Power quality is a general term used to describe the degree of abnormality to several different electrical system characteristics. These characteristics are the frequency and amplitude of the voltage, the balance between phases on a three-phase system and the distortion level of the waveform. The characteristics that are important and what is considered an acceptable level of power quality varies from facility to facility.
Most of the older electro-mechanical equipment was robust and could handle minor power quality related issues with little or no effect on operations. But, due to the shift in the type of loads from electro-mechanical to electronic, power quality has become a real concern in all types of businesses. This includes hospitals, universities, commercial buildings and industrial facilities. Poor power quality results in random equipment malfunctions, data corruption, loss of process control, and heating of cables, motors and transformers.
An ideal power source offers a continuous, smooth sinusoidal voltage, as shown in Figure 1.
Poor power quality as shown in Figure 2 contains noise, harmonic distortion, voltage sags and swells, interruptions and voltage surge.
You might think that poor power quality is primarily the result of weather-related and utility-related disturbances. However, studies have shown that issues such as lightning, other natural phenomena, and utility operations, account for only a small portion of all electrical disturbances.
A large portion of electrical disturbances are from internal sources or from neighboring businesses that share the same building or are in close proximity. Internal sources can be fax machines, copiers, air conditioners, elevators, and variable frequency drives just to name a few.
Typical power quality issues include: voltage transients (surge), harmonics, voltage sag and swell, voltage imbalance and interruptions.
Description — A sudden high energy disturbance in line voltage typically lasting less than one cycle (< one second) which causes the normal waveform to be discontinuous.
Cause — Switching type loads
Issue — Data corruption, equipment malfunctions, equipment damage and process interruption.
Description — Distortion of the current and voltage waveforms caused by the momentary on/off switching of nonlinear loads.
Cause — Elevators, HVAC equipment, rectifiers and welding machines.
Issue — Data corruption, data loss, computer-controlled equipment malfunctions, excessive heat and equipment failure.
Description — A decrease (sag) or increase (swell) in line voltage lasting at least 1/2 cycle (1/120 of a second) to several seconds.
Cause — Utility related events, starting and stopping of large loads.
Issue — If equipment is operated slightly outside the design envelope, random malfunctions and failure may occur. If the equipment is operated significantly outside the design envelope, the equipment will not operate and may fail prematurely. The effects are based on the length, magnitude and timing of the sag or swell.
Description — Differing voltage levels on each leg of a three-phase system, typically < +/-2% of the average.
Cause — Large loads in a building such as HVAC equipment and elevators are three-phase loads. The small but numerous loads such as copiers, control equipment and computers are single-phase loads. Single-phase loads should be equally distributed among the three phases to prevent imbalance. Imbalance can also be caused by poor connections or blown fuses.
Issue — Depending on the level of imbalance, loads can operate erratically, not operate at all or fail.
Description — A significant or complete loss of voltage. The loss can be momentary or sustained.
Cause — Weather, utility equipment failures, internal faults or internal equipment failures.
Issue — A momentary interruption can damage computers and other electronically controlled equipment or disrupt processes. The damage can occur on both the loss and the re-energization of power. Electro-mechanical equipment is generally not affected by these brief outages. Sustained interruptions can last from hours to days. Contingency plans should be developed to address orderly equipment and process shutdown and restarts.
Each occupancy will have a different sensitivity level to poor power quality and will have different sources of poor power quality. However, common to all businesses is the importance of a well-maintained electrical distribution and grounding system. The importance of these systems cannot be overstated. When addressing potential or actual power quality issues, the power and grounding system should be the first item addressed. This will ensure personnel safety, allow for the proper operation of surge protection devices, minimize the potential for excessive currents on neutral conductors, and provide a common reference plane for electronic equipment.
Once the power and grounding system deficiencies have been addressed, the next steps include: power quality walk-throughs, power quality inspections and surveys, and mitigation equipment.
Walk-throughs provide an overview of a facility from a power quality standpoint. In addition to housekeeping and the overall appearance of electrical equipment, items to note during a power quality walk-through include:
The conditions below are considered warning signs for potential power quality issues in a facility. These conditions do not guarantee a problem. A facility with these conditions usually has an increased likelihood of power quality issues.
Based on the results of the power quality walk-through and the type of processes and equipment at the site, the following recommendations are common:
Power quality inspections and surveys identify the types of problems, the extent of the problems, and the potential solutions. Power quality inspections and surveys should only be performed by qualified power quality contractors. In many commercial or light industrial type businesses, only a few loads are affected by power quality issues and only a few loads are susceptible to poor power quality. By identifying these loads during a survey, targeted mitigation techniques can be utilized.
A power quality survey is the monitoring and recording of the power system supplied to a building or specific area of a building. It is important to measure power continuously over an extended period of time such as days or weeks. This will capture all of the intermittent event. Due to the special knowledge needed to identify power quality related issues, it is recommended that only electricians trained in the use of power monitoring instruments be utilized. The equipment should be capable of recording very fast events (less than one cycle) and have data storage capabilities. Since it is difficult to monitor all points simultaneously, selecting the best points to monitor is extremely important. This should be done based on the areas of concern that were identified during the inspection. The equipment must be monitored in its normal operating environment. Do not perform a power quality survey during a shutdown.
The review of the data from the survey will determine the type and severity of the problems and assist in recommending mitigation techniques. The data review should be performed by qualified and experienced power quality engineers.
Prior to selecting any type of mitigation equipment, the power quality deficiencies that are responsible for operational issues and failures must be clearly identified. The next step is to estimate the costs of the power quality related issues. This aids in a budget for the project.
A wide variety of power quality correction products is available utilizing a range of technologies and providing a range of protection. Common mitigation techniques include surge protection devices, isolation transformers, voltage regulators, motor generators, standby power supplies, uninterruptible power supplies and harmonic filters. Each technique has advantages and disadvantages and should be applied based on the discovered problems.
This list defines different types of mitigation techniques available, but it is not a complete list.
Function — Diverts surge events to ground.
Description — A device connected between line and ground which has high impedance at normal frequency system voltage levels and very low impedance at higher than normal voltage levels. Because of this low impedance, the SPD acts as a shunt to ground for voltage surge events. Devices vary in their surge current-handling capability and voltage-limiting capability. Since devices have different voltage and current capabilities, a multi-level approach is required to protect against surge events. The multi-level approach is also known as zones of protection. Each zone experiences a different level of surge event and therefore the SPD should be sized appropriately based on the zone. In general terms, the zones of protection are the service entrance line, the remote distributed panelboards, and at the equipment points-of-use.
Communications and data equipment are also vulnerable to surges. Special surge protectors are available for line protection of this equipment.
Many types of equipment claim to have built-in surge protection. But these are often inexpensive varistors. These devices may or may not provide sufficient protection. They should be supplemented by the field installed units for complete surge protection.
Function — Isolation transformers attenuate common-mode disturbances on the power supply conductors, provide a local ground reference point and allow for voltage output adjustments using internal winding taps.
Description — A transformer with special windings utilizing a grounded electrostatic shield between the primary and secondary. This grounded shield provides attenuation of high-frequency noise. Isolation transformers may step the voltage up or down (i.e., 480v to 208v) or be used for isolation only with no output voltage change (208 V in and 208 V out).
Function — Provide a constant output voltage level for a range of input voltages.
Description — A variety of voltage regulation techniques are available, such as ferro resonant transformers, electronic tap-switching transformers, and saturable reactor regulators.
Function — Provides voltage regulation, noise/surge elimination, voltage distortion correction and electrical isolation between the electrical system and the connected equipment.
Description — A separate motor and an alternator (generator) are interconnected by a rotating shaft and coupling. Typically, the utility is the power supply for the motor which drives the generator to produce clean power.
Function — An inverter and battery backup power system operating as an outage protection system. In normal mode, the inverter is in a standby mode and the load is directly supplied from the input power source. On a loss of input power, the load is switched to the battery supply. There is a momentary break in power when the transfer to and from input power occurs.
Description — Usually comprised of a solid-state inverter, battery, and battery charger.
Function — Maintain uninterrupted supply of regulated voltage for a period of time after a power failure.
Description — A variety of technologies exists. The two common types are rotary and static. A rotary unit consists of a motor generator set with a short ride through capability. A static unit utilizes power electronics and a battery string or other energy storage means as a source of energy during loss of input power. These depend on properly maintained batteries. The battery system is sized based on the load and duration of required time.
Other types include combinations of rotary and static units or UPS systems supplemented with engine driven generators for extended outages.
The design of the backup power supply capability should reflect the criticality and size of the loads to be supplied. Redundancy should be in consideration for installations with significant power loss consequences. Each element of the backup power scheme needs to be viewed as a point of failure. If appropriate the design should provide for functional duplication of each system component.
Function — Acts to reduce the level of harmonic distortion on a power system.
Description — Harmonic filers should be specifically designed to suppress the offending harmonics determined during the monitoring and analysis study. Harmonic filters may be available from equipment manufacturers that manufacturer electrical equipment known to create harmonic distortions on the power lines.
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This material is provided for informational purposes only and does not provide any coverage or guarantee loss prevention. The examples in this material are provided as hypothetical and for illustration purposes only. The Hanover Insurance Company and its affiliates and subsidiaries (“The Hanover”) specifically disclaim any warranty or representation that acceptance of any recommendations contained herein will make any premises, or operation safe or in compliance with any law or regulation. By providing this information to you, The Hanover does not assume (and specifically disclaims) any duty, undertaking or responsibility to you. The decision to accept or implement any recommendation(s) or advice contained in this material must be made by you.
LC FEB 2019-409
171-9262 (1/19)
Power Quality Monitoring has several advantages, like enhancing performance and quality. A PQM System will gather, examine, and interpret raw energy measurement data into useful information. A typical monitoring system measures voltage and electric current, but the ground quality might also be measured if dispersed loads or harmonics are found. There are a number of various reasons to use power quality monitoring. It helps manufacturing plants in energy management, preventative maintenance, quality control and thus saving money in the long run. Today, many end users have telecommunications or computer equipment that does not utilize PQM. This makes them susceptible to power quality problems. If you understand the implications of power fluctuations then you will realize the importance of power quality monitoring.
It is projected that power outages account for up to 40 percent of all business downtime. To monitor their power, modern power plants use digital error recorders, smart relays, voltage recorders, in-plant power monitors, and specific purpose power quality equipment. Consumers of power, such as buildings and factories use power quality meters from manufacturers such as MachineSense to prevent equipment damage and fire.
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MachineSenseTM Power Analyzer toroids are placed directly on incoming power lines to automatically monitor power conditions and detect power anomalies. The sensor data transmits through a self-contained data hub directly to your router and onto cloud-based servers running powerful analytic software. Results are then transmitted from the server to either a desktop or user friendly app where you will view power conditions with helpful advice to correct power anomalies.
Individual Waveform Capture – Allowing engineers and executives to track slowly changing variation in electrical waveforms to root out the cause of mechanical failures well before they happen which can be isolated, recorded and graphically displayed while using the Acuvim IIW.
Power Quality Monitoring provides an analysis of non-linear loads connected to the distribution system, all of which affect electrical frequencies and cause problems such as misfiring, over-heating and voltage spikes. Individual harmonic measurement can be read on all of the MachineSense power quality meters.
Voltage Sags and Swells are a decrease and increase in voltage over a brief time. Voltage sags are the most typical events that lead to affect the quality of energy and are usually the most pricey. They affect gear which range from PLCs, relays, controllers and everything else. When the sag happens, the power source within the device overcompensates which when the sag is reduced enough can harm the internal circuits of the device causing malfunctions.
Though these are generally blamed on the utility company, the reality is that these are usually caused inside the site or building and includes grounding, bonding, and other problems or from powering different equipment through the same power supply.
The deviation of the frequency at which electric current is supplied may confuse logic systems and affect the operating speed of machinery. These deviations in frequency can be effectively monitored using any MachineSense Power Quality Meter.
The ratio of the real power flowing to the load that it can be used for; this 0-1 figure is a most accurate depiction of how viable the electricity supplied is. Low power factor ( usually called “dirty power” ) affects devices and causes inefficiencies in their functioning. All of the MachineSense power quality meters allow users to keep track of this ratio and users can track the historical power factor.
An effective Power Quality Audit using MachineSense power quality monitoring systems can be achieved using MachineSense Power Quality Meters as a permanently installed power quality meter for proactive and comprehensive power quality measurement. The meter can be read remotely via our proprietary cloud-based software and app.
Electrical power runs almost every machinery in the world. As clean unadulterated food is important for the healthy lifestyle of human beings, machines need clean power for longevity and uninterrupted operations. Therefore, high-quality power is absolutely required for the successful operation of the factories and the buildings. IEEE 1159 standard defines the international standard for clean power by limiting the maximum limits allowed for over/under voltage/current conditions, Sag/Swell, poor grounding/earthing, level of different current and voltage harmonics, etc. Power distribution companies maintain this standard while feeding to the transformers at the input to the factories and the buildings. However, power distribution inside the factory or the building may not comply with IEEE 1159 standards since within the factories/buildings power quality degrades due to uneven tapping of single-phase load from 3-phase lines, DC loads like LEDs, UPS, Mobile/Laptop charges, etc. Poor quality is not only responsible for immature death/downtime of the machines/controllers, it also threatens basic fire safety issues since power surges or imbalance may lead to the burning of the wires. In addition, harmonic contents of the power are normally wasted and thus contribute to energy inefficiencies.
Power Quality Meters have wide range of applications - most notable among them are:
Power Quality analyzer has one hardware and 4 software components.
IEEE 1159 -1995 defines the power quality issues that have to be monitored in any Industrial or commercial operation. This includes approximately 37 different kinds of issues but overwhelmingly only a handful of them occur frequently in any manufacturing or building set-up. Most common occurring issues in power quality are:
Poor power quality may lead to a fire in many ways and is responsible for 85% of the fire in the buildings.
All kinds of equipment barring old-style Tungsten lamps are prone to damage due to power quality.
There are several power quality standards but IEEE 1159 is the most commonly followed standard worldwide. IEEE 1159-2019 is the latest which has superseded 1159-2009. For more details, please check
https://standards.ieee.org/standard/1159-2019.html
The following developments in the power sector played a tremendous role on power quality:
Total loss of United States GDP due to 1,2,3 are more than $45.7B a year (https://energycollection.us/Energy-Reliability/Cost-Power-Disturbances.pdf). However, the problem of power quality is very often ignored since it is not monitored. Most of the time end-users get aware of it only when they see frequent breakdowns of the machines or fire coming out of the wires. Waiting for such a long time to know the building has poor power quality is dangerous for the safety of the inhabitants of the buildings as well as utility machines.
The solution to Power Quality problems that have resulted from 1,2,3 are well recorded and recommended in ISA ( International Society of Automation: https://www.isa.org/about-isa/ ). However, to provide ISA compliant clean power to every building and plant, that are already suffering from poor power quality (1-3), one needs a system that:
The commercial challenge for 1 includes cost-effective hardware and cloud platform ( IoT or Cyber-Physical System ) that is affordable by building and plant management. That problem has been solved by MachineSense LLC by using state of the art System on Chips ( SoC), single-board computer like Raspberry Pi and Open Sourced software.
However, the commercial challenge for 2 is far more difficult and critical. As shown in the paper (https://cdn.selinc.com/assets/Literature/Publications/Technical%20Papers/6303_TodaysEngineeringShortage_JP_20071026_Web.pdf?v=20151202-215825), the US now produces only 500 engineers ( reduced from 2000) annually who are capable of such power diagnosis. There are hardly 50,000 power engineers active in the US. It is impossible for 50,000 engineers to address the power quality issues of 13M US buildings ( office, hospitals, plants, etc. ) even if all data to solve the problems are available.
Power Quality Analyzers had a wide range of applications - most notable among them are:
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