Electro Technology Exam TEET-1400-03

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Questions and Answers

What is the primary function of an undervoltage release mechanism (UVR) in generator breakers?

To enhance the power factor of the connected load.

To trip the breaker during severe voltage dips. (correct)

To reduce electromagnetic interference in the circuit.

To regulate the current to maintain stable voltage.

When replacing fuses in a three-phase supply, what is the correct procedure?

Only replace the blown fuse to save time and cost.

Replace all three fuses to ensure reliability. (correct)

Replace the blown fuse and test the others individually.

Keep the previous fuses if they still appear functional.

What is the total KVA for the loads supplied by a 220V alternator specified in the content?

112.5 KVA (correct)

95.5 KVA

100 KVA

132.4 KVA

In the context of the brass rod, what is the role of the mean diameter when calculating magnetizing forces?

It affects the calculation of magnetic field strength. Signup and view all the answers

When a synchronous motor operates at a power factor of 0.5 leading, what could be inferred about its performance?

It generates reactive power back to the source. Signup and view all the answers

What frequency should the incoming generator be adjusted to for proper synchronization with a busbar?

60 Hz Signup and view all the answers

What action should be taken when the synchro scope indicator approaches the 12 o'clock position?

Close the circuit breaker Signup and view all the answers

What component is used in thermal overload relays to protect a 3-phase low voltage induction motor?

Bimetal strips Signup and view all the answers

At what percentage of full load current (FLC) should the thermal overcurrent relay (OCR) be set for a continuous maximum rating (CMR) motor?

105% FLC Signup and view all the answers

During smooth manual synchronization, how fast should the synchro scope indicator rotate for proper adjustment?

Once every four seconds Signup and view all the answers

What occurs if the motor current exceeds the set current on a thermal overload relay?

The NC contact opens and trips the motor Signup and view all the answers

What is the primary purpose of synchronizing two generators?

To ensure they operate in parallel without issues Signup and view all the answers

What characteristic of thermal overload relays allows them to respond to varying current levels?

Inverse time response Signup and view all the answers

What will occur at 120% FLC within two hours?

Tripping Signup and view all the answers

Which component in a PLC is responsible for executing the control program?

Processor unit (CPU) Signup and view all the answers

Which of the following is NOT a basic part of a PLC device?

Relays Signup and view all the answers

Why are PLCs considered more reliable than relay logic systems?

They do not wear out like mechanical relays. Signup and view all the answers

What is one important point to consider when replacing a blown fuse?

The cause of the fault must be identified before replacement. Signup and view all the answers

What device converts AC voltage to DC in a PLC?

Power supply unit Signup and view all the answers

Which of the following statements best compares relay logic to PLC control circuits?

PLCs are easier to troubleshoot compared to relay logic. Signup and view all the answers

What function does the memory unit serve in a PLC?

It stores data and control programs. Signup and view all the answers

Study Notes

Examination Details

Subject: Electro Technology
Rank: 3rd Engineer Officer (KW>3000)
Exam Code: TEET-1400-03
Date: 19/08/1400
Time Allowed: 2.5 hours
Pass Mark: 55

Question 1: Synchronizing Generators

Requirement: Sketch synchronizing with three lamps and describe conditions for paralleling two generators
Method: Incoming generator speed adjusted to match busbar frequency (e.g., 60Hz).
Voltage: Incoming generator voltage adjusted to equal busbar voltage
Synchro Scope: Incomer adjusted for slow clockwise rotation (approximately 4 seconds per revolution) before closing the circuit breaker.
Closing Position: Ideal closing occurs when the indicator approaches the 12 o'clock position (in-phase)
Acceptable Position: Closing between 5-to and 5-past 12 o'clock with slow rotation is satisfactory.

Question 2: Thermal Overload Relay

Purpose: Protecting 3-phase LV induction motors
Component: Bimetal strip
Function: Heated by motor current; bimetal strip bends, opening circuit breaker if overload detected for longer periods
Over Current Relay Setting: Thermal OCRs should be set at the full load current (FLC) rating of the motor.
Trip Time: 120% full load current should cause tripping within two hours.

Question 3: Programmable Logic Controller (PLC)

Purpose: Industrial digital computer for controlling manufacturing processes
Function: A PLC is used for a programmable, control system to control tasks automatically, and requires high reliability and fault diagnosis.
Basic Parts:
- Processor unit (CPU)
- Power supply unit
- Memory unit
- Input/output interfaces
- Communications interface.
Comparison with Relay Logic: PLCs are more reliable and easier to troubleshoot compared to relay-based systems. Relays are vulnerable to wear over time.

Question 4: Fuse Protection Replacement

Critical Steps: Locate and repair the cause of the fault before replacing the fuse. Use the correct current rating, grade, and type of fuse. Always replace all three fuses in three-phase systems even if only one is blown.
Undervoltage Protection Device: A device that trips the breaker when a significant voltage dip (around 50%) in the circuit occurs. This device is included in generator breakers and some feeder breakers, with a function that stops the breaker from being turned on if the voltage is below a safe threshold, often used in situations where there is a dead generator connection.

Question 5: Alternator Load Calculation

Scenario: A 220V, single-phase alternator supplies various loads.
Loads: Lighting/heating (20 kW, unity power factor), induction motor (82.9 kW, 0.8 lagging power factor), synchronous motor (50 kVA, 0.5 leading power factor)
Calculations: Calculate total apparent power (kVA), current, and power factor of the combined load.

Question 6: Magnetic Field Calculation

Scenario: Brass rod wound with a coil (500 turns) carrying 5A current (closed ring configuration).
Parameters: Mean diameter (300mm), cross-sectional area (1000mm²),
Calculations:
- Calculate magnetizing force (H)
- Calculate magnetic flux density (B)
- Calculate the total flux

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Description

Test your knowledge on key concepts related to electro technology, focusing on synchronizing generators and thermal overload relays. This quiz covers essential requirements and conditions for paralleling generators, as well as protective measures for low voltage induction motors.