Muhammad Kashif’s Post

Transient Recovery Voltage (TRV) is a critical parameter for high-voltage circuit breakers, representing the voltage across the terminals after a current interruption. It significantly influences the circuit breaker's ability to interrupt fault currents and maintain system stability. Key factors affecting TRV include system voltage, short-circuit current, source impedance, and fault type. The TRV waveform can vary based on the circuit configuration, with common shapes being cosine, exponential cosine, and triangular waveforms. To mitigate TRV effects, methods such as shunt reactors, shunt capacitors, and controlled switching techniques are employed. These approaches help manage the rate of rise and peak values of TRV, enhancing circuit breaker performance and overall power system reliability. As power systems evolve with increased interconnections and renewable energy integration, advanced circuit breaker technologies and real-time monitoring are essential for effective TRV management. Understanding these dynamics is crucial for selecting appropriate circuit breakers that can withstand transient conditions without failure.

Independent of the circuit-breaker, the peak value of the inrush current may not exceed 100 times the rated normal current of the capacitor, in order to limit the effect of the electrodynamic forces. Factor 100 is a general rule only, at high switching rates the standard IEC 60871-1-07 (Shunt capacitors for a.c. power systems having a rated voltage above 1000V – Part 1: General) recommends limiting the inrush current to lower values. Capacitors are normally equipped with discharge voltage transformers or resistors. If re-closing cycles may occur in normal service, the discharge time constant must be chosen short enough that the capacitor is almost completely (≤ 10 %) discharged before re-energizing. https://lnkd.in/gAkmp_w

"You Ask, We Answer" is an online panel session where industry experts discuss and answer the questions you ask which helps you work better. Use this opportunity to share your questions related to protection, relay, busbar testing, sampled value, and digital substation that revolve around below-mentioned points when you register : ·        Fault Locator ·        Auto reclosure ·        Sampled value ·        Line differential ·        Low impedance REF ·        Generator protection ·        Transformer differential ·        Power swing block (PSB) ·        Line / Distance protection ·        Self-powered relay testing ·        Wrong phase coupling (WPC) ·        Time synch for IEC61850-9-2LE ·        SOTF in the transformer differential ·        ROCOF protection-IEC60255-181:2019 ·        High burden electromechanical relay testing ·        Comtrade playback/disturbance recorder files playback ·        Local Breaker Backup (LBB) Vs Breaker Failure Protection (BFP) Register Now - https://lnkd.in/d6tTHytG #paneldiscussion #youaskweanswer #onlinediscussion #Power #Protection #powerprotection #PSB #megger #meggerindia

Short circuit tolerance of the main transformer of the power plant As you know, the GCB of the power plant must have the ability to cut off the short circuit in critical conditions of Out of Phase Synchronizing and control the return over voltages (TRV) caused by it. But why does the IEC 60076-5 standard consider the ability of the power plant's main transformer to pass this current to be important? As we know, the size of Out of phase current is not greater than Three-phase short circuit current, so why does the standard insist on this issue?

The operation of an earth leakage circuit breaker (or shorten ELCB) is based on the fact that the algebraic sum of the currents in any healthy single phase, three phase and three phase and neutral system is zero. This simply means that in a single phase system the current flowing in the line conductor is equal and opposite to the current in the neutral conductor, and in a three phase system the vectorial current in one line is equal and opposite to the vectorial sum of the currents in the other two lines. The same applies in three phase and neutral systems. If these conductors are passed through a core balance transformer, and the circuit is healthy, no excitation of the transformer results. However, if an earth fault occurs in the system, the earth current returns to the earth connection on the supply transformer via, an earth conductor or general earth. Since these conductors are external to the core balance transformer, the currents passing through the core balance transformer are no longer balanced, and an EMF is induced into the secondary winding of the core balance transformer. Read more https://lnkd.in/dvQy8ynT

Independent of the circuit-breaker, the peak value of the inrush current may not exceed 100 times the rated normal current of the capacitor, in order to limit the effect of the electrodynamic forces. Factor 100 is a general rule only, at high switching rates the standard IEC 60871-1-07 (Shunt capacitors for a.c. power systems having a rated voltage above 1000V – Part 1: General) recommends limiting the inrush current to lower values. Capacitors are normally equipped with discharge voltage transformers or resistors. If re-closing cycles may occur in normal service, the discharge time constant must be chosen short enough that the capacitor is almost completely (≤ 10 %) discharged before re-energizing.

See this Electrical Giant over which several people are hanging? not so enjoyable though:) This demonstrates the Gigantic Size of the Electrical Insulators used in high-voltage (HV) transmission lines. IEC 61109 standardizes the selection and sizing of Electrical Insulators, which separate energized lines from transmission towers and must withstand the entire weight of the transmission lines. Two common types of insulators are tension insulators, as shown in the video, and suspension insulators, which connect lines at both arms of a tower making sure that the tower is insulated. However, insulators must also contend with electrical phenomena such as flashovers and backflashes. A flashover occurs when an insulator becomes conductive due to high voltage, allowing current to flow through the insulator and the tower to the ground. In contrast, a backflash happens when a ground fault causes a potential difference between the tower footing resistor and the transmission lines, resulting in current flowing back into the lines through the insulator. Beased on IEC 61109, careful selection and sizing of insulators enables them to withstand fault currents until Circuit Breakers can isolate the fault. Properly chosen insulators ensure the safety and reliability of HV transmission systems.

Why the Secondary Side of a Current Transformer Should Not Be Open Circuited?? The secondary side of a current transformer should never be open because it causes high voltage build-up, leading to core saturation and potential insulation failure. This can result in overheating and damage to the CT. • Step-up transformer, Increases voltage and decreases current on the secondary side. • If the secondary is open-circuited, the primary draws high magnetizing current. • This leads to very high voltage on the secondary side, risking damage to CT and connected devices. • To avoid this, an external load (burden) is connected to the CT’s secondary Inaccurate Measurements: • An open secondary circuit disrupts the CT’s normal operation, resulting in inaccurate current measurements. • This can lead to false alarms from protection relays, potentially causing unnecessary power outages or equipment damage. *Additional Considerations:* • Always short-circuit the CT secondary with a burden resistor or other appropriate load when the CT is not in use. This provides a safe path for the induced current and high voltage development. • Never perform maintenance or testing on a CT without properly de-energizing and shorting the secondary circuit. •Regularly inspect and maintain your CTs according to manufacturer recommendations to ensure their safe and reliable operation.

Read this blog to know Importance of Low Voltage Switchgears #mcb #mccb #ACCL #Electrical #blog