Short Circuits in the Grid and Ways of Protecting the Grid

Introduction 

During the regular operations of electrical grids, different types of faults interfere with these operations. Faults usually lead to changes in values such as impedance from normal to different values until the fault is corrected. Faults can be considered to abnormal conditions of electrical grids involving an electrical failure of equipment. Faults may also emerge due to insulation and conducting path issues that may lead to short circuits. Additionally, increased capacity to generate electricity due to the addition of new power plants has also resulted in a high number of faults in transmission grids. Electrical engineers today must deal with an increased number of these faults at electricity substations.

The current paper will explore the meaning of short circuits in the grid before examining the various practical ways of protecting the grid from damages caused by faults.

Electrical Faults

A power grid or an electrical grid can be considered to be a system that connects the production, transmission, and delivery of electricity. Electrical grids usually operate at normal current and voltage values under safe or normal conditions. Faults in devices or circuits, however, causes the normal current and voltage values to deviate and lead to high voltage increases, unbalanced phase transmissions, under-voltage, and over current. In turn, this may interrupt the normal operation of the grid. 

Short Circuits

The risk of a short circuit occurring at any part of a power grid is high. It is, therefore, important to understand the meaning of short circuits to find ways of securing the grid against any damages that may be caused by these faults. Short circuit faults occur when the impedance connection between two sections with different potential is abnormally low (Farrokhifar et al., 2013). Short circuits are examples of serious electrical faults. Short circuits are very common as they lead to abnormally high currents to flow through the grid or equipment. Persistence of these faults may result in adverse effects on equipment or industrial sites. These faults emerge due to insulation issues between phase and earth conductors or between phase conductors (Grigsby, 2016). Both causes may also occur simultaneously. The main causes of short circuits include internal grid breakdown, old insulation, deteriorated generator insulation, inappropriate design, inadequate installations, and transformer (Grigsby, 2016). Other causes include overloaded equipment, lighting surges that cause insulation issues, and physical damage by people. Currents that emerge due to short circuits spread massive and damaging energy across the electrical grid. Very large short circuit currents that exceed the ability of protective equipment can produce arc blasts. The produced heat due to short circuits can damage different grid locations and jeopardize substantial parts of the transmission line. Widespread outages can also result from short circuits.

Methods of Protecting the Grid

When faults occur in any part of the grid, engineers must clear it immediately to avoid extensive damage to personnel and equipment and power interruption to consumers. There are various ways of protecting the grid from damages caused by faults. Examples include the use of over-current protective devices (OCPD), current limiters, implementing adequate designs, using relays, and engaging in regular reviews and monitoring.

Using OCPDS

OCPDs are devices that engineers use to safeguard parts of the grid. When the current in the grid reaches a level pre-determined to lead to rapid temperature increases in the transmission lines, the devices activate (Voldman, 2014). The OCPDs deal with short circuit cases by restricting the current level that the lines require. Circuit breakers and fuses are the two kinds of OCPDs are used to protect circuits. Circuit breakers work by allowing the electricity to flow uninterruptedly in cases where the flow is within an acceptable tolerance. If the flow exceeds its level, the device mechanically interrupts electricity flow. Fuses work by melting due to excessive heat caused by interrupting electrical values. Fuses require regular replacements compared to circuit breakers that require resetting only. Before using an OCPD, it is vital to understand the tolerance level that the OCPD can bear without bursting using the short circuit fault analysis.

Current Limiters

The grid can be protected by examining switches to determine their roles and cut-off capacity. Engineers can use the information gained to determine the necessity of using new switches with the required cut-off power or adding current limiters to the grid. For power substations with switches having cut-off volume, engineers can interchange the switch capacity in stages in which the capacity reduces compared to the short circuit level (Ito, 2019). The technique involves installing high power switches and selecting their capacitance based on future current levels. Current limiters reduce energy losses and offer flexibility when installing low-speed power fuses and switches. 

Short circuits can cause issues such as voltage sagging and swelling, frequency changes, and grid break-up (Farrokhifar et al., 2013). Limiters, when used, enhance the power quality by controlling short circuits. Current limiters are usually in sequence in circuits and indicate low impedance during normal operations and instantaneous high impedance during current variations to limit the current (Voldman, 2014). Engineers can introduce limiters by installing different transformers parallel on attached bus-bars. Limiters prevent short circuits by restricting the amplitude of the current to activate the circuit breaker without extra overload. According to Voldman (2014), the process of limiting fault current should not interfere with the security of the grid system. Additionally, limiters should be installed to secure as many switches as possible cost-efficiently. Choosing the position to install limiters occurs after considering the limiting current levels gathered.

Proper Designs

It is also important to increase the consistency of the grid by designing power grids to increase their maneuverability while enabling adequate feeding facilities to get through (Voldman, 2014). When constructing the grid, engineers should consider using series reactors that can resist high short circuit current during faults. Before constructing important substations, engineers can first determine how the bus-bar aligns with the coupling switch and divider. Such actions help to determine the likelihood of splitting of bus-bars and lines maneuvering over bus-bars.

Use of Relays

Relays can also be used to protect the grid from electrical faults (Blackburn & Domin, 2014). Engineers use the relays to compute different parameters to identify issues and initiate circuit breakers to separate equipment and notify them of the issue. The relays measure values such as line power, current, differential current, and voltage. Relays also monitor the grid to ensure that various components are in synchronization. These relays operate circuit breakers and act accordingly based on the sensed faults. Relays are also linked to instrument transformers that indicate the current and voltage of the various stations connected to them. Engineers must also consider the sufficient sequence of relay functioning and timing by first determining the time allowed before initiating circuit breakers and the correct order of circuit breaker operations to adequately separate issues in different areas

Regular Reviews and Monitoring 

Protecting the grid from faults also entails first engaging in regular review to identify fault levels in all vital power substations (Farrokhifar et al., 2013). Engineers can then use the collected information to establish protection zones at each major part of the grid to separate faults and enhance the ease of finding and repairing them. Engineers can trace the protection zones from the source of a fault to the power plant. Isolating major pieces of the grid may involve using fuses or circuit breakers at various pieces connected to a specific substation, which is vital because it prevents faults occurring in a certain location from interfering with the entire substation. For instance, a single transformer with issues in a substation will not affect the grid feeding it as engineers can separate it with breakers. Sagging grid lines into tree limbs will not damage the power plant generator due to the resulting increase in current because the greed will have its protection zone.

Reviewing the grid regularly may also involve continuous monitoring of the grid conditions and applying the required measures based on the prevailing conditions or situations. Control and monitoring can occur semi-manually and include regular communications with field personnel and plant operators (Grigsby, 2016). Automated systems such as the SCADA are useful for reviews due to their ability to remotely manage operations by controlling key generators and act accordingly by either closing or opening circuit breakers to change the grid topology.

Conclusion

While different faults can damage the electrical grid or interfere with power transmission, short circuits are the most dominant and serious faults that can lead to extensive damages to the grid if not addressed immediately. It can be complicated to deal with substantial damages to the electrical grid. There are, however, various ways of protecting the grid from damages that may emerge due to faults. Engineers can use OCPDs, current limiters, ensure proper designs of various grid system equipment, use relays, and regularly monitor the various grid parts to ensure the grid functions properly.

References

Blackburn, J. L., & Domin, T. J. (2014). Protective Relaying : Principles and Applications . Crc Press, Taylor & Francis Group.

Farrokhifar, M., Esmaeilzadeh, R., Heydari, M., & Milani, A. R. (2013). A Study on Practical Methods to Decrease Short Circuit Level in Transmission Grids. IECON 2013 - 39th Annual Conference of the IEEE Industrial Electronics Society . https://doi.org/10.1109/iecon.2013.6699432

Grigsby, L. L. (2016). Power Systems, Third Edition . Crc Press.

Ito, H. (Ed.). (2019). Switching equipment . Cham Springer.

Voldman, S. H. (2014). Electrical overstress (EOS) : Devices, Circuits, and Systems . Wiley.