Тест для электромехаников (CES v5.0)

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Right answers:
1

Which of the following is the minimum acceptable value of insulation resistance for High Voltage equipment?

Your answer is correct:

1 M Ohms.
2

High Voltage systems rely on the installed protective equipment being able to interrupt any fault in the system. Throughout the system, the fault level has been calculated, and under no circumstances must the system be modified to exceed this fault level. What is meant by fault level?

Your answer is correct:

The amount of apparent power that could flow into any fault at any point in the electrical network.
3

When there is a need to interrupt current flow in a High Voltage system it may be very difficult to quench the electrical arc, which is generated at the circuit breaker contacts. Which of the following among media is commonly found in High Voltage marine switchgear?

Your answer is correct:

Vacuum.
4

A High Breaking Capacity fuse found in a Main High Voltage Switchboard will typically have fault level rating of:

Your answer is correct:

40 kA.
5

“Protective discrimination” means the progressive grading of sizes, or tripping times of:

Your answer is correct:

Line fuses and overcurrent relays.
6

This is a typical emitter follower. What is the main reason for use of an emitter follower?

Your answer is correct:

The input impedance is made much larger than the output impedance.
7

The amplifier circuit is a common configuration used to amplify the difference in voltage between two input signals. In this case input 1 and 2. What is amplifier called?

Your answer is correct:

Differential amplifier.
8

Which of the function shown is this operational amplifier circuit performing?

Correct answer:

Integrator.

Your Answer:

Inverting amplifier.
9

Which function is this operational amplifier circuit performing?

Correct answer:

Differentiator.

Your Answer:

Integrator.
10

The figure shows a silicon controlled rectifier with a RC circuit connected in parallel. What is the purpose of the RC circuit?

Correct answer:

Protect the SCR against damage caused by fast high voltage spikes.

Your Answer:

Obtain current resonance.
11

This is a parallel L-C circuit with a curve showing frequency – impedance characteristics. Which of the formula gives the resonant frequency fo?

Your answer is correct:

fo = 1/(2*Pi*sqrt(L/C)).
12

Ordinary thyristors (SCR) must often be protected against reverse overvoltage transients, because even over-voltages of extremely short duration can destroy them. These SCRs have been given such over-voltage protection, but only one of them is correct. Which?

Your answer is correct:

Figure 1.
13

These circuits are all active filters. Which of the circuits is a low-pass filter?

Correct answer:

Figure B.

Your Answer:

Figure C.
14

Diodes are widely used in rectification, or the convension of alternating current to direct current. The sinusoidal input voltage V (in) is applied to the circuit shown. Which of the output voltages is correct?

Your answer is correct:

Figure 1.
15

The circuit symbol is a driver for a solenoid (coil) of a solenoid valve S. What is purpose of the diode IN 4 002 connected in parallel to the solenoid S?

Correct answer:

Allowing stored energy in solenoid to dissipate as freewheel current, and therefore prevent damage to transistor from inductive switching voltage.

Your Answer:

Making voltage drop of approximate 0,5 V between the operational amplifier and the transistor 2N5194 to assist transistor biasing.
16

The diode shown performs which function?

Your answer is correct:

Return inductive current to supply at switch off.
17

The circuit shown is a logic gate with two “high” input signals, A and B, and one output signal Q. Which type of logic function does the gate provide?

Your answer is correct:

OR gate.
18

The wheatstone resistance bridge is often used for measuring resistances in, for example, Pt 100 temperature sensors or strain gauges. This figure shows such a bridge. Under what conditions will the bridge be balanced? I.e. the current through the meter i(m) = 0.

Your answer is correct:

R1/R2 = R3/R4.
19

What function is this circuit performing?

Your answer is correct:

Differentiating.
20

This graphical symbol is a logic gate. Which type of gate?

Your answer is correct:

AND.
21

An important quantity which is useful in circuit analysis is known as conductance G (Siemens). Which of the formulas express the conductance for this circuit?

Your answer is correct:

G = 1/R.
22

A 5 V DC source has an internal impedance of 0,2 ohms. When a load of 2,3 ohms is applied what voltage will be measured at the source terminals?

Your answer is correct:

4,6 V.
23

What principle of measurement are viscosity controllers usually based upon?

Your answer is correct:

Measurement of differential pressure.
24

What is the maximum current that a 15 V, 3 Watt Zener diode can handle without damage?

Your answer is correct:

0,2 A.
25

The inductance, which will induce an EMF of 1 Volt in a conductor, when the current is changing at a rate of 1 Amp per second, is defined as:

Your answer is correct:

One Henry.
26

The typical current gain for a common emitter transistor is:

Your answer is correct:

10-200.
27

The instrument most widely used for testing of semiconductor diodes is:

Your answer is correct:

Multi-meter.
28

A 6-Volt DC relay is to be used with a 12-Volt power supply. The relay requires a current of 0,1 Amp. What is the series resistance required?

Your answer is correct:

60 Ohm.
29

Some ships generate electrical power at 440 V, but then step up this voltage to supply specific electrical equipment. One common example, may be to feed a large bow thruster. Why is this done?

Your answer is correct:

A large bow thruster will draw very large currents at low voltage. Being typically remote from the generator, significant voltage drops would occur at low voltage.
30

When work must be done on High Voltage equipment, it is vital that the equipment is earthed (grounded) after isolation procedures have been carried out. Why is this?

Your answer is correct:

To ensure that no energy remains in the system, and that it cannot be recharged by external influences.
31

When selecting switchgear to work with High Voltage it is important to use an appropriate arcing medium. What is meant by arcing medium?

Your answer is correct:

The gas, liquid or vapour, which will minimise creation of an electric arc as contacts open.
32

Sometimes an early warning of failure in High Voltage switchboards may be an unpleasant smell. If the switchboard uses gas circuit breakers, which of the following may indicate a potential problem?

Your answer is correct:

Rotten eggs.
33

A ship’s electrical system operates at 60 Hz, but when connected to shore supply it is supplied with 50 Hz. Which of the following would you expect?

Your answer is correct:

Electric motors will run at reduced speed, and will tend to overheat.
34

When starting three phase induction motors there is sometimes a need to use a star-delta starter. A star-delta starter exhibits, which of the following characteristics while connected in star.

Your answer is correct:

Reduced current and reduced torque.
35

A 3-phase cage rotor induction motor requires protection by a time delay overload trip. What is the reason for this?

Correct answer:

It will allow for inrush current, or motor specific faults.

Your Answer:

It will tolerate fault conditions during start up.
36

A cable has a resistance of 100 milli-ohms. It supplies a 300 A load over a distance of 100 metres. What is the voltage drop along it’s length?

Your answer is correct:

30 volts.
37

Low voltage ships tend to have insulated neutral systems. What is the reason for this?

Your answer is correct:

In the event of an earth fault vital equipment will not trip.
38

Power is available at a three-phase motor starter, but nothing happens (at starter or motor) when the start button is operated. Which of the following is a likely cause?

Your answer is correct:

Faulty contactor coil.
39

The continuity resistance of a 100 m long x 25 sq. mm cable (rated at 100 A) is to be checked. Which of the following results would you anticipate?

Your answer is correct:

Between 0,1 and 1,0 Ohm.
40

When performing electrical testing of a three phase motor, insulation resistance measurements may be influenced by which of the following?

Your answer is correct:

Temperature, pressure and dampness.
41

A transformer overheats while taking a shore supply. Which is the likely cause?

Your answer is correct:

Incorrect frequency
42

Continuity testing of a delta connected three phase induction motor yields the following results; U1-V1 = 4 Ohms, V1-W1 = 4 Ohms, W1-U1 = 4 Ohms. What is the value of continuity resistance for each winding i. e. U1-U2?

Your answer is correct:

6 Ohms.
43

When considering instrumentation systems, what is typical symptom of a fault with the span of an instrument?

Your answer is correct:

Zero-point is accurate, but 100 % input is not giving 100 % output.
44

Continuity testing of a delta connected three phase induction motor yields the following results: U-V = 3 Ohms, V-W = 3 Ohms, W-U = 6 Ohms. Which of the following is the likely condition?

Your answer is correct:

Open circuit winding between W and U.
45

A 250 V contactor has been fitted to a 220 V supply. Which of the following symptoms might be observed?

Your answer is correct:

Contactor chattering (vibrating).
46

Routine maintenance insulation testing of a three-phase inductuion motor should cover which measurements?

Your answer is correct:

U-E, V-E, W-E, U-V, V-W, W-U.
47

When measuring level of liquids with a conductivity level indicator, measurement is performed by:

Your answer is correct:

Electrodes.
48

When considering instrumentation systems, what is the meaning of the expression “dead-band”?

Your answer is correct:

The controller will not react to a process change in this range.
49

What should be the healthy continuity resistance of a 220 V, 2,2 kW, 10 A heating element, when checked near to it’s rated operating temperature?

Your answer is correct:

22 Ohms.
50

A thermistor, which provides feedback for a thermal control system, is suspected to have failed. Assuming there is no available replacement, which of the following methods may be used to prove it has failed?

Your answer is correct:

Disconnect the thermocouple lead from the controller, and replace with a mV source.
51

A triac is used to provide temperature control of an oven. The galley complain that the oven only reaches approximately 50 % of demanded temperature. Which of the following is a likely cause?

Your answer is correct:

One of the main switching elements in the triac has failed.
52

The coil of a 12 V, 120 mA DC relay must be connected across a 24 V supply. What action should be taken?

Your answer is correct:

Install a 100 Ohm resistor in series with the coil.
53

A galley hot plate uses a Nichrome/Magnesium Oxinde heating element, and is to be tested before being put into service for the first time. An insulation resistance test yields a reading of 0,3 M Ohm. Which action should be taken?

Your answer is correct:

Apply reduced voltage to the element for a few minutes. Then retest, and if ok put into service.
54

What kind of electrolyte is used for Nickel-iron batteries?

Your answer is correct:

Solution of potassium hydroxide (KOH) and water.
55

Two reference points for pressure exist, absolute zero and atmospheric pressure. What are pressures measured relative to absolute zero called:

Your answer is correct:

Absolute pressure.
56

A transformer is rated at 22 kVA, 440/220 Volts, 60 Hz, is used to step down the voltage to a lighting system. The low tension voltage is to be kept constant at 220 Volts. What load impedance connected to the low-tension side will cause the transformer to be fully loaded?

Your answer is correct:

2,2 Ohms.
57

In the circuit diagram shown the starter connects between which terminals?

Your answer is correct:

5 and 6.
58

What is the advantage of a transmitter with a narrow measurement range?

Your answer is correct:

Better linearity and increased accuracy.
59

Some automated control systems use a master controller and a slave controller. What is the meaning of “remote mode” related to a slave controller?

Your answer is correct:

The slave controller receives the set-point from the output signal of the master controller.
60

When turning a cascade control system, which of the following actions should be done first?

Your answer is correct:

Adjust the slave controller with the master controller in manual mode.
61

In the context of an automated process control system, what is understood by the expression Master Controller?

Your answer is correct:

The primary controller in a cascade control system.
62

In which of the following automated control processes will the time constant be of minor importance?

Your answer is correct:

Level control.
63

In terms of automated control systems, what is typical for a continuous control system?

Your answer is correct:

It is possible to predict the control mathematically.
64

Which of the following is typical for a feed-forward control system?

Your answer is correct:

Control of the process inlet side.
65

In the context of an automated control system, which controller must be tuned first in a cascade control system?

Your answer is correct:

The secondary controller.
66

When measuring viscosity with a restricted flow viscometer, the preferred sensing device is:

Your answer is correct:

Capillary tube.
67

The circuit diagrams illustrate four different methods of wiring between a Pt 100 temperature sensor and its signal processing electronics. Which of the wiring methods gives the best measuring accuracy?

Your answer is correct:

Figure 1.
68

In what kind of measuring equipment might we find a Bourdon-tube?

Your answer is correct:

In a pressure transmitter.
69

Which of the following detectors is preferred for detecting smoke from fire?

Your answer is correct:

Ionization type.
70

Which type of temperature sensor is used in this temperature measuring system shown?

Your answer is correct:

Thermocouple sensor.
71

Which electronic component or system is this graphical symbol illustrating?

Your answer is correct:

Bandpass filter.
72

Which device does this graphical symbol illustrating?

Your answer is correct:

Pressure to current converter.
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