Тест для электромехаников (CES v5.0)

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Правильные ответы:
1

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

Правильный ответ:

1 M Ohms.

Ваш ответ:

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?

Правильный ответ:

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

Ваш ответ:

The current level flowing into a symmetrical short circuit fault between all three phases.
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?

Ваш ответ правильный:

Vacuum.
4

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

Ваш ответ правильный:

40 kA.
5

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

Правильный ответ:

Line fuses and overcurrent relays.

Ваш ответ:

Generators and motors.
6

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

Differential amplifier.
8

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

Ваш ответ правильный:

Integrator.
9

Which function is this operational amplifier circuit performing?

Ваш ответ правильный:

Differentiator.
10

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

Правильный ответ:

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

Ваш ответ:

Provide a controlled time delay for the SCR trigger pulse.
11

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

Правильный ответ:

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

Ваш ответ:

fo = 1/(sqrt(1-LC)).
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?

Ваш ответ правильный:

Figure 1.
13

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

Правильный ответ:

Figure B.

Ваш ответ:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

Allowing stored energy in solenoid to dissipate as freewheel current, and therefore prevent damage to transistor from inductive switching voltage.
16

The diode shown performs which function?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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.

Ваш ответ правильный:

R1/R2 = R3/R4.
19

What function is this circuit performing?

Ваш ответ правильный:

Differentiating.
20

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

4,6 V.
23

What principle of measurement are viscosity controllers usually based upon?

Ваш ответ правильный:

Measurement of differential pressure.
24

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

Ваш ответ правильный:

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:

Ваш ответ правильный:

One Henry.
26

The typical current gain for a common emitter transistor is:

Ваш ответ правильный:

10-200.
27

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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.

Ваш ответ правильный:

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?

Правильный ответ:

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

Ваш ответ:

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?

Ваш ответ правильный:

30 volts.
37

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

Temperature, pressure and dampness.
41

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

6 Ohms.
43

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

Ваш ответ правильный:

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?

Правильный ответ:

Open circuit winding between W and U.

Ваш ответ:

Partial fault 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?

Ваш ответ правильный:

Contactor chattering (vibrating).
46

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

Ваш ответ правильный:

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:

Ваш ответ правильный:

Electrodes.
48

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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:

Ваш ответ правильный:

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?

Ваш ответ правильный:

2,2 Ohms.
57

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

Ваш ответ правильный:

5 and 6.
58

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

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?

Ваш ответ правильный:

Level control.
63

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

Правильный ответ:

It is possible to predict the control mathematically.

Ваш ответ:

The output signal is equal to the input signal.
64

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

Правильный ответ:

Control of the process inlet side.

Ваш ответ:

Mathematical calculation of the system response.
65

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

Правильный ответ:

The secondary controller.

Ваш ответ:

Both at the same time.
66

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

Ваш ответ правильный:

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?

Ваш ответ правильный:

Figure 1.
68

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

Ваш ответ правильный:

In a pressure transmitter.
69

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

Ваш ответ правильный:

Ionization type.
70

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

Ваш ответ правильный:

Thermocouple sensor.
71

Which electronic component or system is this graphical symbol illustrating?

Ваш ответ правильный:

Bandpass filter.
72

Which device does this graphical symbol illustrating?

Ваш ответ правильный:

Pressure to current converter.
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