Maintenance of main switchboard

During the exploitation of Switchboards (SB) and Control Panels (CP), the following are performed:

1. turning ON and OFF Generators and consumers of electricity;

2. maintaining nominal values of voltage and current of Generators in operation (in the absence of automatic voltage and frequency regulators);

3. transferring the load from one of the parallel Generators to others and ensuring the economical operation of the Power Management System (PMS);

4. load transfer from ship Generators to power supply from the shore network and vice versa;

5. monitoring the readings of measuring instruments that control the parameters of Generators, coastal network and consumers (voltage, frequency, current, power, insulation resistance, etc.);

6. operation control protection, signalling and blocking devices;

7. overheating control of devices and apparatus tires and current-carrying parts;

8. devices and instruments control of vibration and noise;

9. keeping the switchgear and control room clean.

When preparing the switchgears for operation after a long non-working period, it is necessary to:

1. make an external inspection and make sure that there are no foreign objects, moisture and dust on the current-carrying parts;

2. check the condition of contact connections and fasteners;

3. make sure that all ACB and other switching devices are turned OFF;

4. check the correct operation of all devices by turning them ON without current;

5. check and ensure the proper actuation value of protective fuses;

6. make sure that the dielectric mats of the switchboards and control panels are clean and intact.

Figure 80. Switchboard

 

Figure 81. Switchboard Construction

Consumers of electrical power that can be powered either directly from the Main Switchboard or through the Emergency Switchboard should, as a rule, be powered through the ESB under all operating conditions.

When sailing in difficult conditions, it is not recommended to perform any switching and checks on the Main Switchboard, Emergency Switchboard and control panels unless absolutely necessary.

The doors of the Main Switchboard and distribution switchboards must be locked.

Turning ON and OFF the ACB with a manual drive must be carried out by continuous movement of their handles to the extreme positions (stops). It is not allowed to leave the ACB handles in an intermediate position.

Figure 82. Automatic Circuit Breakers.

Switching ON the ACB after their automatic trip is carried out by transferring the handles to the “OFF” position, and then to the “ON” position.

Note. In ACB with an electric motor drive of the spring mechanism, it is recommended to check the limit switch at the pointer of the electric motor.

The position of the ACB contacts is determined only by special devices or signal lamps.

In case of ACB false trip, it is necessary to turn them ON again. In case of repeated tripping, the switching ON of the ACB is allowed only after the elimination of the tripping cause.

When the ACB trips due to an overload or a short circuit in the protected circuit, the reason for trip should be eliminated before reconnection, the ACB should be inspected and, if necessary, the consequences of the trip should be eliminated. If immediate reactivation of the ACB is required, they should be inspected as soon as possible.

Jamming, as well as the work of ACB with removed arc chutes is prohibited.

Temporary disabling or blocking of ACB releasing gears is allowed, if necessary, only to prevent an emergency situation.

For each fuse in the switchgear and control panel, its purpose and the value of the fuse-link (element) current must be indicated.

Figure 83. Fuses

It is necessary to use only regular fuse-links (elements). Backup fuse-links (elements) and pliers for extracting fuses usually located in the switchgear and control room.

Plug fuses must always be screwed in tightly. It is forbidden to put any metal gaskets or wire under the fusible inserts (elements).

In case of burning (melting) of the fusible insert (element), fuse should be replaced; in case of repeated operation, replacement is permitted only after the cause of melting has been eliminated.

The correct position of the arrows of measuring instruments relative to the scales should be checked at least once a month. The arrows of disconnected ammeters, voltmeters and watt meters should show "0"; switchboard megger - ∞ (infinity); the arrows of frequency meters and phase meters can be in any position.

The duration of the inclusion of pointer synchroscopes, switchboard megohmmeters and voltmeters for measuring the insulation resistance of networks is determined by the diagrams of specific devices and instructions for their operation.

Note. Usually there are 4 switchboard megohmmeters on board of any vessel:

- two on the MSB, one for 230 V consumers and one for 440 V consumers;

- two on the ESB, one for 230 V consumers and one for 440 V consumers.

As a rule, all megohmmeters have “Low insulation alarm”, which is connected to ships Alarm and Monitoring System (AMS), set point of this alarm should be maintained at all times at a value of 0,5 MOhm for 440 V and 0,3 MOhm for 230 V, unless another requirements take place from shipowner side, but not lower.

Preparation for the operation of the Main Switchboard includes the following operations:

1. Check the state of the Main Switchboard, ensuring that the following conditions are met:

a) absence of foreign objects inside the Main Switchboard: tools, fasteners, etc.;

b) cleanliness, lack of moisture on devices, assemblies, parts of the Main Switchboard and their reliable fastening; the contact connections of the busbars are securely tightened, there is no loosening of the fasteners of individual parts of the Main Switchboard.

2. Perform an insulation resistance test in the following order:

a) turn ON all switching devices of the main circuit and connections to the electric power system (EPS);

b) turn OFF the megohmmeter installed on the switchboard;

c) measure the insulation resistance with a portable megohmmeter, choosing appropriate voltage value. If the insulation resistance of the Main Switchboard and ships electrical grid is below the established norm (0.5 MΩ), the insulation resistance of the Main Switchboard should be measured separately from the external circuit.

If at the same time the insulation resistance of the Main Switchboard is below 1 MΩ, then the switchboard must be dried. Drying is carried out with air heated to 80-85°C, which is applied into the Main Switchboard from below.

If drying fails to increase the insulation resistance of the Main Switchboard, then it is necessary to check the insulation of each individual section of the circuit, and then each device. After finding a part or area with low insulation, it is necessary to eliminate the cause or replace the part with a new one.

3. before applying voltage to all ACB, switches and instruments should be set to “0” or OFF position;

4. turn ON the power supply.

Technical maintenance without disassembling is recommended to be carried out at least 1 time in 6 months. At the same time, dirt should be removed from the switchboard and its equipment, the contacts to be tightened, and the operation of manual control equipment to be tested.

A technical maintenance with partial disassembly is carried out at least 1 time per year, the contacts are additionally cleaned, worn parts are replaced, the insulation resistance is brought to normal, and the devices are adjusted. Then the Main Switchboard is tested in operation under load.

When performing maintenance with partial disassembling on the Main Switchboard, the voltage is completely removed, the tires are short-circuited with jumpers and grounded. If this is not possible, then the Main Switchboard should be partially de-energized.

Figure 84. “Dead” Switchboard

Maintenance of Automatic Circuit Breakers

When doing maintenance on a Automatic Circuit Breakers, it is necessary:

1. check and tighten, if necessary, contacts and fastening connections;

2. check the health of the springs and replace worn springs;

3. check the presence of lubrication in the electric motor drive gearbox, bearings and swivel joints, if necessary, lubricate the rubbing parts with the recommended lubricant;

4. remove soot and deposits from contact surfaces;

5. check the simultaneity of closing and the absence of skewed contacts; the magnitude of the contact pressure of the main and arcing contacts, gaps and gaps of the contacts in accordance with the instructions for use;

6. inspect and clean arc chutes;

7. make sure that the moving parts of the ACB work properly and move freely when manually turning it ON and OFF;

8. check the actuation of the ACB when exposed to the tripping mechanism of the disconnecting separators;

9. check the operation of ACB mechanical indicators (switching position, state of the spring mechanism, actuation of releases, etc.);

10. check the condition of the contacts, the correct operation of the safety devices and mechanical locks of the positions of the plug-in ACB.

Figure 85. Automatic Air Circuit Breaker

Deposits formed on the working surfaces of the contacts should be cleaned exclusively with an electro-solvent (manufacturers' recommendations), without disturbing the shape of the contacts. The use of emery cloth (paper) and polishing of contacts are not allowed.

Carbon deposits and soot formed on contacts with silver linings are removed with a rag moistened with a recommended detergent.

Darkening of silver linings is not a sign of their malfunction. In case of severe burning or wear of the working surfaces, the linings or contacts should be replaced.

When the ACB is switched ON, the arcing contacts should be closed first, then the preliminary (if any) and the last - main contacts. When disconnecting the ACB, the opening of the contacts must occur in the reverse order.

In ACB, where the arcing contacts close only during switching ON and OFF, the distance to the arcing contacts (gap) should be 1-1.2 mm.

The value of the contact pressure is measured with a dynamometer; the countdown is made at the moment of falling out of the paper strip placed between the contacts.

When examining ACB arc chutes, dust and metal particles should be removed and make sure that the plates of the deionic gratings are not deformed, and the inner surfaces of the chambers are not burned. If the walls of the chambers have significant carbon deposits in area and depth, and the metal plates have a large melting, the chambers should be replaced.

Figure 86. Automatic Air Circuit Breaker Arc extinguishing camera

 

It is allowed to check the actuation of the breaker from the impact of opening releases, as well as the action of mechanical delays of operation by manually acting on the armatures of the releases when the breaker is ON.

The operation of the remote and minimal releases is recommended to be checked by turning ON and OFF their power circuits; at the same time, the impossibility of switching on the ACB is checked if the armatures of the minimal releases are not pulled.

Particular attention during maintenance of plug-in ACBs should be paid to ensuring the necessary pressing of the contacts and the absence of their overheating; darkening of the contacts may indicate unacceptable overheating.

To prevent possible unacceptable overheating of the contacts of permanently ON ACB due to the deterioration of the contact surfaces and the increase in transient resistance, it is necessary at least once every 3 months, turn ON and OFF the ACB several times in a de-energized state.

If the cause of false trips of the breaker during start-ups of electric motors or with a long flow of currents that do not exceed the rated currents of the ACB releases is the underestimated settings for the operation of such thermal releases or a prolonged increase in the temperature of the air surrounding the breaker, it is allowed to increase the trip settings of the releases in the presence of control means with a graduated scale or pointers "greater than" - "less than", if applicable.

In the absence of such means or indicators, or ineffective adjustment of settings, it is recommended to replace the breaker with similar reserve ones with the nearest higher rated currents of the releases.

During maintenance of Generators and critical consumers ACB, it is recommended to check and, if necessary, adjust the settings and response times of overload releases, undervoltage and GACB protection against reverse power (current) see pct., including separate combined GACB protection devices.

Notes:

1. The specified checks and adjustments must be carried out at least once every 5 years, as a rule, during the docking of the ship.

2. Checks and adjustments of the GACB protection against reverse power (current) must be carried out at least once a year.

Figure 87. Revers power relay

 

Figure 88. Reverse power protection principal of operation

 

Overload releases can be tested by:

1. direct loading of Generator by ship consumers or special loading devices;

2. special devices or protection test stands;

3. current changes in the secondary windings of current transformers (supply releases or protective devices) from an external source and other indirect methods.

The test of undervoltage releases can be carried out using autotransformers.

Checking and adjustment of combined generator protection devices must be carried out in accordance with the operating instructions.

Checking and adjustment of semiconductor releases ACB must be carried out using special technical means.

Maintenance of switches and fuses

Figure 89. Power fuse and rotary switch

 

When operating rotary switches, it is necessary to ensure:

1. no jamming of the rollers and their clear fixation in each position;

2. reliability of contact connections.

When operating rotary switches of chopping action, it is necessary to ensure:

1. clamping tightness in the terminals of buses and wires to prevent overheating of contact connections;

2. reliability of grounding of non-current-carrying parts of devices mounted on the front side of the switchboards.

Knives and sponges of switches of chopping action, in the presence of melting and grooves on them, should be cleaned with an eraser or an electro-solvent, after which all contact surfaces should be wiped with a dry rag.

When servicing tubular fuses, it is necessary to ensure the reliability of contacts between the fuse-links (elements) and their holders. Signs of poor contact may include darkening of contact surfaces and charring of housings.

Figure 90. Control fuses

 

It is forbidden to replace fuse-links (elements) under voltage. If tubular fuses cannot be disconnected by switches, they should be removed and installed only with special pliers or handles.