PSC recently helped a transmission system operator gain critical insight about the impact of planned underground cable reinforcements in an urban region on the risk of temporary overvoltages in the network, while improving their electromagnetic transient (EMT) models.

Challenge

Continued interest in large commercial demand connections in and around the client’s network has created a need to reinforce the transmission system. Due to the urban nature of the locations where development is required it is likely that any circuit reinforcements will be underground cable. Introducing long lengths of AC cable at HV and EHV can cause harmonic distortion issues and temporary overvoltages (TOV).

The client wanted to understand the impact that planned developments around the region would have on the risk of TOV. To do this, the client sought simulation practices that considered the influence of variable network characteristics on harmonic distortion and TOV studies – but first, they wanted to confirm that their Electromagnetic Transient (EMT) simulation approach was consistent with industry best practice.

Solution

PSC developed an updated EMTP-ATP system model for the client network focusing on the region and taking into consideration planned reinforcements. Frequency dependent characteristics of equipment and transformer core saturation models were included based on industry best practice.  To investigate the sensitivity of results to network parameters PSC developed several automation tools to carry out frequency and time domain studies that covered different network parameters and modelling approaches including:

• Impact of load models and load composition
• Impact of modelling detail for the distribution network
• Impact of changing generation patterns and system reinforcement plans

Results

The results showed that the planned developments around the region in question had minimal impact on the risk of TOV.  PSC was also able to advise the transmission operator on the critical aspects to consider in their EMT models based on the relative sensitivity of results.