Frequency keeping control and round power information

Frequency Keeping Control (FKC) ties the North and South Island frequencies together by modulating the HVDC transfer. 

FKC enables the implementation of national reserves and frequency keeping markets which provides benefit to the electricity market through reduced frequency keeping and reserve costs. Roundpower enables the seamless direction change from north to south HVDC transfer and vice-versa. This also enables reverse reserve sharing in the opposite power direction.

NCC business process for managing FKC when roundpower is disabled

  1. Notification of a change to Roundpower
  • A CAN will be issued advising whenever Roundpower will be disabled and the expected duration.
  • There will be no CAN updating the status of FKC during a Roundpower outage.
  1. Disabling Roundpower
  • Roundpower must be disabled for HVDC live line work or an HVDC pole outage.
  • Disabling Roundpower means no reverse reserve sharing is available through zero and in the opposite power direction.
  1. FKC enabled  (each of FSC, SRS and island-based FK is disabled)
  • FKC is the normal mode of HVDC operation. Enabling FKC allows the following items to be modelled:
    • modelled modulation risk = 30 MW
    • NI MFK band = 15 MW; SI MFK band = 15 MW
    • MFK operating single frequency source
    • SIR reserve sharing enabled.
  1. FKC disabled (each of FSC, SRS and island-based FK is enabled)
  • Disabling FKC results in the following changes:
    • modelled modulation risk = 0 MW
    • NI MFK band = 25 MW; SI MFK band = 25 MW
    • MFK operating with island based frequency sources
    • SIR reserve sharing disabled.
  1. Conditions when FKC will be disabled (while Roundpower is disabled)
  • If scheduled HVDC transfer comes close to the pole minimum, FKC will be disabled.
  • In such case, FKC will be:
    • disabled at any time in the schedule when the scheduled transfer is less than 70 MW
    • re-enabled in the schedule when HVDC transfer reaches a sustained 100 MW threshold.
  1. Business process scenario:
    Making a decision to disable FKC when Roundpower is disabled and HVDC transfers are low
  • FKC status will be modelled as disabled on the HVDC schedule as follows:
    • If in the third trading period from now (where now is, for example, trading period 1) and the HVDC transfer is scheduled to be less than 70MW then FKC will be disabled for a minimum of 2hrs (4 trading periods)
    • Note: If actual HVDC transfer is less than 70 MW in the current and next periods (for example, TP1 and TP 2) then the HVDC transfer will be constrained to 65MW by RTD.

FKC status will be modelled as enabled in the NRSS time frame at the start of a 1hr period (2 trading periods) where the scheduled HVDC transfer is continuously greater than 100 MW.

FKC status will be continually monitored to these criteria any time Roundpower is disabled.




Frequency Keeping


Frequency Keeping Control


Frequency Stabilisation Control


Spinning Reserve Sharing

Modulation risk range

FKC is the normal mode of operation and the Modulation Risk is 30 MW.

​Related information

NMIR Definitions.pdf (PDF 334.94 KB)
NMIR scenarios.xlsx (XLSX 176.82 KB)

SPD formulation and RMT specification