GRID CONNECTION CODE FOR RENEWABLE POWER PLANTS (RPPs) CONNECTED TO THE
ELECTRICITY TRANSMISSION SYSTEM (TS) OR THE DISTRIBUTION SYSTEM (DS) IN SOUTH
AFRICA
Target Mchunu and Themba Khoza
Eskom Transmission Division, System Operator
Grid Code Management
2013-10-14 22013-10-14
Presentation Outline
1. Need for Grid Code Requirements
2. Grid Code Objectives
3. Technical aspects regulated by the RE grid code
4. Monitoring and control
5. Conclusion
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Example, the challenge of frequency control
Why Grid Code Requirements?
Need for RPP Code -distribution
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1. Main issue: going from one way to two way power flow
2. Similar type of standards –different aims:
• Maintain local stability –Voltage as main issue
• Ensure power is provided (when needed) in a stable,
reliable manner –Reactive and active power
Legislation Basis for the Grid Code
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• Electricity Regulations Act calls for NERSA to:
• Issue licenses to:
• operate any generation, transmission or
distribution facility;
• import or export of electricity;
• trading of electricity.
• Develop and enforce as license conditions:
• Guidelines,
• Regulations and
• Codes.
Grid Code Objectives
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• The Grid Code establishes reciprocal obligations of Electricity
Supply Industry participants regarding:• Connection and use of the distribution and transmission power systems
• Development of the network
• Operation of the Interconnected Power System (IPS)
• It defines minimum technical requirements (i.e. design capabilities)
for:• Network service providers
• Generator proponents
• Load customers
• It ensures:• Non-discriminatory access to the IPS by both generators and loads
customers
• Adherence to minimum technical requirements
• System integrity & adequate service delivery
• Defined accountabilities
• Information availability where it’s needed
Scope: what is regulated by the codes?
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• Connection process, for example: •Issuing of connection quotes by service providers
•Minimum connection network redundancy and related charges
•Agreements to be put in place between network service providers and
generators (e.g. connection, operating, Use of System, Ancillary Services etc.) ]
•Design requirements (for both generators and network service providers)
•Codes specify mandatory minimum requirements (e.g. unit islanding,
protection, voltage control, frequency control, fault ride through, metering
installations etc. )
•There are also negotiable requirements, these are contracted on a need basis
•Operations and maintenance coordination by the System Operator
•Participants are required to cooperate with SO in this process
•Dispatch of generation and demand side resources in line with the rules
•Information exchange between participants
•Tariffs of the network service providers (Transmission and Distribution)
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RE Technologies Regulated by the Code
PhotovoltaicConcentrated Solar Power
Small Hydro
Biomass
Biogas
Landfill gas
Wind Energy Facility
Categories of RE Facilities
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Sub-Categories Power Range V Connection
A1 0 < x ≤ 13.8kVA LV
A2 13.8kVA < x < 100kVA LV
A3 100kVA ≤ x < 1MVA LV
B 1MVA ≤ x < 20MVA MV & HV
C ≥20MVA HV
Applicability of Grid Code requirements depends on these categories
(i.e. size of the facility and connection voltage)
Steady state performance
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46
47
48
49
50
51
52
0.1 1 10 100 1000
Duration of the incident, Seconds
200ms
Continuous operating range (49.0 Hz to 51.0 Hz)
60
Fre
qu
en
cy
[Hz]
64
MINIMUM OPERATING RANGE FOR RPPs
•Stay within these limits
Sub-Categories Voltage Limits
A1
-15% to +10%A2
A3
B ±10%
C ±10%
Minimum frequency operating range of a RPP (during
a system frequency disturbance Maximum and minimum operating voltages at POC
HV/ MV grid code fault ride through
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2.00.150.0
20.0
Volta
ge (U
) at
PO
C
[p.u
.]
0.2
Time [sec]
0
1.0
0.9
0.9 < Un < 1.1
85%
0.5
0.4
0.3
0.8
0.6
0.7
1.1
Continuous Operating Range
Area A
0.1
Area D1.2
Area B Area C
4.0
• Not to disconnect from network in the event of network faults
• Support with reactive current
• After fault clearance not to extract more inductive reactive power than
prior to fault
• restore active power production to at least 90% upon clearance of fault
Active power control / frequency support
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• Network operator will temporarily limit or disconnect the
RPP if there is risk of;
oUnsafe system operation
oBottlenecks or congestion
oUnintentional islanding
oStatic or dynamic grid instability
o Instability due to frequency increase
RPP Code provides: Frequency control for primary and secondary frequency control, plus over frequency control
50.0049.0048.0047.00
51.00 52.00
Active power
Pavailable
Frequency [Hz]
0
f1 f5
PDelta
Dead band
Control band
f2 f3 f4
Pmin
f6
fmin
fmax
Droop 2
Droop 1
Reactive Power and Voltage Control Functions
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• System generating plants to provide static grid support, i.e.
voltage stability, through reactive power
–Cos (φ) = 0.975 underexcited to 0.975 overexcited (Cat B)
–Cos (φ) = 0.95 underexcited to 0.95 overexcited (Cat C)
MVar and Pf control Voltage control
Active power
Reactive power
Operating point
Power factor control Q control
Inductive
Q-import
Capacitive
Q-export
Voltage
Reactive power
Operating point
Inductive
Q-import
Capacitive
Q-export
Qmin Qmax
Umax
Umin
Droop 2
Droop 1
Monitoring and control
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• Communication is key to smart grid
- SO/ DSO communication
- DSO/ customer
• As a minimum RPP Code often ask for:
- Power production at point of connection
• P and Q
• Voltage
• Frequency
• Transformer tap position
- Plant Status
• Out for maintenance
• Out for high wind/fault etc.
- Meteorological Information
• Current, past and (possibly) future (forecasts)
Enforcement and compliance monitoring
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• Participants are ultimately responsible to ensure that their RE
facilities comply with all applicable codes
• “black box” principle applies whereby compliance is tested at the
connection point
• Enforcement :
• Enforced by NERSA through licenses
• Alternatively through agreements between parties
• Parties must demonstrate compliance to applicable code
requirements prior to connection or commercial operation
• Submission of information required as per Information Exchange
Code
• Compliance monitoring:
• This is mainly NERSA’s responsibility. However. there is an
implied compliance monitoring role by other participants especially
the System Operator
Conclusions
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• RE code sets out technical framework for integrating renewable
energy into the electricity grid
• This ensures industry standardisation, network integrity and non-
discriminatory access to the grid (transmission or distribution)
• Intermittence nature of renewables brings about a different challenge
to the power system.
• RE code is limited to technical aspects and does not regulate power
purchase agreements (PPAs)
• Areas currently under development:
• RE Forecasting, RE aggregation, Compliance testing and monitoring,
energy banking etc.
• Approved versions of the grid codes are available from
www.nersa.org.za
Thank you