Reactive Power and Load Transient Behavior Issues

John Undrill EAC September 2015

100 MVA Generator Manual excitation control

Initial near-instantaneous increase in reactive power output

Initial near-instantaneous increase in field current

Increase in reactive power output fades and reverses as generator field current returns to original value

Supporting increase in reactive output is present for many seconds

0 5 10 15 20 25 30 35 400.9

0.95

1

Vter

m

0 5 10 15 20 25 30 35 400

2

4Ef

d

0 5 10 15 20 25 30 35 402.3

2.4

2.5

Ifd

0 5 10 15 20 25 30 35 4090

95

100

Pg

0 5 10 15 20 25 30 35 40Time, sec

-20

0

20

Qg

0 5 10 15 20 25 30 35 400.95

1

1.05

Vter

m

0 5 10 15 20 25 30 35 402

3

4Ef

d

0 5 10 15 20 25 30 35 402

2.5

3

Ifd

0 5 10 15 20 25 30 35 4090

95

100

Pg

0 5 10 15 20 25 30 35 40Time, sec

0

20

40

Qg

100 MVA Generator Automatic voltage regulator

Initial near-instantaneous increase in reactive power output

Same initial increase in field current

Increase in reactive power output is sustained and augmented by voltage regulator action

Operation of excitation controls in voltage regulating mode is a long-standing requirement

100 MVA Synchronous Condenser Automatic voltage regulator

Initial near-instantaneous increase in reactive power output

Same initial increase in field current

Increase in reactive power output is sustained and augmented by voltage regulator action

0 5 10 15 20 25 30 35 400.95

1

1.05

Vter

m

0 5 10 15 20 25 30 35 401

1.5

2Ef

d

0 5 10 15 20 25 30 35 401

1.5

2

Ifd

0 5 10 15 20 25 30 35 40-5

0

5

Pg

0 5 10 15 20 25 30 35 40Time, sec

0

20

40

Qg

3 4 5 6 7 8 9 10 11 12 13Time, sec

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Vter

m

Time/sec-4 -2 0 2 4 6 8 10 12 14 16

Vl-n/V

120

140

160

180

200

220

240

260

280

300

Voltage dip and recovery

In many cases simulations show results

like this

Now-available recording technology shows recordings of reality

like this

3 4 5 6 7 8 9 10 11 12 13Time, sec

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Vter

m

Time/sec-4 -2 0 2 4 6 8 10 12 14 16

Vl-n/V

120

140

160

180

200

220

240

260

280

300

Voltage dip and recovery

Is there something, incomplete, optimistic, or otherwise wrong with our simulations ??

Delayed voltage recovery like this is observed quite but it is far from universal

Do we know the cause ??

Industrial motors

Time scale of 0.5 - 10 secondsInertia constant H = 0.3 second

Short circuit at terminals of 100KW three phase motor driving a pump -

H = 0.3 second

Motor contributes significant short circuit current

Speed dips during fault - reacceleration is decisive

Immediate negative peak of torque transient approaches six times rated torque

Well understood behavior

Central to circuit breaker rating standards

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ias

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ibs

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ics

2.9 3 3.1 3.2 3.3 3.4-5

0

5

pe

2.9 3 3.1 3.2 3.3 3.40

2

4

6

8

10

qe

2.9 3 3.1 3.2 3.3 3.40

0.2

0.4

0.6

0.8

1

speed

2.9 3 3.1 3.2 3.3 3.4-5

0

5

te

2.9 3 3.1 3.2 3.3 3.4-1

-0.5

0

0.5

1

vas

Short circuit at terminals of 100KW three phase motor driving a pump -

H = 0.3 second

Motor contributes significant short circuit current

Thereby provides voltage support during the transient

Immediate negative peak of torque transient approaches six times rated torque

Speed dips during fault - reacceleration is decisive

Well understood behavior

Central to circuit breaker rating standards

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ias

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ibs

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ics

2.9 3 3.1 3.2 3.3 3.4-5

0

5

pe

2.9 3 3.1 3.2 3.3 3.40

2

4

6

8

10

qe

2.9 3 3.1 3.2 3.3 3.40

0.2

0.4

0.6

0.8

1

speed

2.9 3 3.1 3.2 3.3 3.4-5

0

5

te

2.9 3 3.1 3.2 3.3 3.4-1

-0.5

0

0.5

1

vas

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ias

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ibs

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ics

2.9 3 3.1 3.2 3.3 3.4-5

0

5

pe

2.9 3 3.1 3.2 3.3 3.4-5

0

5

qe

2.9 3 3.1 3.2 3.3 3.40

0.2

0.4

0.6

0.8

1

speed

2.9 3 3.1 3.2 3.3 3.4-5

0

5te

2.9 3 3.1 3.2 3.3 3.4-1

-0.5

0

0.5

1

vas

Voltage dip at terminals of 100KW three phase motor driving a pump -

H = 0.3 second

Current contains AC and unidirectional components

Reactive power reverses during voltage dip - motor contributes to support of voltage

Immediate negative peak of torque transient approaches six times rated torque

Response to alternating torque is observable in speed transient, but only to minimal extent

Voltage dip at terminals of 100KW three phase motor driving a pump -

H = 0.3 second

Current contains AC and unidirectional components

Reactive power reverses during voltage dip - motor contributes to support of voltage

Immediate negative peak of torque transient approaches six times rated torque

Response to alternating torque is observable in speed transient, but only to minimal extent

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ias

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ibs

2.9 3 3.1 3.2 3.3 3.4-10

-5

0

5

10

ics

2.9 3 3.1 3.2 3.3 3.4-5

0

5

pe

2.9 3 3.1 3.2 3.3 3.4-5

0

5

qe

2.9 3 3.1 3.2 3.3 3.40

0.2

0.4

0.6

0.8

1

speed

2.9 3 3.1 3.2 3.3 3.4-5

0

5

te

2.9 3 3.1 3.2 3.3 3.4-1

-0.5

0

0.5

1

vas

Delayed voltage recovery is recognized to be associated with behavior of residential air conditioners

with direct-connected compressor motors

Air conditioner rotor Hmotor ~= 0.05 second

Time scale of tenths of a second

Voltage dip at terminals of 5KW single phase motor driving a residential air conditioner

H = 0.048 second

Speed is pulled down very strongly by the negative electromagnetic torque

Motor stalls and does not restart

Immediate negative peak of torque transient approaches eight times rated torque

Current drawn by stalled motor is five times normal load current

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

ias

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

ibs

1.9 2 2.1 2.2 2.3 2.40

0.2

0.4

0.6

0.8

1

speed

1.9 2 2.1 2.2 2.3 2.40

5

10

15

20

25

tl

1.9 2 2.1 2.2 2.3 2.4-150

-100

-50

0

50te

1.9 2 2.1 2.2 2.3 2.4-500

0

500

vas

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

it

1.9 2 2.1 2.2 2.3 2.4-500

0

500

vt

Voltage dip at terminals of 5KW single phase residential air conditioner motor

H = 0.048 second

Speed is pulled down very strongly by the negative electromagnetic torque

Immediate negative peak of torque transient approaches eight times rated torque

Motor stalls and does not restart

Current drawn by stalled motor is five times normal load current

Reactive load of stalled motors is several times greater than when they are running - prevents recovery of voltage

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

ias

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

ibs

1.9 2 2.1 2.2 2.3 2.40

0.2

0.4

0.6

0.8

1

speed

1.9 2 2.1 2.2 2.3 2.40

5

10

15

20

25

tl

1.9 2 2.1 2.2 2.3 2.4-150

-100

-50

0

50

te

1.9 2 2.1 2.2 2.3 2.4-500

0

500

vas

1.9 2 2.1 2.2 2.3 2.4-200

-100

0

100

200

it

1.9 2 2.1 2.2 2.3 2.4-500

0

500

vt

Motor behavior is sensitive to

Supply system impedance

Load torque-speed characteristic

Load torque-angle characteristic

Electrical phase at moment when voltage dip is initiated

Rate of change of voltage in initiation of voltage dip

Presence of other motors and load on feeders

etc. 1.95 2 2.05 2.1 2.15 2.2 2.25-200

-150

-100

-50

0

50

100

Tele

c nm

1.95 2 2.05 2.1 2.15 2.2 2.250

5

10

15

20

25

Tloa

d, p

u

1.95 2 2.05 2.1 2.15 2.2 2.25-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Spee

d, p

u

1.95 2 2.05 2.1 2.15 2.2 2.25 Time, sec

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Term

inal

vot

age,

V

It is not yet clear how air conditioning load will evolve in the USA

It is likely, though, that the penetration of electronically coupled motors will increase rapidly in across

the full field of driven loads