Electrical power and process production: focus on power systems complements the bottom line

Power factors, harmonics, fluctuations, and outages examined.

10/19/2018


Learning Objectives

  • Learn how to improve system power factor.
  • Know how to mitigate harmonics.
  • Understand techniques for eliminating transient voltage spikes.

Figure 1: Backup power supplies were found near the plant, but it remained vulnerable to outage from a single event. A new switchyard/substation allowed independent connections to the primary and two backup power sources. All images courtesy: Burns & McDonnellThe reliability, resiliency, and near universal availability of electrical power is one of the United States' greatest engineering achievements. Reports from the U.S. Department of Energy, the North American Electric Reliability Corp. (NERC), and others typically place nationwide reliability at 99.97%. Nevertheless, economists estimate that loss of service averaging even 0.03% still costs the U.S. economy more than $100 billion annually.

In refining and petrochemicals, electrical systems are the unsung heroes of plant profitability and operational efficiency. Telltale warning signs, such as poor power factor, voltage fluctuations, or harmonic distortions are often ignored. Yet, until these systems verge on catastrophic failure, they attract scant capital investment.

Service disruptions and failures "behind the meter," i.e., within the industrial facility itself, cause a disproportionate share of economic losses. Plant downtime costs due to electrical system failures can be staggering when factoring in the costs of idle and nonproductive staff in addition to lost production. Being without power for an entire day could mean the difference between profit and loss for an entire month.

Facing a critical upgrade

Kansas City, Mo.-based Burns & McDonnell recently completed an electrical system upgrade project for a major manufacturer of nylon intermediates. These intermediates are critical to production of high-end carpets. Plant output also includes nylon fiber, resins, and other specialty products. The facility, which is more than 50 years old, was productive and profitable, yet, in recent years, experienced increasing power system issues. The problems culminated in a major outage and extended shutdown resulting in millions of dollars of lost production. This incident convinced management it was time to invest.

A team from Burns & McDonnell Power Distribution & Controls (PDC) had studied the facility prior to the outage. A master plan pinpointed needed system improvements to address reliability, safety, and maintenance over the next 20 years. An action plan was brought to bear. Top priority was upgrading the primary 138 kV transmission line with improved protection and a fault-isolation system.

Backup power supplies were found near the plant, but it remained vulnerable to outage from a single event. Both primary and backup sources shared the same relatively short transmission line, which operated with normally closed secondary tie-breakers. In other words, though power came to the plant from multiple sources, it risked power loss because power flowed through a single transmission line to a switchyard inside plant boundaries.

The 138-kV transmission line was modified. A new switchyard/substation allowed independent connections to the primary and two backup power sources (see Figure 1). As important, a redundant fiber optic network was installed, connecting all sites. The enhanced network allowed each power source to be controlled by its own substation transformer for isolation and greater protection in the event of a fault.

The fiber network allowed microprocessor-based protection for current differentials. Additional coordination signals sent to protection systems identify faults and minimize affected areas. Microprocessor relays and protection equipment installed on the 138-kV power line work together to allow advanced fault recording.

A communications network allowed monitoring of all sites within the plant using supervisory control and data acquisition (SCADA). In the event of a fiber optic cable cut or equipment fault, network traffic can reverse around the completely redundant fiber network. This reduces recovery time to seconds rather than hours or days.

The planning process revealed the causes and costs of power quality issues. It's important to know, for example, that barely perceptible power sags can cause big problems in industries that have highly sensitive process parameters.


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