The AEMC has published a final determination on the rule change request from Hydro Tasmania in relation to the definition of the limit allowed for temporary power frequency voltages at a connection point.

On 19 January 2012, the AEMC published a final determination on Hydro Tasmania's rule change request. The final determination outlines the Commission's decision to make no rule in respect of the proposed rule change request.

Background

On 5 May 2011, Hydro Tasmania submitted a rule change request in relation to the definition of the limit allowed for temporary power frequency voltages at a connection point.

Voltage surges, commonly referred to as temporary over-voltages (TOV), may be brief in duration but can be extreme in magnitude. For example, they may cause damage to high-voltage equipment and could compromise the security of the national electricity system.

The National Electricity Rules outline the TOV limits with reference to the normal voltage at a connection point. These limits range from 10% to 30% above the level of the normal voltage.

The principal means by which Network Service Providers (NSPs) can minimise the probability of voltage surges exceeding TOV limits is through the provision of constraint advice to the Australian Energy Market Operator (AEMO) to limit the power flow on transmission lines at connection points. Under low fault level conditions, a disconnection of the line with high power flow can cause a sudden surge in voltage.

An increase in normal voltage would increase TOV limits and allow for greater power flow on transmission lines. However, this increase in normal voltage would require participants to invest in more expensive high-voltage equipment with higher capability design ratings in accordance with the minimum access standards.

To address this problem, Hydro Tasmania proposes to:

• Separate the regulation of TOV limits from the level of normal voltage; and
• Set a reference voltage from which TOV limits can be determined while maintaining normal voltage at its current level.
• On 19 January 2012, the AEMC published a final determination on Hydro Tasmania's rule change request. The final determination outlines the Commission's decision to make no rule in respect of the proposed rule change request.
• All enquiries in relation to this project should be addressed to Sebastien Henry on (02) 8296 7800 or sebastien.henry@aemc.gov.au .