By Fernando Gomez
In today’s world of diverse energy sources, electrical energy has gained popularity among alternatives because of its minimal impact to the environment. However, when we look at the different sources of energy and review the conversion efficiency, we can see that only an average of 34 percent of the energy source becomes electrical energy.
When looking further down the path of electrical energy conversion and distribution, we can see several areas where electrical power is further processed to facilitate delivery from the original source (power plant) to the ultimate destination (commercial or residential user).
In each of these steps, electrical energy conversion equipment such as transformers and distribution systems have the potential to influence the quality of the electrical signal, and subsequently both energy providers and end users have not only the right but also the responsibility to ensure proper supply and safe operation while complying with safety standards and observing appropriate industry regulations.
When issues with power quality arise, measurements made with power quality analyzers will reveal symptoms commonly associated with either impairments created during the conversion and distribution of energy (electrical power supplied by the utility company) or impairments already present at the load (customer-owned equipment making use of the supplied electrical power).
Among the points raised by the test results, it is important to mention that what appears to be normal operation when making a casual current or voltage measurement with a DMM only represents a single point snapshot in time. Any attempt to extract conclusions from a single point measurement may result in an erroneous interpretation of the “state of health” of the power delivery system or the load at the customer’s premises. The international standard IEC61000-4-30 describes how power quality is to be measured with test instruments and also specifies the minimum reliability and repeatability of the measurements made by those test instruments. Power quality analyzers fall under this category of test instruments.
The Problem at Hand
So, what happens when something goes unexpectedly wrong? For example, if a load consumes more energy than was expected or when demand for power outstrips supply? Without proper test instruments, there are no easy answers.
A few simple questions can help assess the situation.
1. Were there any early warning signs of a developing situation?
2. When did the triggering event occur?
3. What do we need to do to prevent situations like this from ever happening in the future?
Fortunately, all of these questions can be answered with the capabilities of modern, reliable and accurate power quality analyzers.
Were there any early warnings? While there is no substitute for hindsight, the ability to observe a trend in the values of current and/or voltage over a period of time can become an indicator of future behavior. This is not to say that the actual behavior of a unit under test can be predicted accurately, however any indication of changing voltages or currents points to a potential fault at the source or at the load. For example, a voltage drop accompanied by an increase in current consumption is attributed to a load that could be experiencing a failure. On the other hand, when a voltage drop and a current drop appear simultaneously, the cause can be attributed to the source/supply side. Common phenomena/events associated with variations in current and/or voltage may be:
• Voltage dips or swells
• Inrush currents
• Waveform distortions
• RMS value fluctuations
• Frequency fluctuation
• Circuit (phase) balance
Transients Caused by Equipment Switch-Ons or Lightning
When did the triggering event occur? It is common to observe changes in the voltage and/or current values when an installed generator or load is turned on, usually because of increased resources needed in a relatively short amount of time. When the test instrument collects data that is associated with a time stamp, the user can determine with a high degree of certainty that a certain piece of equipment or load caused the malfunction at a specific point in time. It is also important to record the transient event, characterized by abrupt swells or dips in current or voltage.
How do we prevent something similar from happening in the future? We not only want to measure, we also need to define a “qualifying event,” or what is considered acceptable and what is not. By creating upper and lower limits for the values of voltage, current and phase balance, we can put the power of recording events to our use and advantage. This means two things:
1. Making proactive measurements as a means of keeping periodic records to detect trends in the measurement results.
2. Stopping and/or generating specific actions when a qualifying event has occurred, which will automatically be generated when a measured parameter falls outside the established range of values.
Last but not least, how can one report the findings? IEC-qualified test instruments offer data export capabilities (e.g., Excel CSV format). For a more comprehensive description of events that have been recorded, there is an opportunity to provide visual and numerical data in a test report format. For example, HIOKI Power Quality Analyzers use PQ ONE Software Tools.
PQ ONE Software provides enhanced data reporting capabilities as follows:
• Able to display what happened and where it happened
• Event statistics over an arbitrary period of time
• Report-ready graphs
• Export to PQDIF format for compatibility with industry practices
In addition to the time-domain data, PQ ONE can also report the harmonics in the signal under test using the FFT Display.
When issues related to power quality lead to equipment or facilities malfunction, it is important to reach out for the proper toolset that provides the capability to monitor, assess and determine an appropriate course of action. Preventive maintenance helps establish a continuous observation of critical parameters in the AC/DC supply and load sides of the energy equation, thereby reducing the risk of operating expensive equipment under non-monitored parameters. Features include:
• Bandwidth and accuracy: Up to 2 MHz, IEC class A instrument
• Inputs isolated from the outputs
• Measure up to 6 kV AC
• Transient measurements at 2 MS/sec, wideband to 700 kHz
• AC/DC current sensors with matching bandwidth
• High order harmonics to 80 KHz
HIOKI power analysis tools effectively answer the questions that enable both utility companies and end users to operate their resources at maximum efficiency and minimum risk. Look for measurement capabilities that extend far beyond 50/60 Hz line currents and voltages. UP
The Author: Fernando Gomez is a product manager with HIOKI USA. Learn more at https://hiokiusa.com.