Planning and designing the electrical system of a facility in the form of a short circuit fault analysis rely significantly on computational methods to determine the configuration and infrastructure that works best for the area. Power tends to fail at times, and it is up to the engineers to ensure that the power system can handle such faults.

A short circuit is a type of power fault that can cause a great deal of damage to the system and the people operating the area. It entails putting in place protective techniques to ensure that the system remains operational and unharmed.

What is a short circuit, and why is it dangerous?

The current flowing through an unplanned pathway of lower resistance is called a short circuit. It is a strange incident involving accidental contact of one or more phases to the ground, voltages connecting, or phases coming in touch together. The near-zero resistance that the flow of current connects with produces unusually high levels of current.

A short circuit current can become too large if not addressed. It causes quick and massive bursts of energy such as magnetic fields, heat or an arc blast, which manifests as an intense explosion. This powerful release of heat can melt electrical components and wiring insulations, disrupting the power system. Arc blasts create shock waves that can transport molten or vaporized metals, which can pose a significant hazard to people unprotected by the right safety gear.

An arc ensuing at the point of fault can be destructive and can start fires in the facility.

What As a Short Circuit Fault Analysis?

A short circuit fault analysis is the study that determines steady-state solutions of linear networks that have a three-phase excitation. The report defines the voltages and currents found in the electrical system in cases of fault. It provides more accurate results than when such values are assumed.

The information determined in a short circuit current analysis is used to design the correct relaying system and decide which circuit breakers are required to meet the interrupting capacity. The linear network consists of the transmission network, generation system, and fault occurring in different locations.

A short circuit study depends on two essential parameters. Firstly, the total impedance from the power source to the fault point and the nominal voltage of the electrical system.

Benefits of a short circuit analysis

• Avoids unintended downtime and outages
• Determines the best relaying system and circuit breakers to use in the system
• Prevents workflow interruption
• Lessens risks for damage to the facility
• Reduces the incidence of fires caused by arc blasts
• Enhances the safety and protection of workers
• Determines the type and level of protective devices required by the system
• Provides the data for National Fire Prevention Association and National Electric Code label compliance

Protective Devices

Circuit Breaker and Fuse

Circuit breakers and fuses protect the electrical circuit from overcurrent conditions that result from a short circuit. These devices cut off the power supply when necessary. Circuit breakers can be used several times and be reset, while a fuse is made for single use only.

Ground Fault Interrupter (GFI)

The Ground Fault Interrupter or GFI detects the difference in the energized conductor’s current flow and the neutral conductor’s return current. These devices are commonly used for homes and are typically in-built to the electrical socket.

How to Conduct a Short Circuit Fault Analysis

Proper calculation techniques drive a successful short circuit fault analysis. It is considerably more accessible now that several software developers have made reliable programs conforming to standards of the IEC, ANSI and other regulating bodies in the industry.

Gathering data

Depending on the set objectives, a short circuit study will require the nature and extent of the power system. A short circuit analysis will cover one or more of these kinds of short circuit:

• Line-to-line fault wherein two phases are shorted together
• Double line-to-ground fault wherein the two phases and ground are connected
• Single line-to-ground fault wherein only one phase comes in contact with the ground
• Three-phase fault wherein all three phases connect and may or may not short to the ground.

By determining the type of fault, it will be easier to build a one-line diagram of the power distribution system. It should allow users to point out the buses or system nodes.

It should also be noted that data usually comes from utility sources since every equipment could be rated differently. Information like voltage and rated MVA are essential in short circuit analysis. Again, the less assumption is made regarding measurements and ratings, the higher the accuracy of the study.

Short circuit calculations

Calculations in a short circuit fault analysis typically make use of a single-line diagram and an impedance diagram that include numerical values for the utility source, transformer and conductor relative to the available voltage each element. For conductor impedance, reactance is used and resistance is often ignored.

The first step is determining the transformer’s full-load amps (FLA). The next step is to find the transformer multiplier, which uses the transformer impedance value (Z) that is typically on the nameplate. Next, determine the let-through short circuit current of the transformer. The “f” factor and “M” are then calculated using the formula to be able to arrive at the short-circuit current for the RMS symmetrical applications.

This method is just a simple point-to-point technique, but again, the calculations depend on the nature, extent, and objectives of the short circuit fault analysis.

Analyzing the results

Comparing the calculated results to equipment ratings is crucial to ensure that the power distribution system is equipped with adequate protective devices at different locations to prevent downtime and damage.

Making the report

Finalizing the analysis is done by publishing a report that includes the calculations of the fault current and evaluation of equipment to be applied to the distribution system. This report will also prove whether the protective devices and equipment are adequately rated to meet the fault current found at various locations in the configuration.

A Service Provider with the Expertise

Risks and hazards from potential short circuit incidents can be effectively reduced or eliminated through a successful short circuit study. If you are looking for a service provider to conduct short circuit fault analysis, Present Group has the expertise and decades of experience. Contact us to learn more.