Short Circuit Analysis

By R.W. Hurst, Editor

A Short Circuit Analysis (SCA) is an indispensable tool for ensuring the safety and reliability of an electrical power system. By identifying potential hazards, selecting and coordinating protective devices, and confirming that equipment is appropriately rated for the system, Short Circuit Analysis helps to prevent short circuits and reduce the risk of explosions known as an arc blast by coordinating the hazardous voltage level in equipment. This ultimately protects both personnel and equipment. Whether designing a new electrical system or conducting a safety audit on an existing one, performing a SCA is crucial for maintaining a safe and reliable system.


Types of Short Circuits

Short circuits can occur in several forms, including line-to-line, line-to-ground, line-to-line-to-ground, and three-phase ground faults. Understanding these fault types allows for more accurate analysis and an appropriate selection of protective devices.

Short Circuit Analysis Process

Analyzing an electrical system involves determining the current that would flow in the event of a short circuit. It also examines the system's components, including equipment and protective devices, to identify potential hazards and ensure proper protection. The analysis starts with a review of the electrical system's documentation, such as equipment specifications and one-line diagrams. This information helps create a model of the system, which is used to perform short-circuit calculations using methods like the per-unit system, symmetrical components, or impedance-based calculations.

Software Tools

Specialized software tools can streamline the analysis process and provide more accurate results. In addition, these tools assist in performing short-circuit calculations and protective device coordination.

Protective Device Coordination

Protective device coordination is a critical aspect of SCA. It ensures that different types of protective devices, like circuit breakers and fuses, closest to the fault conditions operate first, isolating the fault and minimizing damage to the power distribution system. This involves selecting devices with an appropriate short circuit interrupting rating and coordinating their settings for proper operation. In addition, circuit breaker coordination is integral to protective device coordination.

Impact of Short Circuits

Short circuits can lead to equipment damage, system downtime, and potential hazards to personnel. However, proper equipment selection, coordination, grounding, and use of surge protection devices and regular electrical system maintenance can mitigate these risks.

Codes and Standards

Compliance with relevant codes and standards, such as the National Electrical Code (NEC), IEEE standards, and IEC standards, is essential for ensuring the safety and reliability of electrical systems. In addition, these guidelines help direct SCA and equipment selection.

When to Perform a Short Circuit Analysis

Short circuit studies should be conducted for both new and existing electrical systems. For new systems, the analysis is typically performed during the design phase, ensuring that the system is designed with safety and proper protective device coordination. For existing systems, the analysis is often carried out as part of a safety audit, helping to identify potential hazards and confirm that protective devices are correctly installed and coordinated.

Expertise Required

Performing a Short Circuit Analysis necessitates expertise in power system analysis and electrical engineering consulting. A qualified engineer who knows how to perform short circuit studies can help ensure that the analysis is carried out accurately and that the system is adequately protected.

Benefits of Short Circuit Analysis

The advantages of an SCA include the following:

  • Improved safety: Identifying potential hazards and properly protecting the electrical system reduces the risk of electrical fires and safeguards personnel and equipment.
  • Improved reliability: Proper equipment selection and coordination help prevent short circuits and minimize the risk of power outages.
  • Regulatory compliance: SCA may be required by regulatory agencies or insurance companies to ensure that an electrical power system is correctly designed and protected.
  • Cost savings: Identifying potential hazards and inefficiencies in the electrical system allows for improvements that can reduce energy waste and save money over time.