The AC power (alternating current) is a type of electricity where the flow of current and its direction changes frequently. In the early 20th century, AC power is mainly used for residential and commercial sectors; however, as time went by engineers discovered that AC power could be amplified to produce enough power to run factories and industrial complexes. With this discovery came the development of the single phase power supply, as well as 3 phase power supply systems. Three-phase power supply is used to run the high loads and is mostly used for commercial and industrial areas, while the phase power supply is used for residential homes because home appliances require less power.
In this article we will be talking about the difference between single phase and three phase power supplies and how to identify them. You can also see the various 3 phase generators we have for sale on this platform.
What is Phase in Electricity?
The term “phase” in electrical power distribution means the current or the voltage among an existing wire as well as a neutral cable. How the load (electrical) is distributed across the grid is also called “phase.” If a single wire is used, then an additional load will occur on it. On the other hand, if 3 wires are used, then the electrical load will be channeled in all of them separately and creating an amplified power via the Delta-Y connection. This shows that 3-phase connections are more powerful than single-phase.
Single phase connections only has 2 wires (the positive and negative nodes), while in 3-phase connections they will consists of 3 or 4 wires (one for the positive node or phase 1, the other for the negative node or phase 2 and the third one is for phase 3 and then there’s the neutral connection. Both the power systems will use AC power, although there are systems that also use DC (direct current), but these are mostly for small portable motors and generators.
Understanding 3 Phase Power?
The three-phase power supply is designed in a way that it provides more ‘kick’ than the traditional singe-phase power supply. The mechanism behind this is due to the 4 wires that make up the power distribution scheme where one neutral along with three conductor wires. The 3 conducting wires are connected at a certain point but have a phase angle of 120º from each other. The output power from the 3-phase power supply is utilized a single-phase AC power supply, as the 3-phase scheme is only meant to boost the power output.
Due to the nature of the delta and star design configuration of the 3-phase connection, where each leg of alternating current reaches a maximum voltage, only separated by 1/3 of the time in a full cycle, the power output of a three-phase power will never drop to zero and will remain constant for as long as it is in operation. The Delta Configuration requires no neutral wire and only all high voltage systems use it; while, Star Configuration requires a neutral wire and a ground wire.
Having a higher power output than its single-phase counterpart, the 3-phase power supply has plenty of advantages. This design scheme allowed for large facilities and industrial complexes to have unimpeded operation, thus putting a larger mass production output in terms of their products that are to be distributed in various markets. Some of the advantages of 3 phase generators include:
- It requires lesser copper wires making it economically and technically efficient
- The power plant employees who helm operate and maintain this type of system is at minimal risk
- It has a greater conductor efficiency
- Commercial and industrial sectors can purchase this power at a cheaper price
- It has the capacity to hold and function with an extended range of power loads
In electrical engineering, the term “single-phase electric power” means how alternating current electrical power is distributed across the grid, where all the voltages of the supply vary in a uniform direction. Single-phase power distribution is often used for lighter loads such as lighting and heating in residential areas (sometimes it also powers a few large electric motors). When you get power for a single-phase electric motor from a single-phase supply, it will not produce a rotating magnetic field. Single-phase drive motors require something to “kick-start” them and that’s actually the capacitor start motor. These kinds of motors are mostly rated at 10 KW or lower as they do not have enough power to boost their rotating magnetic field. The instantaneous power of a single phase system is not constant, because its voltage reaches a peak value twice in each cycle.
Single Phase Power Pros and Cons
- Lightweight, Compact Unit
Higher transmission voltage means lesser current passing through the line. In the electric motor design, this translates to fewer copper wires will be required to create the conducting coil wound, making the unit lightweight and compact in size. This also means that it will have a lighter supporting tower.
- Efficient Transmission
Low current also reduces I2R losses or power dissipation in the system. This means that the efficiency of the transmission increases, ensuring that the unit operates at its optimum.
- Less Substations Required
When power dissipation (I2R) in a system is reduced, then you can increase the distance between the 2 substations. This means that these types of systems will only require fewer substations, which also reduces power distribution costs. The substations can also be placed close to the high voltage grid, which again factors into the cost-effectiveness of the system.
- High Insulation Costs
The drawback of running a system with high voltage is that it also increases the cost to insulate the wiring of the conductor. The voltage of the unit is directly proportional to the heat that the unit will create once in operation, whereas the thickness of the wire will produce the amount of current in the system. So even if the motor will run with acceptable efficiency, you will find that it is going to be costly to insulate it.
- Not Uniform Torque
Unlike the torque of 3-phase and DC motors, the single-phase motors’ torque is uneven and not very reliable. This is the reason why they are not used in heavy operations like in boats, factories or in electric cars. It is due to the unbalanced frequency that affects operation quality.
- Cannot Handle Overload
Another flaw in single-phase connection is that they are unable to handle electrical overload, whereas DC models can handle a lot of overload quite easily. If your circuit design will eventually overload the system, then it is advisable that you will select a 3-phase motor or a DC motor to handle such loads and ditch the single-phase ones.
How to Identify Single Phase and 3 Phase
Typically all single –phase motors have only 2 terminals (line and neutral). In some cases, they have a separate pin for the ground line. On the other hand, the 3-phase motor has 3 terminals which is required for all 3-phase delta connection. If it has a star connection design, then a fourth terminal is provided for neutral, while the fifth one will be for the ground. However, you do not need to inspect the motor for these information as they all come with a metal tag plate to identify whether it is a single-phase or a 3-phase motor.
All electric motors that have up to 1KW AC capacity are designed to have a single-phase connection. Motors in the 1KW – 5KW range may either have a single or 3-phase connection, but once the power rating exceeds 5KW, then they all are almost driven by a 3-phase connection.
If you want to make a close-in visual inspection and manually connect the wires to the power source, then the first thing that you need to look for in 3-phase motors is the UVW and XYZ terminals (6 insulated power terminals on a mounting plate). The terminals are usually equidistant to each other and are oriented in vertical and horizontal direction. This done so that it can serve a purpose which is to allow small connection plates to easily bridge the connections in either direction to create star or delta connection to the supply system. Single-phase motors have a terminal box mounted on their side. In it you will find 3 or 4 connection points and a space where the start or run capacitor is placed. Some single-phase motors have a centrifugal switch that’s located on the drive shaft. You can see it through the ventilation slots on the rear end.
3-Phase to Single Phase Conversion
It may be the case with you that you found yourself handling a large device with a 3-phase motor in in (i.e. industrial-sized air compressor) and the electrical grid of the area you’re residing in is not designed to power such a machine. Not to worry though because there is a way around it and you can simply replace the 3-phase motor in your machine with a single-phase motor, or other better solutions that we will be talking about later.
There are also ready-made 3-phase converters that you can purchase online or in a physical electronic store in your area. A good example of this is the static converter. It’s a circuit designed to take advantage of the ability of a 3-phase motor to run on single-phase power even though it cannot start on this type of power. The key here is to get the 3-phase motor started and that’s exactly what the static converter does – use high powered capacitors to kick-start the 3-phase motor – but this comes at a price because it will reduce the motor’s lifespan.
Another device that allows a 3-phase motor to run on a single-phase power is called a rotary phase converter. This device acts as a sort of combination of a substitute three-phase motor and an independent generator. The rotary phase converter has a built-in idle motor that when you activate will not cause its parent machines’ moving parts to turn, but instead generate power that simulates a 3-phase power output to allow the 3-phase motor to run efficiently. Then there’s the variable frequency drive (VFD) which uses multiple inverter circuits that can change the frequency of the AC (alternating current) and automatically meet all the requirements of the 3-phase motor to power it.
While they get the job done, these converters are far from being perfect and sooner or later you may encounter problems with them, but they are better than replacing the entire 3-phase machine or get a portable generator set to give you the power needed to run the machine.
Single Phase to 3-Phase Conversion
A single-phase load can be powered using a 3-phase distribution transformer in two ways:
- By connecting its nodes between the phase one wire and the neutral wire.
- By connecting its nodes between the 2 phases.
These two give different voltages from a given supply. For instance, in North America, the phase-to-neutral voltage is 120 volts on a 120/208 three-phase system, while the phase-to-phase voltage is 208 volts. This way, both single-phase lighting and 3-phase motors can connect in a 3-phase distribution transformer with the former connected phase-to-neutral and the latter connected to all three phases. Having a 3-phase distribution transformer essentially negates the need for a single phase transformer.
How Much Does it Cost to Convert from Single Phase to Three Phase?
What is a Three Phase Power Upgrade? Depending on the kinds of appliances you are running at home, then you may have to consider this option. That’s because high-powered appliances and equipment require more than just the regular power from your electric grid.
Under normal circumstances, in any given city or town, the entire electric grid is designed to only run on single phase power, therefore almost all residential areas acquire such power source. Commercial and industrial sectors though have specialized grids so that they can get more power via a 3-phase connection. Big appliances like freezers, fridges, ovens, TVs and dryers will run perfectly on single phase power – even the lights in your house. You may find this surprising but even your tesla AEV (all-electric vehicle) can be charged from a single phase power source!
However, when you do have heavy duty electrical appliances that you’re using in your home, then that’s the time you will require three-phase power. Typically, very large houses that have large capacity centralized air-conditioner, installing an electrical instantaneous hot water service, or when you need to use a commercial sized arc welder with at least 15 Kilowatts of output power. If you also plan on operating farm machinery, then you would most likely need a 3-phase power source.
By spreading the output power evenly across all three phases, 3-phase circuits gives exceeding power density and efficiently distributes the power on all the loads that large motors draw from. In case you already have the 3-phase power circuit setup in your home even though you have no large machinery that may require it, then that’s perfectly fine. You can just use it in the future when you’ll have such equipment. It’s also advantageous because it helps you with your electricity consumption will be shared out across all three phases evenly.
It will cost you $7 – $10 per linear foot if you’ll upgrade from a single-phase service to three-phase service. This is the estimated cost of establishing a connection from the nearest existing three-phase power line in your area. Typically, installations are expensive and often the homeowner pays for everything.
Testing a 3 Phase Motor
Below are the basic steps in determining whether or not your 3-phase AC motor is functional:
- General Inspections
- Earth Continuity and Resistance Test
- Power Supply Test
- AC Motor Winding Continuity Test
- AC Motor Winding Resistance Test
- Insulation Resistance Test
- Running Amps Test
- Check if any part is burned due to overheating, any damage to the device, cooling fan or shaft.
- Try to rotate the motor shaft by hand in order to check the condition of the load bearing. Check to see if the shaft is rotating freely and smoothly without any resistance. If you encounter some resistance, then the load bearing is probably damaged and you may need to replace, repair or do further inspections.
- But you can also skip the steps above just by checking information on the metal name plate on the motor – it provides all the important information you need to know about the device and help you determine the motor’s health. Run amperes test and compare values with what you got versus that rated on the name plate. If your test results match those on the name plate, then that means the motor is in good health, otherwise you may need to run several more tests and do visual and manual inspections to see if it is defective.
Earth Continuity and Resistance Test
Get a multimeter and measure the resistance between the body (or frame) of the electric motor and the ground or earth. The reading should come back 0.5 ohms or less – this means that your electric motor is in good condition. Any value greater 0.5 ohms means there’s wrong with the motor and may require further troubleshooting.
Power Supply Test
The typical voltage for a 230V/400V 3-phase motor is 230 Volts phase to neutral and 400 Volts between each of the three phase supply lines. Confirm that the operational voltages of the motor are accurate using a multimeter. Check to see if the terminal for the power supply is not damaged. Look for the connection bar for the U, V, and W terminals. All 3-phase motors have a connection type of either Star (Y) or Delta.
AC Motor Winding Continuity Test
Check for the continuity of the winding of the motor from phase U to V, V to W, and W to U using a multimeter. In order to approve the motor for use (assuming winding is good), it must have a continuity. You will know if your motor is most likely burnt if any of the test phase fails the continuity test.
AC Motor Winding Resistance Test
Test the resistance of the motor winding using either a multimeter or ohmmeter from phase U to V, V to W, and W to U. The reading should be in ohms (Ω). The ohms reading for each winding must be the same (or nearly the same). Keep in mind that all the 3 phases have similar windings or almost identical ones.
Insulation Resistance Test
If your 3-phase motor fails the insulation resistance test, then this means that it is about to get decommissioned. To measure insulation resistance, use an insulation tester or megger to measure between each motor winding or phase and between each motor phase and motor frame (earth). Set the voltage of the megger/insulation tester to 500 Volts. Check from phase to phase (U to V, V to W, and W to U). Check from phase to motor frame (earth) at the (U to E, V to E, W to E) phase terminals. The minimum insulation resistance of the motor is 1 Mega Ohms (1 MΩ).
Running Amps Test
Start the 3-phase motor and check the full load amps (FLA) using a clamp on ammeter and compare your readings to what the values on the metallic name plate says. If the ammeter values do not match with the values on the name plate, then it means that the motor is problematic and may need repairs or replacement.
How to Convert 3 Phase to Single Phase 220v (and Why You Would Do It)
Use One of the Phases from the System and a Neutral Wire
Connect with a single phase and a neutral wire and ignore the other 2 phases in the 3-phase supply line. While this is an easy way to obtain a single phase out of the three phase system, it is unfortunately inaccurate and somewhat unreliable. You can use this method if the sinusoidal wave of the AC is not an issue with the equipment that you’re using.
Convert the 3 Phase AC Connection to a DC, then to a Single Phase
Another method is by using a rectifier circuit to convert 3-phase AC to DC power. From there, you can now use another rectifier circuit and convert the 3-phase DC power into a single phase AC power. This method is easy to employ and handy too considering you’ll only need a rectifier circuit to convert the current from AC-DC-AC again.
Use a Single Phase Transformer
The single phase transformer is similar to a rectifier circuit, except that it also automatically converts the voltages to the 110/220v for household use. You can use it to easily convert your 3-phase to single phase power supply. This is a rather simpler trick to convert 3-phase into single phase power and you won’t even have to break a sweat to do it because all you have to do is to simply purchase the single phase transformer and setup your system. It’s ideal for 5KV connections or less.
Open Delta Transformers
If your power requirements are higher than 5KVA, then the open delta transformer is best suited to convert 3-phase to single phase power on these levels. Since you’re dealing with higher power outputs, you may want a professional to assist you in setting up the open delta transformer, as you just can’t simply buy it ready-made like the single phase transformer. The connection is simple to setup, sturdy and puts out a lot of power to supplant any load requirements. Consult with a professional electrician or electrical engineer about your power requirements before proceeding.
Scott T Transformers
This transformer type has a connection configuration that not only allows for 3-phase to single phase conversions, but also produces a highly balanced current, which is perfect for sensitive equipment. To make the Scott T Transformer, you will need a teaser transformer and the main transformer and set them up to work in tandem in order to achieve the phase transformation. Your highly sensitive electronics and other machines will not be harmed by imbalanced current fluctuations, which happens in other phase conversions.
This transformer is effective in allowing you convert a three phase with more than 5 KVA and 400 Volts into a single phase. With this transformer, you can achieve accurate conversions which will assure you reliable current to run sensitive machines.
It’s important to convert 3-phase power into single phase power, because 3-phase power is too powerful for household use. While 3-phase power supplies are more efficient, they also operate at 400 Volts, while your household appliances are only rated at 110 Volts (for North American) or 220 Volts for other countries. Once the huge power output from the 3-phase power system is converted to single phase, then you can take advantage of it and use it in various ways as you see fit.