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In a short circuit test on a 132 KV 3–phase system, the breaker gave the following results: Pf of the fault 0.4, recovery voltage 0.95 of full line voltage, the breaking current is symmetrical and the restricting transient had a natural frequency of 16 KHz. What would be the rate of rise of restriking voltage.(assume that the fault is grounded)
  • a)
    4 KV/μs
  • b)
    5 KV/μs
  • c)
    6 KV/μs
  • d)
    7 KV/μs
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
In a short circuit test on a 132 KV 3–phase system, the breaker gave ...
The peak value of phase voltage
= Vmph = 132 √3 × 2 = 107.77KV
Active Recovery voltage
= K1K2Vmphsin⁡ϕ
K1 = 0.95
K2 = 1 (grounded fault)
cos⁡ϕ = 0.4 ⇒ ϕ = cos−1⁡(0.4)=66.42
Sin⁡ϕ = 0.916
Active recovery voltage
= 0.95 × 1 × 107.77 × 0.916
= 93.85KV
Restriking Voltage
= 93.85k(1 − cos⁡ωt)
RRRV = d / dt [93.85 × 103(1 − cos⁡ωt)]
RRRV =93.85 ×103 × ω. sinwt (RRRV) average = 2π(93.85 × 103 × ω)
=2/π × 93.85 × 103 × 2πf
= 4f x 93.85 x 103
= 4 x 16 x 93.85 x 106
= 4f x 93.85 x 10–3 KV/μsec
Average RRRV = 6 KV/μsec
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Most Upvoted Answer
In a short circuit test on a 132 KV 3–phase system, the breaker gave ...
Given data:
- Voltage level: 132 KV
- System type: 3-phase
- Power factor of the fault: 0.4
- Recovery voltage: 0.95 of full line voltage
- Breaking current: symmetrical
- Restricting transient frequency: 16 KHz
- Fault type: grounded

To find: Rate of rise of restriking voltage

Calculation:
The rate of rise of restriking voltage (RRRV) can be calculated using the following formula:

RRRV = 2πfVr/Ip

Where,
- f = Restricting transient frequency = 16 KHz
- Vr = Recovery voltage = 0.95 × 132 KV = 125.4 KV
- Ip = Peak value of symmetrical breaking current

To calculate Ip, we need to first calculate the RMS value of the breaking current using the power factor of the fault:

Pf = Cos θ = Ip/Is

Where,
- θ = Angle between voltage and current
- Is = RMS value of symmetrical fault current = Ip/√2

Ip = Is × Cos θ = Pf × Is = 0.4 × Is

Now, we can substitute the values in the RRRV formula:

RRRV = 2πfVr/Ip = 2π × 16 × 10^3 × 125.4 × 10^3 / (0.4 × Is)

We know that Is = Ip/√2, so we can substitute that:

RRRV = 2π × 16 × 10^3 × 125.4 × 10^3 / (0.4 × Ip/√2)

Simplifying the expression, we get:

RRRV = 6.04 × 10^6 × √2 / Ip

Now, we just need to substitute the value of Ip, which we calculated earlier:

RRRV = 6.04 × 10^6 × √2 / (0.4 × Is) = 6 × 10^3 V/μs (approx.)

Therefore, the rate of rise of restriking voltage is 6 KV/μs (approx.)
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Community Answer
In a short circuit test on a 132 KV 3–phase system, the breaker gave ...
C
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In a short circuit test on a 132 KV 3–phase system, the breaker gave the following results: Pf of the fault 0.4, recovery voltage 0.95 of full line voltage, the breaking current is symmetrical and the restricting transient had a natural frequency of 16 KHz. What would be the rate of rise of restriking voltage.(assume that the fault is grounded)a)4 KV/μsb)5 KV/μsc)6 KV/μsd)7 KV/μsCorrect answer is option 'C'. Can you explain this answer?
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