GE Industrial Solutions CPS6000-M2 - Manual (Page 121)

CPS6000-M2 Installation Guide H5694720
Issue 8 January 2008 121
Low Temperature Compensation
This feature is disabled by default, and can be enabled only if Temperature Slope Thermal
Compensation is enabled. The following are the associated parameters.
Low Comp Limit: Low temperature thermal compensation can be set from -5°C to 20°C. The
factory default setting is 0°C.
Increase: The low temperature slope (rate of increase) can be set from 1mV to 10mV in 1mV
increments. The factory default setting is 3mV.
The Millennium II has a flexible Thermal Compensation feature which provides voltage
compensation from that level established by the Plant Float Set-Point (fsp) or Boost Set-Point
(bsp), dependent on the highest temperature monitored by the temperature probes located at the
plant batteries. Thermal Compensation should be used in a plant containing “sealed” or valve
regulated “maintenance free” batteries. Refer to the Installation Instructions for more details on
wiring and configuring this feature.
Thermal Compensation lowers plant voltage from the fsp for monitored battery temperatures
which are above the ideal temperature established during configuration as the Battery Thermal
Slope Nominal Temperature (ntt). The items in parenthesis are the user configurable points
referred to in the graph shown below. Lowering the plant voltage helps to keep the batteries at
their optimum state of charge while protecting them from thermal runaway. Thermal runaway is a
complex sealed battery phenomenon where, for one or more of a number of reasons, one or more
cells in a string are unable to dissipate the internal heat generated by their charging current and
experience an increase in internal temperature. By lowering the float voltage as cell temperature
increases, the float current is lowered to a point where this destructive behavior can be avoided. If
a cell failure is imminent and the cell temperature continues to rise above the threshold
configured for Battery Thermal Step Temperature (stp), plant voltage drops in a single step to a
level which keeps the remaining cells in the string from overcharging and being damaged. Refer
to the following figure for a graphical view of Battery Thermal Compensation and the
relationship of its various set points.
The Millennium II can also increase plant voltage above that set by the fsp or bsp for colder
environments, again seeking to keep batteries at their optimum charge state. Batteries will lose
capacity as the battery temperature drops below their optimal operating temperature. Increasing
the plant voltage for decreases in temperature will cause more current to flow into the batteries.
This results in electrolysis of the water in the batteries. Since this reaction is exothermic, it also
serves to keep batteries warm. This feature results in an increase in plant voltage, and is required
to be enabled during controller configuration.