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PSRC WG C17 in support of PES WG17 Draft 2 June 15, 2009
Fault current contribution from a wind farm to a transmission system.
This document is prepared to indicate the type of information regarding fault current
contributions from wind farms for use in interconnection impact studies. Knowledge of
contribution of fault current from a wind farm to a transmission system is required to
assess the impact of the wind farm interconnection on the short circuit protection of the
transmission system. Recognizing that it may be difficult to model the wind farm as a
constant voltage source behind a Thevenin equivalent impedance, the contributions from
the wind farm to the faulted transmission system under the following circumstances shall
be provided.
All currents shall be provided as fundamental frequency phasor current values in r.m.s.
amperes (magnitude and angle with respect to pre-fault A phase voltage) in the indicated
time frames. Phasor values for all three phase currents and all three phase to neutral
voltages at the high voltage side of the wind turbine step-up transformer and at the point
of interconnection are required.
Currents and voltages are required for the following time frames:
 Subtransient, 1 fundamental frequency cycle after the fault inception.
 Transient, 0.3 seconds after the fault inception
 In addition, for resistive single line to ground faults, the currents and voltages are
also required 1 second after fault inception.
In all cases, currents and voltages shall be stated for the following fault types.
 Three phase fault (ABCG) zero ohm fault impedance
 Double line to ground fault (BCG) zero ohm fault impedance
 Phase to phase fault (BC) zero ohm fault impedance
 Single line to ground fault (AG) zero ohm fault impedance
 Optionally, single line to ground fault (AG) XX ohm fault resistance (utility to
specify XX)
Voltages and currents for faults at the point of interconnection (shown as location F1 on
the attached system one line diagram)
Voltages and currents for faults at the HV side of the wind farm step up transformer
(shown as location F2 on the attached system one line diagram)
Voltages and currents for faults at the end of one adjacent transmission. This is shown as
location F3 on the attached system one line diagram.
Optionally, voltages and currents for faults at the end of another adjacent transmission
branch. This is shown as location F4 on the attached system one line diagram.
Case 1. Full power generation from the wind farm, all generators on line. All reactive
power support equipment on line under voltage regulation mode.
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PSRC WG C17 in support of PES WG17 Draft 2 June 15, 2009
Case 2. Minimum generation from the wind farm. All generators off line. All reactive
power support equipment in the expected status for this condition and under voltage
regulation mode.
Case 3. Single contingency. Branch L2 on the transmission network out of service (or
other selected contingency), and full power generation from the wind farm, all generators
on line. All reactive power support equipment on line under voltage regulation mode.
Neglect contributions to faults at any given location if the contingency selected results in
no significant electrical connection from the wind farm to the fault location.
Note, all impedances in Figure 1 are in per unit on a 100 MVA base at a base voltage of
XX kV. These impedances are provided as part of the network fault study.
Z1S1=R1S1+jX1S1
Z0S1=R0S1+jX0S1
Z1S2=R1S2+jX1S2
Z0S2=R0S2+jX0S2
Z1L1=R1L1+jX1L1
Z0L1=R0L1+jX0L1
Z1L2=R1L2+jX1L2
Z0L2=R0L2+jX0L2
Impedances from the wind farm to the point of interconnection are provided by the
project proponent. If prefault power flow conditions are important to the fault study,
these shall be provided to the project proponent.
In addition to the various currents and voltages to be provided for the various faults at the
indicated locations for the indicated cases, also indicate if there is a threshold voltage at
the point of interconnection at which the fault current contribution changes suddenly, for
instance if a crowbar function or other electronic control device will operate when the
voltage falls below a certain threshold. Specify the characteristics of the threshold voltage
with respect to voltage balance, i.e., characterize the threshold with voltage depression
(phase to neutral) on only one or two phases and (phase to phase) on two phases, as might
be expected during an unbalanced short circuit. Identify the change in characteristic of
the fault current contribution when the voltage threshold is passed.
S1
L1
L2
F3
HV Terminal of step up tfr.
(Fault location F2)
F4
Point of
interconnection
(Fault location F1)
Wind farm
Figure 1 - Simplified transmission system diagram
2
S2