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Level III Questions, seen recently (from memory bear with me), help?

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  1. SecondGen's Avatar
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    Quote Originally Posted by ElectricalTestTech View Post
    2. How is lagging power factor improved using a synchronous motor?
    A) Raise excitation of field windings
    B) Lower excitation of field windings
    C) Raise excitation of amortisseur winding
    D) Lower excitation of amortisseur winding
    A Synchronous Motor can be made to operate at unity and leading power factor by just increasing its excitation voltage by increasing the field current. I believe the answer is A. But someone please chime in on this one
    I agree with answer A.

    A synchronous motor takes a leading current when over-excited and, therefore, behaves as a capacitor. An over-excited synchronous motor running on no load is known as a synchronous condenser. When such a machine is connected in parallel with the supply, it takes a leading current which partly neutralizes the lagging reactive component of the load. Thus the power factor is improved.

    By varying the field excitation, the magnitude of current drawn by the motor can be changed by any amount. This helps in achieving stepless control of power factor.

    http://ocw.nthu.edu.tw/ocw/upload/12...provement..pdf

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    Transformer liquid temperature gauge test procedure

    Quote Originally Posted by BRAD2121 View Post
    2: What is the best way to test a removable temperature sensor on a transformer?
    - Meter & Loop check
    -Meter & thermocouple tester
    - Heater & Meter
    -IR camera
    Suspend the thermometer’s indicator bulb and an accurate mercury thermometer in an oil bath. Do not allow either thermometer to touch the side or bottom of the container.

    Heat the oil on a hotplate, while stirring, and compare the two thermometers while the temperature increases. If a magnetic stirring/heating plate is available, it is more effective than hand stirring.

    An ohmmeter should also be used to check switch operations. If either dial indicator is more than 5 ºC different than the mercury thermometer, it should be replaced with a spare.

    The alarms and other functions should also be tested to see if the correct annunciator points activate, pumps/fans operate, etc.

    Transformers: Basics, Maintenance, and Diagnostics - https://www.usbr.gov/tsc/techreferen...s/Trnsfrmr.pdf

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    Quote Originally Posted by SecondGen View Post
    Suspend the thermometer’s indicator bulb and an accurate mercury thermometer in an oil bath. Do not allow either thermometer to touch the side or bottom of the container.

    Heat the oil on a hotplate, while stirring, and compare the two thermometers while the temperature increases. If a magnetic stirring/heating plate is available, it is more effective than hand stirring.

    An ohmmeter should also be used to check switch operations. If either dial indicator is more than 5 ºC different than the mercury thermometer, it should be replaced with a spare.

    The alarms and other functions should also be tested to see if the correct annunciator points activate, pumps/fans operate, etc.

    Transformers: Basics, Maintenance, and Diagnostics - https://www.usbr.gov/tsc/techreferen...s/Trnsfrmr.pdf
    I've done this one multiple times. Candy thermometer and a metal coffee can and a torch.

    Use what you've got.

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    Dropping resistor calculation

    Quote Originally Posted by jwdrowe View Post
    Coil A is rated for 24vdc, 500mA, and has a resistance of 48Ω. R1 is sized to limit the current in the coil to 500mA. If the supply voltage is 125vdc, what is the power dissipated in R1?
    A) 12.0 W
    B) 24.0 W
    C) 50.5 W
    D) 77.5 W

    Step 1: Calculate the needed Voltage Drop by subtracting the 2 voltages

    125V - 24V = 101V


    Step 2: Calculate the needed Resistance using ohms law: R = V / I

    101V / 0.500 = 202 Ohms


    Step 3: Calculate Resistor Wattage from the Current and Resistance using P = I2R

    0.500 x 0.500 x 202 = 50.5W

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    Quote Originally Posted by jwdrowe View Post
    Which of the following statements is true pertaining to network protectors?
    A) There is no separate source of control power
    B) They use a low voltage contactor
    C) There are multiple external sources of control power
    D) They use a medium voltage contactor
    Best answer here would be no separate source of control power. Network Protectors obtain control power from the network transformer secondary.

    Westinghouse NWP's, for example, use a control power transformer while GE taps right off the line and steps down voltage with resistors. In either case, the network transformer supplies voltage. If the transformer goes down, there is no other source for control power.

    B and D are just plain wrong, network protectors don't utilize contactors for operation.

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    Quote Originally Posted by jwdrowe View Post
    During a phasing test across a generator tie breaker cell where both sources have the same rotation, the voltage measure across any one phase (A-bus to A-gen) increases as the phase angle:
    A) Increases between 0 and 90 degrees
    B) Increases between 180 and 270 degrees
    C) Decreases between 180 and 90 degrees
    D) Decreases between 90 and 0 degrees
    A) Increases between 0 and 90 degrees - Phase angle would be getting larger, with difference in potential (voltage) increasing.

    B) Increases between 180 and 270 degrees - Phase angle would be getting smaller (moving towards zero) because its now past 180 degrees, voltage would be decreasing.

    C) Decreases between 180 and 90 degrees - Phase angle would be moving back towards zero, voltage would be decreasing.

    D) Decreases between 90 and 0 degrees - Phase angle would be doing same as above, moving closer to being in phase (0 volts) meaning voltage is decreasing.

    Best answer is A.

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    According to the NFPA 70, what is the max allowable time delay results for a ground fault relay to operate?
    A) 1 second at 1200 amps
    B) 3 sec at 3000 amps
    C) 5 sec at 1200 amps
    D) At the actual available fault current
    i found that the book said 1 sec at 3000+ amps


    This is what I found also, so there is technically a right answer. Has any one called out NETA on this? I am finding a lot of questions that don't have a right answer or two right answers. Anyone else feel they are making these tests arbitrary, and like they are written be a six year old? Frustrating.

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    Quote Originally Posted by cansbach View Post
    According to the NFPA 70, what is the max allowable time delay results for a ground fault relay to operate?
    A) 1 second at 1200 amps
    B) 3 sec at 3000 amps
    C) 5 sec at 1200 amps
    D) At the actual available fault current
    i found that the book said 1 sec at 3000+ amps


    This is what I found also, so there is technically a right answer. Has any one called out NETA on this? I am finding a lot of questions that don't have a right answer or two right answers. Anyone else feel they are making these tests arbitrary, and like they are written be a six year old? Frustrating.
    I so agree with you it seems the tests have been made to fail and cost the companies more money and time having you take the test two and three times
    i would say the answer is A i know that this the max setting by NEC and the max clearing time is 1 sec at 3000 amps its the only answer close very badly worded question

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    Quote Originally Posted by SecondGen View Post
    Step 1: Calculate the needed Voltage Drop by subtracting the 2 voltages

    125V - 24V = 101V


    Step 2: Calculate the needed Resistance using ohms law: R = V / I

    101V / 0.500 = 202 Ohms


    Step 3: Calculate Resistor Wattage from the Current and Resistance using P = I2R

    0.500 x 0.500 x 202 = 50.5W

    thank you this really helped!

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    Quote Originally Posted by ElectricalTestTech View Post
    An ATS does not transfer from utility to generator. The generator is running and producing voltage. Which of the following is the cause of it not transferring?
    A) The breaker feeding the ATS did not open ATS is an OPEN TRANSITION transfer, the breaker isn't supposed to open
    B) battery does not have enough charge to operate the ATS Since when do batteries operate an ATS?
    C) Frequency of the generator is too low ATS controllers monitor generator frequency.
    This is probably the correct answer

    D) Service only lost one phase This is a reason to initiate a transfer. This doesn't explain why it didn't transfer
    I see A as being a possible answer. The ATS that I have worked with have an interlock that will not allow the ATS to close in to the generator if the breaker feeding it from the utility side has not opened. This keeps your generator from feeding back to the utility or down the street to the linean trying to repair the lines.

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