Post on 11-Feb-2017
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