Compliance of Solar PV Installation with the New Renewables SA Grid Code Jimmy Goulding, Electrical Technologist, Aurecon, South Africa
Content Introduction Overview of Categories for Grid Connection of Renewable Power Generation Technical Considerations Current Legal Requirement and Exemption Process Conclusions
Introduction The primary objective of the recently released Grid Connection Code for Renewable Power Plants (RPP s) grid connection code is: To specify minimum technical and design grid connection requirements for Renewable Power Plants (RPPs) connected to or seeking connection to the South African electricity transmission system (TS) or distribution system (DS).
Introduction A summary of the those technical requirements as stipulated in the this code is relevant to all forms of renewable power If any specific requirements are relevant to PV only this is identified The technical requirements identified need to be noted by the developers and manufacturers for design purposes There is a process for application for exemption from requirements which needs to be followed
Introduction This presentation simply identifies selected technical requirements in the RPP code that are considered to be the most challenging and hence need careful consideration This latest version of the RPP Connection Code is a document that the System Operator will gladly discuss and debate specific queries
Categories for Grid Connection of RPP Generation There are three Categories which are derived from the voltage connection level and proposed installed capacity: Category A: Small or Micro Turbines connected to LV levels having a size of less than 1MVA. (LV voltages up to and including 1kV)
Categories for Grid Connection of RPP Generation Category A is further split into three sub categories: Category A1: 0-13,8kVA Category A2: 13,8-100kVA Category A3: 100 1MVA Category B: 1MVA-20MVA and generators less than 1MVA connected to the MV System. (MV - 1kV up to and including 33kV) Category C: 20MVA or higher
Looking at those technical requirements that need to be noted by the developers: Section 5.1 - Tolerance of Frequency and Voltage Deviations Normal Operating Conditions Voltage Ranges - ensure compliance as specified, however this is not in line with NRS 048-2 and the SA Transmission Network Code Amendment to the voltage ranges has been requested
Frequency Ranges - ensure compliance as specified These frequency operating ranges are in line with International practice Section 5.2 - Tolerance of Frequency and Voltage Deviations Abnormal Operating Conditions Clause 1 Phase jump ride through at the point of connection (POC)
Network faults, specifically short circuit type) can cause phase jumps larger than the 40 phase jump specified in the RPP code Does this mean disconnection of the generators if above 40 phase shift even within the Low Voltage Ride Through limits? This question has been raised and consideration is being given to limit this requirement between the normal operating voltage range only as specified in the RPP code
Section 5.2.1 - Tolerance to Sudden Voltage Drops and Peaks Abnormal Operating Conditions The Low Voltage and High Voltage Ride Through (LVRT and HVRT) requirements are illustrated in the RPP code for all categories at the point of connection (POC) Category A1 and A2, LVRT only at present is questionable - present proposed penetration levels of RPP into the South African Grid are extremely low
Due to these generators connection at LV levels impact of localised voltage dips due to faults on the network would generally not lead to disconnection of these small plants Even in the case that they do disconnect the impact to the security of SA Grid would not be compromised This requirement for the Category A1 and A2 has been queried either to drop it or postpone until higher penetration levels RPP are reached in South Africa
LVRT and HVRT requirements for categories A3, B and C are defined at the point of connection (POC) Besides staying connected in these defined voltage limits there is a requirement for these RPP s to deliver reactive current in the case that the voltage is outside the normal operating band WRT A3 and B LVRT is technically feasible for inverterdriven generators although demanding
HVRT requirement is of concern for many inverters due to well defined maximum voltage limits Due to the same reasons as mentioned in Category A1 and A2, the low penetration levels of RPP, these voltage increases of short duration would not be expected over the whole system Hence, query raised to consider postponement of this requirement until penetration levels are higher
WRT reactive current support for A3 and C generators benefit is questionable what is the advantage since this is typically to support voltage dips in a system with a large penetration of inverter-driven generators? Low voltage support at MV and LV levels where the electrical protection generally non directional and the fault levels low- tripping selectivity is difficult and incorrect tripping can result Hence system stability can be compromised
The RPP code at present does not allow for disabling of reactive current injection by the System Operator Query raised to consider that A3 inverterdriven generators be exempt from providing reactive current support and allow selectivity of reactive current injection for inverterdriven generators of Category B WRT Category C LVRT and HVRT is technically feasible for inverter-driven generators - demanding
WRT reactive current support for these generators the requirement is supported, however, this support requires fast control The RPP Code defines that this support should be at the point of common coupling (PCC) within specific time intervals would require fast control this may be challenging when considering a large amount of central inverters and communication to and from these
Query raised that this control requirement be at the individual inverters on the LV Terminals instead of at the PCC, with a slightly relaxed settling times Query raised that incremental reactive current limits be used instead of limiting total current and if the reactive current definition at the POC was to remain it would require that the absolute value of voltage should be replaced by a voltage change - both these as shown on the characteristic the RPP code.
Section 6 Frequency Response WRT Category A Requirement is for power curtailment for over frequency conditions - in line with international standards and most PV inverter manufacturers should be able to adjust their equipment to meet the SA requirements WRT Category B and C Requirements are for primary frequency control for over and underfrequency conditions as shown in the RPP code
WRT Category B and C Requirements are for primary frequency control for over and underfrequency conditions as shown in the RPP code This functionality is only required if a specific agreement is made with the System Operator for this capability Internationally this requirement is generally not required from RPP s
This frequency support functionality is assumed to be required during emergency conditions Hence, a query was made again addressing the case that the RPP s initial penetration into the grid is of such a low amount, how much influence would these utilities have under these conditions?
A query also made that perhaps category B and C generators should have the same requirements high frequency response as Category A as a mandatory requirement A query also made that Category B and C generators need only consider the other frequency requirements if a specific agreement with the System Operator was desired
Section 7 Reactive Power Capability Generally speaking, these requirements are in line with international standards Suggestions made that Category A1 and A2 generators should operate at unity power factor with a tolerance band specified and A3 generators operating in the range of 0.95 leading/lagging power factor
Section 8 Reactive Power and Voltage Control These requirements are clear and concise Dynamic control requirements not specific Suggestion made that a clear statement on the dynamic controller requirements for the use and application of Mechanically Switched Capacitors and Reactors (MSC s and MSR s) to comply with the reactive power requirements needs to be made
Conclusions Development of this RPP code in a short time so as to accommodate the intended RPP s connection into the SA Grid - therefore there will be amendments to bring requirements not in line with international requirements into line without compromising the security of the existing system Static and Dynamic Studies by developers and manufacturers are essential to ensure correct design and engineering There are other requirements not mentioned here, however these covered are the ones providing the most concern at present.
Current Legal Requirement and Exemption Process The question was posed to the System Operator and NERSA with regards to the requirements until the revised version is published The existing version 2.6 is the current legal document Hence, if there is a compliance issue of a temporary nature manufacturers / developers will need to apply for temporary exemptions The same applies for permanent non compliance application for this will need to be made
Contact Details For any additional information, please do not hesitate to contact Jimmy Goulding: Email:.jimmy.goulding@aurecongroup.com Phone: +27 21 526 6996 Aurecon SA (Pty) Ltd Thank you