Neutral Deriving Transformer - Neutral Conductor Sizing

[PP26]

I need to size my neutral conductor that will be connected to the H0 terminal of my neutral deriving transformer.
I have never size one before, so I seek advice or recommendations.

Below is the specification of the NDT:

System Voltage: 480V Wye 3-Phase
Transformer Voltage: 480ZZ/277V
Continuous kVA: 57.00
X0 = 0.1759 ohm (plus-minus 10%)
3Io Current Approximately = 4,700A
X0/R0 > 4
Neutral Current: 189A - Continuous, 63A per leg
3963A - 4S

In my understanding, I need to size my neutral conductor to not exceed the total allowed neutral current of the NDT which is 189 amps.
Will a #2/0 AWG copper suffice? Do I need to consider any other things aside from the neutral current rating that my NDT can handle during normal operating conditions?

Thank you and I highly appreciate all the response and assistance.

 

[xformer]

I need to size my neutral conductor that will be connected to the H0 terminal of my neutral deriving transformer.
I have never size one before, so I seek advice or recommendations.

Below is the specification of the NDT:

System Voltage: 480V Wye 3-Phase
Transformer Voltage: 480ZZ/277V
Continuous kVA: 57.00
X0 = 0.1759 ohm (plus-minus 10%)
3Io Current Approximately = 4,700A
X0/R0 > 4
Neutral Current: 189A - Continuous, 63A per leg
3963A - 4S

In my understanding, I need to size my neutral conductor to not exceed the total allowed neutral current of the NDT which is 189 amps.
Will a #2/0 AWG copper suffice? Do I need to consider any other things aside from the neutral current rating that my NDT can handle during normal operating conditions?

Thank you and I highly appreciate all the response and assistance.

The neutral conductor can be larger or might be required to be larger than the allowed neutral current depending on the type of load.

 

[PP26]

The neutral conductor can be larger or might be required to be larger than the allowed neutral current depending on the type of load.

Thank you for the response. Can you please provide any references or material? The reason I am asking is so I can read it and be more familiar with this topic.

 

[curt swartz]

You state the system voltage is Wye. If so you already have a neutral point. ZigZag transformers are normally used on ungrounded Delta systems.

 

[PP26]

You state the system voltage is Wye. If so you already have a neutral point. ZigZag transformers are normally used on ungrounded Delta systems.

You are correct. The system voltage is 480Y 3-Phase. However, the zigzag transformer is for the back-up battery system which is ungrounded.

 

[Jpflex]

I need to size my neutral conductor that will be connected to the H0 terminal of my neutral deriving transformer.
I have never size one before, so I seek advice or recommendations.

Below is the specification of the NDT:

System Voltage: 480V Wye 3-Phase
Transformer Voltage: 480ZZ/277V
Continuous kVA: 57.00
X0 = 0.1759 ohm (plus-minus 10%)
3Io Current Approximately = 4,700A
X0/R0 > 4
Neutral Current: 189A - Continuous, 63A per leg
3963A - 4S

In my understanding, I need to size my neutral conductor to not exceed the total allowed neutral current of the NDT which is 189 amps.
Will a #2/0 AWG copper suffice? Do I need to consider any other things aside from the neutral current rating that my NDT can handle during normal operating conditions?

Thank you and I highly appreciate all the response and assistance.

Wouldn’t you have to do a load calculation to size neutral or apply any possible allowable derating (similar to 70% reduction for some dwellings loads?)

Also did you mean X0 instead of HO for deriving neutral or are you actually deriving a neutral at HO high voltage side primary of transformer?

will 57,0000 VA, 57KVA be enough to support your load. I get 57k / 277 E / 1.732 = 118.8 i amperes on secondary

Therefore I assume the neutral to be sized less than or equal to 119 I amperes after derating and adjustments for non continuous loads and for future expansion

 

[jaggedben]

You are correct. The system voltage is 480Y 3-Phase. However, the zigzag transformer is for the back-up battery system which is ungrounded.

Okay, I'm not an engineer and the NDTs I've installed for the same reason (dozens) are all for single phase systems and much lower VA ratings.

That said, my understanding is that the overcurrent device protecting the ungrounded conductors going to your NDT protect the neutral just like they would for a typical multi-wire circuit. In other words, I've never seen an NDT that required a larger neutral than the ungrounded conductors.

So as long as you have normal loads, and do not need to worry about some crazy out-of-phase or zero sequence neutral current, or something of that nature that is above my pay-grade to calculate, then I believe that your neutral conductor in a wye system can be the same size as your ungrounded conductors. I don't see what's different about it because it's an NDT.

 

[Jpflex]

Okay, I'm not an engineer and the NDTs I've installed for the same reason (dozens) are all for single phase systems and much lower VA ratings.

That said, my understanding is that the overcurrent device protecting the ungrounded conductors going to your NDT protect the neutral just like they would for a typical multi-wire circuit. In other words, I've never seen an NDT that required a larger neutral than the ungrounded conductors.

So as long as you have normal loads, and do not need to worry about some crazy out-of-phase or zero sequence neutral current, or something of that nature that is above my pay-grade to calculate, then I believe that your neutral conductor in a wye system can be the same size as your ungrounded conductors. I don't see what's different about it because it's an NDT.

The only application I know to require the same size but not larger size neutral than the ungrounded conductors is for a corner grounded delta

Zig zag transformers is super rare and something I’ve only heard of in text books