FNN comments on NC HVDC submitted to ENTSO E

Transcription

1 the term HV is not defined > A further definition should be applied since the term is used all through the code A lot of terms from the Network Code RfG are used and should be checked regarding consistency Important definition that are explained in the Explanatory Note document should be part of the Network Code itself Regarding the use of references to other Network Code definitions it might be useful to either define important terms directly in the HVDC Code or create an additional definition paper which applies to all Network Codes. The use of the term maximum output is misleading and needs further explanation. Therefor FNN suggests to use the term "rated power". 1 1 This Network Code establishes common rules for HVDC Systems and DC connected Power Park Modules which are significant according to the provisions of this Network Code. what is a significant grid user? A definition of "significance" in an early stage of the network code development would be useful for the future implementation 3 1 d HVDC Systems embedded within one Control Area and connected to the Distribution Network when a cross border impact is demonstrated by the Relevant TSO, while respecting the provisions of 4(3). The Relevant TSO shall consider the long term development of the Network in this assessment. 3 6 The requirements set forth in this Network Code shall apply to Existing HVDC Systems and Existing DC connected Power Park Modules which are deemed significant according to the provisions of this Network Code. These requirements shall apply in accordance with 62, to the extent this has been decided by the Relevant National Regulatory Authority pursuant to 60 and 61, unless otherwise provided in this Network Code. HVDC Systems embedded within one Control Area and connected to the Distribution Network when a cross border impact is demonstrated by the Relevant TSO, while respecting the provisions of 4(3). The Relevant TSO shall consider the long term development of the Network in this assessment. If this paragraph is not deleted, nearly all requirements have to be changed: throughout the NC, it is always the TSO who gives set points and receives measurements values. This is inacceptable for assets at the DSO s grid. Together with the large power of such an inverter (cross border impact) the respective DSO would lose control of at least a larger part of its grid. The wording should be changed. It should be without any doubt what systems (whether newly installed or not) the Network is applicable for. 7 it is not clearly defined whether the HVDC is allowed to reduce its active or reactive power within the frequency ranges 47,0 47,5 Hz and 51,5 52,0 Hz. A similar requirement compared to 41(7) regarding PPM could be helpful. the defined requirement regarding the 30 min operation time at 47,0 47,5 Hzshould be reconsidered. Obviously the HVDC should stay connected for a wider time period, but we are not sure whether the defined value is appropriate. 7th January 14 1/5

2 8 With regard to the rate of change of Frequency withstand capability, an HVDC System shall be capable of staying connected to the Network and operable at rates of change of Frequency up to a 2.5 Hz/s based on a rolling measurement of Frequency at the Connection Point over a 500 ms window value. With regard to the rate of change of Frequency withstand capability, an HVDC System shall be capable of staying connected to the Network and operable at rates of change of Frequency up to a 2.5 Hz/s based on a rolling measurement (average value) of Frequency at the Connection Point over a 500 ms window value. a better description for measurement would be very useful. 9 1 d.fcr and FRR by static and/or dynamic means. They shall also be capable of allowing Imbalance Netting Power Interchange between the Relevant. FNN strongly recommends to put all used abbreviation's within this Network Code in an extra document which is applicable to this Network Code and to all already drafted Network Codes a The Relevant TSO shall have the right to require that a HVDC System shall be capable of providing synthetic inertia as a quantified response to Frequency changes, activated in low and/or high Frequency regimes by rapidly adjusting the active power injected to or withdrawn from the AC network in order to limit the rate of change of Frequency, while respecting the provisions of 4(3) and 15(8)c) of [NC OS]. Providing further definition or description (e.g.characteristic curves regarding time and quantity) would be helpful 11 Check RfG consistency The use of the term maximum output is misleading and needs further explanation. Therefor FNN suggests to use the term "rated power". 12 (a) The HVDC System shall be capable of adjusting Active Power transmission to the AC Network(s) according to Figure 3 at a Frequency threshold between and including 50.2 Hz and 50.5 Hz with a Droop Shaving a minimum value of 0.1 %. (a) The HVDC System shall be capable of adjusting Active Power transmission at a Converter Station according to Figure 3 at a Frequency threshold between and including 50.2 Hz and 50.5 Hz with a Droop Shaving a minimum value of 0.1 %. Figures 3 and 4 show delta f at the knee point of the graph as an absolute value. This may be obsolete assuming the P axis would be at Zero of the frequency axis. Figures 3 and 4 show the power frequency characteristics at one of the converter stations of a HVDC System. A HVDC System does normally neither contain power generation nor significant energy storage. Therefore, the power exchange needed for frequency control at one station needs to be balanced at other stations connected to the same DC network. The capabilities of an HVDC System to fullfill the requirements of articles 12 and 13 depends on the posilibities to balance power with the connected AC systems. Therefore, s 12 and 13 should distinguish the capabilities of an individual HVDC Station from those of the respective HVDC System. 15 The HVDC System shall be configured such that its loss of Active Power injection in a Synchronous Area, arising out of a transient or permanent fault, shall be limited to a value defined for each LFC Block by the Relevant TSOs, while respecting the provisions of 4(3). Please define LFC. FNN strongly recommends to put all used abbreviation's within this Network Code in an extra document which is applicable to this Network Code and to all already drafted Network Codes (1) refers to the required voltage ranges at the maximum output of the HVDC converter. FNN recommends to substitute "maximum output" by "rated power". All requirements regarding the capability of the HVDC converter shall be related to the rated value. FNN recommends to substitute "nominal value" by "nominal system value" in the tables 4 and 5, because in the respective IEC nominal voltages above 300kV are not defined. 7th January 14 2/5

3 16 1 a Table 4: This table shows the minimum time periods a HVDC System shall be capable of operating for Voltages deviating from the nominal value at the Connection Point(s) without disconnecting from the Network. The Voltage base for pu values below 300 kv. Table 4: This table shows the minimum time periods a HVDC System shall be capable of operating for Voltages deviating from the nominal system value at the Connection Point(s) without disconnecting from the Network. The Voltage base for pu values below 300 kv. FNN recommends to substitute "nominal value" by "nominal system value" in the tables 4 and 5, because in the respective IEC nominal voltages above 300kV are not defined. 19 It does not appear clear, why reactive power capability and reactive power exchange are distinguished in the NC. 19 may be integrated into article 18 because both may be considered contradictory (1) and 20 (3) appear to be contradictory. While 20 (1) describes a strong requirement. 20 (3) makes it relative by the expression UTILISING IST CAPABILITIES. The requirement of 20 (1) can be easily fullfilled by a VSC station, but requires considerably more investment in case of a LCC station. As it is written, LCC stations would be ruled out in many potential applications.a technology neutral approach should be reconsidered or the chosen approach schould be well justified. 21 The Relevant TSO shall assess, while respecting the provisions of 4(3), whether Active Power contribution or Reactive Power contribution shall have priority during low or high Voltage operation and during faults for which faultride through capability is required..within the limits of HVDC capability. editorial 23 1 c figure 6 a justification for the chosen values (e.g. recovery time) could be helpful for further discussion in the upcoming implementation. Right now figure 6 shows the low voltage fault ride through profile. The maximum time Trec of 10 sec appears to be very long from an AC system stability point of view. It should be considered to define a Temporary Overvoltage Curve as well f Consistent with the provisions of 34, undervoltage protection... Consistent with the provisions of 33, undervoltage protection... The cross reference to arcticle 34 should rather point to article 33. editorial 25 2 HVDC Systems with overhead lines shall be capable of auto reclosing for transient faults within the HVDC System. Details of this capability shall be subject to coordination and agreements on protection schemes and settings according to 33 It is proposed to change the title of this article. It is recommended to consider implementing paragraph (1) (Transient faults on HVAC lines) into article 23 The requirements for AUTO RECLOSING are not defined on the DC side. It is proposed ot change the wording of paragraph (2) in a way expressing, that transient faults on the DC line must not cause a permanent trip of the HVDC System. Details of this capability Relevant Network Operator? It is not clear which Network is adressed. FNN suggests to name the AC Network The protection schemes and settings for internal electrical faults shall be designed so as not to jeopardize the performance of the HVDC System in accordance with this Network Code. The protection schemes and settings for internal electrical faults in the HVDC Converter station and cable in line shall be designed so as not to jeopardize the performance of the HVDC System in accordance with this Network Code. 7th January 14 3/5

4 36 2 An HVDC System with Black Start Capability shall be able to energize the remote AC substation to which it is connected from shut down within a timeframe decided by the Relevant TSO(s) while respecting the provisions of 4(3), without any external energy supply. The HVDC System shall be able to synchronise within the Frequency limits defined in 7 and Voltage limits defined by the Relevant TSO or defined by 16, where applicable. Wider Frequency and/or Voltage ranges can be defined by the Relevant TSO where needed in order to restore system security. a further procedure clarificationfor is necessary 38 chapter 3 general comments chapter 3: The close link of Power Park Modules (PPM) and HVDC in "DC connected PPM" should be reconsidered. Not all of the islanded systems (onshore or offshore) may be dedicated nodes for future system expansion, where NC requirements would be relevant. HVDC Systems can be used to connect Power Park Modules to a synchronous AC system in an asynchronous way or they can be used as an embedded system if a parallel AC connection is in place. In the same way, HVDC systems can connect other islanded AC systems. It is recommended to define the interface requirements of all "significant grid users" at their connection point to a "relevant transmission system". A transmission system would be relevant, if its performance has a cross border impact. The requirements of chapter 3 may be applied to nodes of the relevant transmission, not synchronously connected with any synchronous zone today (but may be in the future. The planning for the relevant transmission system should be carried out by the relevant TSO respecting the provisions of 4(3). 38 chapter 3 defines the requirements at theconnection point without defining exactly where that ist. Please check NC RfG art a A DC connected Power Park Module shall be capable of receiving a fast signal from a connection point in the A definition for the term "Fast Signal Response " is needed. Synchronous Area to which. 7th January 14 4/5

5 39 1 b The Remote end HVDC Converter Station Converter Station shall be capable of driving the Network Frequency at the Connection Point. The remote end HVDC Converter Station should have the the wording "shall be capable"needs to be changed into a capability to control voltage and frequency at the technical description. This way the description is misleading. connection point. However, an AC system may be connected to more than one "remote end HVDC Converter Station" and/or other converters, like a PPM. Therefore, it should be defined, how voltage and frequency control are coordinated between all relevant converter stations, including the PPM c The DC Connected Power Park Module(s) and Remoteend HVDC Converter Station(s) with Connection Points in the same synchronously connected Network shall be capable of delivering coordinated Frequency control as defined by the Relevant TSO(s). FNN is interpreting this requirement in that manner that the capability of transferring the Frequency Signal from the HVDC to the PPM shall be possible. Is that correct? Does the same synchronously connected Network include the Offshore AC Island? Please specify a A DC Connected Power Park Module shall be capable of staying connected to the Network and operating within the Frequency ranges and time periods specified by Table 8 Which Network is adressed. Specification needed similar to FNN comments on art. 7. An explanation for the chosen values (especially the longer timescales) would be helpful table 10 4 The HVDC System and DC connected Power Park Module[s] shall have coordinated control The table does not seem to offer a specific additional value. Is it possible to merge both tables? Regarding the chosen values FNN is not sure about what is current practice in existing systems. Please explain "coordinated control" 41 7 DC connected Power Park Module shall be capable of staying connected to the Network and operating without power reduction, as long as Voltage and Frequency remain within the admissible limits pursuant to this Network Code Please clarify that Active Power is being adressed here 7th January 14 5/5