Celebrating the Visions of Synchrophasor Pioneers:

A Technical Symposium in Honor of the Life and Careers of

Arun Phadke and James Thorp

May 9, 2013 Herndon, VA

Robert J. Thomas Cornell University

Background for this talk

•  Jim, Arun, and I worked together on a project the summer of 1981

•  It did not involve synchrophasors •  There is nothing I could say here that others won’t say

better or that would materially contribute to the synchrophasor discussion

•  The breadth of contributions of both Jim and Arun over their joint and separate careers is enormous

•  Their contributions to the topic of this talk is probably not very well known

Sectionalized T-bus

Ring Bus

Fault current for 100-2.5 MW wind turbines with generator voltage of 4.8 kV is 78,000 A. Each wind turbine in this arrangement is protected as though it were a 250 MW machine

Back to the future - 1981

Clusters vs a Single Machine

Integrating a cluster of n wind turbines each of size pT MW is preferable to integrating a single machine of size n*pT MW

The variance-to-mean ratio for n identical machines each of size pT is:

The variance-to-mean ratio for one machine of size n*pT is: €

€

r =

σi2

i=1

n

∑

pii=1

n

∑=

σTn * pT

€

r =σ1p1

So, if the mean rating for the cluster is fixed, the aggregate spectrum for n-machines has a variance to mean ration that is smaller by a factor of

€

1n

So for 100 wind turbines with each having a capacity of 2.5 MW, σ = 1 MW, a 250 MW turbine would have a σ=100 MW whereas a cluster of 100 turbines would have a σ=10 MW

Boeing MOD-2 wind Turbines – 2.5 MW fixed speed. 300 ft blades.

Why Variable Speed?

The max efficiency for a MOD 2 is to maintain Γ = 5.8 Cp is the turbine power coefficient

An AC/DC/AC Interface Proposed by Phadke, Thomas, and Thorp - 1981

Note: Since the voltage depends on the speeds of the various wind machines, it is the current that needs to be controlled by the Controllable Inverter System (CIS)

Inherent advantages of the proposed interface

1.  Generator interactions are eliminated 2.  Resynchronization is unnecessary 3.  Individual generator speeds may vary widely, which means that the

cluster would be able to capture significantly more wind because of the ability of each machine to run asynchronously

4.  The system is self protecting 5.  The output of the cluster can be centrally controlled and in fact can

be scheduled up to the maximum power available at any instant of time

6.  The system is economically attractive since preliminary cost projections (excluding wire and grid interconnection equipment) are in 1976 dollars about $5/kW for the rectifiers and $50/kW for the inverter, or about one-third conventional a-c system protection costs.

Project Contributions

1.  Arun Phadke – A novel HVDC link that requires current control and protection

2.  Jim Thorp – Spatial/temporal wind model, adapting AGC

3.  Bob Thomas – Variable speed induction generator system design and wind system reliability

So what happened?

We suggested a demonstration as a follow on.

The price of oil in the middle east dropped precipitously and the U.S. lost interest in wind.

Boeing went on to build the 787 Dreamliner

NASA focused on the Space Station and other missions

New Transmission Approaches

♦  Multi-terminal HVDC lines using voltage source converter (VSC) technology –  Being explored in Europe for offshore networks –  Further development of protection and control

technology required

♦  Underground (or overground) HVDC lines –  Involves tradeoff between cost of cables and trenching

vs. social and environmental costs –  Shallow directional drilling technology has already

been applied to pipelines

♦  Undergrounding is an important option that needs to be further explored

“R&D Requirements for Integration of Wind Generation”, Smith. O’Malley, Osborn, Piwko, Thomas, HICSS, January 4-7, 2013

Department of Energy Workshop Applications for HVDC Technologies April 22, 2013, Mohamed M. El-Gasseir, Atlantic Grid Development LLC

Department of Energy Workshop Applications for HVDC Technologies April 22, 2013, Mohamed M. El-Gasseir, Atlantic Grid Development LLC