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Alarms
7300A User Manual
5-8
5.9. STANDARD ALARMS
5.9.1. Faults detected
These alarms monitor the following faults:
• supply voltage absent on one or several phases.
• supply frequency outside operating limits
• neutral reference voltage absent (in Star with neutral configuration, code 4S).
• Over Heating (for units
≥
125A)
The supply voltage absent alarm may be caused by supply network faults, blown thyristor or
supply protection fuses, open circuit breakers or line contactors.
The neutral reference voltage absent alarm may be caused by loss of the link to terminal 21
(‘EXT’ terminal block: external reference voltage) or by a blown fuse in the connection to
the supply neutral (see figure 2-9).
5.9.1.1. Availability
Supply fault monitoring (voltage absent or frequency out of range) is fitted as standard to
all 7300A thyristor units, including Base version units.
The neutral reference voltage is automatically monitored under the following conditions:
• Star with neutral load configuration (code 4S) is used, and
• the DLF or/and power control (code VICL) options are selected.
5.9.1.2. Alarm actions
If an alarm is detected, thyristor firing is cut off:
• at the end of the half cycle for a supply fault
• after approx. 5 s of integration for loss of reference neutral.
Alarms are signalled by:
• the position of the Alarm relay contact changes
(the relay is only fitted if one of the alarm options is selected)
• the green ‘ON’ LED flashes.
Also, if an alarm option is fitted, loss of reference neutral is indicated by the red ‘GRF’
LED lit steadily.
Important!
If the supply voltages upline from the thyristor unit are absent and the internal auxiliary
supply option is used (code ‘SELF’) all LEDs on the unit will be unlit.
5.9.1.3. Memorisation
Supply Fault alarms (voltage or frequency) are not memorised.
The indicators for faults detected return to normal (‘ON’ LED and relays in non-alarm
position) after the fault condition ceases.
If the reference neutral voltage connection is lost, the installation needs to be repaired and
the unit is therefore switched off. It is however possible to acknowledge this alarm using
the ‘ACK’ input with the ‘ICO’ option.