KEPCO HSP Series Operator Manual - Manual (Page 31)

HSPSERIES OPR 050614 3-5
The signal generated by the OVP detector is gated with a signal from the fault detector circuit to
produce a selective overvoltage shutdown function which prevents shutdown of operational
power supplies in a parallel-redundant power system configuration. The OVP latches of any
working power supplies are disabled, allowing only the faulty modules to be latched off; system
operation can then return to normal, assuming sufficient load capacity in the remaining modules
to support the load. This function is critical in fault-tolerant power systems, otherwise a single
overvoltage failure could ripple through all of the operating supplies and result in a complete
power system loss.
NOTE: The overvoltage protection circuit senses the voltage directly at the output terminals
of the power supply, not at the error sensing point. When selecting an overvoltage set
point, the user must take into account the expected power lead voltage drop and, if
applicable, the transient response overshoot in order to avoid false shutdowns. The
HSP design is such that the power supply cannot generate an output voltage high
enough to cause internal damage, regardless of OVP setting.
3.9 CURRENT LIMIT CHARACTERISTIC
HSP power supplies provide two different current limiting modes for different applications; selec-
tion of the desired mode is accomplished via switch S1-3, accessed through the top cover of the
HSP (see Figure 2-2). The following describes the operational differences and selection method
of each:
a) Continuous Limiting: This is the factory-set (default) mode of operation. When the output
current of the power supply reaches the programmed current limit, the output regulator
switches to current mode operation and maintains the output current by modulating the out-
put voltage; this operating mode is maintained indefinitely, and recovery to voltage regula-
tion mode is automatic upon reduction of the output current below the current limit point.
This mode is ideal for high-power battery chargers and applications where operation in cur-
rent regulation mode is normal, or where immediate recovery from an overload condition of
any duration is critical.
NOTE: HSP power supplies are designed to maintain continuous delivery of 110% of rated
current indefinitely. When operating parallel/redundant power supply configurations in
continuous limiting mode, the user must size the power supply/load interconnection
conductors to withstand the total maximum load current available from all of the paral-
leled power supply modules.
b) Undervoltage Lockout: This mode is enabled when S1-3 is set to ON (Figure 2-2). The
crossover from voltage- to current-mode operation is the same as for Continuous Limiting;
however, after approximately 15 seconds, the output load regulation circuit is locked off via
the overvoltage protection latch, requiring the user to recycle source power to restart the
power supply (see PAR. 3.8). This mode permits automatic recovery from short-term over-
loads, but eliminates the danger of overheating and damage to the load and load wiring
due to continuous exposure to high current; this is especially useful in redundant power
systems, where the continuous overload current of all of the paralleled power supply mod-
ules can be in excess of twice the normal load current. As the circuit is triggered by the
occurrence of an output undervoltage condition, this circuit can also protect circuits which
may be unduly stressed in the presence of an extended undervoltage condition; an exam-
ple of this are batteries, which can be damaged by discharge voltages below a specified
minimum.
NOTE: When undervoltage lockout mode is enabled, it is necessary to also enable the
Remote Reset function (see PAR. 3.12) in order for the Remote Inhibit function to oper-
ate properly.