EK-General – Section B ( Electrical) Questions & Answers

EARTHING

Q1. (a) Explain, with the aid of a sketch, the principle of operation of an earth leakage detection system of the instrument type (6)

(b) Explain why an insulated neutral system is used extensively on-board ships (2)

(c) State, with reasons, why a single earth fault on an insulated neutral system should always be cleared as soon as possible (2)

ELECTRICAL DISTRIBUTION

Q1. With reference to a THREE phase electrical distribution system:

(a) discuss the advantages and disadvantages of an insulated neutral system; (8)

(b) state how an earthed neutral system is earthed and the measures taken to limit the maximum earth fault current. (2)

ELECTRICAL PROTETCION & DEVICES

Q1. With reference to the protective devices fitted to a main alternating current generator, explain EACH of the following:

(a) overcurrent and short circuit protection; (2)

(b) generator negative phase sequence; (2)

(c) loss of field (excitation); (2)

(d) undervoltage; (2)

(e) reverse power. (2)

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Q2. With reference to electrical system protective devices, explain the purpose of EACH of the following;

(a) overcurrent protection (2)

(b) Short circuit protection (2)

(c) No-volt protection (2)

(d) Reverse power protection (2)

(e) Preferential tripping (2)

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Q3. With reference to electrical short circuits:

(a) state, with reasons, THREE factors that will influence the severity of a short circuit; (6)

(b) explain the role of reactance when selecting protective devices. (4).

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Q4. With reference to the protection of electrical power circuits:

(a) Explain discrimination, describing how it is achieved. (5)

(b) state, with reasons, the type of fuses used for protection; (3)

(c) explain preferential tripping. (2)

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Q5. With reference to the protection of electrical equipment in a distribution system:

(a) state the aims of the protective devices; (3)

(b) list the parameters that are monitored and acted upon by the protective devices; (4)

(c) state, with reasons, THREE causes of electrical fires. (3)

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Q6. With reference to overcurrent protection for electrical circuits:

(a) explain THREE methods of protection, stating where EACH may be used; (6)

(b) explain, with the aid of a diagram, the meaning of the term inverse current time characteristic. (4)

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Q7. (a) State FIVE essential electrical services that are able to be operable under fire conditions. (5)

(b) Explain how electric cables for the essential services in part (a) pass through bulkheads whilst maintaining gas tight and watertight integrity. (3)

(c) State the requirements for the cables which supply electrically driven emergency fire pumps. (2)

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EMERGENCY GENERATOR, EMERGENCY POWER, BATTERY

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Q1. (a) With reference to battery systems for emergency purposes, explain the precautions that must be taken with regard to personnel safety, storage and maintenance.(7)

(b) Explain how batteries are kept at the correct rate of charge. (3)

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Q2.During a complete loss of electrical power, essential vital services can be maintained by means of an Uninterruptable Power Supply (UPS).

(a)Describe, with the aid of a block diagram, the operation of an a.c. input UPS arrangement. (7)

(b)List SIX essential services that the UPS may support. (3)

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Q3. (a) With reference to an alkaline battery cell:

(i) describe a typical cell, stating the materials used; (4)

(ii) describe the electro-chemical process that takes place during discharge and charge.(2)

(iii) state the effect of overcharge. (2)

(b) State the advantages of an alkaline cell compared with a lead acid cell. (2)

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Q4. (a) Sketch a circuit diagram of an emergency generator power supply and distribution system, indicating the essential services provided. (6)

(b) State the emergency generator regulations. (4)

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Q5. With reference to lithium-ion batteries:

(a) explain why this type of battery has been adopted for shipboard use; (4)

(b) state ONE advantage and ONE disadvantage of lithium-ion batteries; (2)

(c) define EACH of the following:

(i) cell drift; (2)

(ii) thermal runaway. (2)

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GENERATOR EXCITATION & AVR

Q1. Describe, with the aid of a circuit diagram, the operation of an automatic voltage regulator (AVR) which employs the use of thyristors. (10)

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Q2.(a)Sketch a circuit diagram of a self-excited a.c. generator. (5)

(b)Describe the operation of the circuit sketched in part (a). (5)

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Q3. (a) Describe, with the aid of a sketch, a static excitation system for a generator. (8)

(b) Explain TWO advantages of static excitation. (2)

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GOVENER THEORY

Q1. Describe, with the aid of a block diagram, the operation of a load sensing electronic governor controller for an a.c. generator. (10)

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ICCP, MGPS SYSTEM

Q10. (a) Describe the principle of operation of a ships Impressed Current Cathodic Protection system. (6)

(b) State the routine maintenance that should be carried out on an Impressed Current Cathodic Protection system. (4)

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INDUCTION MOTOR

Q1. (a) Describe, with the aid of a sketch, the constructional details of a squirrel cage rotor as fitted in an induction motor (7)

(b) Explain why some rotors have a double cage. (3)

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Q2. With reference to braking of a.c induction motors

(a) Explain why braking may be required (2)

(b) Explain why electrical braking is preferable to mechanical braking (2)

(c) Explain the term plugging (2)

(d) Describe how dynamic braking is achieved (4)

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Q3. With reference to star delta starters used for three phase induction motors;

(a) explain in detail why this type of starter is employed. (4)

(b) explain, with the aid of a circuit diagram, the sequence of operation of a star delta starter. (6)

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INSULATION RESISTANCE

Q1. (a) Explain the principle of operation of an insulation resistance test, stating why the test is carried out on a regular basis. (6)

(b) Describe how EACH of the following electrical tests is carried out:

(i) resistance; (2)         (ii) continuity. (2)

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MOTOR STARTERS, STARTING TECHNIC

Q1. (a) State the consequences of using direct online starters for comparatively large sized a.c. induction motors. (2)

(b) Describe, with the aid of a sketch, an electronic soft starting system that may be used for large sized a.c. induction motors. (8)

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Q2. With reference to voltage variation profiles caused by load changes imposed on alternating current generators when starting large motors online:

(a) sketch a voltage dip, showing an acceptable recovery time; (2)

(b) state FOUR salient factors that cause the variation in part (a); (4)

(c) outline FOUR salient factors that assist recovery from the deviation shown in part (a).(4)

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Q3. With reference to three-phase induction motor starters:

(a) explain why star-delta starters are employed; (2)

(b) explain what is meant by reduced voltage starting in the context of star-delta starters;(2)

(c) explain, with the aid of a power circuit, the sequence of operation of a start-delta starter. (6)

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Q4. Describe how the starting torque of electric induction motors may be improved by using EACH of the following: (a) wound rotor; (5) (b) double cage. (5)

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Q5. Describe, with the aid of a sketch, an electronic soft starting system that may be used for large a.c. induction motors. (10)

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PARALLEL OPERATION , LOAD SHARING, POWER MANAGEMNT

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Q1. With reference to automatic Power Management Systems for the control of the operation of main switchboards and generators:

(a) list the features that the Power Management System controls in order to comply with the requirements for a vessel; (7)

(b) explain how the generators and switchboard would be controlled following a failure of the Power Management System. (3)

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Q2. Describe, with the aid of a block diagram, how automatic starting load sharing and stopping of generators in response to load changes is effected. (10)

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*************Unanswered Question **************

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Q3. With reference to the paralleling of a.c. generators:

(a) outline the requirements of synchronisation; (2)

(b) explain how KW power is shared; (1)

(c) explain how Kvar power is shared; (1)

(d) state SIX types of damage that may be caused when machines are incorrectly synchronised. (6)

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Q4. (a) Explain why it is necessary to provide reverse power protection for a.c. generators operating in parallel. (2)

(b) Sketch a generator protecting circuit. (5)

(c) Explain how to check the operation of the reverse power trip. (3)

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SHAFT GENERATOR

Q1. Describe, with the aid of a diagram, a shaft generator that uses a frequency converter. (10)

SURVEY

Q1. State the main electrical items covered in a Classification Society periodical survey. (10)

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TANKER SPECIFIC

Q11. Explain the meaning of EACH of the following types of electrical equipment:

(i) intrinsically safe; (2)     (ii) flameproof; (2)

(iii) increased safety; (2)     (iv) pressurised enclosure. (2)

(b) State TWO types of lighting equipment that may be installed in the pump room areas of a crude petroleum carrier. (2)

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TRANSFORMER

Q1. With reference to large electrical transformers on board ships:

(a) state where these transformers may be used; (1)

(b) state a typical efficiency range for a transformer; (1)

(c) state the regulations pertaining to transformers; (3)

(d) state the protective devices that are fitted; (2)

(e) describe the maintenance requirements. (3)

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