Okay, let's break down this scenario and consider the implications of using buck-boost transformers for your voltage sag issue.

Understanding the Problem



Low Voltage

Your nominal voltage of 475VAC is slightly below the standard 480VAC.

Voltage Sags

The major problem is the voltage sags that occur every 2-3 months and cause machine faults. These sags, even though brief (milliseconds), are disrupting your automated pump control.

Load

The pump control requires 89 amps at 480VAC. This is a significant load.

Proposed Solution: Buck-Boost Transformers Intent

You're planning to use three single-phase buck-boost transformers to increase the voltage from 475VAC to 501VAC.

Functionality

Buck-boost transformers, when properly configured, can either increase (boost) or decrease (buck) the voltage slightly.

Analysis and Considerations


Is the Voltage Boost the Right Solution? Address the Root Cause

The first question is: What is causing the voltage sags? Boosting the voltage might mask the symptoms, but it doesn't fix the underlying problem. Possible causes include:

Utility Issues

Overloads on the grid, switching operations, or equipment failures at the utility substation.

In-Plant Issues

Large motor starts elsewhere in the facility, undersized wiring, or loose connections.

Sag Depth

How low does the voltage drop during the sags? Knowing the minimum voltage during a sag is crucial. A boost to 501VAC will only help if the voltage doesn't sag lower than 470VAC.

Sag Duration

The milliseconds duration is important. Buck-boost transformers provide a continuous voltage correction, but they don't have the same fast response as some other voltage regulation solutions.2.

Buck-Boost Transformer Configuration & Calculations



Wiring

You'll be wiring the buck-boost transformers in an open delta (V-V) configuration to handle the 3-phase load.

Transformer Sizing

This is critical! You need to select transformers that can handle the pump's load (89 amps at 480VAC) and provide the required voltage boost. Use these formulas: `kVA = (Volts_boost Amps_load) / 1000` `KVA = (26V 89A) / 1000` = 2.314KVA per transformer. You'll need three 2.5 KVA single-phase transformers. Always oversize for safety and future growth.

Connections

Follow the manufacturer's wiring diagrams precisely. Incorrect wiring can damage the transformers or equipment. You would connect it according to the buck-boost transformer name plate depending on voltage output. Usually its a parrellel / series connection.3.

Potential Drawbacks and Alternatives



Heat Generation

Buck-boost transformers will generate heat, especially when heavily loaded. Ensure proper ventilation.

Harmonics

Transformers can sometimes exacerbate harmonic issues in the power system. Consider the potential impact on other equipment.

Not a True Voltage Regulator

Buck-boost transformers provide a fixed voltage boost. They don't actively regulate against fluctuations below your baseline.

Alternative Solutions

Before committing to buck-boost transformers, consider these alternatives:

Power Conditioner/Voltage Regulator

A true power conditioner or automatic voltage regulator (AVR) actively corrects for voltage sags and surges. These are generally more expensive than buck-boost transformers but provide better protection.

Uninterruptible Power Supply (UPS)

A UPS provides backup power during outages and can also regulate voltage fluctuations. This is a more robust solution but the most expensive.

Motor Starting Solutions

If the sags are caused by motor starts within the facility, consider using soft starters or variable frequency drives (VFDs) to reduce the inrush current.

Line Reactor/Inductor

These can help reduce voltage sags on motor starts and protect equipment.

Power Factor Correction

Improving your power factor can sometimes help stabilize voltage.4.

Safety Considerations



Qualified Electrician

All electrical work MUST be performed by a licensed and qualified electrician.

Overcurrent Protection

Ensure proper overcurrent protection (fuses or circuit breakers) for the transformers and the pump control panel.

Grounding

Proper grounding is essential for safety and to prevent electrical noise issues.

Arc Flash

Be aware of arc flash hazards and follow appropriate safety procedures.

Recommendations


Investigate the Root Cause

Thoroughly investigate the cause of the voltage sags. Work with your utility company and/or a qualified electrical engineer to analyze the power system. Use a power quality analyzer to record the voltage and current during the sags.2.

Consider Alternatives

Evaluate the alternative solutions (power conditioner, UPS, motor starting solutions) and compare their costs and benefits.3.

Proper Sizing and Installation

If you decide to proceed with buck-boost transformers, ensure they are properly sized, installed, and protected.4.

Monitor Performance

After installation, monitor the voltage and pump control performance to ensure the solution is effective and doesn't introduce new problems.

In summary, using buck-boost transformers could* be a solution, but it's crucial to understand the root cause of the voltage sags and to properly size and install the transformers. Consider the alternative solutions, and prioritize safety above all else. Flag for review