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[is090909]

List the main differences between an ax. and a d.c. switchboard

 

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An AC switchboard and a DC switchboard have some differences, including:

1. Voltage: The primary difference between an AC switchboard and a DC switchboard is the voltage. AC switchboards operate at high voltage of 480V and above, while DC switchboards operate at low voltage of 24V or 48V.

2. Current: Another significant difference between the two is the current they carry. While AC switchboards carry a high current, DC switchboards carry a low current.

3. Circuit Configuration: AC switchboards are usually configured in 3-phase circuits, while DC switchboards are typically configured in 1-phase or 2-phase circuits.

4. Circuit Protection: AC switchboards require circuit protection devices like circuit breakers, fuses, and relays, while DC switchboards require circuit protection devices like circuit breakers and fuses.

5. Equipment: The equipment used in both switchboards also differs. AC switchboards require transformers, motors, and generators, while DC switchboards require batteries, rectifiers, and inverters.

6. Maintenance: AC switchboards require more maintenance due to the high voltage and current levels, while DC switchboards require less maintenance due to the low voltage and current levels.

 

[is090909]

What is the primary function of a circuit breaker?

 

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The primary function of a circuit breaker is to protect an electrical circuit from damage caused by overcurrent, which can be caused by a short circuit, ground fault, or overload. When too much current flows through a circuit, the circuit breaker trips and interrupts the flow of electricity, preventing damage to the circuit and preventing the risk of fire. Circuit breakers come in different types and sizes depending on the electrical load they are designed to protect. They are commonly found in residential, commercial, and industrial electrical systems and are an essential safety feature that helps to protect people and property from electrical hazards.

 

[is090909]

What are the four fault ratings of a circuit breaker? What is the main difference between a relay and a contactor?

 

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The four fault ratings of a circuit breaker are:

1. Interrupting Rating: This is the maximum current that a circuit breaker can interrupt without being damaged. It is usually expressed in amperes (A).

2. Short Circuit Current Rating (SCCR): This is the maximum current that a device or component can safely handle in the event of a short circuit. It is usually expressed in amperes (A).

3. Voltage Rating: This is the maximum voltage that a circuit breaker can safely interrupt without being damaged. It is usually expressed in volts (V).

4. Continuous Current Rating: This is the maximum current that a circuit breaker can carry continuously without being damaged. It is usually expressed in amperes (A).

The main difference between a relay and a contactor is that a relay is primarily used for controlling a small electrical signal while a contactor is used for controlling a larger electrical signal. Relays are designed to switch a small load while contactors are designed to switch a larger load such as a motor or lighting circuit. Contactors can handle higher currents and voltages than relays. Relays are generally used in low-power applications, while contactors are used in high-power applications.

 

[is090909]

1) AC Power P = ________ .

2) The voltage rating of a wattmeter is generally limited to _________V.

3) A 3-phase wattmeter consists of _________ moving coils.

4) The reactive power Q = __________________

5) An electrodynamometer can be used as a wattmeter and power factor meter (T / F).

6) A moving iron meter can be used as a wattmeter and power factor meter (T / F).

7) The vibrating reed frequency meter works on the principle of _____ .

8) In a Weston-type synchroscope, the lamp goes dark when the two voltages are _______ .

9) Generally voltmeters in alternating current circuits are calibrated to indicate the?

10) A switchboard ammeter indicates a reading slightly above ’’zero” when the leads are

disconnected, this is caused by?

 

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1) AC Power P = V x I x Cos(θ), where V is the voltage, I is the current and θ is the phase angle between them.

2) The voltage rating of a wattmeter is generally limited to several hundred volts.

3) A 3-phase wattmeter consists of three moving coils.

4) The reactive power Q = V x I x Sin(θ), where V is the voltage, I is the current and θ is the phase angle between them.

5) True, an electrodynamometer can be used as a wattmeter and power factor meter.

6) True, a moving iron meter can be used as a wattmeter and power factor meter.

7) The vibrating reed frequency meter works on the principle of resonance.

8) In a Weston-type synchroscope, the lamp goes dark when the two voltages are in synchronism.

9) Generally, voltmeters in alternating current circuits are calibrated to indicate the root-mean-square (RMS) voltage.

10) A switchboard ammeter indicates a reading slightly above "zero" when the leads are disconnected because of residual magnetism in the instrument core.

 

[is090909]

FILL IN THE BLANKS



1. Automatic voltage regulators provided on switchboards function to __________

2. The output voltage of a 440 volt, 60 Hz, 4-pole, 1500 r.p.m. alternator is controlled by the _____

3. The AVR is capable of maintaining a steady output when the alternator's between output varies

__________.

4. The output voltage from the main alternator must be within__________ in 1.5 seconds.

5. The output voltage from the emergency alternator must be within _________in 5 seconds .

6. When large DOL squirrel cage motors are started, the power factor may fall to ____________

7. An AVR helps to maintain the output Voltage within _______ %

8. The input to the AVR is taken from the _____________

9. The output of the AVR is connected to _________________

10.The AVR is meant to control ______________

 

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1. Automatic voltage regulators provided on switchboards function to regulate and control the voltage output of generators and alternators.

2. The output voltage of a 440 volt, 60 Hz, 4-pole, 1500 r.p.m. alternator is controlled by the automatic voltage regulator (AVR).

3. The AVR is capable of maintaining a steady output when the alternator's load changes.

4. The output voltage from the main alternator must be within ±5% of the rated voltage in 1.5 seconds.

5. The output voltage from the emergency alternator must be within ±10% of the rated voltage in 5 seconds.

6. When large direct online (DOL) squirrel cage motors are started, the power factor may fall to a very low value, sometimes close to zero.

7. An AVR helps to maintain the output voltage within ±1 to ±2% of the rated voltage.

8. The input to the AVR is taken from the alternator's output terminals.

9. The output of the AVR is connected to the excitation system of the alternator.

10. The AVR is meant to control the excitation current flowing into the alternator's rotor winding, thereby regulating the output voltage of the alternator.