Fault clearing currents were achieved and maintained at discharge rates from C/2 to C/3 at high and low states of charge. The fault clearing plateau voltage is strong function of: discharge current, and voltage-prior-to-the-fault-clearing-event and a weak function of state of charge. Voltage performance, for the range of conditions reported, is summarized

Lurie, C.

English

NASA Technical Reports Server

....f3 _U z_
Nickel-Hydrogen Battery Fault Clearing
at
Low State of Charge
C. Lurie
TRW Space and Electronics Group
Redondo Beach, California 90278
The 1996 NASA Aerospace Battery Workshop
The Huntsville Hilton
Huntsville, Alabama
December 3 - 5, 1966
1996 NASA Aerospace Battery Workshop -3 3 3- Nickel-Hydrogen Session
https://ntrs.nasa.gov/search.jsp?R=19970013731 2020-06-18T00:14:16+00:00Z
BACKGROUND
• Battery fault clearing requires high rate, short duration
discharges.
• Spacecraft batteries may be at low state of charge when a fault
occurs, e.g., during reconditioning discharge to 1.0 volt per
cell in a single battery power subsystem architecture.
• There is little relevant data available for this operating mode.
• Accordingly fault clearing data was obtained experimentally.
• The scope of the effort reported here includes determination of
nickel-hydrogen battery fault clearing capability at low state of
charge and comparison with capability at high state of charge.
Battery fault clearing requires high rate discharges for a short periods of time.
Fault clearing events are assumed to consist of fuse blowing and durations are typically
a few milliseconds. Faults can occur at any time and battery state of charge can vary
from full to very low state of charge. For example, a fault occurring at the end of a
reconditioning discharge, to 1.0 volt per cell, in a single battery system, could require
the fault to be cleared with little faradaic capacity in the battery.
Battery operating data describing short duration high rate discharge at low state
of charge is not available. Accordingly a relevant data base was determined
experimentally. Fault clearing data was obtained at high and low states of charge.
1996 NAS.4 Aerospace Battery Workshop -334- Nickel-Hydrogen Session
APPROACH
• Fault clearing events are simulated by 3-millisecond
discharges into resistive loads.
• The resistive loads are sized to provide data in the range
CI2 to 3C.
• All testing is performed at 10 ° C.
The experimental approach includes several assumptions and constraints.
Fault clearing events are simulated by 3-millisecond discharges into resistive
loads. Fuse blowing generally occurs in less than 3 milliseconds and the load
presented to the battery is closely approximated by a constant resistance.
The resistive loads are sized to provide data in the range C/2 to 3C (75 to 450
amperes with the 150 ampere-hour nickel-hydrogen cells used). This range provides a
broad and conservative data base.
All testing is performed at 10°C. This is a "typical" battery operating
temperature. A single temperature was considered adequate because fault clearing
capability is a weak function of temperature over the usual spacecraft operating
temperature range.
1996 NASA Aerospace Battery Workshop -335- Nickel-Hydrogen Session
PLAN
• Fault clearing discharges are performed at high and low states
of charge.
• Test Sequence
- Charge at the C/10 rate for 14 hours.
- Discharge at the CI20 rate.
- Add the fault clearing load, for 3 milliseconds, at 3 hours
into the C/20 discharge. (High state of charge event
soc = 85%)
- Continue the CI20 rate discharge
- Add the fault clearing load, for 3 milliseconds, at end of
discharge. Three end of discharge voltages were
considered: 0.9, 1.0, and 1.1 volts. (Low state of
charge event)
Comparison of data obtained at low and high states of charge provides
additional insight into the cell level processes taking place during the fault clearing
events.
The test sequence is designed to provide data at a high state of charge defined
by C/20 rate discharge to 85% state of charge and at three low state of charge
conditions defined as C/20 rate discharge to 0.9, 1.0, and 1.1 volts per cell. The
difference in capacity at 0.9, 1.0 and 1.1 volts per cell is small, but, as will be seen from
the data, the difference in fault clearing parametric performance is significant.
1996 NASA Aerospace Battery Workshop -336- Nickel-Hydrogen Session
Test Set Up
I Test Controller (PC) I
I I
Data Logger Data Logger .....
I
Programmable
Power Supply
(Charger)
!
Programmable
Electronic
Load
(SS Load)
Fault Load
(Resistive)
I--"
:-1
I
:-i
:1
,1
I
I
I 1
I
I1
I
_.L_
r
r
r
r
r
Test Cells -- 150 Ah NiH2
• RNH 150-2
• 0,030" slurry Ni electrodes
• 2 layers of Zircar separator
• 31% electrolyte (final)
• Nickel precharge
The test equipment was designed to control all aspects of charge, discharge,
thermal management, and data logging, automatically, with a PC as the primary test
controller. Separate data logging was provided for the low speed requirement to
provide continuous overall charge/discharge data, and the high speed requirement to
provide adequate data during the millisecond fault clearing discharge pulses. The fault
loads were superimposed on the C/20 steady state discharge loads at the appropriate
times.
The test cells were Eagle Picher (Joplin) RNH 150-2 150 ampere-hour nickel-
hydrogen cells packaged in a battery module shown on the next chart.
1996 _r_mS_4Aerospace Battery Workshop -337- Nickel-Hydrogen Session
12-Cell 150-Ah Battery Module
• RNH 150-2 cells
• Cooling via VCHP to
secondary mirror
• Fluid loop cooling capability
• Individual cell bypass
• Modular design
- 11 or 12 cells per module
- 110 to 210 Ah
The test cells were packaged in the 150 ampere-hour battery module shown
above. The packaging is modular in design and can accommodate 11 or 12 cells with
capacities from 110 to 210 ampere-hours. Each cell is protected against cell open
failures by individual cell bypass switches. Thermal management capabilities include
cooling by moving heat from the cells to center-of-gravity mount thermal sleeves and,
using variable conductance heat pipes (VCHP), to a secondary mirror for radiation to
space. Fluid loop cooling capability is also provided for thermal management where
active control is desired. The fluid loop cooling was utilized during the testing reported
here.
1996 NASA Aerospace Battery Work._hop -3 3 8- Nickel-Hydrogen Session
120-AMPERE 3-MILLISECOND PULSE
AT HIGH STATE OF CHARGE
l " " " Minimum cell v°ltage (volts'
1.8 _ -- -- Maximum Cell Voltage (volts) _ ....... t _-
_Current (amperes) _
r
1.4 ......
>0_1.2 ...............
_{ 1.0 ..........F-
J
O
-'1 0.8 ..............
ila
0.6 .............
0.2 ....
0.0
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0
TIME (milliseconds)
' - 3.5 volts
i
125
-- --÷ .......
I
-- 1 ..........
i
I
3.5 4.0 4.5
IO0
76
5O
A
26
S.
E
0
-26 I1_
0
-7S
-125
5.0
The 120-ampere discharge curve shows a typical fault clearing discharge at high
state of charge. Only maximum and minimum cell voltages are plotted because the
cells are well matched and the range of cell voltages is small. As can be seen from the
curves the voltage is very stable during the discharge period. The dip in cell voltage at
the leading edge of the pulse, as well as the "rounding" at the front end of the current
trace, are due to the non-linear (inductance and capacitance) elements in the battery
and test equipment. The large voltage excursion at the pulse turn-off is due, primarily,
to cell inductance.
1996 NASA Aerospace Battery Workshop -339- Nickel-Hydrogen Session
450-AMPERE 3-MILLISECOND PULSE
AT HIGH STATE OF CHARGE
2.0
1.8
1.6
_" 1.4
0
"-'1.2
I.U
<: 1.0I--
..,I
0
0.8
..I
..I
ILl
0 0.6
0.4
0.2
0.0
-0.5
--" Maximum CelI Voltage (volts)
- - - Minimum Cell Voltage (volts)
--Current (amperes)
I 'ii
1
0.0 0.5 1.0 1.5 2.0
I
i
i
!
I
500
400
300
-300
TIME (milliseconds)
The 450-ampere discharge also shows excellent voltage "stiffness" during the
fault clearing discharge. The difference between the starting voltage, e.g., the voltage
prior to the fault clearing event, and the plateau voltage is greater than observed with
the 150 ampere discharge. As will be seen in the succeeding charts the relationship
between the initial and plateau voltages is a function of cell impedance and follows
Ohms Law.
This relationship suggests that the energy expended during the fault clearing
event comes from cell capacitance and that mass transfer processes do not occur to
any appreciable extent.
1996 NASA Aerospace Battery Workshop -340- Nickel-Hydrogen Session
AVERAGE PLATEAU VOLTAGE
3-MILLISECOND PULSES AT HIGH STATE OF CHARGE
1.30
30 Millisecond Pulse, Midpoint Voltage
1.15 I Midpoint Voltage = -0.000512 x Current + 1.327 /
__ 1.10 ...............
=E
Q,
O 1.25>
uJ
°
k-
:3_>"J_O1.20
f
0 50 100 150 200 250 300 350
CURRENT (amperes)
1.05
400 450 500
Midpoint plateau voltage data obtained at high states of charge are summarized
in the plateau voltage versus pulse current chart. The slope of the voltage versus
current plot is the cell resistance; the linear relationship is an expression of Ohms Law.
The 30-millisecond data point is included to demonstrate the stability of the
plateau voltage. Stability in this time domain indicates that voltage decay due to
faradaic and mass transfer effects require longer discharge durations at these
conditions.
1996 NASA Aerospace Battery Workshop -341 - Nickel-Hydrogen Session
AVERAGE MINIMUM VOLTAGE
3-MILLISECOND PULSES AT HIGH STATE OF CHARGE
1.30
_>O1.20
>
1.10
z
u.I
0
1.00
UJ
0.90
=
i
\
\
Minimum Voltage = 2.59 x Current -0.158
1
P
m__
, I
0 50 100 150 200 250 300 350 400 450 500
CURRENT (amperes)
The minimum voltage observed during the fault clearing event may be of interest
in terms of spacecraft bus voltage regulation. This chart shows the relationship
between the average minimum voltage and the pulse current for the fault clearing data
obtained at high state of charge.
It is interesting to note that an excellent fit is obtained with a power curve. If the
voltage dip were due to cell inductance only the best fit would be provided by an
exponential model.
1996 NASA ,4erospace Batter)' Workshop -342- Nickel-Hydrogen Session
75-AMPERE 3-MILLISECOND PULSE
AT LOW STATE OF CHARGE
A
O
>
LU
(9
)--
O
>
UJ
L)
0.959 volt
_____ ..... 7 .......... 1252.5 volt ...... 100
, 0 I-
............... Z
u,,I
.......... -25 IZ
......... -50 _O
....... 75
....... 100
i -125
0.0 0.5 1.0 1.5 2.0 2.5 3,0 3.5 4.0 4.5 5.0
TIME (milliseconds)
The next series of charts shows similar plateau voltage versus pulse current
relationships obtained at low states of charge.
The 75-ampere curve shows fault clearing data following a C/20 discharge to
1.0 volt per cell. As can be seen from the chart the plateau voltage is stable and the
voltage level, following the pulse, returned to within a few millivolts of the starting
voltage. This is interpreted as meaning that very little mass transfer occurred.
1996 NASA Aerospace Battery Workshop -343- Nickel-Hydrogen Session
350-AMPERE 3-MILLISECOND PULSE
AT LOW STATE OF CHARGE
A
m
O
uJ
<C
I-
._1
O
>
_1
_1
uJ
O
- - - Minimum Cell Voltage (volts)
D -- Maximum Cell Voltage (volts)
_Average Cell Voltage (volts)
m . Current (amperes)
1.ooovolt ! / ! i
T_ D__'____
0.794 volt
,C
q
0.985 volt
i ......
3,5
5OO
TIME (milliseconds)
40O
300
100
0
-100
-200
-300
-40O
-500
4.0 4.5 5.0
200 "_
&
E
I--
Z
w
0
The 350-ampere curve shows data following a C/20 rate discharge to 1.0 volt
per cell and is similar to the previous 75-ampere rate curve. However the plateau
voltage is lower than the 75-ampere case and the post fault clearing voltage is lower
than the starting voltage. The lower plateau voltage is simply a function of the higher
current (Ohms Law) and the lower post fault clearing voltage is due to reduction of the
cell capacitance by an amount equivalent to the energy expended during the fault
clearing event.
1996 NASA Aerospace Battery Workshop -344- Nickel-Hydrogen Session
200-AMPERE 30-MILLISECOND PULSE
AT LOW STATE OF CHARGE
2.0
1.8
1.6
A
_. 1.4
0
>
"-" 1.2
UJ
<; 1.0I-
..J
0
0.8
.J
._J
uJ 0.6
0
0.4
0.2
0.0
- - - Minimum Cell Voltage (volts)
-- Maximum Cell Voltage (volts)
_Average Cell Voltage {volts_
_Current (amperes)
I
1.001 v
0.858 v
I i
I
0.961 v
I J i
-5 0 10 15 20 25 30 35 40 45
TIME (milliseconds)
200
150
100
50
0
-50
-1 O0
-150
-200
-250
-300
5O
&
E
ill
I--
Z
UJ
0_
n_
O
Thirty-millisecond pulse data, at low state of charge, is shown to demonstrate
that the plateau voltage trajectory exhibits a negative slope as energy is removed. This
slope, plus the lower post fault clearing voltage, is interpreted as indicating that the cell
capacitance is changing significantly, in this time domain, at these operating
conditions.
1996 ,,_,'_1S,4Aerospace Battery WorKshop -345- Nickel-Hydrogen Session
AVERAGE PLATEAU VOLTAGE
3-MILLISECOND PULSES AT LOW STATE OF CHARGE
1.10
UJ
_-_ 0.90
O.
I-
Z
0.80
o.
a
i
5
0.70
Following Discharge to 1.000 volts
Midpoint Voltage = -0.000583 x Current + 1,00
R 2 = 0,999
t __l l
Midpoint Voltage = -0.000573 x Current + 1.10
R2 =1
Following Discharge to 0.900 volts
.---- Following Discharge to 1.100 volts
0 50 100 150 200 250 300 350 400
CURRENT (amperes)
Midpoint plateau voltage data obtained at low states of charge are summarized
in this plateau voltage versus pulse current chart. As in the case of the high state of
charge data the slope of the linear relationship is cell resistance. Inspection of the
chart reveals that the intercept of the regression line is the voltage at which the fault
clearing pulse was started. The intercept, by definition, is the value of the plateau
voltage at zero current. In fact, the C/20 discharge rate is non-zero, but is low
compared to the fault clearing rates. Simple linear regression analysis yields intercept
values statistically indistinguishable from the starting voltages. The slopes at low
states of charge appear to larger than observed at high state of charge. It is
reasonable to assume that the cell impedance is slightly higher at lower states of
charge, however the statistical significance of the difference is marginal.
1996 NASA Aerospace Battery Workshop -346- Nickel-Hydrogen Session
AVERAGE MINIMUM VOLTAGE
3-MILLISECOND PULSES AT LOW STATE OF CHARGE
1.10 ...........
...... i ....
1.00 ....
_ wing Discharge to 1.100 volts
.____ .....
Followin j Oi=scharg_L ..... J
0.80 Minimum Voltage = 1.56 x Current .o.11s4_
C_ RZ = 0"992 | _
Following Discharge to 0.900 volts
0.70 I I I
0 50 100 150 200 250 300 350
CURRENT (amperes)
4OO
This chart shows the relationship between the average minimum fault clearing
voltage and the pulse current for the fault clearing data obtained at low state of charge.
As in the case of the data obtained at high state of charge, this data can be fit with a
power curve.
1996 NASA Aerospace Battery Workshop -347- Nickel-Hydrogen Session
NiH2 Cell Equivalent Circuits
Millisecond Time Domain
• Applicable to the 3-millisecond pulse
Re
o O
• Applicable to the 30-millisecond pulse
C
II
R
Cell performance can be described by simple equivalent circuits for the
simulated fault clearing events presented here. A complete description of cell
impedance includes inductive, resistive, and capacitive elements, as well as terms
dealing with electrochemical phenomena. A "complete" cell equivalent circuit would
contain all these elements and would be very complex. However, in the time domain,
and at the operating conditions studied, significant simplifying assumptions are
possible.
The "3-millisecond" data can be described simply by an inductance in series with
a resistance. Cell capacitance is large enough and the time constant long enough to
allow the capacitance term to be ignored. Mass transfer effects are insignificant in this
time domain and are also ignored. Because the time constant for the inductive term is
very short it too can be ignored if only the plateau voltage is needed.
If the pulse duration is extended, as in the 30-millisecond pulse data, a
capacitance term is added to provide the proper plateau voltage trajectory.
1996 NASA Aerospace Battery WorL_hop -348- Nickel-Hydrogen Session
SUMMARY
• Fault clearing currents were achieved and maintained at
discharge rates from C/2 to 3C at high and low states of
charge.
• The fault clearing plateau voltage is a strong function of
discharge current and
voltage-prior-to-the-fault-clearing-event
and a weak function of state of charge.
• Voltage performance, for the range of conditions reported, is
summarized as
--(( × _ )-( × _ )× )× +
where
VMPP =
SOC =
IDSCHG =
VSTRT =
Fault clearing midpoint voltage, volts
State of charge, %
Fault clearing current, amperes
Voltage at the start of the fault
clearing event, volts
1996 ?x,2_tS,.!Aerospace Battery lt'orkshop -349- Nickel-Hydrogen Session



Nickel-Hydrogen Battery Fault Clearing at Low State of Charge

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