Ship Power Grid Insulation Fault Finding Practical Training Operation
440V/380V Power System Practical Procedures
I. Operational content
(1) Analog operation of power grid insulation low alarms
(2) Correct operation of the pull-power search method
(3) Testing grid insulation with a hand-operated megohmmeter
(4) Simulated start-up of emergency generator sets
II. Core practical steps
Indicator requirements:The insulation value of the ship's power grid and electrical equipment shallNot less than 1 MΩ. Once the hull insulation resistance has dropped to one volt per volt of supply voltage 100 Ω Below this level (e.g. 44 kΩ for a 440 V network), the audible and visual alarm must be triggered.
1
Initial Disposition:Answer alarms, silencing, and flashing. Observe that the switchboard megohmmeter reads less than 1 MΩ.
2
The essentials of the pull-power search method:
- Disconnect the power switch one by one and observe the megohmmeter; if the insulation is restored in one of the disconnected paths, the control equipment in that path is faulty.
- After confirming the faulty line, cut off the power supply to that line.
- Use a hand-operated megohmmeter at the distribution board to measure branch circuit-to-ground conditions one by one.
- Isolate the faulty branch, close the remaining switches, and restore power to the non-faulty equipment.
3
Hand-operated megohmmeter to confirm (120 r/min):
● Open circuit test:Meter pen open, pointer points to “∞”。
● Short circuit test:Meter pen shorted (light turn), pointer points to “0”。
III. Power system fault finding (No. 1 sea water pump practical training case)
Fault Setting:50 kΩ resistance between phase B of the first seawater pump and the hull.
Alarm phenomenon:
“AC 440V BUS LOW INSUL.” lamp flashes and buzzer alarms.
Failure Analysis:Indicates low power grid insulation. The megohmmeter indicates approximately 0.05 MΩ, and phase B of the ground lamp is dimmed.
