IEEE Power & Energy Magazine - May/June 2016 - 59

The utility-managed DSO will have the responsibility for
maintaining distribution system reliability, and, in that context,
it requires visibility to transactive operations.

time, reservation fee, or the submission of bids and offers.
Table 3 contrasts "congestion management" issues in bulkpower and distribution domains.
At the distribution level, distribution constraint management is a task generally delegated to the DSO. Similar
to wholesale markets, bids and offers submitted by transactive agents may be used to identify successful transactions.
For transactions that do not include the disclosure of prices
to the DSO for whatever reason, the DSO may issue price
signals based on the extent of imminent or potential constraint violation. When no action is taken by the transactive agents to remedy the problem, the distribution system
operator would use priority schemes based on various preestablished criteria such as the impact on constraint relief,
similar to practices prevalent in bulk-power operations and
wholesale markets.

Distribution Capacity Auction to Hedge
Against Limited Distribution Capacity
In wholesale markets, limited transmission capacity is often
auctioned in the form of transmission rights. Using organized wholesale markets (facilitated by ISOs/RTOs) as a
model, a distribution capacity auction mechanism may be
contemplated whereby limited distribution capacity is auctioned on a seasonal, monthly, and possibly daily basis. The
auction winners may then bilaterally trade the capacity. For
example, an EV owner may bid to buy capacity during evening peak hours of the weekdays for a month in the auction
and then, when the EV is charged (or is idle), sell the excess
capacity to others who may want to use the same distribution
circuit elements.
In wholesale markets, power can be sold with various
degrees of certainty of delivery depending on the firmness
of transmission capacity supporting the transaction. The sale
may involve energy or grid services as transacted products.

Similar arrangements may be envisaged in the retail/distribution space. In the example of the EV owner, he/she may
bid to allow for brief but frequent charging/discharging
cycles that the DSO may employ to provide grid services to
the balancing authorities.
Where devices are acting as transactive agents, the
assumption is that each device will be assigned identification
along with any distribution constraint priority rights it may
have. The priority rights may be transacted among intelligent devices in advance of real-time operation.

Seams Issues for the End-to-End
Operation of TE Systems
Effective power system operation under the TE systems paradigm requires coordination of system operation at the seams
between transmission and distribution domains. There are
challenges and risks that must be addressed for seamless
end-to-end operation of the power system. A sample of such
challenges and possible solutions are provided next.

Main Bulk Power/Distribution Seams Issues
Under the TE Paradigm
Increasing levels of consumer/prosumer side DERs impact
the conventional bulk-power and transmission system operations in a number of ways, including the following:
✔ The conventional methods of estimating bulk-power
substation loads using load distribution factors are
based on the assumption of conforming loads across
bulk-power/transmission substations within a "load
zone." This assumption breaks down as the net load
under each substation is impacted by local DERs on
the feeders beneath each substation. There is a need
for closer collaboration between the distribution and
bulk-power system operators to ensure proper forecasting of supply substation loads.

table 3. A comparison of bulk-power and distribution congestion management considerations.
Attribute

Wholesale/Transmission

Retail/Distribution
Distribution "capacity"
Line/transformer loading

Congestion

Transmission capacity
line loading

Reverse flow-protection system limits
Phase imbalance-neutral flow limits
Line voltage-var support-voltage imbalance

may/june 2016

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