KEPCO MST Series - Manual (Page 38)

3-6
MST SERIES 061813
3.7 FAULT PROTECTION
In addition to providing protection against externally generated faults, MST Power Modules
incorporate fault protection circuitry which protects the load in the event of an internal failure or
malfunction which may result in loss of output control. The fault classifications are output over-
voltage, output overcurrent, internal overtemperature, source power loss and open sense wire.
A description of the fault detectors associated with these faults is provided in the following para-
graphs.
The response of the Power Module to any of these faults (except for open sense/power lead) is
a fault shutdown procedure consisting of the following:
• All output power and signal relays are immediately opened, isolating the Power Module
from the load;
• Output voltage and current are programmed to zero;
• The dc-dc converter which powers the output stabilizer is latched off;
• A fault status flag is sent to the Controller indicating a catastrophic failure. Upon receiv-
ing a fault status flag, the Controller removes that Control Bus address from the look-up
table, preventing further commands from being directed to the faulty power module.
If an open sense lead or open power lead condition is detected, the fault shutdown procedure is
as follows:
• All output power and signal relays are immediately opened, isolating the Power Module
from the load;
• Output voltage and current are programmed to zero;
• A fault message is sent to the controller (Load Path Fault in CIIL, Relay Error in SCPI).
3.7.1 FAULT RECOVERY
Recovery from a fault status flag condition (described above) requires that the user cycle source
power off for a minimum of 5 seconds. After reapplication of source power, a device reset com-
mand (RST) must be sent to the module’s Control Bus address to restore the address to the
look-up table. This procedure eliminates any possibility of casual reapplication of a Power Mod-
ule to the system load after symptoms of a catastrophic module failure have been detected.
3.7.2 TRACKING OVERVOLTAGE AND OVERCURRENT DETECTORS
The output stabilizer control circuitry of the MST Power Module includes separate overvoltage
and overcurrent tracking amplifiers. These devices monitor the actual output voltage and current
supplied by the Power Module and compare them to the programmed voltage and current val-
ues. In the event that either parameter exceeds the programmed limit by an amount equal to
10% of the Power Module’s rated voltage or current, the circuit initiates a fault shutdown proce-
dure including a Device Power Loss status flag. The tolerance of the fault thresholds are ±3%.