Amendment no. 3
Protection Design Instruction
Protection of
embedded
generation systems
IMPORTANT DISCLAIMER
As the information contained in this publication is subject to change from time
to time, Endeavour Energy gives no warranty that the information is correct or
complete or is a definitive statement of procedures. Endeavour Energy
reserves the right to vary the content of this publication as and when required.
You should make independent inquiries to satisfy yourself as to correctness
and currency of the content. Endeavour Energy expressly disclaims all and
any liability to any persons whatsoever in respect of anything done or not
done by any such person in reliance, whether in whole or in part, on this
document.
Document no. PDI 5000
Amendment no. 3
51 Huntingwood Drive, Huntingwood NSW 2148
Postal address: PO Box 6366 Blacktown NSW 2148
Phone: 131 081 Fax: (02) 9853 6000
Copyright © Endeavour Energy 2011
PROTECTION DESIGN INSTRUCTION
TRANSMISSION ENGINEERING
PDI 5000
Document no.
Amendment no.
Approved by
Approval date
PDI 5000
3
MTEB
19 August 2010
Protection of embedded generation systems
Contents
1.0
PURPOSE......................................................................................................................4
2.0
SCOPE...........................................................................................................................4
3.0
REFERENCES...............................................................................................................4
4.0
DEFINITIONS AND ABBREVIATIONS .........................................................................4
5.0
ACTIONS .......................................................................................................................5
5.1 Operations ....................................................................................................................6
5.1.1 Operational requirements..............................................................................................6
5.1.1.1. Parallel operation..................................................................................................6
5.1.1.2
Non-parallel operation ........................................................................................6
5.1.1.3 Standby operation (occasional parallel operation)................................................7
5.1.2 Generator control ..........................................................................................................7
5.1.2.1 Synchronising .......................................................................................................7
5.1.2.2 Frequency and load control ..................................................................................8
5.1.2.3 Power system frequency variation........................................................................8
5.1.2.4 Voltage and reactive power control ......................................................................8
5.1.2.5 Voltage control on distribution systems ................................................................8
5.1.3
Islanding ......................................................................................................................8
5.1.4 System earthing ............................................................................................................9
5.1.4.1 HV system earthing ..............................................................................................9
5.1.4.2 LV system earthing .............................................................................................10
5.1.5 Operation of unearthed systems (loss of mains) ..........................................................10
5.1.5.1 Neutral voltage displacement (NVD) ..................................................................10
5.1.5.2 Reverse power or directional protection .............................................................11
5.1.5.3
Inter-trip from feeder circuit breaker (CB) .........................................................11
5.1.6 General technical requirements....................................................................................11
5.1.6.1 Generator technical data ....................................................................................11
5.1.6.2 Fault levels..........................................................................................................11
5.1.6.3 Stability ...............................................................................................................12
5.1.7 Connection security standards .....................................................................................12
5.1.8 Fault clearance times ....................................................................................................12
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Protection of embedded generation systems
Amendment no.3
5.1.9 Protection requirements ..............................................................................................13
5.1.9.1 Internal protection ...............................................................................................14
5.1.9.2 External or interconnection protection ................................................................14
5.1.10 Auto-reclose ................................................................................................................15
5.1.10.1 Generator reclose...............................................................................................15
5.1.10.2 Network auto-reclose .......................................................................................15
5.1.11 Installation maintenance.............................................................................................15
5.1.12 Remote monitoring and control ..................................................................................16
6.0
AUTHORITIES AND RESPONSIBILITIES..................................................................17
7.0
DOCUMENT CONTROL..............................................................................................17
ANNEXURE A1......................................................................................................................18
ANNEXURE A2......................................................................................................................20
ANNEXURE A3......................................................................................................................21
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Protection of embedded generation systems
1.0
Amendment no.3
PURPOSE
To describe the minimum electrical protection and control requirements for privately owned
generation intended to operate in parallel with the Endeavour Energy’s electrical distribution
or transmission network.
2.0
SCOPE
This instruction outlines the technical issues regarding electrical protection at the connection
of embedded generation in the transmission or distribution network, where operation in
parallel with the network is required. It also deals with privately owned generators within a
customer’s network that are directly connected to, and able to run in parallel with, any part of
Endeavour Energy’s network.
3.0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
4.0
REFERENCES
Company Policy 9.2.2 0 Network Protection
ENA National Electricity Network Safety Code (NENS 01-2008)
Integral Energy Network Management Plan 2009-2014
AS/NZ 61000.2.12:2003 Electromagnetic Compatibility (EMC)
AS/NZS 3000:2000 Wiring Rules
Coal Mines Regulation (Electrical – Open Cut Mines) 1984 Division 4
IEC 60255 (BS142) Electrical Relays
Network Service Provider General Terms and Conditions or Customer Connection
Contract
Service and Installation Rules of New South Wales
The National Electricity Code
Engineering Technical Report No. 113 Rev 1(1995) Notes of Guidance for the
Protection of Embedded Generating Plant for Operation in Parallel with Distribution
Systems
Customer Guidelines for the Connection of Private Generation to Integral Energy’s
Distribution Network – June 2005
Protection Design Instruction PDI 4000 – Protection definitions, vocabulary and
symbology
PDI 4001 – Protection design principles
Substation Design Instruction SDI 519 – Communications in substations
SDI 538 – Supervisory Control and Data Acquisition (SCADA)
DEFINITIONS AND ABBREVIATIONS
AEMO
Australian Energy Market Operator.
Connection agreement
An agreement between a Network Service Provider (Endeavour Energy) and the customer
(Generation Company) by which the customer (generation plant) is connected to the
transmission or distribution network and/or receives transmission services or distribution
services.
Customer
The proponent of the generating scheme, finally responsible for ownership and operation of
the scheme.
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Embedded generator
A generator that generates electricity and the generating unit is directly connected to the
transmission or distribution system and includes customers with their own generation.
Grid
Endeavour Energy’s network and its connections to the National Electricity Grid.
Islanding
Islanding occurs when a private generator or generating system remains connected to a
portion of the network and continues to supply electricity to that portion of the network, but is
disconnected from the general electrical network or main source of generation.
Network connection point (NCP)
The point of electrical connection between the apparatus owned by the Network Service
Provider (Endeavour Energy) and the apparatus owned by the customer.
NEC
National Electricity Code.
Network Service Provider
A person who engages in the activity of owning, controlling, or operating a transmission or
distribution system and who is registered in that capacity with AEMO under Chapter 2.
Point of common coupling (PCC)
Point on a public power supply network, electrically nearest to a particular load, at which
other loads are, or could be, connected.
Scheduled generating unit (SGU)
Unless otherwise approved by AEMO under the provisions of clause 2.2.3(b), a generating
unit that has a nameplate rating of 30MW or greater, or is part of a group of generating units
connected at a common connection point with a combined nameplate rating of 30MW or
greater, is classified as a scheduled generating unit.
Synchronism
Synchronism occurs when two (2) a.c. voltages are of the same frequency and magnitude,
and have zero phase difference.
5.0
ACTIONS
There must be proper coordination between the protection systems of the customer and
Endeavour Energy’s network in order to ensure safety of the plant and stable operation of the
electrical network. Typical issues are:
• correct protection grading;
• tripping sequences;
• correct reclosing of faulted lines; and
• machine network synchronising.
The primary aim of protection and stability coordination is to ensure that the protection is
designed and set to rapidly clear faults, or restrain from operating when necessary in order to
maintain the security and integrity of the electrical network. Details of the proposed
protection arrangements associated with the embedded generator’s plant must be submitted
to the Network Service Provider (Endeavour Energy) to determine if additional protection is
required in the interests of safe and stable operation of the network.
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Protection of embedded generation systems
5.1
Amendment no.3
Operations
5.1.1 Operational requirements
Three (3) modes of operation will be considered for private generating units, namely:
Parallel operation: Connected continuously to the network, with or without the ability to
export energy to the grid.
Non-parallel operation (break before make operation): Operating in isolation from the
supply network by way of a changeover switch. For this type of installation, suitable
controlling switchgear is required that can be electrically, mechanically or key interlocked.
The major disadvantage of this arrangement is that the customer load must be interrupted
each time there is a changeover from one supply source to the other.
Standby operation (synchronise, close, transfer trip operation - SCTT): This mode of
operation has similar connection arrangements to the non-parallel scheme, except that both
the normal supply and generator supply may be connected for a short time in order to allow
testing of the generator’s operation without interrupting the customer’s load.
Detailed operating arrangements will be negotiated for each case and included in the
operating agreement between the customer and Endeavour Energy. The general operating
requirements for the different connection methods are listed below:
5.1.1.1.
Parallel operation
The generator continuously supplies energy to the grid. Salient points to consider include:
•
•
•
Protection equipment is required to meet the outcomes specified in this Standard.
Appropriate synchronising equipment is required to connect and disconnect the generator
to and from the network.
Engraved all-weather signs are to be placed at all switch points at which the generator
can be isolated from the network, warning of the generator risks at that point.
Any switch at which the generator and the grid can be separated must switch all phases
simultaneously (this is to reduce the risk of transient over-voltages or voltage unbalances
adversely affecting other customers connected to the network).
5.1.1.2
Non-parallel operation
Operating aspects for non-parallel (alternative) operation include:
•
•
•
•
•
•
Inadvertent parallel connection cannot be made under any circumstances.
Interlocks and suitable deliberate time delays are required between the closing and
opening of the change-over circuit breakers.
Provision of a fail-safe design so that one (1) circuit breaker cannot possibly be closed if
the other circuit breaker in the change-over sequence is closed.
Connection is to be made on the load side of metering equipment.
Switchgear to allow manual or automatic changeover should be located on or adjacent to
the switchboard supplying the electrical load.
Where automatic switch-on and connection of the generator system is possible, suitable
warning hazard notices shall be openly displayed at appropriate locations.
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Protection of embedded generation systems
5.1.1.3
Amendment no.3
Standby operation (occasional parallel operation)
This mode of operation has similar connection arrangements to the non-parallel scheme,
with the exception that both the normal supply and generator supply may be connected for a
short time in order to allow testing of the generator’s operation without interrupting the
customer’s load. Typically, the generator is allowed to synchronise with the network before
the network is disconnected so that the generator then supplies only the customer’s load.
Usually, the conditions that apply to this arrangement are:
•
an assurance that the generator shall be used for standby supply only;
•
the generator will run only in parallel with Endeavour Energy’s network when switching
the generator on and off for generator testing purposes; and,
•
the time period for operation in parallel with the network for any circumstance shall be no
longer than 15 seconds.
The 15 seconds time period includes:
synchronising with the electrical network;
closing the generator isolating device to the network at zero power import or export
increasing the generator load to the desired test level; and,
isolation from the network.
The period for reconnection includes:
synchronising the generator with the network;
removing the generator load; and,
disconnecting the generator.
Other aspects of standby opration are:
• The switching scheme must incorporate blocking to ensure that the generator does not
attempt to energise a dead Endeavour Energy connection.
• The installation must be approved before commissioning.
• Switching times must be scheduled with System Operations.
• The transfer process must not adversely affect the quality of the supply to other
customers.
5.1.2 Generator control
5.1.2.1
Synchronising
Automatic synchronising on to the network will be required:
•
•
To connect a generator in parallel with the grid.
To re-connect an isolated system to the network.
Whenever such synchronising is required, in addition to meeting the generator’s own
parameters, the settings shall be such as to maintain the voltages (transient and steady
state) on the network at the point of connection within the normally accepted bounds for the
voltage level concerned. Special conditions may be imposed at certain critical points of the
network, and these will be advised on a case-by-case basis.
The generator shall parallel with the grid without causing a voltage fluctuation at the network
connection point greater than ± 5% of the prevailing voltage level at the NCP.
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Protection of embedded generation systems
5.1.2.2
Amendment no.3
Frequency and load control
The prime mover must be equipped with suitable speed and power controls to allow the plant
to respond rapidly and without overshoot should the system frequency rise or fall, or a
sudden change in load occur.
5.1.2.3
Power system frequency variation
All plant shall operate with a nominal frequency of 50Hz. The main grid frequency may vary
in the range of 49.8 Hz to 50.5 Hz and generators are expected to be able to operate safely
over this range. Continued operation is also expected during system disturbances, when the
frequency may go as low as 47.0 Hz or as high as 52.0 Hz for periods of 10 to 20 cycles.
Safe operation can include controlled shut-down or continued operation under load,
depending on the machine capability.
5.1.2.4
Voltage and reactive power control
Automatic control equipment will be necessary to ensure that the voltage and power factor at
the point of connection are within the limits required by Endeavour Energy’s connection
agreements. In general, the Australian Standards on voltage and disturbance limits (AS
61000 series) apply. The generator must ensure a stable and well-damped response under
all operating conditions within the designed range. Where two (2) or more generators are in
close proximity to each other, appropriate control circuitry is required to ensure that the
possibility of interaction between the machines causing deleterious impacts on the grid are
minimised. The voltage control performance will be assessed on the basis that stable voltage
control must be maintained following the most severe credible single contingency.
5.1.2.5
Voltage control on distribution systems
There is a range of voltage variations that can exist on the network because of load
variations, load rejection, short circuit or open-circuit faults. These may include:
• Voltage dips, typical duration between 0.1 and 1 second [5 – 50 cycles] of random
magnitude and on any one (1) or more phases simultaneously due to fault clearance.
• Voltages may rise above the nominal voltage level on one or more phases under fault
conditions.
• Voltage variations due to tap-changer operations, variation of other customer loads,
sudden load shifts due to switching.
It is the responsibility of the generator operator to ensure the safe operation of the machine,
and that any adverse effects of the generator on the grid are minimised under the conditions
prevailing at the connection point. In particular, the generator operator must:
• be satisfied that the fault clearance times are within the transient stability requirements of
the machine; and,
• ensure that the steady state output of the machine is stable for all expected operating
conditions at the network connection point.
5.1.3
Islanding
Islanding is an occurrence where a generator or generating system, that continues to supply
electricity, is disconnected from the general electrical network. In this state, the embedded
generator is potentially out of synchronisation with the grid. The electrical load being supplied
by the generator may be only for itself or may include some of the Network Service
Provider’s (Endeavour Energy) network.
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Protection of embedded generation systems
Amendment no.3
All reasonable precautions must be taken to prevent the intentional or unintentional islanding
of private generation systems where there is a loss of supply from the network, unless
special provisions have been negotiated within the Customer Connection Agreement.
The generator may continue to supply the customer’s own plant downstream of the network
connection point from local generation, but there must be no connection to the grid.
Other issues to be considered include:
•
Islanding can cause potential quality of supply problems for other customers and the
legal implications of acceptance of risk and liability must be resolved before providing
isolated supply to other customers.
•
Automatic reclosing may be installed on network overhead lines. There could be a
possibility of severe generator equipment damage if the network feeder is reclosed out of
synchronism onto a live generator.
•
Anti-islanding protection must complete its operation in less than five (5) seconds, or less
than half of the feeder reclose time, whichever is the less.
•
The reclose time delay varies for different parts of the network.
•
Faults on the network must be isolated from all sources of supply.
5.1.4 System earthing
Earthing is required to be independent of the network. Satisfactory earthing is required to:
•
•
Prevent electric shock.
Cause protection equipment to operate when required.
All earthing must meet all statutory requirements under all operating conditions.
5.1.4.1
HV system earthing
System grounding (neutral grounding) refers solely to the method of power source grounding
and not to the earthing of metal structures for personal safety. Earthing of the generator
neutral must be coordinated with the network earthing. Network earthing may be solid or
consist of neutral earthing resistors or reactors. The possible earth fault current will depend
on the neutral earthing system used.
Under some fault conditions, it may be possible for a portion of unearthed network to remain
energised with no current flow at phase to ground fault. It is important that the protection
system detects this condition and isolates the generator from the network. This is dealt with
in more detail in section 5.1.5.
If a generator is to continue operating on a network isolated from the grid, all relevant system
and safety earthing criteria must be met, including but not limited to AS 3000.
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Protection of embedded generation systems
5.1.4.2
Amendment no.3
LV system earthing
For LV system neutral earthing, solid earthing principals should apply. If neutral earthing
impedances are used to limit the generator earth fault currents, a generator transformer must
be used to ensure compliance with all statutory and supply authority safety earthing
requirements on the LV system for all operating scenarios.
The neutral busbar must be continuously connected to the source of supply as well as being
locally earthed. At all times, the provisions of the Wiring Rules and the Service and
Installation Rules apply.
5.1.5
Operation of unearthed systems (loss of mains)
The sensitivity of loss of mains protection depends on the relative mismatch between the
generation capacity and the connected load if an islanding situation develops. It is essential
that the generator’s protection equipment isolate the generator before a network reclose
occurs, after a fault has caused the network protection to trip the mains supply. If the ratio of
the generation capacity to the minimum load on the connecting feeder is greater than 70%,
or if other protection such as rate of change of frequency (ROCOF) or vector shift protection
is difficult to set, an inter-trip may be required in addition to the loss of mains protection.
The generator’s operator is responsible for calculating and applying the loss of mains
protection settings. The assumptions used to calculate the settings and the final settings are
to be approved by Endeavour Energy before they are put into service.
Set out below are the commonly accepted methods of addressing the issue of not allowing
embedded generation to supply an unearthed network.
5.1.5.1
Neutral voltage displacement (NVD)
In the case of the interconnecting ungrounded transformer (delta winding on the line side) at
NCP, the voltage on the ungrounded systems will experience a voltage shift under a phase
to earth fault condition and no fault current flows in the isolated unearthed portion of the
network.
One way to detect this condition is to connect a voltage sensing relay (59N) to three (3) VTs
in a broken delta configuration. A 3-phase, 5-limb broken delta voltage transformer is
typically installed on the delta winding side (line side) of the connected step up transformer.
The earthed star point of the VT primary provides a reference point for the neutral and allows
a zero phase sequence voltage to be generated on the broken delta secondary under earth
fault conditions.
During normal conditions, the voltage unbalance will be minimal and the zero sequence
voltage will be minimal. When a phase to ground fault occurs, the faulted phase voltage
collapses and the zero sequence voltage (3V0) across the voltage sensing device increases
to as much as full secondary phase to ground voltage. Primary voltage increases as much as
1.73 x nominal line to ground voltage. Protection Design should consider the following::
•
Faults on adjacent feeder(s) could cause the NVD protection relay to respond and pick
up. Therefore, NVD settings should be graded with other earth-fault protection relays.
•
The NVD relay needs to be set with sufficient time delay in order to allow other feeder’s
protection earth-fault relay(s) to clear their own feeder’s earth-fault first. For example
time delay setting of the NVD relay in the 11kV systems should be greater than 2.0 secs
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Protection of embedded generation systems
Amendment no.3
in order to allow the other earth-fault relay(s) in the neighbouring circuits to clear the
earth-fault.
•
Sustained arcing faults because of the generator supply infeed.
•
Change of reach on nearby distance relays.
•
Earth fault contribution needs to be calculated based on two (2) separate earthing
systems.
•
Impact on other protection relays as a result of the sudden removal of the earth.
5.1.5.2
Reverse power or directional protection
If the agreed maximum generation is at all times less than the total customer load, or there is
no intention to export power onto the grid, reverse power or directional current protection can
be used to detect a loss of mains condition. The criteria for deciding if this is possible are:
•
The export at the NCP has a defined maximum value, and if this value is exceeded, a
loss of mains condition is assumed to have occurred and the generator is separated from
the grid.
•
The export is less than 70% of the expected minimum feeder load, with all other
generation included.
5.1.5.3
Inter-trip from feeder circuit breaker (CB)
An alternative to indirect measurement of loss of mains is to use a direct inter-trip from
Endeavour Energy’s CBs controlling the portion of the network to which the generator is
connected. If stability analysis shows that the fault clearance time could cause instability of
other generators or the network, inter-trip facilities (which ensure stability) will be necessary.
The inter-trip circuit must be supervised automatically, and inhibit generation if the inter-trip is
not available.
5.1.6
General technical requirements
5.1.6.1
Generator technical data
Generator system operating characteristics such as PQ, voltage, ratings, lead and lag limits.
Machine characteristics such as Xd, Xq, _ve and 0 sequence impedances, time constants,
and inertia constant. Machine control characteristics such as droop, AVR, and governor. All
relevant data is required for installation as set out in Annexure A1.
5.1.6.2
Fault levels
Generators in parallel with the network may raise fault levels beyond the fault rating of
existing installed equipment. Calculations may be required of the contribution of the
generation plant to fault levels on the network in order to determine:
• Contribution to fault levels by the generator.
• The impact on neighbouring installations and customers.
• The level of protection required as a result of changed fault levels.
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Protection of embedded generation systems
Amendment no.3
The customer will be responsible for all costs associated with:
• The required system studies.
• Upgrading protection facilities as a result of connection of generation that requires
additional protection equipment at other points in the network.
5.1.6.3
Stability
Synchronous generating units must operate in a stable manner at all times when connected
to the network. Any generator unit connected to the grid should:
•
•
•
Disconnect from the grid for a power system disturbance that causes in unstable
operation.
Provide damping of the system oscillations.
Maintain steady state voltage stability criteria.
Endeavour Energy will provide information on the design criteria and all data related to the
network necessary to carry out the stability and other system studies. The proponent of the
scheme is responsible for the execution of all required system studies. Steady state and
transient stability study should include:
• The impact of embedded generations on the dynamics of a distribution feeder.
• The impact of embedded generations on the dynamic of an entire bulk power system.
• Effects on transient stability.
• Impact on damping.
• Effect on voltage stability.
5.1.7
Connection security standards
All high voltage plants and apparatus shall comply with the relevant Australian Standard.
Plant and apparatus shall be designed, manufactured and tested in accordance with the
quality assurance requirements of Australian Standard AS/NZ ISO 9001.
Each connection between a customer and the network must be controlled by a circuit
breaker and related equipment capable of interrupting the short circuit current at the
network connection point (NCP).
For connection to sub-transmission voltages, the protection system may be required to be
fully duplicated, and operate separate trip coils of each circuit breaker. The provisions of
Endeavour Energy’s Substation Design Instructions and Protection Design Instructions apply
in all cases.
Details of the proposed protection arrangements, along with general technical information of
the proposed generating plant, as mentioned in Annexures A1 and A2, must be submitted
to Endeavour Energy by the customer to determine if additional protection is required in the
interests of safe and stable operation of the network.
.
5.1.8 Fault clearance times
Fault clearance times (from fault inception to circuit breaker arc extinction) can vary
depending on circuit breaker technology, age, and the system characteristics. The fault
clearance times must be adequate to minimise equipment damage. In the case of the 132kV
system, the fault clearance times, set out in the National Electricity Rules (NER) for both
main protection and for breaker fail protection, must be achieved for all connected plants.
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Protection of embedded generation systems
Amendment no.3
If there are transient stability critical clearance time limits imposed by a generator, the cost of
upgrading all protection systems in the affected area is the responsibility of the customer.
5.1.9
Protection requirements
A generator should be automatically disconnected from the power system in response to
abnormal conditions, including:
• Loss of synchronism.
• Sustained high or low frequency outside tolerance limits.
• Voltage excursions beyond defined steady state limits.
• Electrical fault on the network feeder.
• Mechanical faults within the generator.
• Power system disturbance that results in unstable operation.
Normal operations of the network should not cause unnecessary tripping, and protective
devices should not operate in cases of:
• Switching of capacitor banks.
• Faults on remote equipment.
• Load swings (ensure adequate loss of mains protection settings).
• Transformer automatic tap changing.
• Other normal operating contingencies.
The distribution system will usually carry short bursts of high frequency signalling for load
control purposes. This is generally at 1050Hz or 750Hz or 283Hz and can typically have a
magnitude of 2-3% of the system nominal voltage. Under abnormal (system resonance)
conditions it may have excursions to 10% of nominal voltage. The generator protection and
control systems must be able to cope in the presence of these signals.
All protection associated with the generator and its connection to the grid must be designed
with overlapping zones of protection to ensure that any fault is detected and cleared by at
least one protective device.
Circuit breaker failure protection must be provided at the NCP circuit breaker to cover the
circuit breaker failing to operate when required. This circuit breaker failure protection must
be arranged to isolate the generator from the grid to avoid the possibility of out-ofsynchronism operation.
All generation plant connected to the 33kV or above sub-transmission network shall have at
least two (2) schemes of protective equipment installed for each zone of protection. This
includes provision of duplicate trip coils on the circuit breakers. All primary equipment shall
have ratings suitable for the expected duty in the presence of the generation. This includes,
but is not limited to, such things as ensuring adequate circuit breaker class for the system
X/R, insulation coordination and power frequency voltage withstand capability.
The settings of the protection equipment installed on a generating unit should:
•
•
•
•
•
Maximise plant availability.
Protect the grid and other customer plant from damage.
Assist the control of the power system under emergency conditions.
Minimise the risk of inadvertent disconnection.
Promote plant safety and durability.
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Protection of embedded generation systems
5.1.9.1
Amendment no.3
Internal protection
This covers generator and transformer faults as well as any other equipment within the
generating plant. It is the responsibility of the customer to ensure that adequate protection is
installed for their own equipment. Any protection scheme installed downstream of the
network connection point does not need to be graded with Endeavour Energy’s protection
systems, except as required by regulation. The following factors should be considered in the
design of the generator protection schemes:
•
Each generator shall have protection installed that will operate within a minimum time
having regard for network performance, stability and grading requirements.
•
Generator protection must cover permanent and transient faults under all permutations of
phase and ground short-circuit.
•
Each generator must have protection to trip the generator and, where appropriate, shut
down the excitation and the prime mover.
•
The protection should operate for all electrical or mechanical faults within the generator,
transformer and prime mover.
•
Where a number of generators are operating in parallel, each machine should be
equipped with reverse power protection to prevent motoring.
In order to provide adequate protection of the generator, the following protection is
considered as minimum:
• Earth fault
• Overcurrent
• Over/under voltage
• Under/over frequency
• Negative phase sequence
• Reverse power
• Generator and/or transformer differential
• Field failure protection (reverse VAR)
• Pole slip (out of step)
• Transformer protection – winding gas
• Synchronism check
• Circuit breaker fail
5.1.9.2
External or interconnection protection
This includes the protection installed on the circuit breaker that interfaces the customer with
Endeavour Energy’s network and has the potential to impact on power system security. The
protection must operate before any automatic reclose operation can occur.
The protection at the network connection point must grade satisfactorily with Endeavour
Energy’s protection schemes, so that any fault internal to the customer’s plant will be cleared
below or at the network connection point before any Endeavour Energy protection operates.
The grading at the network connection point will be checked by Endeavour Energy and must
be approved in terms of the customer connection process before operation commences.
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Protection of embedded generation systems
Amendment no.3
Protection arrangements and settings will depend on the individual installation and local
requirement. The basic requirements must include the detection of:
• Over and under voltage
• Over and under frequency
• Phase fault
• Earth fault
• Loss of mains
• Battery under voltage
• Circuit breaker fail
The following loss of mains protective functions are considered as typical requirements:
Negative phase sequence (46N)
Neutral voltage displacement (59N)
Rate of change of frequency (81)
Voltage vector surge (96)
Directional overcurrent (67)
Reverse power (46)
Intertrip
5.1.10 Auto-reclose
5.1.10.1
Generator reclose
Generators connected to the 11kV and 22 kV (distribution) networks may use synchronising
facilities to automatically reconnect the generation plant following a system disturbance no
earlier than 60 seconds after the main supply is restored.
Generators connected to the sub-transmission network may be reconnected only with
agreement from Endeavour Energy system operators, or as negotiated in the Connection
Agreement.
Generator reclose is not allowed on to a dead feeder, except where there is an agreement
for islanding.
5.1.10.2
Network auto-reclose
Endeavour Energy’s network provides automatic reclosing function on all of its overhead
lines so that if a protection relay trips the line as the result of a fault, the circuit breaker will
automatically close after a defined time delay. This delay time can vary for different parts of
the network. The embedded generator must be disconnected from the network before any
auto-reclose takes place.
5.1.11
Installation maintenance
All protection equipment associated with the generator must be:
•
•
Tested and verified on site prior to connection to the network.
Tested at least once every three (3) years, or as specified by the Customer Connection
Agreement.
Settings of the protection relays and control equipment or associated wiring must not be
altered unless written authorisation is received from the Network Service Provider
(Endeavour Energy).
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Protection of embedded generation systems
Amendment no.3
Protection equipment must comply with the relevant parts of IEC 60255 or equivalent.
5.1.12 Remote monitoring and control
Remote monitoring and control equipment is required for remote operational purposes, intertripping, load or voltage control. This requirement will be negotiated for each situation, as
any such requirements depend on the relative capacities of the generator and grid at the
connection point. A Supervisory Control and Data Acquisition (SCADA) system is the
preferred method of providing control and monitoring functions. A communication media
between the generator premises and Endeavour Energy’s control centre is required in order
to send and receive data.
If remote inter-tripping is required to Endeavour Energy’s installation, the preferred option is
for a dedicated optical fibre link. Alternatives include a dedicated copper wire link and UHF
radio or, if no other option is practical, a leased telecommunications circuit. The reliability of
leased links can be very poor. Generation may be inhibited while the link is out of service,
but supply of load to the customer’s installation will not be interrupted.
A list of signals that are to be sent and received via SCADA systems must be negotiated with
Endeavour Energy. The signals include but tot limited to the following:
•
•
•
•
•
Status Indications of all relevant generator and feeder circuit breakers.
Analogue indication of 3-phase Amps, volts, kW and kVAr.
Feeder CB fail to trip alarm.
Protection operation alarms as agreed.
Low battery/battery warning alarms.
The generator must also provide the following:
•
A suitable remote terminal unit compatible with Endeavour Energy’s SCADA system. At
present only the ABB RTUs are used in Endeavour Energy's system.
•
Confirmation that a communication path is readily available for SCADA.
•
SCADA equipment in accordance with SDI 538.
•
SCADA equipment may have to comply with IEC 61850.
•
Communications equipment installed in accordance with SDI 519.
•
Wiring connection schedule for the RTU to allow the software to be developed for the
master station and the RTU.
•
Software development for the RTU and the master station.
•
Testing and commissioning of above.
In addition to the above requirements, if a generator is scheduled in terms of the National
Electricity Rules, additional remote control and monitoring equipment must be installed, if
required by AEMO, on each scheduled generating unit in accordance with the rules. The
specific requirements for scheduled generators and rules compliance are covered in
Endeavour Energy’s customer connection guidelines.
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Protection of embedded generation systems
6.0
Amendment no.3
AUTHORITIES AND RESPONSIBILITIES
It is the responsibility of all protection engineers/protection specialists to be familiar with the
contents of this Standard.
7.0
DOCUMENT CONTROL
Documentation content coordinator:
Network Protection & Control Manager
Documentation process coordinator:
Branch Process Coordinator
PDI 5000
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Protection of embedded generation systems
Amendment no.3
Annexure A1
Generator characteristic data (for all rotating machines)
Rotating frequency: (rpm)
Neutral grounding resistor (if applicable):
Additional information for synchronous generating units
Synchronous reactance (PU): Xd
Synchronous reactance (PU): Xq
Transient reactance (PU): X’d
Transient reactance (PU): X’q:
Subtransient reactance (PU): X”d
Subtransient reactance (PU): X”q
Neg sequence reactance (PU): X2
Zero sequence reactance (PU): Xo
KVA base:
Field voltage: (Volts)
Field current: (Amps)
Additional information for synchronous machines:
Electrical data for transient studies (armature R, time constants)
AVR data (if applicable)
Governor data (if applicable)
Additional information for induction generating units
Rotor resistance, Rr:
Stator resistance, Rs:
Rotor reactance, Xr:
Stator reactance, Xs:
Magnetising reactance, Xm:
Short circuit reactance, Xd”:
Exciting current: temperature rise:
Frame size:
Total rotating inertia, H: per unit on KVA base:
Reactive power required in vars (no load):
Reactive power required in vars (full load):
Additional information for induction generating units that are started by motoring:
Motoring power: (kW)
Transformer data (if applicable, for customer-owned transformer):
Will a transformer be used between the generator and the point of interconnection? Yes/No
Will the transformer be provided by customer? Yes/No
Nameplate rating: (kVA)
Single or three (3) phase
Transformer impedance on kVA base: (%)
Vector group:
Transformer primary: (Volts)
Transformer secondary: (Volts)
Transformer fuse data (if applicable, for customer-owned fuse):
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Protection of embedded generation systems
Amendment no.3
(Attach copy of fuse manufacturer’s minimum melt and total clearing time-current curves)
Manufacturer:
Type:
Size:
Class/speed:
Interconnecting circuit breaker:
Manufacturer:
Type:
Load rating:
Interrupting fating:
Trip settings:
Protection current transformer data:
(Enclose copy of manufacturer’s excitation and ratio correction curves)
Manufacturer (HV):
Type:
Class and accuracy:
Manufacturer: (LV)
Type:
Class and accuracy:
Potential transformer data:
Manufacturer (HV):
Type:
Accuracy class:
Manufacturer (LV):
Type:
Accuracy class:
Interconnection protective relays:
(If microprocessor-controlled)
List of functions and adjustable setpoints for the protective equipment or software:
Function
1.
2.
3.
4.
5.
6.
PDI 5000
Setpoint
Minimum
Copyright © Endeavour Energy 2011
Maximum
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Protection of embedded generation systems
Amendment no.3
Annexure A2
General technical detail
•
A copy of plant electrical single line diagram (SLD) showing the configuration of all
generating facility equipment, current and potential transformers, and protection and
control elements and all other relevant power system elements up to the network
connection point.
•
A copy of any applicable site documentation that indicates the precise physical location of
the proposed generating facility.
•
Proposed location of protective interface equipment on property.
•
A copy of any applicable documentation that describes and sets out in detail the
operation of the protection and control schemes.
•
A copy of applicable schematic drawings showing philosophy of protection and control
circuits relating to the network connection, including relay current circuits, relay potential
circuits, and alarm/monitoring circuits (if applicable).
•
Any other information pertinent to this installation.
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Protection of embedded generation systems
Amendment no.3
Annexure A3
Additional points, general comments, typical settings and other information
Rate of Change of Frequency (ROCOF): typically 0.4Hz / sec, 0.5 sec trip time (this high
level is specified to ensure minimum spurious tripping).
Vector shift: Typically 6 degrees, 0.5 sec trip time (it is susceptible to spurious tripping due
to grid disturbances).
Neutral voltage displacement (NVD) settings: NVD plug = 30%; NVD Time delay > earthfault clearance time of other earth-fault protection relay(s) in the connected network.
Typical examples of interconnection protection requirements
Following are five (5) cases of generation connections and the typical examples of the
protection requirements.
The factors that define which case applies are:
• Generation site capacity.
• Generator type.
Interconnection protection, case 1
• All types of generator
• The maximum cumulative export capacity is less than half the minimum distribution line
(or captive) load
• the maximum export capacity is less than 5MW.
Protection required:
• Overcurrent and earthfault
• Under and over voltage
• Under and over frequency
• Three phase vector shift, subject to generator preference (optional).
Interconnection Protection, case 2
All types of generator
The maximum cumulative export capacity is less than 0.8 times the minimum captive load,
and the maximum export capacity is less than 5MW.
Protection Required
Overcurrent and earthfault
Under and over voltage
Under and over frequency
3 phase vector shift
Optional
True ROCOF may be used as well as vector shift. True ROCOF detects the islanded
condition rather than the onset of islanding. Some ROCOF relays may also be sensitive to
an initial change in voltage vector.
Interconnection protection, case 3
All types of generator except mains excited generators defined in case 5.
PDI 5000
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Protection of embedded generation systems
Amendment no.3
The maximum cumulative generation export capacity is greater than 0.8 times the minimum
captive load, such that load/generator balance is possible, and the maximum export capacity
is less than 5 MW.
Protection required
Overcurrent and earthfault
Under and over voltage
Under and over frequency
3 phase vector shift,
Rate of Change of Frequency (ROCOF)
Neutral Voltage Displacement (NVD)
Dead line check
Interconnection protection, case 4 (1)
All types of generator
The maximum export capacity of an embedded generation site is greater than 5 MW.
It is preferred that the embedded generator is connected directly to the primary bus rather
than teed into an HV distribution feeder.
Protection required
Overcurrent and earthfault
Under and over voltage
Under and over frequency
Intertripping from primary bus intake
Parallel earthing or NVD protection
Interconnection protection, Case 4 (2)
If the Embedded Generator is teed into a distribution feeder, the following is also required:
•
Intertripping from the feeder breaker, or fault throwing or reverse VAR protection, where
applicable.
•
Generators larger than 5 MW will be encouraged to obtain more secure connections.
For large generators remote from the primary bus, adequate security may be achieved only
by double circuit connection to the primary bus.
Interconnection protection, Case 5 (1)
Mains excited asynchronous (induction) generator with local power factor correction less
than the reactive power demand, or a line commutated inverter. The network/circuit
capacitance is not sufficient to self excite the generator. The maximum cumulative connected
generation export capacity is greater than 0.8 times the minimum captive load. No
synchronous generation or self-excited generation are connected.
Protection required
Overcurrent and earthfault
Under and over voltage
Under and over frequency
3-phase vector shift
The total generation connected to a primary substation using the vector shift method for loss
of mains protection, shall not exceed 20MW.
The general requirements are covered with synchronous machines in cases 1-4.
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Protection of embedded generation systems
Amendment no.3
Inverters commonly include proprietary protection methods, including ROCOF.
However, it is the responsibility of the generating company to demonstrate that the protection
meets acceptable levels of dependability and reliability.
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