What is the difference between a Comprehensive Study and a ANSI study?

 ANSI fault follows ANSI C37 standards for calculating equipment ratings. The comprehensive fault follows a traditional Ohm’s Law calculation for fault current.

For Low voltage systems, the calculations are the same except for two items:
1) ANSI calculates the X/R ratios based on separate X and R networks whereas Comprehensive uses a single complex network.
2) ANSI uses the X/R ratio to adjust the calculated short circuit value to compare directly with molded case and power circuit breaker ratings based on ANSI test power factor. In other words, the calculated short circuit value is increased if the X/R ratio is larger that the ANSI test power factor.

For Medium and High Voltage systems: The momentary calculations are similar. The largest difference is in Interrupting Calculations: ANSI uses the ANSI C37 tables and curves to simulate AC and DC decay for interrupting calculations, whereas Comprehensive accounts for the system DC decay but ignores the AC machine decay in all cases.

What is the difference between ground current and unbalance current?

1. Ground fault current: The current flowing in the grounding system. In the event of insulation failure, equipment malfunction, or wiring errors causing a ground fault, a portion of the current may flow through unexpected paths to the ground, potentially posing safety hazards, electric shock, and equipment damage.
2. Unbalanced current: In a balanced three-phase system, the current ideally should be evenly distributed among the three phases, with each phase carrying an equal load of current. However, when there is unbalanced loading, uneven distribution of loads, or faulty equipment, the currents in the three phases become unbalanced, with the currents in the three phases no longer being equal. This results in unbalanced current. Unbalanced current can lead to various issues, including increased losses in the system, voltage fluctuations, overheating of equipment, and reduced system efficiency.

The two can sometimes be confusing, but there is a difference between them. In the case of unbalanced current caused by uneven three-phase loading, it only flows through the neutral path. On the other hand, in the event of a ground fault, the fault current flows through the grounding path.