Division C Limited frequency sensitive mode underfrequency

In addition to the requirements of Article 11, the following shall apply with regard to limited frequency sensitive mode — underfrequency (LFSM-U):

1. (a)

   the HVDC system shall be capable of adjusting active power frequency response to the AC network or networks, during both import and export, according to Figure 4 at a frequency threshold f2 between and including F149.8 Hz and F249.5 Hz with a droop S4 adjustable from F30.1 % upwards;

2. (b)

   in the LFSM-U mode the HVDC system shall be capable of adjusting active power up to its maximum HVDC active power transmission capacity;

3. (c)

   the active power frequency response shall be activated as fast as inherently technically feasible, with an initial delay and time for full activation determined by the relevant TSO and notified to regulatory authority in accordance with the applicable F4... regulatory framework;

4. (d)

   the HVDC system shall be capable of stable operation during LFSM-U operation. When LFSM-U is active, hierarchy of control functions shall be organised in accordance with Article 35.

The frequency threshold and droop settings referred to in point (a) of paragraph 1 shall be determined by the relevant TSO and be notified to the regulatory authority in accordance with the applicable F5... regulatory framework.

Figure 4: Active power frequency response capability of HVDC systems in LFSM-U. ΔΡ is the change in active power output from the HVDC system, depending on the operation condition a decrease of import power or an increase of export power. f_n is the nominal frequency in the AC network or networks the HVDC system is connected and Δf is the frequency change in the AC network or networks the HVDC is connected. At underfrequencies where f is below f₂, the HVDC system has to increase active power output according to the droop s₄ .