World-Gen Nov/Dec 2016

WORLD-GENERATION NOVEMBER/DECEMBER 2016

FERC 827 RULING

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can cause system voltage to sag, preventing

real power to flow through the lines. In

extreme cases, insufficient reactive power

resources can result in voltage collapse and

even power outages. Because of this,

utilities and grid operators have taken

careful measures to regulate reactive power

so they can deliver nominal voltage under

varying load conditions. This is in part the

reason why we have strict interconnection

requirements for both synchronous and

non-synchronous generators, so that each

power facility can contribute to the reactive

power supply on the utility grid.

REACTIVE POWER COMPENSATION

TECHNOLOGIES

To control reactive power on the utility

grid or when interconnecting generation

facilities, system operators and developers

have a variety of technologies that can help

implement their control strategies. From

smart inverters and advanced wind

converters to Static Var Compensators and

STATCOMS (Static Synchronous

Compensators), the location of the

renewable facility and the condition of the

surrounding electrical network will by and

large dictate the solution required to help

meet the local grid codes and this new

FERC 827 requirement.

TECHNOLOGY IN ACTION: STATCOMS

Although many modern wind turbines

are able to fulfill voltage control

requirements by themselves, wind parks as

a whole sometimes still need additional

reactive power compensation to cover the

balance of plant. When Type-I and Type-II

wind farms in particular are in operation,

dynamic VAR compensation devices can be

useful to meet the grid requirements. One

of the devices which can enable this is the

Static Synchronous Compensator

(STATCOM).

STATCOM is one of the members of

the FACTS (Flexible AC Transmission

System) family. It is a low voltage power

electronic based device which acts as a

source or sink for the reactive power. The

major components of a STATCOM are a

DC capacitor, a power converter, filters and

a step up transformer connecting it to the

grid.

A STATCOM will be able to quickly

respond to grid events (with a response

time of one to two cycles), providing

dynamic voltage control, regardless of the

wind farm layout. Even on weak grids, the

STATCOM device has the capability to

control reactive power and ultimately

enhancing the power output of the wind

farm.

As our society move towards cleaner

sources of power such as wind and solar,

maintaining the integrity of the electrical

grid will continue to be a priority.

Regulatory bodies such as FERC have

issues several orders to help ensure safe

and reliable connection of non-synchronous

generators (i.e. wind and solar) to the

transmission network.

As October 14, 2016, the new FERC

ruling requires newly interconnecting non-

synchronous generators to meet dynamic

reactive power requirements. However, for

already existing facilities that are making

upgrades and making new

interconnections, such requests will be

exempt from these requirements as it

“could expose entities with existing power

purchase agreements to unforeseen

expenses.” This can be subject to change if

the transmission provider’s System Impact

Study shows that meeting the reactive

power requirement is necessary to ensure

safety or reliability.

For the rest of the newly

interconnecting non-synchronous

generators, they will be required to meet

the reactive power requirements at the high

side of the generator substation, and not

the Point of Interconnection. This means

that in most cases advanced wind turbine

converters can provide enough reactive

power control, so that no further

technology is needed. However, in areas

where the grid is weak, or the surrounding

load is variable, additional dynamic reactive

power compensation is required.

PERSPECTIVE

operation, and a 7 kV line was tripped off.

But, there was so much solar on the line, it

remained energized beyond the six-cycle

time limit, and six more feeders tripped off

as a result.

In both of these cases, one problem

looms: lack of control. Much of that problem

stems from centralized control that takes too

long to really react to rapidly-changing

conditions from intermittent generation.

THE OPEN FIELD MESSAGE BUS APPROACH

A few years ago, engineers at Duke

Energy were trying to coordinate solar and

storage installations. To that end, they

clocked the round trip from sensors on an

inverter to the head-end system, through

the computation cycle and then back to the

inverter. It took some 40 seconds. This is

what got Duke started down the path of

OpenFMB

, a reference architecture that

provides a framework for distributed

intelligence.

Working with Duke and other industry

players, SGIP’s OpenFMB

working group

shepherded this architecture through the

standards process. It was ratified as a

standard by the North American Energy

Standards Board (NAESB) in March of 2016

and, at SGIP’s 2016 Grid Modernization

Summit held in Washington, DC November,

we launched a collaborative website where

people can access the OpenFMB

code

itself.

OpenFMB

supports grid-edge

coordination of distributed energy resources

and the grid itself because it facilitates local

data exchange on a circuit segment, which

enables decision making without centralized

system control. That’s crucial because

Supervisory Control and Data Acquisition

(SCADA) systems typically collect grid-

status data every four or five seconds, and

that’s just not fast enough when you have a

protective scheme that must operate in six

cycles.

BACK ON CAMPUS

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