NOTICE DATE:  November 13, 2008       

NOTICE TYPE:  M-D111308-01 Legal    

SHORT DESCRIPTION:  Protocol Interpretation Request on Reactive Power
Capability Requirements

INTENDED AUDIENCE:  All ERCOT Market Participants

LONG DESCRIPTION:  An Entity has submitted to ERCOT a Protocol
Clarification/Interpretation Request (PIR) regarding subsection (2) in
Protocol Section 6.5.7.1, Generation Resources Required to Provide VSS
Installed Reactive Capability, and subsection (5) in Protocol Section
6.7.6, Deployment of Voltage Support Service.  Specifically, the PIR
seeks clarification on issues surrounding Reactive Power capability
requirements.

  

ERCOT provides the following guidance to the questions submitted by the
Entity.

1.	Clarify if the power factor capability of +/- 0.95 is required
at all levels of generation.

 

Yes.  Protocol Section 6.5.7.1(2) sets the Reactive Power capability
requirement for all Generation Resources that provide Voltage Support
Service (VSS).  The section states that a Generation Resource is
required to have and maintain an Unit Reactive Limit (URL) with a power
factor capability of +/- 0.95, determined at its net max output to the
transmission system, and that this capability must be maintained - no
exceptions are provided.  

2.	Clarify the minimum reactive capability requirements at lower
levels of generation and exactly how this is calculated.

 

There is no minimum Reactive Power capability requirement.  The Reactive
Power requirement is set forth in Protocol Section 6.5.7.1, Generation
Resources Required to Provide VSS Installed Reactive Capability.
Specifically, subsection (2) states:

Generation Resources required to provide VSS except as noted below in
items (3) or (4), shall have and maintain a URL which has an
over-excited (lagging) power factor capability of ninety-five hundredths
(0.95) or less and an under-excited (leading) power factor capability of
ninety-five hundredths (0.95) or less, both determined at the generating
unit's maximum net power to be supplied to the transmission grid and at
the transmission system Voltage Profile established by ERCOT, and both
measured at the point of interconnection to the TDSP.  

As described in the response to Question 1, Protocol Section 6.5.7.1(2)
states that a Generation Resource must provide the MVAR requirement (+/-
0.95 power factor) calculated at the maximum net output to the ERCOT
Transmission Grid, and that level must be available at all MW output
levels.  

ERCOT, or TSPs designated by ERCOT, have the right to instruct
Generation Resources to make adjustments for voltage support within the
URL capacity limits.  However, dispatching a Generation Resource within
a URL range is the right of the system operator, and is unrelated to,
and does not affect a Generation Resource's obligation to maintain a
power factor capability of +/- 0.95 when dispatched by ERCOT or TSPs.

Protocol Section 6.7.6(5) confirms the power factor capability
requirement in Protocol Section 6.5.7.1(2).  Specifically, the first
sentence reads:

At all times a Generation Resource unit required to provide VSS is
On-Line, the URL must be available for utilization at the generating
unit's continuous rated active power output, and Reactive Power up to
the unit's operating capability must be available for utilization at
lower active power output levels.  

Therefore, under this Protocol as well, the power factor capability
requirement does not decrease with decreasing generation output.  A
Generation Resource must be able to maintain the MVAR capability
requirement as described in Protocol Section 6.5.7.1(2) even with
decreasing power output.  

The second sentence in Protocol Section 6.7.6(5) states:

In no event shall the Reactive Power available be less than the required
installed reactive capability multiplied by the ratio of the lower
active power output to the generating unit's continuous rated active
power output, and any Reactive Power available for utilization must be
fully deployed to support system voltage upon request by ERCOT, or a
TSP.

This sentence does not conflict with the power factor capability
requirement in the first sentence or Protocol Section 6.5.7.1(2) by
establishing a minimum reactive capability requirement.  In fact, as
described above, the requirement in 6.5.7.1(2) is confirmed in the first
sentence of this section.  The language in the second sentence of this
section merely accounts for situations in which a Generation Resource
encounters equipment-related issues or other unforeseen circumstances
that may cause the Reactive Power capability to be less than the
requirement in Protocol Section 6.5.7.1(2).  If the Reactive Power is
less than the calculation described in the second sentence, then the
Generation Resource's ability to support system voltage may jeopardize
the reliability of the ERCOT Transmission Grid.

3.	Clarify the definitions for "generating unit's maximum net
power" as indicated in Protocol Section 6.5.7.1(2) and "the generating
unit's continuous rated active power output" as indicated in Protocol
Section 6.7.6(5).

 

Both references above refer to the Net High Capability Limit provided by
the Generation Resource to ERCOT through resource registration.  Net
High Capability Limit is the net high MW generation output based on the
rating of plant equipment minus plant Load.

CONTACT:  If you have any questions, please contact your ERCOT Account
Manager. You may also call the general ERCOT Client Services phone
number at (512) 248-3900 or contact ERCOT Client Services via e-mail at
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