Pamalit sa mga paraan sa pagbawas sa overvoltage sa EHV

Paspas nga Pagbutang sa Shunt Reactors

Kalihukan:

Ang mga shunt reactors gisulbaran sa pagkompensar sa kapasidad sa mahabang transmission lines, sumala kini mao ang makapadako sa overvoltages ug reactive power issues. Sila naghatag og secondary benefit sa pagbawas sa switching overvoltages sa panahon sa pagkonekta, pero dili kini kasagaran ang primary rason sa utilities aron silay isulbar. Ang primary objectives sa shunt reactors nagsama sa:

• Kapasidad Compensation: Ang mahabang transmission lines adunay significant kapasidad, lalo na sa Extra High Voltage (EHV) levels. Kini nga kapasidad makapadako sa overvoltages, lalo na sa panahon sa light load conditions o kon ang line open. Ang shunt reactors makatabang sa pagbawas niining overvoltages pinaagi sa paghatag og reactive load nga mag-counteract sa capacitive effects.

• Switching Overvoltage Reduction: Kon dili primary purpose, ang shunt reactors usab makapabawas sa switching overvoltages. Sa panahon sa circuit breaker opens o closes, transient overvoltages makapadayon. Ang shunt reactors makapatabang sa pag-absorb sa uban niining transients, resulta mao ang bawasan sa magnitude sa overvoltages.

Application:

• Ang shunt reactors kasagaran isulbaran sa substations sa mahabang transmission lines, lalo na sa EHV systems diin mas pronounced ang kapasidad effect.

• Dili sila kasagaran gi-isulbaran lang aron mapabawas ang switching overvoltages tungod kay uban pang measures (sama sa closing resistors o controlled closing) mas effective para sa specific purpose.

Closing Resistors

Kalihukan:

Ang closing resistors gigamit aron mapabilin sa acceptable limits ang voltage sa receiving end sa transmission line sa panahon sa energization. Ang primary goal mao ang pagpabilin sa voltage sa around 2 per unit (p.u.), aron maprevent ang damage sa equipment ug ensure system stability.

Operation:

• Sa panahon sa energization sa transmission line, ang sudden surge sa current makapadako sa significant voltage rise sa receiving end, resulta mao ang overvoltage conditions.

• Ang closing resistors temporary connected in series sa circuit breaker sa panahon sa closing operation. Sila naglimit sa initial current surge ug dampen any resulting transients, resulta mao ang prevent sa voltage sa pag-exceed 2 p.u.

• Kon ang transients na subside, ang resistors bypassed, ug ang line operates normally.

Benefits:

• Voltage Limitation: Nagpabilin sa receiving-end voltage sa safe limits, protecting equipment ug ensuring stable operation.

• Transient Suppression: Nagbawas sa magnitude sa switching overvoltages, sumala kini importante sa EHV systems.

Staggered Pole Closing

Principle:

Ang staggered pole closing nagsangpot sa pag-close sa individual poles sa three-phase circuit breaker one-half cycle apart. Ang idea mao ang allow transients sa first phase to attenuate before the next phase is closed, resulta mao ang reduce the likelihood of severe overvoltages.

Operation:

• Sa three-phase system, ang cada phase closed sequentially, with a delay of half a cycle (10 ms at 50 Hz or 8.33 ms at 60 Hz) between each phase.

• Sa staggering sa closing, ang transients generated by the first phase adunay time to decay before the next phase is energized. Kini nagbawas sa cumulative effect sa transients ug minimize the risk of overvoltage events.

Benefits:

• Transient Attenuation: Allows transients from the first phase to dissipate before the next phase is closed, reducing the overall severity of overvoltages.

• Simplified Implementation: Dili require complex control systems, making it a relatively simple and cost-effective method for mitigating overvoltages.

Line Terminal Arresters

Kalihukan:

Ang line terminal arresters isulbaran sa ends sa transmission lines aron maprotektahan sa overvoltages caused by lightning strikes o switching operations. Sila naglimit sa overvoltages sa points diin sila isulbaran sa protective level sa arrester.

Operation:

• Ang arresters designed to conduct excess energy away from the system when overvoltages exceed a certain threshold. Sila clamp the voltage to a safe level, preventing damage to equipment ug ensuring the integrity of the transmission system.

• Typically, ang arresters placed at both ends sa transmission line (sending and receiving terminals). Pero, sila only limit overvoltages sa uban niining specific locations ug dili provide protection along the entire length sa line.

Benefits:

• Overvoltage Protection: Effectively protects equipment sa line terminals from overvoltages caused by lightning o switching.

• Targeted Protection: Provides focused protection sa critical points sa system without the need for additional equipment along the entire line.

Controlled Closing

Principle:

Ang controlled closing mao ang advanced mitigation measure nga gigamit dynamic controller aron analyze the differential voltage across the circuit breaker, predict future voltage minima, ug close the breaker sa optimal moment aron mapabilin sa minimum overvoltages. The entire process must be completed within less than 0.5 seconds aron ma-effective.

Operation:

• Ang dynamic controller continuously monitors the voltage difference across the circuit breaker.

• It identifies the minimum voltage points ug predicts when future minima will occur.

• The controller then closes the breaker sa predicted minimum voltage point, ensuring that the closing occurs during a low-voltage period ug minimizing the risk of overvoltage.

• This method requires fast ug accurate control algorithms, as well as precise timing aron ensure the breaker closes sa optimal moment.

Benefits:

• Minimized Overvoltages: By closing the breaker sa optimal voltage point, controlled closing significantly reduces the magnitude sa overvoltages.

• Improved System Stability: Helps maintain system stability aron prevent excessive voltage surges during line energization.

• Advanced Technology: Offers a more sophisticated ug effective solution compared to traditional methods like staggered pole closing o closing resistors.

Overvoltage Profile in EHV Long Lines

Ang figure showing the overvoltage profile sa EHV long line demonstrates the effectiveness sa various overvoltage limitation options. Each method adunay iyang own impact sa overvoltage levels, ug ang choice sa method depends sa specific requirements sa system.

• Fast Insertion of Shunt Reactors: Reduces overvoltages due sa line capacitance ug provides some reduction sa switching overvoltages.

• Closing Resistors: Limits the receiving-end voltage sa 2 p.u., effectively controlling overvoltages during line energization.

• Staggered Pole Closing: Reduces the cumulative effect sa transients sa pag-allow sa them to attenuate between phase closings.

• Line Terminal Arresters: Protects the line terminals from overvoltages pero dili provide protection along the entire line.

• Controlled Closing: Minimizes overvoltages sa pag-close sa breaker sa optimal voltage point, offering the most effective control over transient overvoltages.

Each of these methods can be used individually o in combination aron achieve the desired overvoltage mitigation sa EHV long lines, depending sa system's specific needs ug constraints.