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