Power quality
Many problems can result from poor power quality, especially in today's complex microelectronics environment. In the past, electrical disturbances on mechanical equipment went unnoticed. Now, however, electrical disturbances can upset today's high-tech equipment operations severely.
Approximately 80 percent of power quality problems originate from the customer's side of the meter. It's important for facility owners, managers, designers and other high-tech equipment users to understand and learn how to avoid power disturbances. Review the following for a general overview of power quality:
Residential and small commercial: Power Quality in Your Home (PDF)
Commercial/industrial: Understanding and Avoiding Commercial Power Disturbances (PDF)
Power quality and voltage stability
It's normal for your electric service voltage to vary within the prescribed limits. These fluctuations can result from the normal operation of a utility's electric transmission and distribution system, among other reasons. Voltage changes will not usually cause problems for your equipment or facilities. Certain electronic equipment may be sensitive to these fluctuations, however, which may cause problems.
You are responsible for obtaining any devices needed to protect your sensitive equipment that can't operate within the voltage variations of our normal electric service. Electric Rule 2, on file with the California Public Utilities Commission, specifies these variations. PG&E is not liable for damage to your equipment or any other damage from variations in service voltage allowable under this rule.
Power-quality problems
Power-quality problems arise when system incompatibility occurs between the AC power and the equipment. Either the quality of the AC distribution system or the AC voltage can contribute to power quality problems. In order to find the right solution or solutions, it’s important to diagnose the problems correctly. Some typical power quality problems are:
- Processing errors
- Soft failures such as computer reset or lockout
- Hard failure of electronic components
- Nuisance tripping in process control equipment
Analyze power-quality problems
When analyzing a potential power-quality problem, it’s important to keep a trouble log. This helps to connect the problem to other events such as equipment operations or even utility problems. Check out PG&E's “Checklist to Solve Power Problems for Sensitive Equipment” to help identify and mitigate power problems for sensitive equipment.
The checklist includes questions you should answer in your trouble log to help identify possible causes and solutions. Once you've diagnosed the problem (e.g., voltage sags, outages, impulses, harmonics, electrical noise, voltage and current imbalances, interference or wiring and grounding, etc.) correctly, you can take preventive measures to mitigate the problem. Sometimes the solution can be as simple as adjusting your equipment to make it less sensitive to power variations. Be sure to adjust in a manner that does not void any warranties.
Download the checklist to solve power problems for sensitive equipment (PDF)
Power Notes
Our PG&E Power Notes on the following topics may help you identify and solve your power-quality problems or concerns.
- Learn about power system harmonics, their potential problems and solutions.
Download Power System Harmonics (PDF) - Learn about voltage ranges, power components, electrical disturbances and more.
Download Understanding Electric Power Characteristics (PDF) - Review our computer industry guideline for data center electrical distribution environments.
Download Voltage Tolerance Boundary (PDF) - Learn what causes sags, their impacts and possible solutions.
Download Short Duration Voltage Sags can Cause Disruptions (PDF) - Learn how to safeguard almost any facility, equipment or person.
Download Lightning Protection (PDF) - Review the basics of telecommunication interferences.
Download Telecommunications Interference (PDF) - Learn the basics of grounding design and applicable NEC grounding requirements. Additional guidance is presented beyond the NEC requirements to establish maximum performance associated with sensitive electronic equipment grounding.
Download Performance Grounding and Wiring for Sensitive Equipment (PDF)
- Review a general description of operating issues and learn about nuisance tripping issues.
Download Desensitizing Electric Motor Controls (PDF) - Learn how the power factor adjustment is calculated and when it may be appropriate to make corrections.
Download Economics of Power Factor Correction in Large Facilities, >400kW (PDF) - Learn about voltage and current measurement of non-sinusoidal AC power.
Download Voltage and Current Measurement of Non-Sinusoidal AC Power (PDF) - This Power Note discusses open-phase protection issues for motors.
Download Open-phase Protection Issues for Motors (PDF)
- Learn how to select an appropriate transient voltage surge suppressor for your needs.
Download Surge Suppressors (PDF) - Learn how to select a UPS for small, standalone, single-phase computer applications.
Download Uninterruptible Power Supply (PDF) - This Note focuses on solutions to voltage sags.
Download Voltage Sag Ride-through Mitigation in Sequence by Increasing Cost (PDF)
- Learn how to apply line reactors or DC link reactors to variable frequency drives (VFDs).
Download Application of Line Reactors or DC Link Reactors for Variable-Frequency Drives (PDF) - Purchasing a new VFD? You can specify the sag ride-through options, but you must also program the drive to use them.
Download Methods for Mitigating Voltage Sag Impact on Variable-Frequency Drives (PDF) - Learn simple precautions you can take to avoid premature failure in your drives.
Download Effect of Variable-Frequency Drive Output Voltage on Motor Insulation (PDF) - Minimize EMI problems by separating and shielding power conductors from control conductors.
Download Solutions for EMI Problems from Operation of Variable-Frequency Drives (PDF)
Power Quality Bulletins
PG&E's Power Quality Bulletins may also help you identify and solve your power-quality problems or concerns.
A black box is a device or system with external wires that supposedly can do something something beneficial. In many cases, what's inside the box is a mystery. Many devices and systems on the market claim to improve the power quality or reliability of electric service. Some devices also claim to save energy. Often the technological claims are not clear or have not been verified in accordance with industry standards. Learn more in our Bulletin on the subject.
Have you ever been shocked when you touched a metal fixture near a swimming pool or when you touched the showerhead fixture in your home? And for dairy farmers, have you noticed a reduction in milk production? These may all be symptoms of stray voltage. Learn more in our Bulletin on the subject.
Interruptions in manufacturing processes can be very costly. They can cause potentially millions of dollars in lost revenue per day. Such interruptions can be due to voltage sag events, which are the most important power-quality problem facing many industrial customers, especially those with a process. Learn more in our Bulletin on the subject.
Additional resources
For more information
If you have questions or need additional power quality information, email us at PowerQualityWeb@pge.com.