Home > Phase Changer offer an introduction to the benefits of three phase power against single phase power

Phase Changer offer an introduction to the benefits of three phase power against single phase power

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article image Three phase power is a more reliable source to drive larger loads than single phase power

Phase Changer  know the benefits of three phase power, however to really make sense of these benefits, three phase power needs to be compared to the more domestic single phase power and how this relates to other fundamental sources such as the basic DC (direct current) battery.

Batteries have a designated positive and negative end. When applied to a DC motor, swapping these two connections will change the direction the motor rotates. Most electronics, including the modern LED torch, are sensitive to this polarity and require the correct connection for the equipment to work.

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 domestic AC power outlets resembles this reversing battery effect, except it runs at a higher 230 Volt level with ultra smooth changes in polarity.

There is a lot of value in using AC over DC power, because AC can pass through a power transformer to easily increase or decrease the voltage according to individual needs. However, if the voltage is stepped up by passing it through a transformer, then the available current to flow through the circuit will fall proportionally, with the overall energy reaching the equipment remaining about the same.

The single phase AC supply can be conveyed along long distances with relatively few losses on just two wires, making it fine for lighting and electronic appliances in domestic households, but there is still an issue. As the voltage passes from positive to negative, it must also pass through a zero voltage point. This means that there are instances in time when no energy is being delivered to the customer load. This is not a problem for small loads, but when trying to drive larger loads, such as electric motors, this effect can impact the energy levels reaching the equipment.

The invention of three phase power systems by British engineer John Hopkinson in 1882 provided a solution to this problem. Essentially, a three phase power system is three single phase power sources staggered one-third of a cycle apart, meaning that at any moment in time where one phase of power is passing through the zero point, the other two phases are still delivering worthwhile power to the load.

Usually three phase power is delivered over three wires called the delta format, and sometimes a fourth common or neutral wire is added and described as the star format. While this sounds complicated, it is worth the extra effort.

The Australian voltage standard for single phase power is 230V, however with three phase power the standard voltage will be close to 400V, the higher voltage helping to deliver more energy to commercial and industrial loads.

Another limitation with single phase power that without the addition of 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. The staggered phasing arrangement of three phase power instantly tells the motor which way to rotate, so complicated start capacitor stages are not needed.

As the energy in a three 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. This means that there are fewer issues with power dips and flickering lights when larger motors are being started.

Three phase motors are also cheaper to manufacture and are more efficient to operate than their single phase counterparts. This means manufacturers of equipment like metalworking machines, vehicle hoists and refrigeration systems actively use three phase motors in their designs, thus forcing customers to install a three phase power connection if they want their machine to work.

If a three phase connection does not already exist, organising access can be an arduous task. Firstly, the power company needs to be consulted to see if three 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 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. If the existing switchboard is small, then the entire switchboard may need replacement and re-wiring. Lastly, new cables will need to be installed from the switchboard to each machine that uses three phase power.

With the large costs and time taken for the upgrade, the preparation work often outweighs the cost of the three phase machine. Furthermore, some parts of Australia charge an extra daily connection fee for the privilege of having a three phase connection present in a building, so consumers will often experience an increase in operating costs, even if the actual energy being used by their 3-phase appliance is small.

Some techniques do exist, however, for taking a standard 230V single phase supply and converting it into a useable form of three phase power. The better of these methods being rotary power converter units.

Typically, rotary power converter units are boxes the size of a short filing cabinet which use a pilot motor and power transformer to create three phase power from available single phase power. These are a semi-portable device that generate 400V, three phase power where needed from around 1.5 to 50 horsepower.

While the cost of such phase changers usually start at around two thousand dollars, they often work out to be the cheaper option as they become an asset that can be easily relocated, and with three phase power looking to be with us for many years to come, it may just be a sound investment for the future.

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