. Most modern electronics will be sensitive to this polarity and will need the right connection for the equipment to work. Regardless of polarity, a simple light globe will shine just as bright connected either way.
If some kind of mechanical contrivance were to unplug a battery from a lamp circuit, reverse it and put it back again very fast, at say fifty times per second, the lamp would appear to remain steadily lit and there would be something approaching a 50 cycle (or Hertz), Single Phase AC (alternating current) power source. The energy received from the domestic power outlet resembles this reversing battery effect, except it runs at a higher 230 Volt level and it has very smooth changes in polarity.
There is value in using AC over DC as AC can pass through a power transformer, easily increasing or decreasing the voltage to suit energy needs with few energy losses in the change. The available current to flow through the circuit will fall proportionally if the voltage is stepped up by passing it through a transformer while the overall energy reaching the equipment to be operated via a transformer will remain roughly the same.
Single Phase AC supply is versatile and can be transmitted for long distances with comparatively few losses on only two wires. If the Earth is being used as a return path, occasionally only one wire is required. This makes it suitable for lighting and electronic appliances in domestic households, but it still has a couple of concerns. As the voltage passes from Positive to Negative, it must also pass through a zero voltage point, meaning there are instants in time when no energy is being delivered to the customer load. This is not problematic for small loads, but when trying to drive larger loads, such as electric motors, the energy levels reaching the equipment can be affected.
Without the addition of a component called a capacitor, most types of Single Phase motors have difficulty in deciding which way to turn when first activated, or may not turn at all. This is another small limitation.
British Engineer John Hopkinson patented the three phase power systems for distributing power in 1882. The three phase power system is essentially three single phase power sources staggered one-third of a cycle apart. This means that at any moment in time where one phase of power is passing through the zero point, the other two phases still deliver worthwhile power to the load.
Three phase power is typically delivered over three wires called the Delta format, and are generally labeled L1, L2 and L3. A fourth common or Neutral wire is occasionally added, and this is described as the Star format.
The voltage standard for Single Phase Power in Australia is 230V, but with three phase power the standard voltage between each of the three wires will be close to 400V. The higher voltage helps to deliver more energy to commercial and industrial loads.
One of the real advantages to 3-Phase Power is in how electric motors perform. The staggered phasing arrangement immediately communicates to the motor which way it should rotate, meaning that complicated start capacitor stages are not required.
As the energy in a 3-Phase circuit is spread over all three connections, the peak start current is about half of the level needed for similar sized single phase motors, meaning that there are fewer issues with power dips and flickering lights when larger motors are started.
Three phase motors are cheaper to manufacture and are more efficient to operate than their single phase counterparts. All this adds up to many manufacturers of equipment like metalworking machines, car hoists and refrigeration systems, actively using three phase motors in their designs. This practically forces the customer to install a three phase power connection if they want their machine to work.
Organising access to three phase connection if it does not already exist can be an onerous task.
First it the power company should be contacted to see if 3-phase power is available in the area. It is likely that the cable from the street to the switchboard may need to be replaced with a new one with the three wires inside. An electrician will also need to upgrade the switchboard with a new tariff meter and fit special three phase circuit breakers and if the existing switchboard is small, the entire switchboard may need replacement and re-wiring. Finally, new cables will need to be installed from the switchboard to each machine that uses 3-Phase power, and unfortunately, this preparation work can often exceed the cost of the operation of the 3-phase machinery. It is not uncommon for a 3-Phase upgrade process to be spread over several months, so sufficient time should be allocated if this work must be carried out with a particular deadline in mind.
It is important to note that certain areas of Australia charge an extra daily connection fee for the privilege of having a three phase connection, so consumers must be prepared for an increase in operating costs, even if the actual energy being used by their 3-phase appliance is small.
There are a few techniques that exist for taking a standard 230V single phase supply and converting it into a useable form of three phase power. The better of these methods are rotary power converter units. This is usually a box the size of a short filing cabinet which uses a pilot motor and power transformer to create three phase power from available single phase power.
These semi-portable 3 phase converters generate 400V and three phase power where required, from around 1.5 to 50 Horsepower. Such units usually work out to be the cheaper option as they become an asset that can be easily relocated.
