Question

Question:Rework Problem 13.18 for a lossy line with a constant series resistance 0.3 $\mathbf{\Omega }$/km . Lump half of the total resistance at each end of the line.

Short answer

Answer

The value of station-class arrester rating is 84 KV MCOV.

The range of the maximum discharge voltage for an 84 KV MCOV arrestor is from 183.96 KV to 200.76 KV.

Step-by-step solution

Write the given data from the question.

Rework Problem 13.18.

Consider the following data:

The maximum 60 Hz voltage for a system under 115 KV specific system circumstances is 1.08 per unit, according to the ratings for choosing a station-class metal oxide surge arrester.

Determine the value of station-class arrester rating.

Determine the line to neutral voltage of the given system.

$1.08\left(115/\sqrt{3}\right)=71.7 \text{kV}$

From the information in Table 13.2 of the textbook, pick a station class surge arrestor that has an 84 KV MCOV. The surge arrestor's rating at this value is the lowest one ,71.7 KV surpassing, giving the system the widest margin of safety.

Therefore, the station-class arrester rating is 84 KV MCOV.

Determine the value of maximum discharge voltage for an MCOV arrestor.

The maximum discharge voltage varies from to of the MCOV for the 84 KV MCOV surge arrestor for an impulse current wave cresting in.

Converting these values into , using the base of .

$2.19\times 84\text{kV}=183.96\text{kV}$

Also,

$2.39\times 84\text{kV}=200.76\text{kV}$

Therefore, the range of the maximum discharge voltage for an84 KV MCOV arrestor is from183.96 KV to 200.76 KV.

Determine the safety margin for the 84 KV MCOV surge arrestor for system equipment with a BIL should be determined.

$450\text{kV}-200.76\text{kV}=249.24\text{kV}$

Also,

$450\text{kV}-183.96\text{kV}=266.04\text{kV}$

Therefore, the protective margin ranges between 249 KV and 266.04 KV.