An overview of the grounding system (ungrounded)

1. An overview of the grounding system (ungrounded) The subjects: Ungrounded system Derivation of the common expression in an ungrounded system Advantages and disadvantages of the ungrounded system Efficient and inefficient grounding concept Earthing coefficient and earth fault factor Neutral underground or underground system Prior to 1950, the electrical system was often ungrounded. Such a system had repeated arcing patterns, insulation failure, and difficult earth protection. Each phase has an inherent distributed capacity with respect to earth. If an earth fault occurs on phase B, the distributed capacity is discharged via the fault. The capacity is charged and discharged again. Because of this server voltage oscillation is reached in the healthy phases. These voltage oscillations cause stresses on the insulation of the connected equipment.

2. Ic2 = jCwv2 Ic3 = jCwv3 Ic = jCwv2 + jCwv3 Ic = jCw (v2 + v3) Now drawing the phasor diagram as shown below, wecan writes: VN + V2 = v2 VN + V3 = v3 Substitution of equation -02 and equation-03 into equation-01: Ic = jCw (VN + V2 + VN + V3) Ic = jCw (2VN + V2 + V3) Voltage phasors V3 can be resolved in the direction of V N and in the direction perpendicular to V N likeV3Cosθ and V3Sinθ. Likewise voltage phaser V2 can be solved as V2Cosθand - V2Sinθ Therefore: V2 + V3 = V3Cosθ + V3Sinθ + V2Cosθ - V2Sinθ V3 = V2 V3Cosθ + V2Cosθ = V N By substituting in equation-05 we obtain: V2 + V3 = VN = V1 (V1 being shorted, soVN = V1) By substituting equation 06 for equation 04, we get:

3. Ic = jCw (2VN + VN) The total capacitive charge and discharge current of the healthy phase is: </ p> Ic = j3CwV1 For an ungrounded system: If = IC2 + IC3 = IC = j3CwV1 in the earthing system the fault current to earth, totally depends on capacitive return current via the phase-to-earth capacitances of the network. This is the reason for breakdown voltage in the healthy phases of the ungrounded system. Since there is no return path available for the fault current in an ungrounded system, detection of the earth current is therefore difficult. This is another drawback of the ungrounded system. Advantages of the ungrounded system The ungrounded system has some advantages: 1.Ungrounded the system has negligible earth fault current 2.Some essential continuous and auxiliary process or system in which a single phase the ground fault should not trip the system

4. Disadvantages of the ungrounded system However, the disadvantages of the ungrounded system listed below outweigh the advantages: 1.Ungrounded the system experiences multiple arcs 2.Insulation failure occurs with single-phase ground faults. 3.It is difficult to protect the earthed system against earth faults. 4.The voltage from lightning flashes does not find a way to earth. In order to overcome the aforementioned technical and operational problems, the concept of system grounding has been introduced. The grounding of the system consists of connecting the neutral of the system to the ground. At each voltage level, the neutral of the transformer is considered as neutral of the system. There are two types of system grounding: 1.Efficient grounding: Efficient grounding is also referred to as solid grounding without resistance or reactance. In this case, the earthing coefficient is greater than 80% 2.Non-effective grounding: When the neutral connection to the ground is made through a resistor or reactance, the system is said to be not properly grounded. In this case, the earthing coefficient is greater than 80% Earthing coefficient and earth fault factor The earthing coefficient is the ratio that is measured during the single- phase earth fault: </ p>

5. Ce = Highest phase voltage to earth of the healthy phase / Phase to phase voltage In a system without neutral earth ( refer to figure 1 ), phase-to-earth phase-1 and phase-2 voltage rises to 3 times the phase-to-phase voltage Vrms during a single-phase earth fault on phase 3. In a system to neutral earth, the healthy phase voltage rises to this time Vrms. So the value of Ce: For an effectively ungrounded system Ce = 1 For an efficiently grounded system Ce <0.8. The nominal voltage of the surge arrester is , therefore,> 0.8 V RMS value The instantaneous kV overvoltage is taken to be 2.5 times the line insulation critical bypass voltage (CFOV) . So the discharge current is given as: I = (2.5 (CFOV) - Surge arrester residual voltage) / Line overvoltage impedance Earth fault factor is a calculated ratio at the selected point of the power system for a given system. Earth fault factor = V1 / V2 V1 = Maximum effective voltage between phases of healthy phases ( phases 2 and 3 refer to figure 1 ) during the earth fault on phase-1 V2 = RMS value of the phase-to-earth voltage at the same location, the fault relating to defective phases being eliminated Burraq Engineering Solutions is the best training institute in Lahore which is providing practical training of Electrical Automation and Short Electrical Courses including PLC course, SOLAR SYSTEM Installation and DESIGN COURSE, ETAP course, DIALUX course, Panel FABRICATION course, VFD course, ADVANCED Course Panel, SWITCHERGEAR design course,

6. Building Electrical design course, and all electrical diploma courses. Both online and physical classes available. We introduce a platform Lyskills from where you can get lifetime access to your desire courses in very reasonable price.