Ship lighting system insulation fault finding practical training operation

Practical Training Guide

I. Operational content

(1) Analog operating lighting circuit 220 V grid insulation low alarm;
(2) Operation of the pull-power search method;
(3) A hand-operated megohmmeter to test the insulation of the power grid.

II. Practical steps

💡 Technical Background:The insulation value of the ship's power grid, the insulation value of the electrical equipment should not be less than 1 MΩ. There are many factors that cause the insulation performance of the electrical equipment to decrease, we should try to avoid, once the insulation performance is reduced in time to rule out. Measurement of lighting grid insulation to ground, the lower the insulation resistance of the grid or power to ground, the greater the deflection of the meter pointer, when a phase of the ground, the meter pointer deflection is the largest, indicating that the insulation resistance is 0. For the newly constructed ships, most of the classification societies have stipulated that: for electric power, heat and lighting insulation distribution system, whether primary or secondary distribution network, should be equipped with a continuous monitoring device for monitoring the insulation resistance of the hull, and the insulation resistance should not be less than 1 MΩ once the insulation performance is reduced. Insulation resistance relative to the hull of the ship, and in the case of abnormally low insulation resistance sound and light signals. An alarm device shall be triggered as soon as the insulation resistance of the hull drops below 100 Ω per volt of supply voltage.

(1)

Answer alarms, silencing, and flashing.

(2)

Observe the reading of the distribution board megohmmeter to see if the reading is less than 1 MΩ, if so, then the grid insulation failure, otherwise you can pull the power to find or energized to find the way to find out the insulation performance of the part of the equipment.

(3) The proper operation of the pull-power search method:

① Switch observation:Disconnect the power switches one by one, observing the megohmmeter while disconnecting the switches. If you disconnect a switch, the insulation is back to normal, it shows that the switch controlled by the electrical equipment insulation is not good. Then the other disconnected switches one by one, while observing the megohmmeter readings, if the readings become smaller after the closure, then the circuit insulation is not good.

② Disconnect the power supply:Upon discovery of a ground fault line power supply switch, cut off the power supply to that line.

③ Secondary search:Use a hand-operated megohmmeter (commonly known as: a rocking meter) at the distribution panel (if present) to locate the secondary distribution network. Measure the insulation condition of the branch circuits to ground one by one.

④ Restore power supply:After locating the grounded branch circuit, pull off this distribution switch, close the rest of the switches, and close this distribution switch in front of the main switchboard to supply power to the rest of the equipment.

(4) The proper use of a hand-operated megohmmeter:

① Confirmation of good and bad:

A. Open circuit test:120 r/min speed shaking megohmmeter, two pens open circuit, megohmmeter pointer points to “∞”.
B. Short circuit test:Gently turn the handle, two pens short circuit, megohmmeter pointer points to “0”.

② Find the grounding point:In the case of a lighting system, when looking for a specific grounding point, you can use the(Maoism) one divides intwoThe grounding is done by disconnecting from the intermediate junction box to measure and determine which small area is grounded. After that, there are only a limited number of power supply points in each small area, and each power supply point should be checked one by one, mainly checking part of the leads of lamps, plugs and switches, and checking the internal conditions of lamps, plugs and switches. If no grounding point can be found after these checks, the cable from the junction box to the appliance should be checked until a grounding point is found.

III. Analysis and treatment of single-phase faults in lighting systems

Set the point of failure:Ground the kitchen light phase A in the lighting grid.

Phenomenal manifestations:

“AC 220V BUS LOW INSUL.” lamp flashes and the buzzer alarms as shown in Figure 7-5.

ANALYSIS: The light indicates low insulation of the lighting grid.

Figure 7-5 220V Low Insulation Fault Alarm

Treatment:Silence the sound and flash, acknowledge the alarm, as shown in Figure 7-6, use the pull method to locate the secondary network where the insulation fault occurred, and then use a hand-operated megohmmeter to locate the specific grounding point.

lamp/buzzer sound off

FLICKER STOP

Figure 7-6 Alarm Handling Buttons

SOP (Sequential Operating Procedures)

(1) Status verification:Ground gas lamp and distribution board type megohmmeter as shown in Figure 7-7, press the ground gas lamp button, in which the A phase lamp goes out, indicating that the A phase is connected to ground. Turn on the switchboard megohmmeter to measure the lighting network, the megohmmeter indicates 0 at this time.

(2) Main screen troubleshooting:In front of the main power distribution board, pull off the lighting distribution switches one by one to see if the megohmmeter indication returns to normal values.

(3) Recommendations for gate pulling sequence:Crew living area → Deck lighting area → Cabin lighting area → Pilot's station navigation facilities.

(4) Fault localization:After locating the distribution switch where the ground fault occurred, cut off the power supply to the circuit and check whether the megohmmeter indication returns to normal value.

(5) Secondary search:In front of the sub-distribution box, use a hand-operated megohmmeter to find the secondary distribution network and measure the insulation condition of the branch circuits to ground one by one.

(6) Partial recovery:After locating the grounded branch circuit, pull off this distribution switch, close the rest of the switches, and close this distribution switch in front of the main power distribution board to restore power.

(7) Regional pairs of points:When looking for a specific grounding point, disconnect from an intermediate junction box (e.g., in the middle of two rooms) to determine which small area (e.g., room) is grounded.

(8) Precision verification:There are only a limited number of power supply points in a small area (room), generally no more than 5 points, each power supply point should be checked one by one, mainly checking part of the leads of lamps, plugs and switches, and checking the internal condition of lamps, plugs and switches. If the grounding point still cannot be found after these checks, the cables from the junction box to the appliances should be checked until the ground fault point is found.

图 7-7 Ground Gas Lamp and Distribution Board Megohmmeter