Changes in Load Composition and Its

Impact on Power System Reliability

Presentation at 2018 IPCGRID Workshop

by

Dmitry Kosterev

Bonneville Power Administration

1

US Department of Energy estimates that

80% of the nation’s electricity will flow

through power electronic devices by 2030

Have difficult time believing ?

2

BPA Headquarters

701,184 sq.ft. building downtown

Portland, OR

Constructed in 1987

Highly efficient building, exceeds

LEED-Platinum

Multiple energy efficiency upgrades

Percentage of electronically-connected load is estimated close to 80%

3

Variable Frequency Drives run most motors in the building

LED lighting, data center and workstations

VFD-Controlled HVAC Chiller VFD-Controlled Pumps

VFD-Controlled Fans 4

2007 vs. 2017

5

2007 2017

“rabbit ears” indicates high penetration of electronic drives

BPA installed continuous point-on-wave voltage and current data recorders

Building load is lower

Load power factor is higher

Building voltages are slightly higher

System impact of electronically connected generation

(solar, wind) has received significant attention recently

by FERC, NERC, IEEE, etc..

But what about the system impact of electronically

connected loads ?

6

BPA End-Use Test Lab

Fan with Electronically-

Commutated Motor under test

Controllable power supply with test

recording equipment

Voltage sag test

7

“What is difference between electronically connected

and conventional loads”

Conventional loads have natural characteristics that help to maintain stability

when the power grid is stressed:

- Incandescent light dims when its voltage declines (power consumption is

proportional to voltage squared)

- Directly connected fan or pump motor slows down when its supply frequency

dips (power consumption is roughly proportional to the square of frequency)

Most power electronic loads (VFD-connected fans and pumps, Electronically

Commutated Motors, consumer electronics, computer chargers, etc) are

programmed to be constant power, they consume the same power regardless of

the grid voltages and frequency

Power electronic loads have “binary” behavior – they either ON or OFF

8

What will high percentage of constant power loads

do to the stability of the power grid

Constant power loads:

- Make conservation voltage reduction programs ineffective because loads

are no longer sensitive to grid voltages

- Make distribution voltage control more challenging

- Make the grid less stable

- Increase voltage oscillations

- Increase risk of load loss during large voltage and frequency events

9

Initial Studies

Higher percentage of constant power load results in reducing transmission

reliability margins, and therefore additional transmission investments may be

needed to keep the existing transfer capabilities

0 5 10 15 20 25 30400

450

500

550

600

650

Time (sec)

Volt

age

(kV

)

Basline

50% Constant Current / 50% Constant Power

100% Constant Power

10

Initial Studies

Higher percentage of constant power load results in lower system frequency

drops following generation outages, and therefore, increased requirements for

Frequency Responsive Reserves

0 5 10 15 20 25 3059.4

59.5

59.6

59.7

59.8

59.9

60

Time (sec)

Fre

qu

en

cy

(Hz)

Basline

50% Constant Current / 50% Constant Power

100% Constant Power

Under-Frequency Load Shedding

Unacceptable Loss of Load11

Silver Lining

However, there is good news:

- While power electronic loads are programmed to be constant

power today, they can be re-programmed to be different

(when allowed by application)

- We were able to reprogram Variable Frequency Drives in the

BPA end-use lab to be voltage-sensitive (work done in

collaboration with University of Wisconsin)

- Making at least half of electronic loads voltage sensitive has

shown to alleviate most of grid problems

12

Being Practical

We recognize that some power electronic loads may need to

stay constant power:

- You do not want your HDTV to flicker

- Precise manufacturing process, such as paper machines

However, there are many processes that will be perfectly fine

with being voltage sensitive for small voltage variations

Charging is the main application

Applications of Variable Frequency Drives for energy efficiency is

another

13

Moving Forward

1) Utility

Utilities to perform similar system impact studies of high percentage of

power electronic loads to “size up the problem”

- Transmission level – composite load model is available

- Distribution level – impact is likely to be more significant

2) Industry

Industry to work with NERC to develop desired load characteristics, similarly

to work done by SAMS on Fault-Induced Delayed Voltage Recovery

3) Regulatory

Industry to engage with DOE on outreach programs to communicate desired

load characteristics to manufacturers and trade organizations, similarly to

work done with AHRI on air-conditioners

14

Participants

Ryan Quint – NERC Staff

Joe Eto – LBNL, DOE

Bernie Lesieutre – University of Wisconsin

John Undrill – Arizona State University

Dmitry Kosterev – BPA Planning

Steve Yang – BPA Test and Measurements

Gordon Matthews –BPA Technology Innovation

15

Thank You

16