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CC.6.3.15.1
Fault Ride Through requirements applicable to Onshore Synchronous Generating Units
connected to the Onshore Transmission at Supergrid Voltage
(a) Short circuit faults on the Onshore Transmission System at Supergrid Voltage up to
140ms in duration.
(i)
(ii)
Each Onshore Synchronous Generating Unit shall remain stable and
connected to the network without tripping for a close up solid three phase
short circuit fault or any balanced fault on the Onshore Transmission
System operating at Supergrid Voltage for a total fault clearance time of up
to 140ms.
Following clearance of the fault as detailed in CC.6.3.15.1(i), each Onshore
Synchronous Generating Unit is required to remain connected and stable
where the post fault voltage profile as measured at the Grid Entry Point is
above the heavy orange line defined in the voltage against time curve
shown in Figure 1D. The voltage against time profile defines the lower limit
of the phase to phase voltage at the Grid Entry Point during a symmetrical
fault as a function of time before and after the fault. Appendix 4 provides
an explanation and illustration of these requirements.
Figure 1D
(iii)
(iv)
For the avoidance of doubt, the requirements of CC.6.3.15.1(i) and
CC.6.3.15.1(ii)) apply only for balanced faults on the Onshore Transmission
System operating at Supergrid Voltage lasting up to 140ms in duration. The
post fault voltage profile is dependent upon the short circuit fault infeed at
the Grid Entry Point.
NGET shall specify the following parameters in the Bilateral Agreement
(v)
(vi)
a. the pre fault minimum short circuit capacity at the Grid Entry Point in
MVA
b. the pre-fault Active and Reactive Power of the Onshore Synchronous
Generating Unit at the Grid Entry Point
c. the pre and post fault voltage at the Grid Entry Point
d. the post fault minimum short circuit capacity at the Grid Entry Point in
MVA.
For Generators considering connecting to the National Electricity
Transmission System prior to applying for a CUSC Contract, the pre and
post fault short circuit data at each Grid Entry Point shall be published in
the Electricity Ten Year Statement. For fault ride through assessment
purposes the Generator should ensure that each Onshore Synchronous
Generating Unit is operating at Rated MW output at 0.95 Power Factor
lead.
In addition to the requirements of CC.6.3.15.1(a)(i),(ii),(iii),(iv)and (v) each
Onshore Synchronous Generating Unit shall be designed such that upon
clearance of the fault on the Onshore Transmission System as detailed in
CC.6.3.15.1(a)(ii) and within 0.5 seconds of restoration of the voltage at the
Grid Entry Point to the minimum levels specified in CC.6.1.4, Active Power
output shall be restored to at least 90% of the level available immediately
before the fault. Once the Active Power output has been restored to the
required level, Active Power oscillations shall be acceptable provided that:-the total Active Energy delivered during the period of the oscillations is
at least that which would have been delivered if the Active Power was
constant
-the oscillations are adequately damped
During the period of the fault as detailed in CC.6.3.15.1(a)(i) for which the
voltage at the Grid Entry Point is outside the limits specified in CC.6.1.4,
each Onshore Synchronous Generating Unit shall generate maximum
reactive current without exceeding the transient rating limit of the Onshore
Synchronous Generating Unit.
(v)
(b)
In the case of unbalanced faults Generators are required to satisfy the
requirements of CC.6.3.15.1(a)(i),(vi) and (v).
Supergrid Voltage dips on the Onshore Transmission System greater than 140ms in
duration.
In addition to the requirements in CC.6.3.15.1(a) each Generating Unit shall:
(i)
Remain transiently stable and connected to the System without tripping of any
Onshore Synchronous Generating Unit for balanced Supergrid Voltage dips and
associated durations on the Onshore Transmission System anywhere on or
above the orange line shown in Figure 2D. Appendix 4 Figures CC.A.4.A.3 (a), (b)
and (c) provide an explanation and illustration of Figure 2D.
Figure 2D
(ii)
provide Active Power output at the Grid Entry Point during Supergrid Voltage
dips on the Onshore Transmission System as described in Figure 2D at least in
proportion to the retained balanced voltage at the Grid Entry Point and shall
generate maximum reactive current (where the voltage at the Grid Entry Point
is outside the limits specified in CC.6.1.4) without exceeding the transient rating
limits of the Onshore Synchronous Generating Unit and
(iii)
restore Active Power output following Supergrid Voltage dips on the Onshore
Transmission System as described in Figure 2D, within 1 second of restoration
of the voltage at the Onshore Grid Entry Point for directly connected Onshore
Synchronous Generating Units to the minimum levels specified in CC.6.1.4 to at
least 90% of the level available immediately before the occurrence of the dip.
Once the Active Power output has been restored to the required level, Active
Power oscillations shall be acceptable provided that:
-
-
the total Active Energy delivered during the period of the oscillations is at
least that which would have been delivered if the Active Power was
constant
the oscillations are adequately damped.
For the avoidance of doubt a balanced Onshore Transmission System Supergrid
Voltage meets the requirements of CC.6.1.5(b) and CC.6.1.6.
(iv)
CC.6.3.15.3
NGET shall specify the following in the Bilateral Agreement
a. the short circuit capacity at the Grid Entry Point in MVA
b. the pre-fault active and reactive reactive power of the Onshore
Synchronous Generating Unit at the Grid Entry Point
c. For the avoidance the pre and post fault short circuit capacity at the Grid
Entry Point would be expected to be the same.
Other Requirements
(i)
……..
(v)
Onshore Synchronous Generating Units are required to satisfy the
requirements of CC.6.3.15.1(a) and CC.6.3.15(b) unless the protection scheme
for internal electrical faults requires the disconnection of the Onshore
Synchronous Generating Unit from the Transmission System. The protection
schemes and settings shall be agreed with NGET prior to issue of an
Energisation Operational Notification (EON) and shall not jeopardise fault ride
through performance.
(vi)
Notwithstanding the requirements of CC.6.3.15.3 (v) the under voltage
protection at the Grid Entry Point shall be set by the Generator to the widest
possible range unless otherwise agreed with NGET.
Appendix 4C – Fault Ride Through Requirements for Onshore Synchronous Generating Units
CC.A.4C.1
Scope
The fault ride through requirements for Onshore Synchronous Generating Units are
defined in CC.6.3.15.1(a) and CC.6.3.15.1(b). This appendix provides illustrations by way
of examples only of CC.6.3.15.1(a) and CC.6.3.15.1(b) and further background and
illustrations to CC.6.3.15.1 and is not intended to show all possible permutations.
CC.A.4C.2
Short circuit Faults at Supergrid Voltage on the Onshore Transmission System up to
140ms in duration
For short circuit faults at Supergrid Voltage on the Onshore Transmission System up to
140ms in duration the fault ride through requirement is defined in CC.6.3.15.1(a) and
Figure 1D which is reproduced in this Appendix as Figure CC.A.4C.1D and termed the
voltage against time curve.
The voltage against time curve is not a voltage – time profile that the Onshore
Synchronous Generating Unit would be required to meet to an Onshore Transmission
System fault, nor a voltage duration curve where each point on the profile (ie the heavy
orange line) represents a voltage level and associated time duration which connected
Onshore Synchronous Generating Units must withstand or ride through. Rather the
voltage against time curve represents permitted boundary of the post fault voltage
profile following clearance of a fault at the Grid Entry Point for a period of up to up to
140ms.
Figure CC.A.4C.2D
The Fault Ride Through requirements are based on a voltage-against-time profile at the
Grid Entry Point, which reflects the worst voltage variation during a fault and after its
clearance (retained voltage during a fault and post-fault voltage recovery) which is to be
withstood. Onshore Synchronous Generating Units are required to stay connected and
stable for at close up solid three phase balanced or unbalanced short circuit fault lasting
up to 140ms in duration and the post fault voltage response as measured at the Grid
Entry Point should remain on or above the heavy orange line shown in Figure
CC.A.4C.3D(a).
Figure CC.A.4C.3D(a)
NGET does not require the actual voltage recovery curve to be of the shape of the
voltage-against-time-profile. The actual voltage recovery curve will have a free
controlled response during the post-disturbance recovery period that will be primarily
dependent on the short circuit strength of the Transmission System at the Grid Entry
Point and secondly on the behavior of the Generating Unit under post fault conditions.
An example of trip condition would be were the post fault voltage profile transits
through the heavy orange line is shown in Figure CC.A.4C.3D(b).
Figure CC.A.4C.3D(b)
Figure CC.A.4C.4D shows an equivalent single machine network. Under these
conditions, NGET shall provide the pre fault and post fault short circuit level at the Grid
Entry Point and specify the pre fault operating conditions of the Onshore Synchronous
Generating Unit.
Insert Fig CC.A.4C.4D – Equivalent network – Example to be included depending upon option agreed by
Working Group.
Workgroup discussion – Are further examples and studies required here.
Details relating to compliance and simulation with this requirement are defined in CP.A.3.5.
CC.A.4C.2
Supergrid Voltage dips on the Onshore Transmission System greater than 140ms in
Duration
For balanced Supergrid Voltage dips on the Onshore Transmission System having
durations greater than 140ms and up to 3 minutes, the fault ride through requirements
are defined in CC.6.3.15 (b)(i) and Figure CC.A.4C.2D below which is reproduced in this
Appendix as Figure CC.4C.5D and termed the voltage-duration profile.
This profile is not a voltage-time response curve that would be obtained by plotting the
transient response at a point on the Onshore Transmission System to a disturbance or
the free and uncontrolled post fault voltage profile following a 140ms fault as described
in CC6.3.15.1(a). Rather, each point on the profile (ie the heavy orange line) represents
a voltage level and an associated time duration which Onshore Synchronous Generating
Units must withstand or ride through.
CC.A.4C.5D (a),(b) and (c) illustrate the meaning of the voltage-duration profile for
voltage dips having durations greater than 140ms.
Figure CC.A.4C.5D
Figure CC.A.4C.5D (a)
Figure CC.A.4C.5D (b)
Figure CC.A.4C.5D (c)
CP.A.3.5
Fault Ride Through
CP.A.3.5.1
The Generator shall supply a time series simulation study to demonstrate the capability
of an Onshore Synchronous Generating Unit to meet the requirements of CC.6.3.15 by
submission of a report containing:
(i)
(ii)
a time series simulation study of a 140ms solid three phase short circuit fault
applied on the nearest point of the National Electricity Transmission System
operating at Supergrid Voltage to the Onshore Synchronous Generating Unit.
a time series simulation study of 140ms unbalanced short circuit faults applied
on the nearest point of the National Electricity Transmission System operating
at Supergrid Voltage to the Onshore Synchronous Generating Unit. The
unbalanced faults to be simulated are:
1.
2.
3.
a phase to phase fault
a two phase to earth fault
a single phase to earth fault
For an Onshore Synchronous Generating Unit the simulation study should be
completed with the Onshore Synchronous Generating Unit operating at full
Active Power and maximum leading Reactive Power. NGET shall specify the
minimum pre and post fault short circuit level in the Bilateral Agreement.
(iii)
a set of time series simulation studies of balanced Supergrid Voltage dips
applied on the nearest point of the National Electricity Transmission System
operating at Supergrid Voltage to the Onshore Synchronous Generating Unit.
The simulation studies shall include:
1. 33% retained voltage lasting 0.14 seconds
2. 50% retained voltage lasting 0.45 seconds
3. 85% retained voltage lasting 180 seconds
For an Onshore Synchronous Generating Unit the simulation study should be
completed with the Onshore Synchronous Generating Unit operating at full
Active Power and maximum leading Reactive Power. NGET will specify the
minimum fault level at the Grid Entry Point in the Bilateral Agreement. For the
avoidance of doubt, the pre and post fault minimum fault levels at the Grid
Entry Point shall be the same.