Learn How ETAP DC Arc Flash Analysis Solves the Safety Concern During the Maintenance Activity

ETAP DC Arc Flash methods and their capabilities can be utilized to expand and evaluate incident energy at the generator brush/collector rings assembly. Collaboration with the university to support and perform research in this area is vital to helping companies conduct significant research and development.
By Mr. Zia Salami, Senior Management Specialist at CDM Smith

This presentation addresses the critical and dangerous maintenance of worn-down collector rings and brushes, electrical safety, lack of standards and guidelines, and the first possible calculation method. For some generator exciter systems, collector rings and brushes provide energy from the exciter to the rotating field. The brushes wear down and constantly need to be replaced with the unit online. While the brush/ring assembly is still energized, it is a risky and unsafe maintenance operation and may cause serious harm: a potential shock and arc-flash hazard.

CDM Smith is a global, privately owned engineering and construction firm. It provides water, environment, transportation, energy, and facilities engineering services to public and private clients worldwide. The company is headquartered in Boston, Massachusetts, and employs over 5,000 people. As a full-service engineering and construction firm, CDM Smith stays ahead of tomorrow’s changing needs and implements lasting impacts today that propel their client services, quality results, and enduring value across the project life cycle.

Location: Charlotte, North Carolina, United States

Year: 2022

Ensure safety maintenance of generators according to standards

Challenges

  • Providing an electrical network model with a generator equipped with collector rings and brushes. They provide energy from the exciter system to the rotating field, which is the DC system. The brushes are graphite blocks and must be constantly replaced while assembly is energized.
  • Arc Flash incident energy calculations using IEEE-1584 and NFPA-70E Standards. There are no established DC standards, guidelines, or methods to quantify this potential instant energy level and to determine the proper PPE for these unique applications.
  • Analyzing existing analytical tools and finding a relevant system of calculation, which can be recommended for engineers to use and is sufficient to ensure safety in this specific case.
  • Identifying the factors that impact the amount of the IE if the brush and collector ring were shorted out or a fault occurred during maintenance on the site.

Which solutions did they choose?

Selected applications

They chose the ETAP game of software with the Arc Flash Analysis package, and ETAP Digital-Twin Modeling as a first solution to analyze, calculate, and conduct the research.

ETAP ensured compliance with all available electrical standards for designing and calculating arc flash incidents.

Why do they use ETAP?

Main Customer Benefits

  • In the ETAP model, researchers could consider multiple variations of excitation and field components, such as Static Solid-State Exciters and Shaft-Driven AC Exciter Systems. The large ETAP symbols and behaviors library includes transformers, rectifiers, voltage regulators, breakers, collector rings, generators, motors, and others.
  • ETAP is a really electrical software tool which includes arc flash studies for typical and specific industry applications.
  • A combination of ETAP Transient Stability and ETAP DC Arc Flash modules was used to estimate incident energy by building a proper exciter and field discharge circuits.
  • Researchers found how dangerous is maintenance on site for people. If using Max Power method, the energy can be 400 cal/cm². Potential shock and arc-flash hazards must be considered in all time.
  • Safety procedures were provided.

What do they think about ETAP?

Opinions

If we have a circuit and create an event, such as a loss of excitation for the generator, we can define that event in ETAP. Therefore, we can provide a field current discharge or decay characteristic based on the actual system.
We can obtain the field current from the Transient Stability module in ETAP considering they also established the exposure time in mainly here referring to the field discharging and determine the instant energy from the field winding circuit.
By Mr. Zia Salami, Senior Management Specialist at CDM Smith

Going back to the DC discussion, DC calculation in ETAP, currently they based on the three different methods: Maximum Power, Paukert and also Stokes method.
By Mr. Zia Salami, Senior Management Specialist at CDM Smith



Videos

Generator Brush Collector Ring’s Arc Flash Hazard, A Safety Concern!

For some types of generator exciter systems, collector rings and brushes are used to provide energy from the exciter to the rotating field. The brushes wear down and constantly need to be replaced with the unit on-line and while brush/ring assembly is still energized, a risky and unsafe maintenance operation and may cause a serious harm. A potential shock and arc-flash hazard. This presentation addresses the important and dangerous maintenance of worn-down collector rings and brushes, electrical safety, lack of standards and guidelines, and a first possible calculation method.


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