1. BPA Air Conditioner Test Results
Tests on November 22nd and 28th, 2016

2. Key Takeaways Stalling Depends on many factors
There is no single “correct” set of stall values to use
These tests support the WECC phase 2 default values of Vstall=0.45 and Tstall=2 cycles as reasonable conservative values
More optimistic values that are still within the realm of reason are:
Vstall=0.45 and Tstall=5 cycles
Vstall=0.40 and Tstall=3 cycles or even 5 cycles

3. Factors which impact air conditioner stalling
Factors impacting AC stalling
Voltage dip magnitude
Voltage dip duration
Time to ramp down from initial voltage to dip voltage
Final voltage (recovery voltage)
Time to ramp up from dip voltage to final voltage
Ambient temperature
Fault initiating on the positive crest, zero crossing, or negative crest of the voltage wave cycle
With all of these factors, there is no single “correct” value to use for Tstall and Vstall

4. Voltage Dip Test Variables
Vrecovery
Vdip
Tramp
Trecovery
Tdip t

5. Test Background
These tests were conducted with a “Train” brand reciprocating compressor air conditioner
Tests were conducted on Nov. 22nd with an ambient temperature in the mid 90s F, and Nov. 28th with an ambient temperature at about 100 F

6. Nov. 22nd BPA Lab Tests
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
2 cycles
0.4
ramp
0.85 recovery
0.5 cycle ramp, crest
yes
22-Nov
mid 90's
0.45 no
3 cycles
0.5
4 cycles
5 cycles
6 cycles
9 cycles
12 cycles
Tests assumed a 0.5 cycle ramp down to Vdip, ramp started at the crest, and an instantaneous recovery to 0.85 pu
Key result here is that at Vdip=0.5 pu the air conditioner does not stall even for long dips (Tdip at 6 cycles, which is longer than 500 kV and 230 kV normal clearing times)
The data here also supports Vstall=0.45 and Tstall=32 ms as conservative WECC default data
May or may not stall for Vdip=0.45 and Tdip=3 cycles
Note it did stall for V=0.45 and Tdip 3 cycles. Didn’t stall until 12 cycles for Vdip 0.5

7. Nov. 28th BPA Lab Tests
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
2 cycles
0.45
ramp
0.85 recovery
0.5 cycle ramp, 0 xing no
28-Nov
100
3 cycles 99
0.4
yes
4 cycles
Tests assumed a 0.5 cycle ramp down to Vdip, ramp started at the zero crossing, and an instantaneous recovery to 0.85 pu
Temperature was slightly higher than the Nov. 22nd tests, also we applied the ramp starting a zero crossing instead of starting at the crest
Key result here is that recommending Vstall=0.45 and Tstall=0.032 s is conservative. A sensitivity study can decrease Vstall to 0.40 and Tstall to 3 cycles and still be within the realm of reason. Results show the air conditioner may or may not stall at this point

8. Nov. 28th BPA Lab Tests (2)
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
comments
2 cycles
0.45
ramp
0.85 recovery
0.5 cycle ramp, 0 xing no
28-Nov
100
no recovery ramp
0.5 cycle recovery ramp
1 cycle recovery ramp
0.4
yes
Tests assumed a 0.5 cycle ramp down to Vdip, ramp started at the zero crossing, and varied ramp up to recovery of 0.85 pu
Temperature was slightly higher than the Nov. 22nd tests, also we applied the ramp starting a zero crossing instead of starting at the crest
Key result here is that contactors consistently opened for Vdip=0.40 pu and consistently did not open for Vdip = 0.45 pu, regardless of whether recovery voltage was instantaneous or ramped over a cycle
Another result is that adding a 1 cycle ramp to the recovery voltage did not necessarily make the air conditioner more prone to stalling, at least not for Tdip=2 cycles.

9. Nov. 28th BPA Lab Tests (3)
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
comments
4 cycles
0.45
ramp
0.85 recovery
0.5 cycle ramp, 0 xing no
28-Nov 99
no recovery ramp
0.5 cycle recovery ramp
1 cycle recovery ramp
5 cycles
Tests assumed a 0.5 cycle ramp down to Vdip, ramp started at the zero crossing, and varied ramp up to recovery to 0.85 pu
Temperature was slightly higher than the Nov. 22nd tests, also we applied the ramp starting a zero crossing instead of starting at the crest
Key result here is that when doing sensitivity studies it is reasonable to set Vstall=0.45 and increase Tstall to 5 cycles. Also, assuming a 1 cycle ramp up to the recovery voltage of 0.85 does not necessarily increase likelihood of stalling

10. no recovery ramp, repeat test
Nov. 28th BPA Lab Tests (4)
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
comments
3 cycles
0.4
ramp
0.85 recovery
0.5 cycle ramp, 0 xing
yes
28-Nov
100
no recovery ramp no 99
no recovery ramp, repeat test
4 cycles
1 cycle ramp, 0 xing
5 cycles
Key result here is that assuming a 1 cycle ramp down for Vdip instead of a 0.5 cycle ramp down significantly improves performance
If a 1 cycle ramp is assumed, then Vstall=0.4 and Tstall=5 cycles is within the realm of reason
For a 0.5 cycle ramp, the air conditioner may or may not stall for Vdip=0.40 and Tstall=3 cycles. This supports the WECC recommended Vstall=0.45 and Tstall=0.032 s as conservative parameters
V=0.4 and Tdip=5 cycles in even more optimistic than what I put in the takeaway slide

11. Nov. 28th BPA Lab Tests (5)
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
2 cycles
0.4
ramp
0.85 recovery
0.5 cycle ramp, 0 xing no
yes
28-Nov
100
no ramp, 0 xing
no ramp, crest
Key result here is that assuming a 0.5 cycle ramp instead of no ramp has a significant impact on performance

12. Nov. 28th BPA Lab Tests (6)
Tdip
Vdip
POW
recovery
ramp, starts at
Stalled?
Contactors opened?
date
temp
2 cycles
0.4
ramp
0.85 recovery
no ramp, crest
yes
28-Nov
100
no ramp, crest, negative no
Key result here is assuming the dip starts on a negative crest gives a different result from assuming the dip starts on a positive crest
This may be because the air conditioner has an auxiliary winding with an in-run capacitor, so the positive voltage crest looks different from the negative voltage crest to the motor
If a 0.5 cycle ramp is assumed, then Vstall=0.4 and Tstall=2 cycles is within the realm of reason

13. Single Phase Motor Schematic
Note the in-run capacitor on the aux winding
Because of this, a positive voltage peak looks different than a negative voltage peak

14. Plots from Lab tests
These plots are from Tests done November 22nd and November 28th, 2016 at BPA using a Train brand reciprocating AC
Results are sorted in order of Vdip from highest to lowest (best to worst case)
For a given Vdip, results are sorted by Tdip from lowest to highest (best to worst case)

15. Tdip
POW to start ramp down on
Recovery voltage
Ramp duration
Vdip (% of initial voltage)
date
Initial voltage

16. Main winding voltage
Hi pressure chamber
Aux winding voltage
Main current
Aux current

31. Zoomed out view of a stall

32. Zoomed in view of the same stall

53. This one stalled and then managed to restart on its own