Getting the Most from Power Quality Meters

Power Quality Meters (PQMs) can offer rich insight into conditions in a power distribution system and the quality of power reaching load equipment. Using many meters across a power distribution system provides detailed information for evaluation while using fewer meters can provide strategic value.

The Value of Power Quality Information

Sensitive electronics and high-value equipment, such as imaging machines in a hospital or select IT equipment in a data center, can be susceptible to operational impacts from aberrations in line voltage, frequency, harmonics, and more. These aberrations can originate in power supplied by a utility or from operations and events within a building’s power distribution system. Power quality meters can collect and archive a variety of data regarding power conditions impacting power distribution circuits and load equipment. The information they provide can be used to address power issues before they cause problems in the following ways:

• Monitor harmonics to mitigate excessive heating and premature failure of transformers
• Use trending and alarming features to notify users of power fluctuations, outages, and other events
• Provide time-stamped data for analyzing event sequences
• Identify root cause by assessing electrical faults
• Identify power quality issues, including frequency variation, voltage fluctuations and imbalance, and harmonics
• Allocate power costs among users or uses
• Compare electrical consumption for specific date and time ranges

Metering Strategies

Power Quality Meters provide the most precise evaluation of power quality impacts on devices when they are located close to the loads they serve. However, when a facility operates many devices sensitive to power quality, numerous meters could be used to assess device-specific impacts, as shown in Figure 1. In practice, this arrangement presents cost and complexity that is likely unnecessary for most facilities.

Figure 1: Power Quality Meters at every load would provide comprehensive data but is typically unnecessarily complex and costly.

A more cost-effective approach can be used to show the quality of power that is being provided to the site. Placing a PQM at the utility service entrance can be a high-value solution for this need. This arrangement, shown in Figure 2, can be used to monitor electrical anomalies originating from a utility feed and provide an overall insight into power conditions and usage.

Figure 2: Locating a PQM at the service entrance provides insight into the quality of incoming power.

Notably, Service Entrance Automatic Transfer Switches can also be fitted with a PQM, as detailed in Figure 3. For suitable applications, this solution ingrates a transfer switch, service disconnect breaker, and PQM into a single enclosure, streamlining specification, procurement, and installation.

Figure 3: A Service Entrance Automatic Transfer Switch with a PQM

Another approach involves collecting power data from central locations in a distribution system. This provides comparable information about the conditions occurring across the power distribution system. Because transfer switches are positioned between power sources and load equipment, they are good locations for collecting power quality data from both the utility source and the generator, something that cannot be done with a single meter at the service entrance. Located closer to loads than the service entrance, placing PQMs here can reveal conditions that are affecting a limited number of loads on a particular branch of the system. The arrangement is shown in Figure 4.

Figure 4: Providing PQMS on transfer switches helps differentiate conditions between branches of the Power Distribution System.

Schneider Electric PM8000 PQMs are readily installed as accessories for ASCO transfer switches. Depending on the circumstances presented, these can differentiate whether certain conditions originate upstream or downstream of the meter. Meters in these positions can detect local power conditions on each branch, and a comparison of the resulting data can help pinpoint problems. Because the respective branches serve a subset of loads, they can be used to allocate power usage and costs to respective departments, processes, cost centers, or tenants. Figure 5 shows a PQM.

Figure 5: A Schneider Electric PowerLogic PM 8000 Power Quality Meter

In many cases, a hybrid approach (Figure 6) provides comprehensive data that can be used to protect critical equipment at an optimized cost. By placing a PQM at a service entrance (Position 1), incoming power quality can be readily assessed. By locating PQMs at each transfer switch (Position 2), power conditions can be compared across the power distribution system to assess overall performance, troubleshoot problems, and allocate costs. By placing a PQM near the most critical load equipment (Position 3), a facility can identify and respond to power conditions and anomalies that could impair the performance of specific sensitive equipment or damage high-value devices. In addition, placing meters at multiple points along the power path can show power event progress through the power network and how it impacts locations throughout the system. Comparing data from different positions in a power distribution system can help identify causation and support forensic evaluation of power conditions and events.

Figure 6: Selective metering at multiple levels can provide a comprehensive view of system conditions as well as detailed power quality information for critical loads.

Summary

The following table summarizes the advantages and disadvantages of each approach described above.

In practice, the available strategies and configurations for deploying Power Quality Meters are as diverse as the power distribution systems they support. To learn more about power quality metering and its applications, consult an ASCO Power or Schneider Electric representative.

Further Reading

ASCO White Papers:

Applications for Service Entrance Automatic Transfer Switches
Benefits of Custom-Engineered Transfer Switches

For additional information, contact a local ASCO representative or ASCO Customer Care.