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Single Phase VFD with 220V input/output

This paper is intended to be a general guide or tutorial for the installation of VFDs on single phase power supplies. The two supply voltages discussed will include 220V (230V, 240V) and 480V Single Wire Earth Return (SWER) systems.

Single phase VFDs capacity include: 1HP, 2HP, 3HP and 5HP.

A VFD (variable frequency drive) provides many benefits including:


  •  Soft starting of the motor & load reducing mechanical stresses & reduced water hammer with pumps.
  •  Significantly reduce the starting current, from 600-800% down to <110-150% of the motors rated FLC.
  •  Automation & process control using the built-in electronics to provide constant pressure / flow systems for irrigation or other pumping applications.
  •  Ability to control the speed of the motor.
  •  Energy Savings: Substantial energy savings may be achievable for Fan & Pump loads.

The Power, Motor & Variable frequency drive Combination


The VFD required will be dependent upon both the motor and the power source available. The general rule to remember is that a VFD can convert single phase into three phase power but, it cannot provide a higher voltage out than what you put in. Therefore if you only have a 220V 1phase power supply input, you cannot get three phase 415V output. It will only provide 220V 3 phase output. If you have a 480V power supply you can output three phase 415V – a lower voltage.

There are basically 4 situations you may have:
Power Supply
Motor
Comments
220V single Phase
220V Delta / 415V Star
220V variable frequency drive; connect motor for 220V Delta
220V single Phase
415V Delta
Motor suitable for 415V only, will need step-up transformer to increase input voltage to >415V and a 415V variable frequency drive with DC bus choke.
480V single phase Single Wire Earth Return
415V Delta
480V variable frequency drive with DC bus choke; connect motor for 415V Delta
480V single phase Single Wire Earth Return
220V Delta / 415V Star
480V variable frequency drive with DC bus choke; connect motor for 415V Star

The Variable Frequency Drive


The standard VFD is designed to operate from both a single phase & three phase power supply making it ideal for Single Wire Earth Return Line or single phase supply systems.
  • The standard VFD can operate from a 480VAC single phase power supply (Single Wire Earth Return) and provide a controlled 415V three phase output to the motor.
  • The standard VFD (or equivalent) can operate from a 220VAC single phase power supply and provide a controlled 220V 3 phase output to the motor.
When selecting the VFD it is important to determine the motors full load current at the voltage in which it will operate. To do this, it is useful to know the relationship between star and line voltages & currents.

This is especially important when a 415V star / 220V Delta motor is being used on a single phase 220V power system.
motor star connection
Eg. 1.5kW; 3.4Amps 415V star

Star Connected:

IL = IP
VL = 3 x VP



motor delta connectionWhen Delta Connected:


VL = VP
IL = 3 x IP



Therefore, the Line current or Full Load Current of the motor when connected in single phase 220V Delta is 5.9Amps. A VFD capable of a continuous output of 5.9 Amps is required.

Issues of using variable frequency drives on Single Phase Power Supplies


The operation of a VFD on a single phase power line is simple, but you do need be aware of some of the issues and how they may be addressed.

1. EMC Compliance:
All variable frequency drives satisfy the requirements of the certain standards. To achieve these standards it is necessary to install the equipment as per the manufacturers instructions. This may require screened VFD cables from the variable frequency drive to the motor. Additional measures may be required for installations which may be sensitive to RFI. Additional measures & alternatives to screened VFD cables are available such as High Performance Output Filter.

2. Harmonics
All variable frequency drives produce some form of harmonics on the line power, which is significantly increased when operating on a single phase power supply and particularly so, on Single Wire Earth Return or rural environments where the loading on smaller supplies may be relatively high. A DC bus choke is mandatory for variable frequency drives operating on a Single Wire Earth Return supply. The sizing of the transformer and the variable frequency drive/motor loading on the power supply needs to be taken into consideration when concerned about harmonics. The effect of excessive harmonics may cause overheating of electrical components such as transformers and cables. For the smaller motors operating from a 220V 1Phase power supply, harmonics are some what lower and a DC bus choke may not be required.

3. Temperature rating
Because Single Wire Earth Return line systems only occur in rural areas, where higher ambient temperatures may be experienced, the ambient temperature must be considered. Some manufacturers offer VFDs with a continuous rating of 50degC ambient. An IP66 enclosed VFD is also available so the equipment can be direct wall mounting without further enclosing. This promotes better cooling and lower internal operating temperatures.

4. DC Bus Choke
A DC Bus choke is mandatory for operation on a 480V Single Wire Earth Return supply and on some single phase 220V installations depending on the motor size. There are numerous benefits provided by a DC bus choke which include:
  •  Reduction of Power Line Harmonics
  •  Improved Power Factor
  •  Transient Filter
  •  Reduce peak inrush currents
5. Supply Current Capacity
Since the variable frequency drive acts as an inverter and produces a 3 Phase power supply from a 1 Phase supply, the current is expected to be higher on the input then the output. It is therefore important to determine what level of supply current is required for the intended motor. As a guide the RMS AC line current to be allowed for, is 1.84 times the motor phase current.

6. VFD Rating
When a VFD is operating from a single phase Single Wire Earth Return supply, the standard VFD must be rated accordingly. Other considerations when selecting the most suitable VFD is the ambient temperature and the type of load. Your VFD manufacturers can assist with selecting the correct VFD for your application. The VFD should be selected based on the full load current in the manner which the motor is connected.

7. Motor Suitability
The motor should be suitable for operation on a VFD and comply with certain standards.

Single Phase VFD


The VFD operates from the single phase power line connected to L1 and L2.

1. 480V Single Wire Earth Return Supply: The variable frequency drive takes the 480V single phase AC power and converts it to a 3 Phase output suitable for a standard 3phase 415V motor.
single phase VFD for 3phase 415V motor
2. 220V single phase power: The variable frequency drive takes the 220V single phase AC power and converts it to a 3 Phase output suitable for a standard 3 phase 220V motor (see the single phase to three phase VFD).
single phase VFD for 3phase 220V motor

More Benefits from VFD


The VFD actually does more than just convert from 1 phase power to 3 phase power supply. The variable frequency drive controls the output waveform to allow the speed to be controlled by changing the frequency to the motor from 0-200Hz. The normal power frequency is 50Hz, so the VFD actually allows you to over speed the motor if desired. With full control of the motor speed, you have direct control of the load, enabling manual or automatic control of a process, such as water pressure or flow. The VFD also has total control over the rate which a motor accelerates and decelerates, providing a smooth controlled soft start and soft stop.
single phase VFD output voltage / speed curve
The VFD offering a robust IP66 enclosure and a 50°C rating.
  •  Allows direct mounting close to the motor (protection from sunlight required)
  •  Protection against the ingress of dust & moisture
  •  More efficient cooling and reduces internal operating temperatures
  •  Increased life expectancy of electronic components
  •  No air filters to clean, eliminating nuisance over temperature trips from poor ventilation.
  •  Robust metal enclosure
Other enclosure types are also including; IP30 & Stainless Steel IP66.

The VFD has the technology built-in to provide automated control systems and to interface with external control systems.
Including:
  •  Digital & Analogue I/O for remote controls and interfacing with control systems.
  •  PID control for automated process controls such as constant pressure system.
  •  'Hibernation' mode to automatically switch the output on and off with demand.

Variable Frequency Drive Installation


The installation of variable frequency drive is simple as shown.
single phase VFD installation diagram
Speed control can be manually using the controls provided or remote speed potentiometer. A Pressure control system can be easily achieved using the VFDs internal PID control and an external pressure transducer.
Refer to the instruction manual for comprehensive details on installation, in particular using screened motor cables.

VFD Selection & Power Requirements


For assistance in the selection of a suitable VFD please contact your suppliers.

Factors that need to be considered are:
  • Motor Nameplate Full Load Current (FLC) and voltage.
  • Type of load.
  • The environment:
    • Enclosure IP rating.
    • Ambient Temperature.
    • Protection from Sunlight & other heat sources.
  • Actual Supply Voltage.
  • Appropriate derating for Single Phase operation.
  • Adequate Supply Capacity Available.
  • Variable frequency drive Options required.
  • Special requirements from motor or pump manufacturer.
For more information on how to select/operate a VFD, it's better to contact the VFD manufacturers.

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