HVDC Circuit Breakers: Types, Operation, and Applications
High Voltage Direct Current (HVDC) systems provide an efficient method for transmitting power over long distances. These systems are increasingly used in green energy production. Protecting the expensive equipment connected to these high-voltage transmission lines is very important.One of the key protective devices used is the circuit breaker. However, traditional AC circuit breakers are unsuitable for DC systems. This is due to the inherent differences in current behavior. This is where HVDC circuit breakers play a significant role.
Table of Contents
Table of Contents
What is a Circuit Breaker?
A circuit breaker is a mechanical switch. It is designed to protect a circuit from damage. The damage can be caused by fault currents. It automatically interrupts the circuit when it detects an excessive current flow. The current flows can be due to overloading or a short circuit. Additionally, it can be manually operated for maintenance or fault clearance. The primary functions of a circuit breaker include:
- Momentarily withstanding fault currents.
- Safely interrupting the circuit.
- Quickly extinguishing the arc.
- Withstanding voltage after breaking.
- Preventing arc re-striking.
How Circuit Breakers Detect Fault Currents
Circuit breakers detect fault currents, which are typically very high, using mechanisms such as:
- Heating Effect: The rise in temperature due to excessive current.
- Electromagnetic Effect: The magnetic field generated by the current.
- Current Sensors: Using Current Transformers (CTs) to measure current levels.
Once a fault is detected, the circuit breaker trips. And interrupts the current flow. This is achieved using stored mechanical energy, such as springs or compressed air, to separate the contacts. Alternatively, the fault current itself can be used to separate the contacts.Which is achieved through thermal expansion or electromagnetic fields generated by solenoids.
Arc Extinction in Circuit Breakers
When the contacts separate, an arc is generated due to the high voltage between them. This arc can cause significant damage due to the heat it produces. To prevent this, various arc extinction techniques are employed:
- Cooling the Arc: Reducing the temperature of the arc to recombine ionized particles, increasing the dielectric strength of the medium.
- Air Blasting: Using compressed air to replace ionized air with non-ionized air, increasing resistance and extinguishing the arc.
- Increasing Arc Length: Separating the contacts further apart to increase the voltage required to maintain the arc.
- Reducing Arc Cross-Section: Decreasing the contact size to increase the voltage needed for the arc.
- Deflecting the Arc: Using magnetic fields to direct the arc into an arc chute where it cools and extinguishes.
- Splitting the Arc: Dividing the arc into multiple smaller arcs to increase resistance and reduce current.
- Zero Current Quenching: Opening the circuit at the zero-current point in AC systems.
- Charged Capacitor in Parallel: Introducing artificial zero current in DC systems using a capacitor and inductor.
Comparison of AC and DC Circuit Breakers
AC circuit breakers leverage the natural zero-crossing points in AC waveforms to extinguish arcs, as the current fluctuates and crosses zero multiple times per second. In contrast, DC current remains steady, with no natural zero-crossing points, making arc extinction more challenging. DC circuit breakers require additional circuitry to create artificial zero currents, making them more complex than their AC counterparts.
HVDC Circuit Breakers: Specialized Protection
HVDC circuit breakers are specifically designed to handle high voltage DC systems. The absence of natural zero-crossing points in DC systems; means that the arc generated during circuit interruption will not extinguish on its own. Which can be potentially damaging for the breaker and also connected equipment. To address this, HVDC circuit breakers must:
- Create artificial zero-crossing points.
- Dissipate stored energy in the LC circuit.
- Withstand voltage between contacts.
- Prevent arc re-striking.
An LC circuit is often used in parallel with the breaker to generate artificial zero current, ensuring safe circuit interruption.
Applications of HVDC Circuit Breakers
HVDC technology has found diverse applications beyond power transmission, including:
Photovoltaic Plants
Photovoltaic plants convert solar energy into DC electrical energy. These systems often combine multiple strings of photovoltaic panels. To increase voltage and current ratings. Now, Protecting the expensive converters and batteries in these systems is really important. HVDC circuit breakers are used to isolate faulty sections during maintenance or faults.
Electric Traction
DC power is widely used in electric traction systems, such as trains, trams, and trolleybuses, due to the favorable speed-torque characteristics of DC motors. A single conductor supplies current to the vehicle, with the rail acting as the return path. HVDC circuit breakers protect the various loads connected to these systems.
HVDC Power Transmission
HVDC is primarily used for long-distance power transmission. The conversion terminals between DC and AC are expensive and must be protected from fault currents. HVDC circuit breakers are installed to safeguard these terminals and isolate transmission lines for maintenance.
MTDC Grid Systems
Multi-Terminal Direct Current (MTDC) systems offer flexibility and control in power distribution across multiple grids. These systems have multiple circuit branches, each requiring its own HVDC circuit breaker for fault isolation and maintenance.
Conclusion
HVDC circuit breakers play an important role in protecting high-voltage DC systems. These breakers ensure safe and efficient power transmission and distribution. Their design and operation are more complex. If we compare them with AC circuit breakers. This is due to the challenges of arc extinction in DC systems. However, their applications in photovoltaic plants, electric traction, HVDC transmission, and MTDC grids highlight their importance in modern power systems.
Follow Us on Social:
Subscribe our Newsletter to get the latest updates in Electrical Engineering.
HVDC #CircuitBreaker #HVDCBreaker #HighVoltage #PowerGrid #ElectricPower #ElectricalEngineering #EnergyTransmission #GridReliability #PowerSystem #SmartGrid #ElectricalSafety #EngineeringTech #Electricity #SustainableEnergy