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Transient Recovery Voltage Part-1

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Karthikeyan Sandhanam
Karthikeyan Sandhanam

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Transient Recovery Voltage Analysis Part-1 By Karthikeyan.S
When a Circuit Breaker is closed, the voltage at each terminal are be same and the voltage across the breaker which is called longitudinal voltage is zero. When the circuit breaker is opened, it separates the original circuits into two circuits which has difference in responses.
In TRV Analysis, the system voltage across the circuit breaker is called The Prospective TRV. Where the Problem starts:
When the breaker receives a open order. The contact separate, but the current is not interrupted like away. An arc is formed and the current is circulated. When the current sinusoidal wave reaches zero crossing the arc extinguishes and the circuit is opened. The circuit breaker interrupts the current at the zero crossing. Because of the arc instability around the zero crossing, a small current of 3-10A can be chopped which can create even more challenging TRV. The chopping current magnitude depends on the types of circuit breaker (SF6/Vacuum/Air) and the topology of the network. When the arc extinguishes, the circuit breaker is still opening and its poles are separated by a gap. The voltage withstand of this gap depends on the distance between the contact. When the circuit breaker starts to open, automatically the withstand voltage start to increase and reach its maximum when the CB is fully opened. The longitudinal voltage withstand of the circuit breaker is called the inherent TRV. It is very hard to know precisely the withstand voltage of circuit breaker gap. Standard exists to classify Circuit Breaker. For a given voltage rating and current interruption capability, the voltage withstand envelope is provided. Circuit Breaker manufactures must ensure that the circuit breaker have a withstand capability equal or superior to the standards. This is why for TRV analysis , standard Inherent TRV is being used. The graph of Standard Inherent TRV envelope is super imposed with the Prospective TRV. One of the main constraints of successfully opening of Circuit breaker is that the prospective TRV remains inside the Inherent TRV Envelope i.e., not the case there is a risk of Geo electric breakdown across the
Circuit breaker. If this happens before a quarter cycle following the opening, it is called re-ignition. If this happens after the quarter cycle following the opening, it is called as re-striking. The most challenging opening is that when the circuit breaker opens just before the current zero crossing. In this situation, the risk of reignition is maximum. This is why it is usually a device is considered during the TRV analysis and it is default option in EMTP. This device is named as Point on Wave Controller which monitors the current & voltage and operates the circuit breaker so the contacts completely open at the current zero crossing. This solution can theoretically reduce the risk of reignition even though studies must be done considering the precession of equipment and its risk of failure. When comparing the prospective and inherent TRV, there are two particular points of assumption. 1. When the TRV following the current interruption at this moment, then rate of rise of recovery voltage is considered. 2. When the TRV reaches its peak value. Most of the time when the circuit breaker is completely open it is need to be verified that the Peak TRV is lower than the maximum withstands voltage of the circuit breaker. The engineering objective during the TRV studies is to make sure that the circuit breaker successfully opens in any situation. Most of the analysis considered here would be the worst-case scenario. They are 1. Giving the worst RRRV, by simulating the single-phase hotline faults 2. Giving the worst TRV Peak, by simulating the three phase terminal faults. In all cases, the circuit breaker considered to be opening at the current zero crossing.
Engineering Challenges: Credits to: EMTP Learner World.

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Transient Recovery Voltage Part-1

  • 1. Transient Recovery Voltage Analysis Part-1 By Karthikeyan.S
  • 2. When a Circuit Breaker is closed, the voltage at each terminal are be same and the voltage across the breaker which is called longitudinal voltage is zero. When the circuit breaker is opened, it separates the original circuits into two circuits which has difference in responses.
  • 3. In TRV Analysis, the system voltage across the circuit breaker is called The Prospective TRV. Where the Problem starts:
  • 4. When the breaker receives a open order. The contact separate, but the current is not interrupted like away. An arc is formed and the current is circulated. When the current sinusoidal wave reaches zero crossing the arc extinguishes and the circuit is opened. The circuit breaker interrupts the current at the zero crossing. Because of the arc instability around the zero crossing, a small current of 3-10A can be chopped which can create even more challenging TRV. The chopping current magnitude depends on the types of circuit breaker (SF6/Vacuum/Air) and the topology of the network. When the arc extinguishes, the circuit breaker is still opening and its poles are separated by a gap. The voltage withstand of this gap depends on the distance between the contact. When the circuit breaker starts to open, automatically the withstand voltage start to increase and reach its maximum when the CB is fully opened. The longitudinal voltage withstand of the circuit breaker is called the inherent TRV. It is very hard to know precisely the withstand voltage of circuit breaker gap. Standard exists to classify Circuit Breaker. For a given voltage rating and current interruption capability, the voltage withstand envelope is provided. Circuit Breaker manufactures must ensure that the circuit breaker have a withstand capability equal or superior to the standards. This is why for TRV analysis , standard Inherent TRV is being used. The graph of Standard Inherent TRV envelope is super imposed with the Prospective TRV. One of the main constraints of successfully opening of Circuit breaker is that the prospective TRV remains inside the Inherent TRV Envelope i.e., not the case there is a risk of Geo electric breakdown across the
  • 5. Circuit breaker. If this happens before a quarter cycle following the opening, it is called re-ignition. If this happens after the quarter cycle following the opening, it is called as re-striking. The most challenging opening is that when the circuit breaker opens just before the current zero crossing. In this situation, the risk of reignition is maximum. This is why it is usually a device is considered during the TRV analysis and it is default option in EMTP. This device is named as Point on Wave Controller which monitors the current & voltage and operates the circuit breaker so the contacts completely open at the current zero crossing. This solution can theoretically reduce the risk of reignition even though studies must be done considering the precession of equipment and its risk of failure. When comparing the prospective and inherent TRV, there are two particular points of assumption. 1. When the TRV following the current interruption at this moment, then rate of rise of recovery voltage is considered. 2. When the TRV reaches its peak value. Most of the time when the circuit breaker is completely open it is need to be verified that the Peak TRV is lower than the maximum withstands voltage of the circuit breaker. The engineering objective during the TRV studies is to make sure that the circuit breaker successfully opens in any situation. Most of the analysis considered here would be the worst-case scenario. They are 1. Giving the worst RRRV, by simulating the single-phase hotline faults 2. Giving the worst TRV Peak, by simulating the three phase terminal faults. In all cases, the circuit breaker considered to be opening at the current zero crossing.