The demand for energy is expected to double in the next 20 years. Alternative and renewable energy sources are helping meet that increasing energy appetite, with wind power already a critical part of the equation.
Protecting generator circuits
Wind turbine generators require a unique circuit breaker that can handle high continuous alternating current (ac) and voltage, and then safely switch through extreme out-of-phase voltages and high-stress asymmetrical currents for reliable and robust power generation. Located at the base of the tower, generator breakers must be capable of high continuous current levels without overheating.
Eaton designed the VCPW-G family of generator circuit breakers for utility-scale wind, hydropower, and smart-grid applications. Because generator circuits have unique characteristics, they require specially designed and tested circuit breakers. The Institute of Electrical and Electronics Engineers (IEEE) developed a special industry standard, C37.013 and C37.013a-2007, to address these rigorous service duty requirements.
Unique fault-current conditions
The transformer and generator can be in close proximity to the circuit breaker. Applications with high continuous-current levels require connections with large conductors of low impedance. This construction causes unique fault current and voltage conditions.
System-source or transformer-fed faults can be extremely high. The full energy of the power system feeds the fault and the low impedance of the fault current path does little to limit the fault current. Circuit breakers that have demonstrated high interruption ratings (up to 75 kA) with high direct current (dc) fault content up to 75% are ideal for interrupting such high fault currents.
Furthermore, generator-source faults can cause “delayed current zero,” a severe fault condition. The high ratio of inductive reactance to resistance (X/R ratio) of the system can cause the dc component of the fault to exceed 100%. The asymmetrical fault-current peak becomes high enough and its decay becomes slow enough that the natural current zero is delayed for several cycles. The circuit breaker experiences longer arcing time and more electrical, thermal, and mechanical stress during interruption. The IEEE standard requires verification that the breaker can interrupt under these severe conditions.
Voltage condition requirements
Generator circuits typically produce fast rates of rise of recovery voltage (RRRV) due to the high natural frequency and low impedance and low stray capacitance. These circuits should use breakers designed to interrupt fault-current levels with fast RRRV in accordance with C37.013 and C37013a.Additionally, generator circuit breakers should have a distinct ability to perform in out-of-phase conditions when the generator and power-system voltages are not in sync. The voltages across the open contacts can be as high as twice the system’s rated line-to-ground voltage. The IEEE standard requires demonstration by test that the generator circuit breaker can switch under specified out-of-phase conditions.
The VCPW-G vacuum breaker is designed for generator circuits so it provides superior performance and versatility. These circuit breakers are capable of interrupting large short-circuit currents to increase reliability in the nacelle’s control systems and equipment at the base of the turbine tower. WPE