Okay, let's break down this situation and address the use of the 4160/2400Y - 480/277Y transformer as a temporary solution.

Understanding the Situation Existing Setup

You have a 480/277V supply stepped up to 4160V to feed remote buildings and pumps. This uses a 480D-4160D transformer.

Failure

The original transformer has failed, requiring generator backup.

Available Transformer

You have a 75kVA 4160/2400Y - 480/277Y transformer on hand.

Primary Load

The 4160V side feeds primarily single-phase 4160-120/240V transformers (L-L connection) and a 4160D-480/277Wye stepdown at the pump shed.

Constraint

Difficulty in running a neutral conductor to the transformer location due to the existing conduit fill.

Is the 4160/2400Y - 480/277Y Transformer Usable?Potentially, YES, but with very significant caveats. Here's a detailed analysis:1. Voltage Mismatch on the Primary

This is the BIGGEST problem. Your available transformer is rated for either 4160V Wye or 2400V Wye. You are stepping up from 480V, so it is acting as the primary side. You need a 4160V nominal output on the high voltage side. However, since your existing input voltage on the low side is fixed, your output is not fixed. Your output voltage will be proportional to the ratio between the input and rated primary side. Assuming that the windings and insulators are suitable for the 4160 volts that will be on the primary side, which may be a problem, we need to determine what voltage would be supplied to the high voltage side. Since this transformer is 4160/2400Y - 480/277Y, that means the turns ratio for the 4160v section is 4160:480, or about 8.67:1. The transformer is being supplied by 480 volts. 480 8.67 = 4161.6 So, for the primary of 4160v, you should have a close enough voltage for the existing setup.2.

Neutral Requirement

This is a complex issue with Wye-Wye transformers.

Ideally

A solidly grounded neutral on both the primary (4160V) and secondary (480/277V) is preferred for stable operation, voltage regulation, and fault protection, especially if you have significant line-to-neutral loads on either side.

Your Situation

You don't have a neutral to the 4160V side. This is problematic. Wye-Wye transformers without a neutral connection can exhibit ferroresonance under unbalanced load conditions. Ferroresonance is a type of resonance that can cause high overvoltages and damage to the transformer.

No L-N on Primary Side

The key to this actually working as a TEMPORARY solution is that you have NO line-to-neutral loads on the 4160V side. All your loads are either L-L (4160-240V transformers) or Delta configured transformers (4160D-480/277Wye stepdown at the pump shed).

Impact

The absence of L-N loads on the 4160V side reduces the risk of ferroresonance. However, it doesn't eliminate it entirely. Even slight imbalances in your single-phase L-L loads can introduce some circulating current and potential issues.

Mitigation (If You Proceed)



Monitor closely. Check for overvoltages, excessive noise, or overheating. Consider a loading resistor. A small resistive load connected L-N on the 480/277V secondary side could help stabilize the neutral and dampen potential oscillations. This requires careful calculation to avoid overloading the transformer and would need to be sized to handle any imbalances.3. Delta Connection on Secondary of Remote Wye-Delta Transformer

This is potentially a BIG problem. If the delta side does not have a ground reference, then you could have a floating voltage and potentially an overvoltage when there is a fault. This would need to be carefully checked to make sure that the center tap of one winding is grounded.4.

KVA Rating

The 75kVA rating should be sufficient if it matches your existing transformer. Verify your load calculations to ensure you aren't exceeding the capacity.

Recommendation

Given the voltage mismatch and the potential for ferroresonance, using the 4160/2400Y - 480/277Y transformer as a permanent replacement is NOT recommended.

IF you use it as a temporary solution, follow these precautions and be prepared to take it out of service if any issues arise


Verify the insulation

Make sure that the windings and insulators are suitable for the 4160 volts that will be on the primary side.2.

Monitor. Continuously monitor voltages, currents, and temperature.3. Assess loads

Make sure to calculate your loads and that you are not overloading the transformer.4.

Correct grounding

Confirm that the secondary side of the 4160/2400Y - 480/277Y transformer and delta side of the remote transformers have proper grounding to prevent floating voltages.

Best Course of Action1. Order the Correct Replacement ASAP

Get the correct 480D-4160D transformer as quickly as possible.2.

Detailed Load Analysis

Perform a thorough load analysis of the entire 4160V system to ensure proper transformer sizing and to understand potential imbalances.3.

Grounding Audit

Review the grounding configuration of the entire system, especially at the remote transformers.

Disclaimer: This information is for informational purposes only. Consult with a qualified electrical engineer for any electrical work or installations. Your situation is complex, and a professional on-site assessment is crucial. Flag for review