Step up transformer to step down

[Tom Drake]

I have a small step up transformer. 240 to 480 single phase that runs from the main house that goes to a step down transformer 480 to 240 to the front gate about 1500 feet away. It runs gate, lights, and 5hp fountain. Wired with two #4s and one ground wire. Neutral is derived at gate from step down. Problem is line to ground is 132v on A phase and 97v on B phase. What is proper way to ground this system or any idea what causes this

 

[augie47]

sounds as if you have not bonded your neutral to ground on the gate transformer secondary.
(you should also have a grounding electrode system..see 250.30)

 

[templdl]

I have a small step up transformer. 240 to 480 single phase that runs from the main house that goes to a step down transformer 480 to 240 to the front gate about 1500 feet away. It runs gate, lights, and 5hp fountain. Wired with two #4s and one ground wire. Neutral is derived at gate from step down. Problem is line to ground is 132v on A phase and 97v on B phase. What is proper way to ground this system or any idea what causes this

Excellent idea but you have omitted some details. Are you an electrician by chance?
If I make as few assumptions you have not stated what what the ratings of the transformers are. Can I assume that the step up transformer ihas been built specifically as a step up or is it a stock sterp down being used as as sterp up. This will determine where the taps asre as well as if there is an issue with the 240v side connections.
Then, the 480- 240v stepdown transformer. Again, I may assume that it is a basic 1ph 480 primary to a 120/240 secondary configured in a common 1ph3w with X1, X2,X3,X4 connections with X2and X3 connected together for a neutral and also the point of grounding. For 240 the connection would be from X1-X4 and 120v from either X1-X2/X3 or X4-X2/X3. And then please advise what the taps on the transformer are.
I would also "assume" that you have a small load center with breasker's for over current protection also.
I get concerned when so may details are omitted to that are very important to know.

 

[iwire]

I agree with Gus, it sounds like the derived neutral was never bonded to ground.

This would be the first thing I would look into.

 

[kwired]

I have a small step up transformer. 240 to 480 single phase that runs from the main house that goes to a step down transformer 480 to 240 to the front gate about 1500 feet away. It runs gate, lights, and 5hp fountain. Wired with two #4s and one ground wire. Neutral is derived at gate from step down. Problem is line to ground is 132v on A phase and 97v on B phase. What is proper way to ground this system or any idea what causes this

Did you measure line to neutral and line to ground when taking measurements? Where in the circuit did you take measurements? Bonding jumper installed at first disconnecting means?

If that neutral is properly grounded - you have an open circuit between the source and the point you are measuring to, or a defect in the transformer.

 

[Tony S]

I installed a similar setup last year. A house fed from a farm 1Km away. I used 900V (UK armoured cable is rated 600/1000V). 433/900V step up 900/240V step down transformers. The saving in cable size more than made up for the cost of the transformers.

As has been said earthing (grounding) is everything to get a stable system. Remember we use 240V and not 120-0-120V

I can think of better things to be doing than being sat in a muddy hole jointing cables. It took four 250m drums.

 

[Tom Drake]

sounds as if you have not bonded your neutral to ground on the gate transformer secondary.
(you should also have a grounding electrode system..see 250.30)

That is what I was thinking. There is no electrode system at gate. 480 goes to disconnect - step down transformer - then to panel, and neutral and ground are not bonded together

 

[Tom Drake]

I installed a similar setup last year. A house fed from a farm 1Km away. I used 900V (UK armoured cable is rated 600/1000V). 433/900V step up 900/240V step down transformers. The saving in cable size more than made up for the cost of the transformers.

As has been said earthing (grounding) is everything to get a stable system. Remember we use 240V and not 120-0-120V

At the gate where the step down is, there is no electrode system and the CB panel has neutral and ground separated. Lines to neutral are balanced. Only the lines to ground are off balance. I assuming this was always the issue. Just never noticed since most items at gate are 120v except fountain pump of which they are now experiencing problems

 

[Tony S]

At the gate where the step down is, there is no electrode system and the CB panel has neutral and ground separated. Lines to neutral are balanced. Only the lines to ground are off balance. I assuming this was always the issue. Just never noticed since most items at gate are 120v except fountain pump of which they are now experiencing problems

I would think that is where your problem lies. Earthing (grounding) the neutral via a rod should sort the problem.

There is another way, if I tried it here I would be shot at dawn and I’m sure you would get the same reaction.

 

[Tom Drake]

Did you measure line to neutral and line to ground when taking measurements? Where in the circuit did you take measurements? Bonding jumper installed at first disconnecting means?

If that neutral is properly grounded - you have an open circuit between the source and the point you are measuring to, or a defect in the transformer.

Neutral to line is well balanced. Problem is line to ground. I did not see an electrode system nor is the neutral bonded to ground in CB panel. I believe by achieving both of these. It should correct problem. All 120v circuits are working fine. The problem was noticed when the 240v fountain pump was replaced

 

[templdl]

Neutral to line is well balanced. Problem is line to ground. I did not see an electrode system nor is the neutral bonded to ground in CB panel. I believe by achieving both of these. It should correct problem. All 120v circuits are working fine. The problem was noticed when the 240v fountain pump was replaced

Back to my first reply, the neutral being grounded as I pointed out. This is a very basic and simple configuration which I'd used commonly is airports. I have sold combination to provide 120/240v power to avionics systermms located a great distance from the power souce. As an example I have 2 sets of pad mounts at the international airport on the island of Guam and another set at the lake front sair port in New Orleans.
This setup should be a piece of cake.

 

[kwired]

That is what I was thinking. There is no electrode system at gate. 480 goes to disconnect - step down transformer - then to panel, and neutral and ground are not bonded together

But measurements from "hots" to neutral will still be 120 volts and any connected 120 volt equipment will still see 120 volts. The system simply has no ground reference and will measure funky readings to ground - and can create hazards should there be a ground fault. Some electronic equipment may be looking for a ground reference and may have abnormal operation because of this though.