Friday, December 6, 2019

Can I operate my three phase power supply from WYE and Delta AC inputs?

Before addressing how we connect, or even if we can connect, a three phase power supply to an AC voltage source, I think we should review some background information.

AC-DC power supplies that are rated higher than 2.5kW frequently have a three phase AC input.  In the US the voltage can be 208/220Vac or 480Vac.  In Europe it is a “harmonized 400Vac” which in actuality is 415Vac in the UK and 380Vac for Europe.  A higher input voltage allows more power to be drawn from the incoming AC at a lower current.  These three phase AC voltages can be one of two configurations – Delta or Wye (pronounced “why”).

The following should also clarify what three phase input voltage would be best suited for a large power system.  Just as important, how to read a manufacturer’s datasheet to make sure that power supply can be used in the US, Europe and globally.

Typically very high voltage power is transmitted from the power generation plants to local substation transformers (where it is reduced in voltage) and then to facilities in a Delta configuration (Figure 1).  Note that a Delta configuration only uses three wires and has no neutral or ground wire.  This saves the cost of a fourth wire, which is not needed during transmission.

Figure 1: Delta wiring configuration (US voltage shown)

I will start with the US first.  Figure 2 shows a basic overview of what a manufacturing facility receives from the Grid, at what point it is lowered in voltage and how it is distributed to the loads.

Figure 2: Typical US facility power distribution

Starting at the left, a 480Vac Delta three-wire feed enters the facility from the substation.  From the incoming distribution panel, 480Vac Delta is supplied to electrical equipment needing a large amount of power.  Large ovens, test equipment for semiconductors, burn in chambers and machines fabricating metal (including laser cutting and additive manufacturing) would typically use 480Vac Delta.  It is important to note that equipment connected to this voltage feed can reduce the size of the Delta-Wye step down transformer, saving cost, energy losses and floor space.

To supply the rest of the facility, the three phase is reduced from a 480Vac Delta configuration to a 4 wire 208Vac phase to phase Wye configuration (Figure 3) via a step-down Delta-Wye transformer.  

Figure 3: 208Vac phase to phase Wye configuration

From the distribution panel, in addition to being able to supply 208Vac phase to phase, 120Vac is available by connecting to either one of the Lines (L1, L2 or L3) and neutral N.

As very rough order of magnitude, 208Vac three phase would be used for mid-sized loads, greater than 5kW and less than 25kW and single phase 208Vac for smaller loads greater than 1.5kW.  We are all aware of the 120Vac wall outlet which can support around 1kW.  The amount of power depends on the wiring size and fusing, consult your local qualified electrician!

There may also be a second Delta-Wye transformer in some facilities.  As discussed in another blog, this provides 277Vac feeds to lighting and HVAC (Heating, Ventilation and Air Conditioning) equipment.

In Europe the arrangement and voltages are different than the US, see Figure 4.

Figure 4: Typical European facility

Again starting on the left, high voltage (11kVac in a Delta configuration in the UK) is provided by from the Grid and a step down transformer delivers three phase in a four wire Wye configuration to the facility’s distribution panel.  See Figure 5.  As explained earlier 380V/220Vac is mainly used in mainland Europe, 415/240Vac in the UK.

Figure 5: 380/415Vac phase to phase Wye configuration

From the distribution panel, in addition to being able to supply 380/415Vac phase to phase, 220/240Vac is available by connecting to either one of the Lines (L1, L2 or L3) and neutral N. 
Returning to the subject of three phase AC-DC power supplies, we shall review some examples from TDK-Lambda’s product offering.

The HWS1800T-24 is a 1.8kW rated power supply accepting a 170-265Vac 3 phase input.  This would be suitable for operation on a standard US type of 208Vac three phase Wye input.  It could also be operated in Europe, but would require a 400Vac to 220Vac three phase Wye-Wye step down transformer.

The TPS4000-24 is a 4kW rated power supply accepting a 350-528Vac 3 phase input, either Delta or Wye.  This would be suitable for operation in the US and in Europe without the need to change connections to the power supply, or additional transformers.

The Genesys+ series of programmable power supplies has a large number of models ranging from 1.5kW to 15kW.  Depending on the power level the units have different input voltages, covering most of the global input voltages.

GH1.5kW / G1.7kW:                     1ø 85 to 265Vac
G2.7kW / G3.4kW:                       1ø 170 to 265Vac or 3ø 208Vac or 3ø 400Vac
G5kW / GSP10kW & 15kW:        3ø 208Vac, or 3ø 400Vac or 3ø 480Vac

Ensure that the manufacturer has internal fuses fitted, as some low cost power supplies do not.  A high voltage fuse is required for each phase.  They are bulky and are not inexpensive.

After reading this blog, you might even take a second glance at those big grey mystery boxes surrounded by chain link fencing and high voltage warnings in the company parking lot!

Power Guy

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