220kV voltage class internal and external bridging line black-start system and method for hydropower station without high plant transformer

The invention discloses a 220kV voltage class internal and external bridging line high-plant-transformer-free hydropower station black-start system. The system comprises a first hydro-generator, a first 10kV circuit breaker, a first 10kV isolation knife switch, a first three-winding transformer, a first 220kV isolation knife switch, a second 220kV isolation knife switch, a first 220kV circuit breaker, a third 220kV isolation knife switch, a fourth 220kV isolation knife switch, a first 220kV line, a first 6kV switch and a first 6kV bus. According to the system, a first hydro-generator utilizesa speed regulator oil pressure system to store energy, guide vanes are opened and adjusted to rated speed, an excitation system is operated to build voltage at a generator end to rated voltage, a superior transformer substation is assisted to recover power supply, normal operation of a power grid load is guaranteed, and power failure loss is reduced; the system is not provided with a special high-voltage station transform