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ANNEX IIU.K. Requirements applying to frequency sensitive mode, limited frequency sensitive mode overfrequency and limited frequency sensitive mode underfrequency
A.Frequency sensitive modeU.K.
1.When operating in frequency sensitive mode (FSM):U.K.
the HVDC system shall be capable of responding to frequency deviations in each connected AC network by adjusting the active power transmission as indicated in Figure 1 and in accordance with the parameters specified by each TSO within the ranges shown in Table 2. This specification shall be subject to notification to the regulatory authority. The modalities of that notification shall be determined in accordance with the applicable national regulatory framework;
the adjustment of active power frequency response shall be limited by the minimum HVDC active power transmission capacity and maximum HVDC active power transmission capacity of the HVDC system (in each direction);
Figure 1: Active power frequency response capability of an HVDC system in FSM illustrating the case of zero deadband and insensitivity with a positive active power setpoint (import mode). ΔΡ is the change in active power output from the HVDC system. fn is the target frequency in the AC network where the FSM service is provided and Δf is the frequency deviation in the AC network where the FSM service is provided.
| Parameters | Ranges |
|---|---|
| Frequency response deadband | 0-±500 mHz |
| Droop s 1 (upward regulation) | Minimum 0,1 % |
| Droop s 2 (downward regulation) | Minimum 0,1 % |
| Frequency response insensitivity | Maximum 30 mHz |
Table 2: Parameters for active power frequency response in FSM
the HVDC system shall be capable, following an instruction from the relevant TSO, of adjusting the droops for upward and downward regulation, the frequency response deadband and the operational range of variation within the active power range available for FSM, set out in Figure 1 and more generally within the limits set by points (a) and (b). These values shall be subject to notification to the regulatory authority. The modalities of that notification shall be determined in accordance with the applicable national regulatory framework;
as a result of a frequency step change, the HVDC system shall be capable of adjusting active power to the active power frequency response defined in Figure 1, in such a way that the response is:
as fast as inherently technically feasible; and
at or above the solid line according to Figure 2 in accordance with the parameters specified by each relevant TSO within the ranges according to Table 3:
the HVDC system shall be able to adjust active power output ΔΡ up to the limit of the active power range requested by the relevant TSO in accordance with the times t1 and t2 according to the ranges in Table 3, where t1 is the initial delay and t2 is the time for full activation. The values of t1 and t2 shall be specified by the relevant TSO, subject to notification to the regulatory authority. The modalities of that notification shall be determined in accordance with the applicable national regulatory framework;
if the initial delay of activation is greater than 0,5 second, the HVDC system owner shall reasonably justify it to the relevant TSO.
Figure 2: Active power frequency response capability of an HVDC system. ΔΡ is the change in active power triggered by the step change in frequency.
| Parameters | Time |
|---|---|
| Maximum admissible initial delay t 1 | 0,5 seconds |
| Maximum admissible time for full activation t 2, unless longer activation times are specified by the relevant TSO | 30 seconds |
Table 3: Parameters for full activation of active power frequency response resulting from frequency step change.
for HVDC systems linking various control areas or synchronous areas, in frequency sensitive mode operation the HVDC system shall be capable of adjusting full active power frequency response at any time and for a continuous time period;
as long as a frequency deviation continues active power control shall not have any adverse impact on the active power frequency response.
B.Limited frequency sensitive mode overfrequencyU.K.
In addition to the requirements of Article 11 the following shall apply with regard to limited frequency sensitive mode — overfrequency (LFSM-O):
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 3 at a frequency threshold f 1 between and including 50,2 Hz and 50,5 Hz with a droop S3 adjustable from 0,1 % upwards;
the HVDC system shall be capable of adjusting active power down to its minimum HVDC active power transmission capacity;
the HVDC system shall be capable of adjusting active power frequency response as fast as inherently technically feasible, with an initial delay and time for full activation determined by the relevant TSO and notified to the regulatory authority in accordance with the applicable national regulatory framework;
the HVDC system shall be capable of stable operation during LFSM-O operation. When LFSM-O 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 national regulatory framework.
Figure 3: Active power frequency response capability of HVDC systems in LFSM-O. ΔΡ is the change in active power output from the HVDC system and, depending on the operational conditions, either a decrease of import power or an increase of export power. f n is the nominal frequency of the AC network or networks the HVDC system is connected to and Δf is the frequency change in the AC network or networks the HVDC is connected to. At overfrequencies where f is above f 1 the HVDC system shall reduce active power according to the droop setting.
C.Limited frequency sensitive mode underfrequencyU.K.
In addition to the requirements of Article 11, the following shall apply with regard to limited frequency sensitive mode — underfrequency (LFSM-U):
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 49,8 Hz and 49,5 Hz with a droop S4 adjustable from 0,1 % upwards;
in the LFSM-U mode the HVDC system shall be capable of adjusting active power up to its maximum HVDC active power transmission capacity;
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 national regulatory framework;
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 national 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. fn 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 .