Hawaiian Electric State of the System Summary
Hawaiian Electric Company
State of the System
Summary for ESS RFP
April 23, 2014
HECO-Transmission Planning
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Hawaiian Electric State of the System Summary
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Hawaiian Electric State of the System Summary
HECO Electrical System
The Hawaiian Electric Company (HECO) electric utility system serves the island of Oahu. The system load
has a daytime peak of approximately 1100MW and a daytime minimum load of approximately 800MW.
The evening peak is roughly 1200MW. Historically, the system load has been served primarily by
conventional generation including baseload steam reheat units, cycling steam units, and peaking
combustion turbine units.
Within the past five years the HECO system has experienced a large growth in variable renewable
generation from photovoltaic (PV) and wind generation. By the end of 2013 there were roughly 250MW
of PV capacity (primarily rooftop PV systems) and 100MW of wind capacity. The forecast for renewable
generation on Oahu is expected to continue to grow at a high rate. The total PV and wind energy
forecast for the next 10 years is shown in Figure 1, which shows how the forecasted renewable
generation compares with the projected system loading. 1
Figure 1
HECO Forecasts
1400
1200
Power (Net MW)
1000
Total Renewables
800
Total PV
Total Wind
600
Eve Peak
Day Peak w/o PV
400
2011 Day Min
200
0
2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023
Forecast Year
1
The ‘2011 Day Min’ is based on historical loading. There is currently no forecast for daytime minimum loading for
future years.
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Hawaiian Electric State of the System Summary
Generator Minimum Operating Limits
The amount of renewable generation that can be accepted on the system is limited by how low our
conventional generation can go down in total MW output and still provide the required downward
regulation required for the loss of a feeder, transformer or an increase in variable generation. Each
generator has a minimum MW output rating including downward regulation.
In general, by subtracting the total minimum operating limits from the forecasted system loading, we
can get a rough “ceiling” of the amount of renewable generation that can be accepted with minimal
curtailment. In order to accommodate more renewable generation additional conventional generators
must be turned off.
System Impact
As renewable generation increasingly displaces conventional generation, the system’s ability to respond
to contingencies such as loss of a generating unit, line faults, or rapid changes in system loading due to
the variability of the renewable generation becomes compromised. At some point the amount of
renewable generation that the system can accept reaches a point where the reliability of the system
becomes unacceptable without some form of mitigation.
System Stability
Conventional generators provide ancillary services such as inertia and quick load pickup which provide
instant response to help maintain system frequency and system stability for contingencies such as loss
of generation or system faults. HECO’s load shed scheme is also designed to help maintain system
stability by reducing system load during contingency events. As more renewable generation displaces
conventional generators, the system loses inertial and quick load pickup response which results in more
loads shed for common contingencies and ultimately could lead to system collapse.
This has already been seen in an April 2013 event in which the loss of the largest generator (AES) on
HECO’s system resulted in the system frequency dipping down to 58.35Hz initiating three blocks of
under-frequency load shed. Approximately 79,000 customers experienced an outage. Exacerbating the
event was the loss roughly 60MW of rooftop PV generation that tripped at 59.3Hz following the IEEE
1547 under-frequency trip setting.
In addition, simulation of various transmission line faults led to frequency exceeding 60.5 Hz for over 10
cycles due mainly to the high-speed reclosing action. Most rooftop PVs will trip on over-frequency
under IEEE 1547 settings. The loss of significant amounts of generation during line faults can lead to
system instability. To allow for greater amounts of renewable generation, more conventional
generating units must be taken off the system, reducing system inertia and making the system less stiff
to frequency excursions.
For transmission line faults with delayed clearing, simulations showed rooftop PVs tripping on undervoltage protection under IEEE 1547 settings for voltage below 50%. The loss of PV generation on undervoltage results in system frequency decay initiating multiple blocks of under-frequency load shed.
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Hawaiian Electric State of the System Summary
Not all PV on the system will trip due to under-voltage since voltage is a local quantity and is not the
same everywhere for the same fault. PV tripping due to under-voltage depends on the severity of the
voltage depression and is sensitive to PV location relative to the fault location.
Ramp Rate Capabilities
Conventional generators like the ones in HECO’s fleet have ramp rate capabilities/limitations.
Historically, the HECO generator dispatch has been well-capable of following the normal variation in
system load. However as the amount of renewable generation increases on the system, the
conventional generators must try to accommodate the additional variability of system load due to the
variability of the renewable generation which relies on highly variable sources such as sun and wind.
The down ramping capability for renewables is limited by the total on-line generator up ramping
capability. When the ramping of renewables exceeds the capability of the on-line generators, system
frequency will drop and in extreme cases load shedding may occur.
As conventional units are turned off, the available generator ramping capability is reduced which
adversely impacts the system’s ability to load follow the growing variability from renewable generation.
Figure 2 shows the estimated ramping rates of total renewables at different MW levels compared to the
available ramping capability of HECO’s conventional generators for different generation dispatch
scenarios.
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Hawaiian Electric State of the System Summary
Figure 2
1 Minute Day Ramping Rates
Ramping Rate (MW/1 minute)
35
30
All Baseload Units On
K1,K2 or K3,K4 Off
K5,K6 Off
K1,K2,K3,K4 Off
25
K1,K2,K5,K6 Off
W7,W8 Off
AES Off
AES,K1,K2 or AES,K3,K4 Off
20
AES,K5,K6 Off
Total Renewables
15
300
400
500
600
700
Total Renewables (MW)
END OF ATTACHMENT G
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