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> 71-000302-CLN-01

***TO: DISTRIBUTION***

FROM: C NEUMEYER\
SUBJECT: STUDY OF OH COIL COOLING vs. REP RATE

***References:***

\[1\] 71-000222-CLN-01, "OH Rep Rate Minimization, Minutes Of Meeting"

\[2\] NSTX-CALC-13-3, "OH Thermal Simulation"

A study has been performed \[2\] to determine the OH ∫i^2^(t)dt
allowables at repetition periods of 300, 450, and 600 seconds.

A FORTRAN program was used to simulate the heating and cooling of the OH
coil during a sequence of pulses. This program divides the coil
conductor length into small sections from which heat is transferred into
slugs of water which move from section to section as time progresses.

Parameters were set to those corresponding to one of the two-in-hand
conductors in the outermost layer of the coil, which amongst the 8
cooling paths has the longest length. The water flow was set equal to
the trip setting of the water flow switch. Simulation parameters are
summarized in Table 1.

**Table** 1 **-- Simulation Parameters**

  --------------------------------------------- ------------- -----------
  **Parameter**                                 **Value**     **Units**

  Path length                                   362.2         feet

  Conductor cross sectional area                0.2192        in^2^

  Cooling hole diameter                         0.1880        in

  Water inlet temperature                       10            ^o^C

  Water flow rate                               0.65          GPM
  --------------------------------------------- ------------- -----------

The temperature vs. time simulation at the end of the conductor (where
the water exits the coil copper) was compared against an actual OH coil
outlet water temperature strip chart recording taken during ISTP-001,
and reasonably good agreement was obtained (Figure 1). It is noted that
the temperature measurement was made using a thermocouple taped over a
metal section of pipe which is in the water stream after a section of
plastic hose approximately 30 feet downstream of the actual outlet from
the coil copper.

![](media/image2.pct)Figure 1: Calculated vs. Measured Cool Down

Simulation runs were made to determine the ∫i^2^(t)dt allowables and
ratched start of pulse (SOP) inlet water temperature at the three
repetition periods with the constraint imposed that the maximum copper
temperature at any time should not exceed 90 ^o^C. This allows for the
fact that, should a fault occur at I~oh~=24kA and T~oh~ = 90 ^o^C, the
final temperature will not exceed 100 ^o^C following an L/R decay of the
current.

Table 2 summarizes the results obtained.

# Table 2 -- Simulation Results

  ----------------- ----------------- ----------------- -----------------
  Repetition Period 300 sec           450 sec           600 sec

  Allowable         155.5 kA^2^-sec   262.1 kA^2^-sec   288.0 kA^2^-sec
  ∫i^2^(t)dt                                            

  Allowable         54%               91%               100%
  ∫i^2^(t)dt                                            

  T~sop~            43.4 ^o^C         15.3 ^o^C         10.0 ^o^C
  ----------------- ----------------- ----------------- -----------------

Figures 2 through 7 depict the copper temperature vs. time at the end
(water outlet) of the winding for a series of 5 pulses, and the copper
temperature vs. time at the start (water inlet), middle, and end (water
outlet) of the winding for the last of a series of 5 pulses (i.e. after
ratcheting has taken place).

Note that, after the ratcheting stabilizes, the peak temperature at end
of pulse is ≈ 90 ^o^C, although this is not immediately evident on the
curves (figures 2, 4, and 6) which depict the temperature evolution
during the sequence of pulses because it occurs for a brief period only
(until the entrained water and copper equilibrate a few seconds
following the pulse) which is within the sampling interval of the
graphics. Decay from the peak is visible, however, on figures 3, 5, and
7 which show the cooldown following the last pulse in the sequence, with
5 x smaller interval between plotted points.

![](media/image3.pct){width="6.0in" height="5.120138888888889in"}

Figure 2: Temperature at End of Winding Due to Five Pulses in Sequence,

600 Second Repetition Period

![](media/image4.pct){width="6.0in" height="5.120138888888889in"}

Figure 3: Temperature at Start, Middle, and End of Winding During and
After Fifth Pulse, 600 Second Repetition Period

![](media/image5.pct){width="6.0in" height="5.120138888888889in"}

Figure 4: Temperature at End of Winding Due to Five Pulses in Sequence,

450 Second Repetition Period

![](media/image6.pct){width="6.0in" height="5.120138888888889in"}

Figure 5: Temperature at Start, Middle, and End of Winding During and
After Fifth Pulse, 450 Second Repetition Period

![](media/image7.pct){width="6.0in" height="5.120138888888889in"}

Figure 6: Temperature at End of Winding Due to Five Pulses in Sequence,

300 Second Repetition Period

![](media/image8.pct){width="6.0in" height="5.120138888888889in"}

Figure 7: Temperature at Start, Middle, and End of Winding During and
After Fifth Pulse, 300 Second Repetition Period

The Rochester Instrument Systems (RIS) protective device provides an
∫i^2^(t)dt function along with a single time constant exponential decay.
This simple model cannot effectively simulate the OH coil temperature
vs. time because of the more complex behavior of the OH coil with its
very long cooling paths and the attendant "cooling wave" effect.
However, the RIS can still be used, in combination with the outlet water
temperature interlock, to protect the coil. In this case the role of the
RIS is to ensure that the ∫i^2^(t)dt during a pulse is within the
allowable, while the role of the water interlock is to ensure that
sufficient cooling has take place prior to the pulse (i.e. that the
start of pulse temperature is sufficiently low).

In order to be used this way the RIS ∫i^2^(t)dt accumulated during a
pulse needs to decay more or less completely prior to the start of the
next pulse. The RIS single time constant model was added to the
simulation to allow comparison with the simulated coil temperature
behavior. The simulation was set up with the RIS "action integral"
normalized to the coil rated ∫i^2^(t)dt corresponding to an 80 ^o^C rise
from 10 ^o^C starting temperature, and the simulated coil temperature at
the end of the coil normalized to 90 ^o^C rise, i.e. 288 kA^2^-sec.
Considering that, to cover the 3 repetition rates, the RIS action must
decay in as little as 300 seconds, a decay time constant of 60 seconds
was selected. Simulation results for the three repetition periods are
given in Figures 8, 9, and 10.

![](media/image9.pct){width="6.0in" height="5.120138888888889in"}

Figure 8: RIS and Temperature Simulation,

600 Sec Repetition Period

![](media/image10.pct){width="6.0in" height="5.120138888888889in"}

Figure 9: RIS and Temperature Simulation,

450 Sec Repetition Period

![](media/image11.pct){width="6.0in" height="5.120138888888889in"}

Figure 10: RIS and Temperature Simulation,

300 Sec Repetition Period

Thus if we set the RIS "rated action integral" to 288 kA^2^-sec, and RIS
"% trip" to the value from Table 2 which is appropriate for the desired
repetition period (54% for 300 seconds, 91% for 450 seconds, 100% for
600 seconds), and "tau" to 60 seconds, then the RIS will limit the
∫i^2^(t)dt appropriate for the repetition period. With the water
interlock set to ensure proper starting temperature, the protection
scheme is complete.

### CONCLUSIONS

The following steps need to be taken:

1)  Proper OH coil outlet water temperature monitoring needs to be
    implemented and interfaced with the Water Systems PLC and EPICS.

2)  The water flow and flow switch calibration to the 8 OH cooling paths
    needs to be carefully measured/re-calibrated when the center stack
    is reinstalled prior to the next run period.

3)  During the start up ISTP-001, the temperature measurements need to
    be recorded again (this time with better quality and correlation to
    actual pulse characteristics), and the simulation model described
    herein validated (using the measured flow rates instead of the set
    points as described herein) in terms of waveshape and amplitude.

4)  Based on 3), the water temperature interlock settings need to be
    established in the Water System PLC for the 3 repetition periods.

5)  Work needs to begin on a digital coil protection (DCP) system to
    replace the RIS. As soon as the algorithms are established they
    should be installed in the PSRTC control software which can provide
    redundancy to the DCP.

6)  Until the DCP is implemented the RIS can be used in conjunction with
    the water temperature interlock to limit the ∫i^2^(t)dt during a
    pulse.

cc:

M Bell

W Blanchard

R Camp

D Gates

J Chrzanowski

W Blanchard

T Egebo

R Herskowitz

M Kalish

S Kaye

R Marsala

J Menard

D Mueller

M Ono

G Pearson

M Peng

S Ramakrishnan

A Von Halle

M Williams

R Woolley

NSTX File