Since “the greatest threat to a power system is the short circuit,” it is vital to perform short circuit fault analysis, according to a study conducted by Daljeet Kaur, Dr. SK Bath, and Darshan Singh Sidhu from the Department of Electrical Engineering in PTUGZSCampus, Bathinda, India.
The Spark that Starts a Short Circuit
The study, titled the Short Circuit Fault Analysis of Electrical Power System Using MATLAB, defines a short circuit as a fault that happens when the current flow bypasses the normal load. This can occur for many different reasons, but common instigators of a short circuit are lightening, an accident in which a vehicle strikes a pole, high winds, tornadoes, earthquakes, and aging equipment.
The short circuit currents spread an immense, destructive energy across the grid in the form of heat and magnetic force. In the case of a short circuit current which is very large, exceeding the capability of protective devices, an arc blast can be produced.
The heat of such an event can destroy parts of the grid, causing a cascade effect in which significant portions of the network are in jeopardy. In some circumstances, short circuits can cause widespread outages.
Risks of Short Circuits
Short circuits present a great risk to human life and the economy. For instance, on 28 September 2016, nearly the entire state of South Australia suffered a widespread outage that plunged 1.7 million people into darkness for several days. The source of the problem was the destruction of parts of the grid caused by two tornadoes that triggered the power system to shut down. Shutting down of the network was necessary to protect the infrastructure that was not directly damaged by the storm.
In a separate incident on 4 January 2018, a short circuit caused by faulty wiring triggered an arc flash and ignited a fire that gutted a shopping mall in the southern province of Davao in the Philippines, killing 38 people.
Keeping the Grid Safe and Efficient
The purpose of a short circuit fault analysis ultimately is to provide means to keep the grid safe and operating. A short circuit fault analysis calculates the amount of short circuit current from a system, then compares that figure with the interrupting rate of the devices that protect sections of the grid. These devices are called overcurrent protective devices (OCPD). National standards govern the values of the interrupting rates.
Types of OCPDs and Their Importance
OCPDs protect the grid by activating if the current reaches a specific amount pre-determined to cause the temperature to increase rapidly in the conductors. The OCPDs handle overcurrent situations whether they be overload current or short circuit current. The OCPD limits the amount of current that the conductors need. An overload current is a current that is beyond the standard operating values. However, a short circuit current is one that travels outside the standard path of the grid.
There are two basic types of OCPDs: fuses and circuit breakers, both of which protect electrical circuits.
- Fuses melt when they reach the interrupting value from excess heat. They will need to be replaced.
- Circuit breakers, on the other hand, operate quite differently. Circuit breakers allow the uninterrupted flow of electricity if the flow is within their tolerances. However, when the flow exceeds their rating, the device breaks the flow of electricity mechanically. They can be reset to work again repeatedly.
Industrial circuit breakers are classified into three voltages: low voltage, medium voltage, and high voltage. There are several types of circuit breakers in a power grid system: oil circuit breaker, air circuit breaker, cross-blast circuit breaker, axial blast circuit breaker, SF6 Circuit breaker (sulfur hexafluoride), and vacuum circuit breaker. All are basically an automatic switch mechanism that operate when a predefined condition occurs. They switch off the current that flows to the conductor.
To determine the correct OCPD to use in a system, it is essential to know the interrupting rating that the OCPD can tolerate without rupturing. The short circuit fault analysis helps to determine this rating.
The analysis takes place when designing a new system, or when adding to an existing system. The short circuit calculations are also updated regularly to protect the equipment in the grid and to ensure the safety of any workers. The analysis helps with monitoring and predictive maintenance of the parts of the grid.
How to Conduct a Short Circuit Fault Analysis
- Locate the appropriate software to design a replica of the power grid. This will include power sources, transformers, motors, transmission lines, and generators as well as any specialized equipment.
- Design a line grid of the system.
- Gather the specifics for each component of the grid with reference to a single short circuit MVA (maximum voltage) factor.
- Relate the delta connected components to the wye connections.
- Complete a hierarchical database of all of the specifications.
- Use the software to input all of the specifics for your power grid.
- The software will calculate the 3-phase bolted fault short circuit Mega Volt Amp to obtain the short circuit values.
Once you know the fault current value in the system, you can select the correct OCPD.
Who Do I Turn to for Short Circuit Fault Analysis?
Your best defense in protecting your power grid system is a highly competent company to conduct a short circuit fault analysis so that the correct OCPDs can be installed. Select a company that:
- Has experience;
- Is well-informed about the changing regulatory standards;
- Is willing to partner with you; and
- Prides itself in its high standards of operations.
To learn more about how we can help you regarding fault analysis, contact us today.