Okay, let's break down the possible causes of these "line surges" and how they could fry components in a vendor skid, even with minimal load. While "line surge" is a somewhat imprecise term, we'll interpret it as transient overvoltages.Here's a structured approach to investigating the problem

1. Understanding the Scenario
Low Load vs. No Load

Even if the skid has very little active load (motors running, etc.), it still has components that are sensitive to voltage spikes: Control transformers (powering PLC, relays, etc.) PLC power supplies Relays/Contactors (coil voltage) Sensors (especially with sensitive electronics) Power supplies for instruments (pressure transmitters, etc.)

"Fried" Components

Knowing which components failed is crucial. Were they on the input side (like the transformer primary)? Were they downstream (PLC power supply, sensor power supply)? This gives clues to the nature of the overvoltage.

Temporary Power

Temporary power is often less "clean" than permanent power. It may be run from a generator or from a temporary distribution panel, and these can be more prone to voltage fluctuations and surges.

2. Potential Causes of Transient Overvoltages (Surges)

Let's consider several possibilities, categorized by where they might originate: External to the Skid (on the Temporary Power System)



Switching Surges



Capacitor Bank Switching

Switching capacitor banks on the utility grid (or even on the temporary power system if it's large) creates very fast voltage transients that can propagate through the system. These are extremely common.

Transformer Energization

Energizing (turning on) a transformer creates a high inrush current, which can cause voltage dips and, sometimes, oscillatory overvoltages when the inrush current is suddenly cut off. Think about other large transformers on the temporary power system being switched on and off.

Motor Starting (Nearby)

Starting large motors creates voltage sags and, occasionally, associated overvoltages when the motor is switched off.

Lightning

Even distant lightning strikes can induce significant voltage surges on power lines.

Grounding Issues

Poor grounding can exacerbate surge problems. If the temporary power system doesn't have a solid, low-impedance ground, surge currents may find alternate paths through sensitive equipment.

Utility Grid Issues

Problems on the utility grid can propagate through to the temporary power system.

Generator Instability

If the temporary power is supplied by a generator, voltage regulation problems with the generator itself can create surges.

Internal to the Vendor Skid



Switching Inductive Loads

Even small inductive loads (relays, small motors) within the skid can generate voltage spikes when they are switched. If there is inadequate surge suppression on these devices, the spikes can damage other components.

Resonance

If the internal wiring or components create a resonant circuit, a transient voltage can be amplified to a damaging level. This is less common but possible.

3. Investigation Steps1. Talk to Construction

Get more details from the construction team: When did the failures occur (time of day, weather conditions, etc.)? Were any other equipment failures observed at the same time? Were there any specific events happening (e.g., motor starting, capacitor bank switching) shortly before the failures? Where is the temporary power sourced from (generator, temporary distribution panel, etc.)?2.

Inspect the Damaged Components

Examine the failed components closely. Are there signs of overvoltage damage (burned components, blown capacitors, etc.)? This can help determine the polarity and magnitude of the surge. Note the voltage ratings of the damaged components. Were they appropriately sized for the 480V system?3.

Grounding Inspection

Verify that the vendor skid is properly grounded to the temporary power system's ground. Check the grounding conductor size and connections. Measure the ground impedance. It should be very low (ideally less than 1 ohm). A high impedance ground can make the system much more susceptible to surges.4.

Power Quality Monitoring

This is the most definitive step. Use a power quality analyzer to record voltage and current waveforms on the 480V supply to the skid. Look for: Voltage transients (spikes, surges) Voltage sags (dips) Harmonic distortion Ground currents Frequency variations (if a generator is the source)The power quality analyzer will need to be able to capture fast transients (microseconds). Record data for several days to capture a representative sample of the power quality. Trigger the recording on voltage disturbances to capture intermittent events.5.

Evaluate Surge Protection

Is there any surge protection currently installed in the vendor skid or on the temporary power panel feeding it? If so, what type (MOV, silicon avalanche diode, etc.) and what is its surge current rating? Is it adequate for the expected surge environment? Check the surge protection devices to see if they have been activated (sacrificed their life) - some surge protectors have indicator lights.

4. Mitigation Strategies

Based on the findings of the investigation, here are some mitigation strategies: Improved Surge Protection

Install or upgrade surge protection devices (SPDs) at the following locations:

At the main temporary power panel

A robust SPD at the source can help protect all downstream equipment. Consider a Type 1 SPD if the location has exposure to lightning.

Inside the vendor skid, at the 480V input

This will protect the skid's internal components from surges that make it past the main panel's SPD. A Type 2 SPD is often suitable here.

On sensitive control circuits

Consider adding surge protection on the DC power supplies for the PLC, sensors, and other sensitive devices.

Proper SPD Selection

Choose SPDs with appropriate voltage ratings and surge current ratings for the expected environment. Consider using SPDs with a visual indication of their health (e.g., LED indicators).

Improved Grounding

Ensure a solid, low-impedance ground connection for the temporary power system and the vendor skid. Use proper grounding techniques, such as running a dedicated grounding conductor back to the source.

Line Reactor or Isolation Transformer

A line reactor placed upstream of the skid can help reduce the rate of rise of voltage transients. An isolation transformer can block common-mode noise and provide some surge protection.

Power Conditioner

A power conditioner combines surge protection, voltage regulation, and noise filtering to provide a clean and stable power supply. This is a more expensive option but can be very effective.

Coordinate with the Temporary Power Provider

Discuss the power quality issues with the company providing the temporary power. They may be able to take steps to improve the power quality (e.g., adjust generator settings, add surge protection at their source).

Relocate Sensitive Equipment

If possible, move sensitive equipment away from sources of electrical noise or potential surges (e.g., away from large motors or welding equipment).

Shielding

Use shielded cables for sensitive control circuits to reduce the effects of electromagnetic interference (EMI).

Important Considerations



Safety

Always work with qualified electricians when dealing with electrical systems. Follow all safety precautions.*

Documentation: Document all findings, measurements, and corrective actions taken.By systematically investigating the problem and implementing appropriate mitigation strategies, you can protect the vendor skid from future damage. Power quality monitoring is the key to understanding the nature and source of the surges. Flag for review