What Causes Undervoltage and Overvoltage in Factories?

Undervoltage and overvoltage are among the most common power quality problems in industrial facilities. In real production environments, they rarely originate from a single cause.

Based on long-term observation in factory power systems—particularly in facilities using industrial voltage stabilizers and transformers—voltage issues usually result from a combination of utility-side instability, internal load behavior, and improper power system design or management.

From the perspective of an voltage stabilizers equipment manufacturer such as ZHENGXI, abnormal voltage is one of the most frequent root causes behind motor failures, PLC resets, inverter alarms, and unexplained production downtime. When left uncontrolled, it can damage motors, PLCs, inverters, transformers, and other sensitive equipment, leading to product defects, unplanned shutdowns, and rising maintenance costs.

This guide explains the real causes of undervoltage and overvoltage in factories, based on practical engineering experience and long-term manufacturing insight from industrial power applications.

What Is Undervoltage and Overvoltage?

Undervoltage

This occurs when the voltage is lower than the acceptable range, i.e., -10% of the nominal voltage.

Overvoltage

This occurs when the voltage is higher than the acceptable range, i.e., +10% of the nominal voltage.

In a continuous production system, even minor fluctuations in voltage can cause a decrease in the reliability of the equipment and a shortening of the life of the equipment.

Main Causes of Undervoltage in Factories

1. Heavy Load Start-Up

Large industrial loads such as motors, compressors, crushers, and rolling mills draw high inrush current during startup.
This sudden current demand causes a temporary voltage drop across transformers and distribution cables.

Typical scenario:
Multiple large motors starting simultaneously on the same feeder—something frequently observed in workshops that expand capacity without upgrading the original power system.

2. Insufficient Power Supply Capacity

When the utility transformer or internal distribution transformer is undersized, voltage drops occur whenever load demand increases.

In many factories, long-term operation close to or above rated capacity leads to chronic undervoltage, especially during peak production hours. From practical field experience, this issue often becomes noticeable only after new machines are added.

3. Long Cable Runs & Poor Wiring Design

In large industrial plants, long-distance power transmission increases line impedance.

Voltage drop becomes more severe when:

• Cable cross-sections are too small
• Conductors are aged or of poor quality

Under load, these factors combine to produce excessive voltage loss at the equipment terminals.

4. Utility Grid Voltage Sag

Some undervoltage events originate outside the factory and are beyond direct control, such as:

• Grid faults on nearby feeders
• Substation overloads
• Peak demand periods

These conditions cause short-term or recurring voltage sags, which can still disrupt sensitive industrial processes.

5. Poor Power Factor

Low power factor increases current draw for the same real power output.

Higher current results in:

• Increased voltage drop
• Transformer and cable overheating

In many factory audits, poor power factor is one of the most underestimated contributors to long-term undervoltage problems.

Main Causes of Overvoltage in Factories

1. Sudden Load Rejection

When large loads are abruptly disconnected, system voltage can rise sharply.

Common situations include:

• Emergency stops
• Large motor shutdowns
• Fault clearing events

Such transient overvoltage is especially harmful to electronic control systems.

2. Incorrect Transformer Tap Settings

If transformer tap changers are set too high, the secondary voltage increases.

This often occurs after:

• Utility voltage adjustments
• Load profile changes

without proper recalibration of on-site transformers.

3. Power Factor Correction Problems

Improperly designed capacitor banks can cause overcompensation, leading to:

• Voltage rise
• Resonance with system inductance

From an engineering standpoint, this risk is significantly higher in systems with nonlinear or fluctuating loads.

4. Unstable or Poorly Regulated Utility Supply

In light-load grid conditions, utility voltage may drift above nominal levels.

Factories located at the end of distribution lines are particularly vulnerable to this type of overvoltage.

5. Harmonics & Nonlinear Loads

Equipment such as:

• VFDs
• Rectifiers
• UPS systems
• Welding machines

introduce harmonics that distort voltage waveforms. In practice, harmonics can create effective overvoltage conditions that accelerate insulation aging and interfere with control electronics.

Why Undervoltage and Overvoltage Are Dangerous

Effects of Undervoltage

• Motor overheating and torque loss
• PLC resets and control failures
• Increased current stressing cables and transformers
• Production interruptions and unplanned downtime

Effects of Overvoltage

• Insulation breakdown in motors and transformers
• Immediate damage to electronic components
• Shortened equipment lifespan
• Nuisance tripping of protection devices

From manufacturing experience, both conditions often coexist in the same facility at different operating stages, increasing overall system risk.

How Factories Can Prevent Voltage Problems

Practical Mitigation Measures

Effective voltage control in factories typically requires a system-level approach, including:

• Industrial Automatic Voltage Regulators (AVR) or voltage stabilizers
• Proper transformer sizing and realistic load planning
• Dedicated feeders for heavy or impact loads
• Soft starters or VFDs for large motors
• Power factor correction combined with harmonic filtering
• Continuous power quality monitoring

Standards such as IEEE 1159, IEC power quality guidelines, and best practices adopted by industrial solution providers all emphasize proactive voltage management rather than reactive fault repair.

Undervoltage vs Overvoltage: Quick Comparison

FAQ

Q1: Can undervoltage permanently damage motors?
Yes. Continuous undervoltage increases motor current, causing overheating, accelerated insulation aging, and eventual failure.

Q2: Is overvoltage more dangerous than undervoltage?
Both are harmful. Overvoltage can cause immediate electronic damage, while undervoltage usually leads to long-term thermal stress.

Q3: How do factories monitor voltage problems?
By using power quality analyzers, smart meters, and continuous monitoring systems compliant with IEEE and IEC standards.

Expert Tip for Industrial Plants

From long-term factory application experience, if voltage fluctuations occur frequently, installing an industrial-grade voltage stabilizer or AVR at the main distribution level is often one of the most effective and economical long-term solutions—especially for facilities with expanding production lines or sensitive equipment.