Rating Application Levels

The rating application levels applied by AEMO are defined below.

3.1 NORM

A continuous rating value. The NORM value is applied under pre-contingent conditions. This applies to security analysis and constraint equation application. This alarm level is used in monitoring and control of actual power flow through equipment without considering contingent events. For transformers the rating applied to this alarm level may be a fixed constant rating or the peak value of a continuous cyclic rating where the cyclic rating is comparable to the equipment loading profile.

Any continuous ratings provided for this purpose will be assumed valid by AEMO unless otherwise advised by NSP control room staff.

3.2 EMER

A rating value to be applied for a sustained period in emergency conditions. The EMER value is applied under post-contingent conditions. This applies to security analysis and constraint equation application. This alarm level is used in monitoring and control of actual power flow through equipment following the occurrence of a contingent event. For transformers the rating applied to this alarm level may be a fixed constant rating or the peak value of an 'emergency use' cyclic rating where the cyclic rating is comparable to the equipment loading profile.

The Emergency rating is subject to the NSP's assessment of the impact of the prevailing operating conditions and known ambient weather conditions at the time. When requested, the TNSP will assess the amount of EMER rating that is available for use in emergency conditions.

The same rating value as used for the NORM level of alarm will be used in this place if no value is supplied by a NSP.

3.3 LDSH

A short time rating. The LDSH value is applied under post-contingent conditions. The LDSH limit applies to security analysis and selected constraint equation application. This alarm level is used in monitoring and control of actual power flow through equipment following the occurrence of a contingent event.

Any short time ratings provided for this purpose will be assumed valid by AEMO unless otherwise advised by NSP control room staff.

The same rating value as used for the EMER level of alarm will be used in this place if no value is supplied by a NSP.

• Transmission Line or Cable Definition A short time transmission line or cable rating. The minimum time applicable is 15 minutes. A time greater than 15 minutes for lines or cables may be provided by an NSP however this nominated time must be consistent within the NSP boundary.
  Note that a NSP may supply shorter time based rating values to be applied in specific agreed circumstances such as those included in contingency plans. Time based values of less than 15 minutes will be dealt with independently and will not be entered into the ESCA LDSH data fields for routine application.
• Transformer Definition:
  A short time transformer rating. Nominal time applicable is 2 hours. For distribution transformers times other than 2 hours may be provided by a NSP however this nominated time should be consistent within the NSP boundary. For main grid tie transformers times other than 2 hours may be provided by a NSP on a case by case basis as required for routine operational purposes.