The conventional method of testing by a “megger” is done when the motor is at the same temperature as its surroundings. The megger reading may be well within the prescribed parameters for the motor to be started.
This, however, could lead to motor failure as very often considerable difference between resistance at working temperatures compared with the resistance of idle machinery at ambient temperature.
Damage Repair. However much preventive care is taken, accidents will occur, such as flooding, and the machinery becomes totally inoperative.
In such cases it is now almost always possible to repair the damaged motors or cables in-situ.
As a case in point, the Norwegian rig had two of its main pillars flooded with seawater. As a result, there was extensive damage to the steering motors, ballast and seawater pumps, and all associated cables. The pillars were cleared of seawater and all machinery, including cable ends, was washed down with fresh water.
In the initial stages of repair, two such special machines were used to treat the cables and motors for the ballast and seawater pumps. After 24 h, the first seawater pump was dried out and back in full operation and it was decided to increase the number of these machines to five. After 23 days, all ballast and seawater pumps had been satisfactorily treated, as well as over 100 cable courses with diameters ranging from 1.5 mm>2 to 240 mm>2.
The alternative method of repair would of course, have meant removing all motors ashore and no doubt the re-installation of some cabling.
* Сушка электрооборудования на месте.
Hometask: Ex. 10, 15, 18, 19.
The third class period
20 3
Listen to the sentences and define in each of them the meaning of the word “spare”.
1. I cannot spare my junior electrician just now. 2. The: spare parts set for the electrical equipment comprises parts and assemblies which can be used for the repairs to be carried out on the ship. 3. When ordering spares, please, quote the type designation and serial number of the machine. 4. Can you spare me some minutes? 5. “Oh, dear, spare me”,— she cried. “I can’t do what you ask me to”.
Listen to some requirements to the arrangement of the equipment and give them a free translation.
1. Instruments and devices shall be, so far as practicable, simple in design, easy for maintenance and safe in operation. 2. The equipment of a ship shall have high degree of reliability to ensure its durable operation under shipboard conditions. 3. Instruments and devices intended for being constantly under operating conditions shall be designed for durable and continuous operation. 4. All instruments and devices shall be designed for specific operating conditions and be capable of withstanding mechanical and climatic tests. 5. Instruments and devices shall be provided with proper supporting fittings for efficient securing in the regular places. It is allowed to use adequate shock absorbing appliances.
6. All lids, covers, doors and other removable parts of cases of the splash-proof type instruments which provide access to replaceable elements and components shall be so constructed as to allow their opening, closing, removal and replacement without applying any special tools. Free access to fuses shall be provided without applying any tools. 7. Removable slide and drop units of instruments shall be efficiently secured in the regular place in operating position. 8. Locking gear shall be provided to ensure efficient fixing, in open position, of the slide, book-type and drop units of instruments as well as partially removable lids, covers, doors, etc.
22 3
Instruct your electrician as to requirements to the arrangement of the equipment. Use ex. 21.
23 5
Fulfil or explain the following:
1. Name 10 parts and assemblies of the spare parts set for the electrical equipment which, can be used for the repairs to be carried out on the ship.
2. Define the term “in-situ method”.
3. Explain the construction and use of a wattmeter.
24 8
Record your answers on a tape.
