Electrical modeling tools essential for complex facilities

As electrical power systems grow more complex, electrical distribution system modeling and analyses for safe and reliable operations becomes vital

By Zia Salami and Beth Charis-Molling April 28, 2020

Learning objectives

  • Discover major electrical software tools and several factors for selecting these tools.
  • Learn about the main objectives for using these tools.
  • Review a sample of modeling and system modification with an electrical software tool, ETAP.

As electrical power system facilities such as health care, industry complexes, water pumping stations, water treatment, generation or processing plants expand and become more complex, electrical distribution system modeling and analyses for safe and reliable operations becomes vital. Complex electrical distribution systems with large numbers of certain components require intelligent and advanced industrial electrical power system software tools to model and evaluate different operational scenarios to understand the possible issues and the worst-case system conditions.

These components include:

  • Buses, cables, transformers and loads.
  • Protective devices (i.e., circuit breaker, fuse, relay, etc.).
  • Variable frequency drives.
  • Renewable power sources such as solar and wind.

Accurate simulations of such systems must consider that it is a “living” entity that changes significantly over time as:

  • Loads increase.
  • Equipment is replaced and/or upgraded.
  • System enhancements are planned and constructed.
  • Grid interconnections change.

Planning and operating such a complex system require a variety of system studies to ensure personnel safety and improve system sustainability and reliability. System studies are critical for equipment protection, proper equipment sizing, protective device rating and device coordination, design margin, load growth, operability and cost saving evaluations.

Electrical power system software

There are numerous intelligent and advanced industrial electrical power system software currently available, such as ETAP, SKM PowerTools, EasyPower, PowerWorld, PSS E, PSCAD, CYME, Matlab, DIgSILENT, etc. These tools are capable of building complex alternating current and direct current electrical distribution systems and performing a variety of system studies. Studies may include load flow, motor starting and voltage stability, short circuit, protective device coordination and equipment protection, arc flash, harmonic and reliability analyses. Such software tools, like ETAP, are capable of performing real-time automation, control and monitoring design and analyses.

Each facility may select and prefer to use one or more of these software tools based on factors including the specific application, module availability, cost, prior experience, vendor support and training, software quality, verification and validation programs or user friendliness. Regardless of which electrical software tool is used, it is important for a facility to have such a model available.

Why use modeling software tools?

Using an electrical distribution system model of a facility and performing system analyses will improve resiliency and reliability, increase safety and help engineers with the following:

  • Conceptual system design and modification, and equipment selection and sizing.
  • Operability evaluation and cost savings.
  • Evaluate equipment overloading conditions such as transformers, cables and other components within the system.
  • Determine adequacy of equipment protection and ratings.
  • Ensure protective devices, such as fuses, circuit breakers and relays will operate in a coordinated fashion to clear a faulted condition.
  • Estimate arc flash incident energy at each piece of electrical equipment and provide technical recommendations to identify system modifications or changes that would reduce the estimated arc flash incident energy at a location within an electrical system for personnel safety.
  • Estimate the transient conditions associated with motor starting and to evaluate electrical system adequacy to start and sustain large motor loads.
  • Identify risks to system reliability as a result of equipment failure or unplanned outage.
  • Estimate current and voltage harmonic distortion within an electrical system produced by equipment such as variable frequency drives, uninterruptible power supplies, solid state lighting, power inverters, etc.
  • Real-time system monitoring, automation and control.
  • Design, evaluate and analyze the impact of renewable energy such as photovoltaics and wind power.
  • “What if” scenarios and evaluation of future modifications.

Case study: having a facility model

The following case study illustrates the need for an electrical software tool to model a water treatment facility, evaluate the existing conditions and determine whether replacing an existing motor with one with a higher horsepower rating is possible and what other modifications are necessary to support this change.

This facility is fed from two 13.8 kilovolt circuits via a 1,500 kilovolt-ampere service transformer and two on-site backup generators with 750 and 1,000 kilowatt ratings. The facility is N+1 redundant and only requires one train for its operation and processing. A simplified electrical distribution system including load flow results when fed from 13.8 kilovolt-system feeder is shown in Figure 1. Based on the facility’s existing condition, system voltage, available fault currents and rating of equipment such as service transformer (XFMR-A) and cable-1 are within the acceptable range.

This facility is planning to upgrade and increase one of the motor loads (pump No. 1) from 200 to 500 horsepower and consequently increase its productivity as shown in Figure 2. As previously mentioned, one of the main advantages of having a facility electrical distribution system model is to simplify the calculation and “what if” scenarios and future modification.

Having the existing model available will expedite time and accuracy to perform such modification and provide possible impact to the facility’s equipment (if any) and to determine new system parameters such as available fault current and bus voltages.

Based on a simple model change to reflect this future modification and rerun the load flow and short-circuit analyses, several notable results, as shown in Figure 2, are obtained:

  • The 1,500 kilovolt-ampere service XFMR-A transformer is overloaded. The new power flow after the modification indicates 1,742 kilovolt-ampere flow-through transformer. This may cause transformer overheating and subsequent failure. This equipment should be increased to higher ratings (e.g., 2,000 kilovolt-ampere).
  • Cable-1, 3-1/C 250 kcmil, is overloaded and it should be modified.
  • Approximately 1% to 2% additional voltage drop at 4.16 kilovolt switchgear-A and 480-volt motor control center-1 (MCC1). This voltage drop may be acceptable depending on system performance and equipment’s voltage capability and limitations.
  • Possible of primary and secondary protective device ratings issue. PD ratings and settings should be checked and upgrade if needed.
  • Larger motor will have more short-circuit contribution, in this case increasing from 165 to 413 amperes to the faulted location at switchgear-A. Therefore, the feeder to this load including its protection should be further evaluated.

Codes and standards

The following major standards are applicable to performing power system studies such as the load flow, short circuit, protective device coordination, motor starting, harmonic, reliability and arc flash analyses.

Any change or system modification within a facility without having proper modeling and system analyses to evaluate the overall impact will typically end up with a costly failure and may expose personnel safety. It is highly recommended to invest and build its electrical distribution system models — especially for the facility that is more complex — and perform adequate and necessary analyses to understand its capability, available margin and vulnerable areas to have a safe and reliable system.

Author Bio: Zia Salami is a subject matter expert in electrical power systems at CDM Smith. Salami has more than 21 years of industry and academic experience in electrical power systems and has served in several roles as an advisory engineer, consultant and academic professor. Beth Charis-Molling is an electrical engineer at CDM Smith. Charis-Molling focuses on electrical power system design and analysis.