The Problem in Detail
Enspec were asked to provide a 2.5MVAr shunt reactor to an offshore Wind Farm project in Scotland. As part of this Enspec were also contracted to carry out the TRV study to ensure the planned circuit breaker was sufficiently rated to switch the reactor and to interrupt likely fault currents. This assessment was done in-line with the IEC 62271-100 standard.
Finding the Solution
Enspec liaised with the customer and key equipment suppliers to obtain all of the required site data. This was then used to build a representative model in PSCAD. A detailed model of the Wind Farm and surrounding network was built including an accurate representation of stray capacitances typically caused by transformers, voltage transformers, circuit breakers and disconnectors.
Making it all Work
The built model was used to carry out a validation and ensure the model provided fault currents in-line with those provided in the Long Term Development Statement (LTDS) for the network area. Then the model was used to investigate the Transient Recovery Voltage and Rate of Rise Recovery Voltage (RRRV) when the shunt reactor was de-energised and when single-phase and three-phase faults occurred.
What that means for the project now
The study revealed that the TRV values slightly exceeded the breaker ratings for some switching and fault scenarios. Even though the fault scenarios were assumed to be unlikely it was important to ensure the breaker was sufficiently rated so re-strikes and re-ignitions could not occur. Enspec were contracted to design and supply an appropriately design RC snubber which ensured this was the case.