Types of faults & their causes Switchgear and Protection MSBTE Solution

Types of Electrical Faults 

Types of questions asked on the topic of Types of Electrical Faults & their causes

1. List types of faults.

2. Classify faults.

3. State the different types of faults.

4. What are the common faults likely to occur? Suggest protections against such faults

5. List out any four types of faults that can occur in a system and give causes for the same.

6. State the different faults in the power system.

7. List the various types of faults that occur in a power system.

8. Explain the following terms and write down one example for each type :

(1) Symmetrical fault

(2) Unsymmetrical fault.

Types of faults & their causes Switchgear and Protection MSBTE Solution

Alternating Current (AC) faults can be classified as :
  • Single line to ground fault
  • The line to line fault
  • Double line to ground fault
  • Simultaneous fault
  • Open circuit fault
  • Three-phase fault
Mainly faults can be classified into two categories:

   (a) Symmetrical faults 
   (b) Unsymmetrical faults.

Define Symmetrical faults and Unsymmetrical faults

Symmetrical faults: 

That fault that gives rise to symmetrical fault currents (i.e. equal magnitude of fault currents with 120° phase displacement is called a symmetrical fault.

The most common example of symmetrical fault is when all the three conductors of a 3 phase line are brought together simultaneously into short circuit condition with each other including or excluding the ground.
Unsymmetrical faults: 

Those faults which gives rise to unsymmetrical currents (i.e. with an unequal magnitude of fault currents with unequal phase displacement it simply consist of 2 phases) are called unsymmetrical faults.

The unsymmetrical faults may take one of the following forms:

(a) Single phase to ground (L-G) :
  • A short circuit between any one of the phase conductors of 3 phase system and earth is called a single phase to ground fault.
  • It may be due to the failure of insulation between a phase conductor and earth or due to a phase conductor breaking and falling to the ground.
(b) Two-phase to ground fault (L-L-G) : 
  • A short circuit between any two phases and earth is called a double line to ground or a two-phase to ground fault.
(c) Phase to phase faults (L L) :
  • A short circuit between any two lines (phases) is called a line to line or phase to phase fault.
(d) Open circuited phases :
  • This type of fault is caused by a break in the conducting path. Such faults occur when one or more phase conductors break or a cable joint or joint on the overhead lines fails.
  • Such a situation may also arise when circuit breakers or isolators open but fail to close one or more phases.
  • Due to the opening of one or two phases, unbalanced currents flow in the system, thereby heating rotating machines.

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