IEEE Power & Energy Magazine - November/December 2019 - 84

Requirements should be no more specific than they need to be to
avoid overdesigned equipment and reduced efficiency, but they
should be specific enough to maintain adequate system reliability.
generation is typically not located in the places of the
conventional plants they are displacing. As a result, even
though the new transmission-connected plants provide
reactive power and voltage control to meet grid codes,
they may be insufficient to address local problems that
result during various dispatch scenarios. Distributionconnected plants may only be operating in a power-factor control mode. To ensure adequate voltage support,
it may be necessary to add grid-connected reactive
power sources, convert conventional units to synchronous condensers to provide the voltage support where
it's needed, or modify the control mode of distributionconnected generation.
✔ Low short circuit strength issues, appropriate modeling
and study approaches, and effective solutions to address
these issues: The short circuit ratio is a metric used to assess the voltage stiffness of the grid in a local area. Areas
with a low short circuit ratio (<3) are classified as weak
networks. They typically require more detailed assessments to confirm voltage-regulator stability, control interactions with other nearby devices, and coordinate protective relays, for example. Fault-induced delayed voltage
recovery is more of a problem in weaker grids.
✔ Subsynchronous oscillations, including resonance and
control interactions, between groups of power electronic resources and with the grid: Subsynchronous torsional interaction is the interaction between the mechanical
torsional masses in a turbine-generator unit, such as a
wind turbine generator and the wind turbine (hub and
blades), and a power electronic device, such as high-voltage (HV) dc or flexible ac transmission systems. The
power electronic device can exhibit negative damping
to subsynchronous frequencies. Subsynchronous control interaction is the interaction between a power electronic device (e.g., type 3 wind turbine generator) and a
series-compensated transmission line. These cases require specialized studies with electromagnetic transient
(EMT) models.
✔ Aggregate modeling and impacts of DERs on the BPS:
An increasingly widespread penetration of DERs, such as
rooftop solar PVs embedded in the distribution grids, will
require the emergence of an active distribution grid and
technologies to enable transmission operators responsible
for system security to closely watch and control operations. Accurate aggregated models will need to be developed and added to transmission models to test the impact
of ride-through capability.
84

ieee power & energy magazine

Grid Code Trends
Grid codes are a massive subject of their own. A large portion
of grid code changes occurring around the world are driven by
renewable generation. Trends in several representative regions
illustrate how new requirements have resulted from growing
inverter/converter-based penetration.

Grid Code Trends in Canada
In 2005, the Canadian Wind Association (CanWEA) noticed
that the Canadian provinces were developing their own grid
codes largely in isolation. At the time, there were roughly
600 MW of installed wind capacity across Canada, but significant growth was expected. CanWEA worked with the transmission system operators to develop a minimum set of common
interconnection requirements. The base code covered the following main areas:
✔ Frequency tolerance: Systems should be able to continue
to operate over a wide frequency range.
✔ Voltage tolerance: Systems should continuously operate within ±10% of nominal voltage. Higher voltage ride
through was considered a special case.
✔ Power control: Operators should be able to limit maximum power output and control ramp rates.
✔ Reactive power capability/control: Systems should provide power factors of 0.9 lagging and 0.95 leading at full
power output. A portion should be dynamic. The size of
this portion differs for every province.
✔ Voltage control: Operators should be able to control the
voltage at the point of interconnection.
✔ Frequency response: No requirement has been established yet for frequency response, but a requirement may
eventually be set.
✔ Low-voltage ride through: Systems must support ride
through for a predefined low-voltage envelope.
✔ Power system stabilizers: No requirement has been made
related to power-system stabilizers.
✔ Data provision: Operators must supply accurate stability
models.
✔ Operational monitoring: The system must provide information to the transmission system operator, such as
power, reactive power, wind speed, and site temperature.
The wind plant must be able to accept commands from
the transmission system operator.
The Canadian provinces originally used the base code as a
framework but then developed their own unique grid code language over several years. Manitoba and Quebec, for example,
adopted a unique requirement that ensures ride through for
november/december 2019



IEEE Power & Energy Magazine - November/December 2019

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2019

Contents
IEEE Power & Energy Magazine - November/December 2019 - Cover1
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