## Delta Wye Transformer Zero Sequence Voltage

## Delta Wye Transformer Zero Sequence Voltage

(OP)

Hello fellas,

Is it correct that for a delta (High) wye (low side grounded )transformer, wye side line to neutral zero sequence voltage is always zero? I used the following equation to get this, I assumed n is equal to (square root of 3 times voltage ratio)

On wye side, Van= 1/n (VAN-VCN) = VAC (Delta side line voltage)

Vbn= 1/n (VBN-VAN) = VBA

Vcn= 1/n (VCN-VBN) = VCB

Then Va0= 1/3(Van+Vbn+Vcn)=0; For delta side, VAC0 (zero sequence line voltage) is also 0. These equations should hold true regardless of the system balance. However, I modeled a simple power system using computer software, I faulted wye side phase a to ground, the result I got is the opposite, the computer shows delta side line to neutral zero sequence voltage is zero (VAN=0) and wye side zero sequence line to neutral voltage Vao is not zero. I am struggling to find out where I was wrong. I would greatly appreciate it if anybody can let me know where the error is!

Is it correct that for a delta (High) wye (low side grounded )transformer, wye side line to neutral zero sequence voltage is always zero? I used the following equation to get this, I assumed n is equal to (square root of 3 times voltage ratio)

On wye side, Van= 1/n (VAN-VCN) = VAC (Delta side line voltage)

Vbn= 1/n (VBN-VAN) = VBA

Vcn= 1/n (VCN-VBN) = VCB

Then Va0= 1/3(Van+Vbn+Vcn)=0; For delta side, VAC0 (zero sequence line voltage) is also 0. These equations should hold true regardless of the system balance. However, I modeled a simple power system using computer software, I faulted wye side phase a to ground, the result I got is the opposite, the computer shows delta side line to neutral zero sequence voltage is zero (VAN=0) and wye side zero sequence line to neutral voltage Vao is not zero. I am struggling to find out where I was wrong. I would greatly appreciate it if anybody can let me know where the error is!

## RE: Delta Wye Transformer Zero Sequence Voltage

## RE: Delta Wye Transformer Zero Sequence Voltage

You are right, but for the balanced condition for the three phase distribution system. When a fault occurs, the zero sequence voltage appears, which drives the ZS current.

So the always zero, when the system is balanced!

## RE: Delta Wye Transformer Zero Sequence Voltage

You might want to keep in mind that a ground fault on the wye side though will look like a phase to phase fault on the delta side due that side only providing phase shifted negative and postive sequence components.