The Duties of an Electrical Engineer on Board Ship

Seagoing electrical engineers are charged with the care of all the electrical machines and devices of the ship. They can be employed on the installation, maintenance and operation of marine electrical equipment. They will not be concerned with the design of machines and apparatus but rather with their performance and characteristics, so that lay-outs, switchgear, and electrical circuits can be dealt with in a practical manner. An understanding of typical connection diag­rams and the behavior of machines and apparatus is of immense help in efficient operation and maintenance.

The duties of an electrical engineer on board ship are diverse and multiple. He is at the head of the group of electricians and plans their daily work. On motorships the electrical group consists of one, two or three electricians and the electrical engineer. The electrical group of an electrically propelled ship includes the chief, the second, the third, the fourth electrical engineers and a few electricians. All the electrical engineers, except the chief one, keep watch, The elect­rical group on atomic ice-breakers consists of a large number of elect­rical engineers.

During mooring or departure of the ship as well as under difficult navigational circumstances the electrical engineer stands by the main distribution board which requires much skill and knowledge.

The electricians examine the electrical equipment every day, find out troubles and report about them to the electrical engineer. Under his guidance they find out possible reasons of the troubles and elimi­nate them. According to schedule they make prophylactic repairs.

The electrical group on board deals with the hull and deck machi­nery, with the navigation and communication equipment.

The electrical engineer of a modern vessel should be well-read in different branches of electronics.

5

B. With great pleasure. I'll try and do my best.

B. Yes, they are.

B. They meet the demands pla­ced on generators for ocean­going ships. B. Certainly, they do.

B. Oh, yes. Their reliability is unmatched by any other ma­ke of generators. B. They should be clean of dirt and dust. Their bearings should be occasionally lub­ricated.

B. They are replaced by a sili­con diode rectifier.

B. It's mounted on the shaft.

. Work in pairs. Ask your friend the following questions and let

him answer them:

A. Will you, please, give me some information about brushless a.c. generators.

A. Are conventional alternators being replaced by brushless generators?

A. Why have the brushless ge­nerators found worldwide ac­ceptance?

A. Do these generators resist to vibration?

A. Are the brushless generators reliable?

A. What maintenance do they require?

A. What are the alternator slip-rings and brushgear repla­ced by?

A. Where is this rectifier moun­ted?

Now change the parts. Let your friend ask you and answer his questions.

^ySpeak about the advantages of brushless generators, give rea-sonsJor their installation on modern oceangoing ships. The following words and expressions may help you: 1) to be replaced by 2) to find worldwide acceptance 3) to meet the demands (requirements) 4) to be subject to abrasion 5) to eliminate all routine electrical main­tenance.

Part II

Assignment: while reading the text get ready to speak about the excitation of the generators discussed.

F General description

The brushless alternators are specially designed for duty on board marine vessels. The series alternators are driven by diesel, turbines or main propulsion units. The ^outpjit/characteristics are plotted in the curve in Fig. 1. These electrical characteristics have been determined, so thatj)large |Squin-ebcage/motors can be started without difficulties arising. .

3 Jhese alternators are self-excitingjthe excitation being effected by means Ж "a Brushless (thyristor/ exciter. i'The alternator and exciter are combined in one complete screen-prbtected, splash-proof unit?

By using a thyristor exciter, the advantages of the brushless exciter and the static exciter are combined, no maintenance of bru­shes and slip-rings Js required, and rapid regulation is achieved.

For a starting^urrent surgg causing a 15% transient voltage drop, the^recoverv time is approximately 0.1 sec.-The voltage "control accu­racy! is better than ± 1 %.

*~ The standard alternators have been dimensioned so that the tran­sient/voltage drop, has a maximum of 1,5% during^starting current surge ol' approTimately 100% of the^ratecPaSrehj^cT the alternator. For alternators of 1000 kVA and above the corresponding value is somewhat lower.

fOQ\—I 1 1 I I 1 1 I 1 ~

60c/s BOO720 900 1200 1600 Speed 50C/S 750 WOO 1500 К p.m.

Fig. 1. The output characteristics

Overload s^The. alternators may be loaded with the current loadings, listed below (at rated voltage and .specified frequency) without da­mage being caused.⁵

110% for 2 h at P. F. 0.8 ^olz

120% for 1 h at P. F. 0.8

150% for 2 min at P. F. 0.5

Wave form. The maximum deviation of the line voltage from a sinu­soidal wave form during no-load conditions is 5% of the amplitude, Direction of rotation and phase'sequence^ The desired rotational direc­tion must be stated when ordering. ^When stating the direction of rotation, clockwise or anti-clockwise, rotation is determined as seen from the exciter end of the alternator. The phase sequence of the alternator is SI—S2—S3 for clockwise rotation and SI—S3—S2 for anti-clockwise rotation.!

The main exciter is a synchronous alternator with salient poles fitted on the stator member.

The auxiliary exciter is a synchronous alternator provided with a rotating field. In order to achieve a short assembly, the auxiliary exciter has been positioned and/ mounted inside the main exciter. Axi-ally positioned outside the exciter units, in the same .housing, is the rotary rectifier disc provided with diodes and thyristorsTTThe disc also embodies the rotary transformer secondary windings. Trie prima­ry windings are wound on a static plate, positioned behind the rotary rectifier disc.

The rotating part of the exciter is mounted on the alternator shaft, t the static part of the exciter being directly bolted to the alternator and shield.],The regulator and terminals are situated above the exci­ter stator.fThe regulator, which apart from the regulator circuits also contains trigger equipment, is situated in a small .enclosure and completely embedded in a compound.IThis has made tfeTegula-tor very resistant to vibrations and^gisture.

The rotary rectifier bridge is connected to the alternator field by means of cables laid in the alternator shaft.