Application Solutions

Points to consider when selecting a power supply for operation on a three phase input

Posted by Martin on January 28, 2020

Power supplies with a rated output of greater than 2,500W often require, or have an option for, a high voltage three phase AC input. A load of 3,000W, for example, operating from a single phase 230Vac input will consume 13A (3000W / 230V = 13A). The same load operating from a 400Vac three phase input will draw just 4.3A (3000W / (400V x √3) per phase.

Using a three phase input avoids the use of large diameter conductors for the AC wiring, a high current AC connector or even a hard wired (fixed) connection to a distribution panel. It also mitigates current balancing issues for a facility’s three phase input, which will occur if large amounts of current are drawn from a single phase.

When selecting a power supply, it is very important to know where it will be operated and what input voltages are available. In Europe, the AC three phase voltage is a “harmonised” 400Vac. Actually, the voltage in mainland Europe is 380Vac and 415Vac in the UK. In the US, however, the three phase voltage can be 208Vac or 480Vac.

In most countries power generation plants produce and transmit high voltages in a three phase Delta configuration (see Figure 1) to multiple local substation transformers. Here it is reduced in voltage and supplied to the end customer. Note that a Delta configuration only uses three wires and has no neutral or ground wire. This saves the cost of extra wires, which are not needed during transmission.

Figure 1: Delta configuration

Taking the UK as an example, the utility transformer close to a facility will receive 11kV in a Delta configuration from the National Grid. A step-down transformer converts the Delta configuration into a three phase, four wire Wye or star configuration (Figure 2), for connection to the facility’s distribution panel shown in Figure 3.  As explained earlier, 380V/220Vac is mainly used in mainland Europe, 415/240Vac in the UK.

Figure 2: 380/415Vac phase to phase Wye (star) configuration

Figure 3: Available voltages in a typical European facility

From the distribution panel, in addition to being able to supply 380/415Vac single and three phase (measuring across phase to phase), 220/240Vac is available by connecting to one of the Lines (L1, L2 or L3) and neutral N.

380/415Vac is used for mid-sized loads, typically greater than 5kW. This could include large ovens, test equipment and burn in chambers, or machines for metal fabrication, laser cutting and additive manufacturing.  220/240Vac is used for loads less than 5kW and regular wall sockets.

In the US, a facility will receive a 480Vac Delta three-wire feed from the local substation (see Figure 4).

Figure 4: Typical US facility power distribution

Step-down Delta-Wye transformers are used to provide power to loads less than 25kW. This provides 208Vac single and three phase and single phase 120Vac (Figure 5). Unlike Europe, equipment requiring large amounts of power will utilise three phase 480Vac Delta directly, without being stepped down by a transformer, reducing cost, energy and space on the factory floor.

Figure 5: 208Vac phase to phase Wye configuration

TDK-Lambda’s GENESYS+™ series of AC-DC 1,500W to 15kW programmable power supplies offers a wide selection of input voltage ranges, depending on the output power level. 

On the higher power GENESYS+™, if only European operation is required, then a three phase 342 to 460Vac input would be selected for a 400V nominal input. If exporting to the US is also desired for the power system, then the extended 342 to 528Vac input range should be chosen. The three phase input for the GENESYS+™ is suitable for both a three wire Delta and Wye connection, plus ground.

Alternatively, if a system is being built just for US use, then it must be determined in advance if 208 or 480Vac three phase will be needed.

The 4,000W rated TPS4000 series of industrial power supplies also accepts a 350 to 528Vac, Delta or Wye 3 phase input and can be used internationally too.

If global use is important, it is advisable to check if a power supply will operate from both a high voltage Delta and Wye connection. Lower cost products may only operate with a 230Vac Delta connection or a 400Vac Wye source. This may force the end customer to require the installation of a large, expensive step-down transformer.