Advances in microprocessor-based electronic metering technology enable utilities to perform PQ (power quality) measurements at no additional cost. These measurements can help utilities increase power distribution system reliability by detecting potentially harmful system conditions and improving customer service with the detection and prevention of power quality problems that may interfere with customers’ business operations.
Not many years ago, performing PQ measurement functions required an expensive piece of dedicated equipment, costing anywhere from $5,000 to $13,000. Most utilities could justify the purchase of only a couple of these instruments. With so few units available, the utility typically used them only if there were customer complaints or symptoms of a power quality problem. These portable test instruments were taken to the customer site and connected to the load with PTs and clamp-on CTs. After some number of days, someone went back to the customer site to retrieve the data and the PQ instrument.
The application of microprocessor technology has dramatically reduced the price and increased the capability of 0.2 Accuracy Class revenue meters. This increase in processing power has allowed the addition of PQ features to meters. Electronic meters have now essentially become information platforms with communications (optical port, EIA-232, Ethernet, etc.) a local display, and a data acquisition system.
HARMONICS A POTENTIAL PROBLEM
Thirty years ago, the electric system load consisted primarily of resistive and inductive loads, such as incandescent lighting and induction motors. These linear loads were not very sensitive to power quality and generated few harmonics. Now there are many loads in all customer classes, from residential to industrial, that generate large amounts of harmonics. Computer power supplies, electronic lighting ballasts, and variable speed motor controls are but a few examples of nonlinear loads that can generate significant harmonics.
Harmonic current can cause overheating of transformers and voltage regulators, even when they are operating well below their kVA rating. These harmonics also have the potential to damage or trip off capacitors used for Var support. The electronic meter allows the utility to monitor the customer load for these potentially damaging harmonics.
Customers have also become increasingly sensitive to interruptions. Even short power interruptions at almost any kind of business will stop all productivity while the employees wait for their computers, cash registers, and manufacturing equipment to restart. Power quality has become crucial to modern businesses. With PQ features in a high-end meter, electric utilities can monitor PQ for all their largest customers. If the customer complains about a problem or enquires about an outage, the utility can retrieve PQ information from the meter.
Voltage level is another important aspect of power quality. Several supply-side problems can be detected with the voltage sag-swell-interrupt (VSSI) recording function:
- A voltage regulator or tap changer could be operating incorrectly and provide too high or low voltage.
- The control could have a problem, resulting in too frequent tap changes.
- A failed unit on a capacitor bank could cause a voltage imbalance and decrease the efficiency of the distribution system.
- Frequent momentary power interruptions could be a sign of a misoperating hydraulic recloser.
The electricity meter is ideal for recording these measurements because, in most cases, it can indicate if the problem is on the supply or the load side.
With PQ measurement capabilities in a meter, the utility can be proactive in detecting and mitigating PQ problems that might degrade the efficiency and reliability of the distribution system. The revenue meter is a permanently installed piece of equipment that can always be monitoring and recording PQ data. All the infrastructure costs are covered by the metering installation: instrument transformers, utility-accessible meter location, meter reading communications, and the cost of the meter itself. This makes the cost of PQ metering essentially free.
Because power quality monitoring can now be provided at no additional cost, the question is not: “Why put PQ measurement in a meter?” but: “Why not?”