Ship-440V-Power Grid Insulation Fault Finding Practical Training: Pulling Method and Pumping Exhaustion-SOP

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.

Initial Disposition:Answer alarms, silencing, and flashing. Observe that the switchboard megohmmeter reads less than 1 MΩ.

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.

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.

Standardized process for power equipment troubleshooting

STEP 1
Mute the sound and flash to confirm the alarm. Initial lockout of phase B fault by megohmmeter with ground gas light.

Key!
Important pumping operations:The standby unit must be started first to replace the currently operating unit, and direct shutdown is strictly prohibited!

STEP 2
Stop each pump and ventilator in turn. Observe the megohmmeter: when the insulation of a motor is restored by stopping it, the faulty machine is locked.

STEP 3
Faulty equipment is shut down and de-energized for targeted treatment to improve insulation (e.g., drying, cleaning).