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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
What is locked rotor in three phase induction motor?
A motors locked rotor current is the same as the motors starting current. This is the point where the voltage is applied to a non rotating motor, time cycle zero. Because the motor is not rotation and generating a back EMF to oppose the inrush current, the current will go as high as 6 times the running current of the motor.
Does the formula used to calculate the turns ratio uses the phase voltages and phase current?
For a transformer, the turns ratio always applies between its primary and secondary windings. So the turns ratio for a three-phase transformer is the ratio of primary to secondary phase voltages, not between line voltages.
What is the result of running a 480 volt 3 phase 60hz motor with 415 volt 3 phase motor?
Running a 480 volt motor at 415 volts can lead to decreased performance and efficiency due to the lower voltage supply. It may result in lower torque, higher current draw, and potentially overheating of the motor if not designed to handle such voltage differences. It's recommended to use a motor designed for the specific voltage it will be operating on to ensure optimal performance and longevity.
Power can be measured by placing a power meter in each of the lines. Each power meter has its curent coil in series with the line and its voltage coil between the line and neutral.
Provided the lower ends of the voltage coils are connected together, the sum of the three reading is equal to the total power. They do not have to be connected to the neutral. They could be connected to the other live wire, which leads to the two-wattmeter method:
Two wattmeters are connected with their current coils in two of the live wires. The voltage coils are connected between those two live wires and the other live wire. The sum of the two readings is the total power on the three-phase system.
Additional Information
Blondel's Theorem (Andre Blondel was a French electrical engineer) states that, for both balanced and unbalanced three-phase loads, one can measure the total power by using one less wattmeter than there are number of conductors joining the supply to the load. For example, for a three-phase, three-wire, system, one can use two wattmeters (this particular connection being known as the 'two-wattmeter method', as described in the original answer). For a three-phase, four-wire, system three wattmeters can be used.
Provided the wattmeters have been connected correctly (i.e. provided the polarity markings on their current- and voltage-coil terminals have been taken into account), if one any of the wattmeters reads 'downscale' (i.e. backwards), then either its current or its voltage coil (but not both) must be reversed, and the resulting reading must the be deducted from the total power read by the other instrument or instruments.
What is meant by main contact and auxiliary contact in magnetic contactor?
The main contact controls the load current to the motor, whereas the auxiliary contact is part of the control circuit -usually connected in parallel with the 'on' pushbutton switch to maintain the control circuit in the energised state, once the on pushbutton has been pressed.
How many voltage are in 3 BATTIER?
3 batteries likely refer to 3 individual batteries. Each battery typically provides a voltage around 1.5 volts. So, in total, 3 batteries would provide approximately 4.5 volts.
How do you use a one phase motor in place of a three phase motor?
To use a single/one phase motor instead of a three phase motor is possible if you have a three phase power supply as you will only need to tap one of the three phases together with neutral and an earthwire, however to use a three phase motor instead of a single phase will require the provision of three phase power supply.
How can a three phase induction motor reverse direction of travel without changing input phase?
A three-phase induction motor can reverse direction of travel by swapping any two of the three input phases. This changes the rotating magnetic field direction, causing the motor to rotate in the opposite direction. No change to the input phase sequence is required.
When the resistance is 960 ohms and the current is 2 amperes, we can use the formula for inverse variation: ( current \times resistance = constant ). Thus, ( 2 \times 960 = constant ), which is ( 1920 ). So, if the resistance changes to a new value, we can find the new current by dividing the constant by the new resistance.
Why high voltages might be used to move an electrical charge through the distribution grid?
Losses are I squared R,
or proportional to the square of the current.
For a given power, the higher the voltage, the lower the current.
AnswerIt is a myth that the primary reason for transmitting electrical energy at high voltages is 'to reduce line losses'. This is certainly one of the advantages of doing so, but not the main reason. The primary reason is to limit the voltage drop along the line to realistic values -at lower voltages, the voltage drops would be absolutely enormous, making energy transmission impossible. The secondary reason is the enable cables of manageable cross-sectional area and weight to be utilised.
What are the phase voltages if the line voltages are 100volts?
It depends on the type of three-phase system. If it's a three-wire system, then the phase voltage is numerically equal to the line voltage. If it's a four-wire system, then the phase voltage is numerically equal to the line voltage divided by 1.732 -in your example, this works out to be 5.77 V.
How can you detect your neutral missing in 3 phase 4 wire system?
In typical residential wiring it is the white wire. If you look in the electrical panel behind the panel you'll see all white wire are "bussed" together and the black "hot" wires are attached to breakers. The bare "Ground" wires are also all bussed together. The White and bare wires are typically bonded together in the main electric panel.
If you have a volt meter and you wanted to check for neutral without taking off an outlet cover you could ground one lead and then touch the other lead to each side of a receptacle and if you get 120V that is the hot side and zero is the neutral.
Danger - if you are removing electric panel covers and exposing the internals of the electric box there is a danger of getting electrocuted.
What is the use of single phase variac in circuits?
A single phase variac is used to adjust the output voltage in a circuit. It is often used for testing equipment, controlling motor speed, or regulating the output of power supplies. The variac can provide a variable AC voltage to the circuit, allowing for precise adjustments as needed.
What happened when one phase missing of a 3 phase load?
When one phase is missing in a 3-phase load, the load will experience an imbalance which can lead to overheating and potential damage to the equipment. The motor may run slower or produce less power, and the efficiency of the system will decrease. It is important to address the missing phase quickly to prevent further damage.
What is the difference between an AC and DC generators?
AC generator, the brushes run on slip rings which maintain a constant connection between the rotating coil and the external circuit. This means that as the induced emf changes polarity with every half-turn of the coil, the voltage in the external circuit varies like a sine wave and the current alternates direction. DC generator, the brushes run on a split-ring commutator which reverses the connection between the coil and the external circuit for every half-turn of the coil. This means that as the induced emf changes polarity with every half-turn of the coil, the voltage in the external circuit fluctuates between zero and a maximum while the current flows in one constant direction
What color phasing tape should be used for a three-phase 575V system?
The industry standard for low voltage (120-208V) conductors is: A phase: black B phase: red C phase: blue As you look at a three phase panel, the phases go left to right (the same way we read). Therefore, the supply conductors should be black, red, blue, left to right. (A phase is not typically marked as the wire insulation is already black in color.) The branch circuit conductors should always be the same color of their phase supply conductor. This is a critical industry standard although it is not required by the National Electrical Code. <><><>
As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
What does qmb stand for in a qmb panelboard?
QMB stands for "Quick Make and Break". It refers to a type of panelboard with disconnect switches that have the capability to quickly make or break electrical connections. These panelboards are commonly used for high-amperage applications in industrial settings.
What voltage would be measured from any phase to ground on a 480 volt 3 phase wye system?
A voltage of 277 is the line to neutral (ground) voltage of a 480 volt wye three phase system.
L1- N, L2 - N and L3 - N will give you 277 volts.
L1 to L2. L2 to L3 and L3 to L1 will give you 480 volts.
What is the mean of 220-440 connection of 3 phase motor?
Star 220 v and delta 400 i star 58 percent only voltage applied delta 400v applied
AnswerThese figures do not represent three-phase, four-wire, system voltages, because if the line voltage were to be 440 V, then the phase voltage would be 254 V; or, if the phase voltage were to be 220 V, then the line voltage would be 381 V.What is voltage drop calculation?
Voltage drop calculation is a method used to determine how much the voltage decreases in an electrical circuit due to the resistance of the wires and components. It helps in ensuring that the voltage at the intended load is within the acceptable range for proper operation. This calculation is important to ensure that the voltage supplied to the load is sufficient for it to function correctly.
What happens to the speed of a three phase motor if frequency is increased?
If the frequency supplied to a three-phase motor is increased, the motor speed will also increase following the relationship known as the synchronous speed. This increase in frequency will lead to a corresponding increase in motor speed, assuming that the load on the motor remains constant.
What can a split phase motor use to energize and deenergize the start winding?
A split-phase motor uses a centrifugal switch to energize and de-energize the start winding. The switch is connected in series with the start winding circuit and is typically set to open when the motor reaches about 75-80% of its operating speed, disconnecting the start winding from the power supply.
Is it true a transistor changes alternating current into direct current?
Not usually. A transistor is an amplifier, that can be used as a switch. If set up correctly it can be used to rectify AC current (i.e. convert it into DC), however it will need a capacitor to smooth the DC current (i.e. keep the voltage constant or nearly the same).
What is typically used is a rectifier, a small circuit consisting of one or more diodes.
How does ohm's law relate to heat capacity?
Ohm's law describes the relationship between current, voltage, and resistance in electrical circuits. Heat capacity, on the other hand, measures the amount of heat energy required to change the temperature of a substance. These two concepts are not directly related to each other.
Can you use single phase kwh meter for three phase load?
No, a single phase kWh meter is designed to measure the energy consumption of single phase loads only. To measure the energy consumption of a three phase load, you would need a three phase kWh meter specifically designed for that purpose. Using a single phase meter for a three phase load would not provide accurate energy consumption readings.
