frequency control concerns in the North American Power Grid

Table of Contents
FIGURES................................................................................................................................ iv
ACRONYMS........................................................................................................................... v
PREFACE.............................................................................................................................. vii
1. INTRODUCTION ............................................................................................................. 1
2. A PERSPECTIVE ON FREQUENCY CONTROL............................................................3
2.1. FREQUENCY REQUIREMENTS UNDER NORMAL CONDITIONS....................3
2.2. FREQUENCY RESPONSE UNDER CONTINGENCY CONDITIONS ...................4
2.3. FREQUENCY CONTROL COORDINATION AND IMPORTANCE......................5
2.4. FREQENCY RESPONSE CAPABILITY: REQUIREMENT VS. MARKET............8
2.4.1. Coupling of Frequency Response, Inadvertent Energy and Markets ................8
2.4.2. Block Schedules and the Impact on Frequency .................................................9
3. FREQUENCY STANDARDS AND CONTROL PERFORMANCE ..............................11
3.1. CONTROL METRICS EVOLUTION.......................................................................11
4. CONCLUSIONS................................................................................................................17
4.1. METRICS AND MONITORING SYSTEMS RECOMMENDATIONS..................17

iv
Figures
1. Power system frequency deviates whenever generation fails to track load precisely......1
2. Generators and transformers have limited volts-per-hertz capabilities............................3
3. Contingency reserves rebalance the system after the sudden loss of generation.............4
4. Frequency is tightly controlled under normal conditions and coordinated under all
conditions..................................................................................................................................5
5. Generation is controlled to minimize ACE. ACE contains a frequency bias term to
help bring the system back to 60 Hz..........................................................................................7
6. Average system frequency error rose when A1&2 were replaced with CPS1&2.
This is not necessarily bad for reliability.................................................................................12
7. Frequency and ACE Variations (Start Time is 7:00 AM, May 3, 2002) .......................13
8. Frequency and ACE Variations (Start Time is 3:00 PM, May 1, 2002)........................14
9. Coherence Function Between Frequency Variations and CPS1 and A1 (Control
Area 1) .................................................................................................................................15
10. Coherence Function Between Frequency Variations and CPS1 and A1 (Control
Area 2) .................................................................................................................................15
11. Coherence Function Between Frequency Variations CPS1 and A1 (Control Area 3) ..16
12. Coherence Function Between Frequency Variations and CPS1 and (Control
Area 4) .................................................................................................................................16

v
Acronyms
ACE area control error
AGC Automatic Generation Control
CPS Controlled Performance Standard
ERCOT Electric Reliability Council of Texas
IEC International Electrotechnical Commission
NERC North American Electric Reliability Council
OCPS optimal control performance specification
ORNL Oak Ridge National Laboratory
VFD variable frequency drive

vii
Preface
Purpose
This paper examines the relationship between system frequency, reliability and markets. It was
prompted by the frequency deviations recently experienced at 2200 hours daily but is more
generally concerned with the question of what frequency control is necessary. The paper does
not provide new information or document new research. Nor is it intended to educate readers
concerning power system engineering. Instead, the purpose is to reexamine well known truths
concerning the power system and to freshly explore the basic relationship between frequency,
reliability and markets: stepping back, if you will, to see if we are collectively missing
something.
The concern of this paper is with frequency and reliability. Off-nominal frequency can impact
reliability and markets efficiency (as we are using the term here) in four


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