Short-circuit studies are carried out to determine the magnitude of currents flowing throughout the power system at various time intervals after a fault occurs. Determining short-circuit fault current levels is one of the most important aspects of designing power distribution systems. Short-circuits and their effects must be considered in selecting electrical equipment, circuit protection devices, and carrying out arc flash analysis. A short-circuit study is performed to

1. Calculate the fault currents at various locations in the system under various operating conditions.
2. Identify whether the system and the equipments could withstand the available fault current.
3. Specify the ratings of the equipments for future expansions.
4. Improve reliability of the system.
5. Determine protection relay settings.
6. Carry out protection coordination studies.

The purpose of harmonic study is to ascertain the distribution of harmonic currents, voltages, and harmonic distortion induces in a power system. Majorly due to application of power electronic devices, power system voltage and current quality is affected and current and voltage components other than that of fundamental frequency are found to exist in the distorted voltage and current waveforms. These components usually are the integer multipliers of the fundamental frequency, called harmonics. The presence of harmonics in a power system can give rise to a variety of problems including equipment overheating, reduced power factors, deteriorating performance of electrical equipment, the incorrect operation of protective relays, interference with communication devices, and in some cases, circuit resonance to cause electric apparatus dielectric failure and other types of severe damage. Even worse, harmonic currents generated in one area can penetrate into the power grid and propagate into other areas, resulting in voltage and current distortions for the entire system.

During the motor starting period, the starting motor appears to the system as a small impedance connected to a bus. It draws a large current from the system, about six times the motor rated current, which therefore results in voltage drops in the system and imposes disturbances to the normal operation of other system loads. Since the motor acceleration torque is dependent on motor terminal voltage, in some cases the starting motor may not be able to reach its rated speed due to extremely low terminal voltage. This makes it necessary to perform a motor starting analysis. The purpose of performing a motor starting study is twofold: to investigate whether the starting motor can be successfully started under the operating conditions, and to see if starting the motor will seriously impede the normal operation of other loads in the system.

In a power system, the protective devices such as relays are used to protect the system in the event of a fault. The function of protective devices in a power system is to detect system disturbances and isolate the disturbance by activating the appropriate circuit-interrupting devices. A relay coordination study is required to properly select the necessary settings of overcurrent relays so that the intended goals of protection, viz., selectivity, coordination, speed and reliability are achieved. The most convenient way of determining the proper settings of overcurrent relays is by plotting the time-current curves. These curves are drawn on standard log-log graph and illustrate the time-current characteristics of each of the relays as well as the protective criterion to be met. Thus, such curves illustrate the time-current coordination between devices. Time-current curves are generally drawn up to the maximum available fault current level for the system being illustrated.

In a balanced three-phase power system, there will not be any ground currents during normal operation. However, in the event of system faults, there will be significant currents through the neutral conductors and ground paths. Such fault currents tend to increase the voltage on the surface of the substation and equipment connected to the substation. In order to limit the voltage rise on the surface and equipment, loops of ground grids are introduced below the surface of the soil. The ground grids are designed to limit the voltage on the surface and on the equipment. The allowable touch and step voltages in a substation area, and the ground grid design to limit the step and touch voltages are calculated in this particular study. The acceptable step and touch voltages are calculated based on the IEEE standard 80. The grounding system can be designed such that the step and touch voltages are kept within the calculated safe limits. The analysis consists of the following steps:

1. Investigation of soil characteristics
2. Determination of maximum ground current
3. Preliminary design of the ground system
4. Calculation of resistance of the ground system
5. Calculation of step voltages at the periphery
6. Calculation of internal step and touch voltages
7. Refinement of preliminary design

The power transmission capacity of an insulated cable system is proportional to the product of the operating voltage and the maximum current that can be transmitted. Power transmission systems operate at fixed voltage levels so that the delivery capability of a cable system at a given voltage is dictated by the current carrying capacity of the conductors. The delivery capability is defined as the "ampacity" of the cable system. The operating voltage determines the dielectric insulation requirements of a cable, while the conductor size is dictated by the ampacity rating. These two independent parameters (insulation and conductor size) of the cable system are inter-related by thermal considerations; a bigger conductor size results in higher ampacity, while increases in insulation material results in lower ampacity. The parameters of great influence in determining ampacity are the cable size, thermal resistivity of the soil, depth of burial and the horizontal spacing between the circuits. There are several types of cable installations used in the power system applications. The type of installation depends on the system voltage, MVA to be transmitted and the distance of transmission. Some of the typical cable installations in use are:

1. Cables in duct banks buried at a depth for low voltage applications.
2. Concrete encased cable circuits.
3. Low-pressure oil filled single conductor cable systems, for short lengths.
4. Low-pressure oil filled three conductor cables for 20 kV through 69 kV.
5. Medium pressure oil filled cable circuits.
6. High-pressure fluid filled pipe type cables for high voltage applications.
7. High-pressure gas filled cables for high voltage applications.

All the above-mentioned cable installations need site-specific ampacity calculations and temperature rise evaluations to ensure safe operation.

The load shedding studies are performed to preserve maximum load, shedding of minimum load during system disturbances and also the maintenance of system stability based on short-term, multi-cycle and sub-synchronous oscillations.