Post on 08-Mar-2019
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 (continued)
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 (continued)
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 (continued) − 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
Technical Considerations
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
Technical Considerations
(continued)
− 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)
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
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
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
− 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 inverter-
driven generators – although demanding
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
− The RPP code at present does not allow for
disabling of reactive current injection by the
System Operator
− Query raised to consider that A3 inverter-
driven generators be exempt from providing
reactive current support and allow selectivity
of reactive current injection for inverter-
driven generators of Category B
− WRT Category C
− LVRT and HVRT is technically feasible for
inverter-driven generators - demanding
Technical Considerations
(continued)
− 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
Technical Considerations
(continued) − 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.
Technical Considerations
(continued) 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
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
− 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?
Technical Considerations
(continued)
− 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
Technical Considerations
(continued)
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
Technical Considerations
(continued)
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
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
Contact Details