# Power Systems : Fault Analysis | DFCCIL 60 Day Study Plan | Electrical Engineering

Dedicated Freight Corridor Corporation of India Limited (DFCCIL) is a Public Sector Undertaking under the administrative control of the Government of India (Ministry of Railways), has given the notification of 1074 Vacancies for recruitment of Junior Executive, Executive, and Junior Manager in Civil, Electrical, S&T, Operations & BD, and Mechanical Departments of DFCCIL. This is a great opportunity for Electronics and Electricals students to work with one of the top PSUs and make their career. As Competition is high, so the aspirants need to prepare with a good strategy and proper planning to clear this exam.

BYJU'S Exam Prep Brings you 60 Days Study Plan for the preparation of DFCCIL Electricals & Electronics Engineering. This Study Plan will be free and will be very beneficial for the students preparing and targeting the DFCCIL Exam. Save this article as it will get updated on a daily basis as scheduled.

### Different Types Of Fault Occur in Power System

Symmetrical Components

A three-phase system is said to be symmetrical when the system viewed from any phase is similar. Thus, in a three-phase symmetrical system the self-impedance of all the three phases are equal and the mutual impedances, if any between the three phases are the same any three phase system having unbalanced phasor quantities can be represented in terms of three phase balanced phasor components as a combination of positive, negative and zero sequence component, which are as follows

Positive Phase Sequence Components

It represents a set of balance phasors Va1, Vb1 & Vc1 These components have three phasors equal in magnitude displaced by 120o and having same phase sequence as original phasors.

Negative Phase Sequence Components

These components have three phasors Va2, Vb2 & Vc2 equal in magnitude displaced by 120o but having phase sequence opposite to original phasors. It represents a set of balanced phasors.

Zero Sequence Components

These phasors Vao, Vbo & Vco are equal in magnitude and having zero phase displacement.

Sequence Impedance

The positive sequence impedance of an equipment is the impedance offered by the equipment to the flow of positive sequence current. similarly, the negative sequence or zero sequence impedance of the equipment is the impedance offered by the equipment to the flow of corresponding sequence current.

Sequence Impedance of a Transmission Line

Positive sequence impedance Z1 = Zs - Zm

Negative sequence impedance Z2 = Zs - Zm

Zero sequence impedance Z0 = Zs + 2Zm + 3Zn

where, Zs = Self-impedance per phase

Zm = Mutual impedances between phases

Most of the faults that occur on power systems are not the balanced (i.e., symmetrical) three-phase faults but the unbalanced (i.e., unsymmetrical) faults, like single line-to-ground (SLG) faults. The typical frequency of occurrence for the three-phase, SLG, line-to-line, and double line-to-ground (DLG) faults as 5%, 70%, 15%, and 10% respectively.

In general, the three-phase fault is considered to be the most severe one. However, it is possible that the SLG fault may be more severe than the three-phase fault under two circumstances:

(1) the generators involved in the fault have solidly grounded neutrals or low-impedance neutral impedances

(2) it occurs on the wye-grounded side of delta-wye-grounded transformer banks.

Single Line to Ground Fault:

In general, the SLG fault on a transmission system occurs when one conductor falls to ground or contacts the neutral wire.

Line to Line Fault:

In general, a line to line (L-L) fault on a transmission system occurs when two conductors are short circuited.

Double Line to Ground Fault:

In general, the Double Line to Ground fault on a transmission system occurs when two conductors fall and are connected through ground or when two conductors contact the neutral of a three-phase grounded system.

SYSTEM GROUNDING

A system neutral ground is connected to ground from the neutral point or points of a system or rotating machine or transformer. Thus, a grounded system is a system that has at least one neutral point that is intentionally grounded, either solidly or through a current-limiting device. For example, most transformer neutrals in transmission systems are solidly grounded. However, generator neutrals are usually grounded through some type of current-limiting device to limit the ground fault current.

The methods of grounding the system neutral include

• Ungrounded
• Solidly grounded
• Resistance grounded
• Reactance grounded
• Peterson coil grounded
• You can avail of Online Classroom Program for all AE & JE Exams:

## Online Classroom Program for AE & JE Exams (12+ Structured LIVE Courses and 160+ Mock Tests)

You can avail of BYJU'S Exam Prep Test Series specially designed for all AE & JE Exams:

## BYJU'S Exam Prep Test Series AE & JE (160+ Mock Tests)

Thanks,

Team BYJU'S Exam Prep

Sahi Prep Hai to Life Set Hai !!!

Download BYJU'S Exam Prep APP , for best Exam Preparation , Free Mock Test, Live Classes