Does the impulse withstand voltage required for a line depend on neutral earthing?

True: earthing changes the arrester rating and hence the required BIL

False: BIL depends only on disc size

True: earthed systems need a higher BIL

False: earthing affects only power-frequency current

With an effectively earthed neutral, healthy phase voltage rise is about:

0.8 of line voltage, allowing an 80% arrester

1.0 of line voltage with a 100% arrester only

For a 220 kV line, what does effective earthing allow?

Reduced BIL, such as 900 kV instead of 1050 kV, and fewer discs

More discs than an ungrounded system

2075 Bhadra · 1+3 marks

T/F: impulse withstand and neutral earthing

Short answer

True. Effective earthing reduces temporary overvoltages, allowing a lower-rated arrester and reduced BIL (e.g., 900 kV instead of 1050 kV for 220 kV). Isolated or ungrounded neutral requires full insulation level.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: Impulse withstand voltage of an overhead transmission line insulator depends on system (neutral) earthing condition.

TRUE.

The insulation level (impulse withstand voltage, BIL) is chosen as protection ratio × protective level of the surge arrester.
The arrester rating depends on the earthing coefficient: with effectively (solidly) earthed neutral the healthy-phase voltage rises to only about 0.8 of line voltage, so an "80% arrester" with a lower protective level is used. With isolated neutral, a "100% arrester" is needed.
So effective earthing allows a reduced BIL (e.g. 220 kV: 900 kV instead of 1050 kV), and fewer insulator discs; an ungrounded system needs full insulation.

The impulse strength of a given disc does not change, but the required impulse withstand level of the line does depend on neutral earthing.

✓ Answer checked by Claude Opus 5.5 (high effort)

T/F: earth wire choice depends on circuit and voltage · Transmission and Distribution System Design, chapter 3
T/F: span choice depends on voltage only · Transmission and Distribution System Design, chapter 4
T/F: pin insulator cost vs voltage · Transmission and Distribution System Design, chapter 3
T/F: switching surge ratio vs system voltage · Transmission and Distribution System Design, chapter 3 · asked 4×
Number of insulator discs for 220 kV line · Transmission and Distribution System Design, chapter 3
Neutral earthing and insulation level · Transmission and Distribution System Design, chapter 3 · asked 3×
True/false: load rejection raises terminal voltage · High Voltage Engineering, chapter 3
True/false: protective ratio and grounding · High Voltage Engineering, chapter 4
True/false: derivative controllers always used with others · Control Systems, chapter 7 · asked 3×
True/false: air conditioner is closed loop · Control Systems, chapter 1

All Transmission and Distribution System Design chapter 3 questions →

T/F: impulse withstand and neutral earthing

Related questions