Английский язык для судовых электромехаников - [50]

The turbo is always started manually since it is never used as a stand-by set and the taking into operation of a turbo is based on the fact that you know that the steam power supply will be sufficient for some time. Furthermore, there are often certain visual checks to be done when starting up a turbo.

37

Home exercise. Check vour reading skills. See ex. 32, Section I, Unit 2.

Part V. Supervision 20

Each set is protected against damage which could occur in the event of deviation from normal values. Such deviations are sensed by means of transmitters in the automatic equipment or on the set. If a fault is detected, an alarm will be initiated but this can be delayed for up to 60 s.

An alarm may initiate tripping, stopping and blocking of the starting procedure on the set concerned. Alarm indications are provided in the control panel, where resetting of the alarm can also take place. The alarms can be either non-critical (NCR) or critical (CR). A critical alarm will stop the engine automatically immediately, since the set is considered to be in danger of sustaining damage. Non-critical alarms cause shutting down in accordance with the ordinary shutting-down program and the starting procedure is blocked.

Fill in the blanks in such a way that it makes sense.

1. Such deviations are sensed ... in the automatic equipment or on the set. (a) by means of each set; b) by means of transmitters; c) by non-critical alarms

2. An alarm may initiate ... of the starting procedure on the set concerned. (a) resetting of the alarm; b) shutting down; c) tripping, stopping and blocking

3. A critical alarm will stop the engine immediately, since ... (a) the starting procedure is blocked; b) the set is considered to be in danger of sustaining damage; c) such deviations are sensed by means of transmitters.

Now record your time and results.

Hometask: Ex. 36, 37.

The fifth class period

Review of “Automatic Control System for Ships Electrical Power Plants”.

38 15

Check your reading skills. See ex. 32, Section 1, Unit 2.

Part VI. Black-out Program

In the event of a black-out, the automatic equipment will start a certain number of diesel alternators. The set which is the first to acknowledge the frequency receives the instruction to switch onto the busbars. If the first set does not succeed in switching onto the busbars, it will be blocked and the next is allowed to make the attempt, etc. The reason for starting more than one diesel is primarily to prevent a fault on one set from delaying the clearing of the black-out condition, and in addition, the load often increases rapidly when the black-out condition has been cleared, and it is then advantageous to have at least one additional alternator about to be synchronized onto the busbars. The black-out condition is sensed by the automatic equipment by the fact that there is no voltage on the busbars and that all breakers are tripped. Both of these conditions must thus be satisfied.

Fill in the blanks in such a way that it makes sense.

1. The set ... receives the instruction to switch onto the busbars, (a) which is the first to acknowledge the frequency; b) which will be blocked; c) which delays the clearing of the black-out conditions.

2. If the first set does not succeed in switching onto the busbars,

(a) the automatic equipment will start a certain number of diesel alternators; b) it is then advantageous to have at least one additional alternator about to be synchronized onto the busbars; c) it will be blocked and the next is allowed to make the attempt, etc.

3. .. .is sensed by the automatic equipment by the fact that there is no voltage on the busbars and that all breakers are tripped, (a) delaying the clearing of the black-out condition; b) the black-out condition;

c) switching onto the busbars.

Now record your time and results. Compare them with ‘ previous ones.

39 15

Work in pairs. Dwell with your fellow-student on work with automatic control system for ships electrical power plants. Mind advantages and disadvantages (if any) of the system. Use ex. 17—19, 22, 24, 35—38.

40 35

Home exercise. Read the text. Write the number of logical units in each sentence. Draw a flow chart of programming of large loads. Make up as many questions on the text as you can and write a summary of it.

Part VII. Programming of Large Loads

If a relatively large load is switched onto the network, a load surge will occur and this may cause overloading and in the worst case, tripping of the circuit breakers due to overcurrent. The risk of not taking this fact into account is illustrated by the starting current of a directly starting induction motor being 5—10 times the rated current.

For preventing such damages automatic control system is provided with unit, designed to control switching in such large loads.

The request for switching in a certain load is made in the form of a closing contact function. The load to be switched in is exceeded, switching in of the load is blocked until conditions render this possible, i. e. until a new diesel has been synchronized onto the busbars. If the power limit is not exceeded, clearance is given for immediate switching in of the load. When the load is switched in, the simulation is switched off, since the load will be metered by the ordinary equipment.