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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 happens to current in a step-up transformer?
Actually current transfomer is step up voltage transformer n step down current transformer as current transfomer is having single primary turn of thick conductor but having more number of secondary turn of thin wires..so wkt tansformer ratio
k= n2/n1=v2/v1=i1/i2.
so it steps up volatge n steps down current...so we use current transformer as a step up transformer almost in all generating stations.
Current transformers typically have terminals for a voltmeter on their case and a hole through that case. If you run your current carrying lead through the hole and connect an appropriate voltmeter (the voltmeter's design and resistance may affect the results) to the voltage terminals, the voltmeter will indicate the current in the lead times some factor which should be marked on the current transformer. If you thread the current lead through the hole N times then the voltmeter will indicate N times what it would read with the lead going through once (assuming that the ampere turns resulting do not cause saturation of the transformer's core.
What is HT and LT current and voltage?
A 'bushing' is a tubular insulator used to insulate a conductor that passes, for example, from the inside of a transformer or circuit breaker to the outside, enabling the internal components to be connected to external supply lines.
High-voltage (or 'high tension') bushings have thicker walls and are longer than low-voltage bushings, as they have to withstand higher voltages.
What is the reason for using a neutral current transformer on a transformer?
A current transformer is primarily used at the neutral point of a transformer for earth fault protection.
A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply of electricity to the transformer.
What is the current in a 100 volt circuit with 25 ohms of resistance?
Using Ohm's law V:IR .I:V/R..I:100/5-20...I-20ampere
Does electromagnet work only on DC?
They normaly are. AC ones tend to buzz.
The core has to be of soft iron or laminate, so that the field collapses properly when the current is switched off.
How do you measre the running amps a star delta motor?
Measure the current on the incoming side of the starter.
Difference between load break switch and isolator?
An isolator(disconnecting switch)operates under no load conditionand used for disconnecting the CB from the live part of the maintenance.Isolators are used in addition to the CB to make and break the circuit under normal and short circuit condition.
A circuit breaker(CB) is an equipment which can open or close a circuit under normal as well as fault conditions and it can be operated manually under normal conditions and automatically under fault conditions.For the latter operation a relay is used with a CB.
How do you make a good earthing for home?
To make a good earthing for your home, you have to use coal and wood powder in equal proportions.
What would happen to a three phase motor if two of the three phases are lost?
The motor will keep on running for a while but the current will rise on the other two phases and the overload relay will fall out, if its properly set and the motor will stop if the overload relay is set to high the motor will burn out
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in the start Motor will start to shake the if there is no protection devices for over-load on the motor it will simple explode:)
I have a personal experment on that.
Which phase change is an exothermic process?
Change of phase from gas to liquid to solid are exothermic reaction. Condensation, deposition and freezing are exothermic processes that undergo change in phase.
What does an emitter resistor do?
The emitter of a bipolar transistor (junction or point contact type) emits charge carriers(electrons in an NPN, holes in a PNP) through the base towards the collector.
How do you calculate overload setting?
IDEALLY OR AS PER STANDARD: KNOW EXACLY WHAT IS WRITTEN IN A MOTOR NAMEPLATE AS EXAMPLE ON THE FOLLOWING PARAMETERS; A. FULL LOAD CURRENT(AMPS) = SAY 50 AMPS. B. SERVICE FACTOR = USUALLY DECLARED AS = 1.15 THE NORMAL AND ACCEPTED PRACTICE IS TO MULTIPLY THE FLA = 50 AMPS BY 125% AND THE RESULT IS 62.5 AMPS. THIS IS THE MAXIMUM ALLOWABLE OVERLOAD CURRENT TO PROTECT THE MOTOR FROM INSULATION OR WINDING DAMAGE. THE 25% PERCENT ALLOWANCE = 62.5 AMPS WILL BE SET TO AN OVERLOAD RELAY TO CUT OFF WHEN REACH. IF THE SERVICE FACTOR IS AVAILABLE = 1.15 -- THIS MEANS THE MOTOR IS CAPABLE OF RUNNING UP TO 15 PERCENT HIGHER (OVERLOAD) THAN FULL LOAD CURRENT WITHOUT DAMAGE BUT REDUCING BEARING AND INSULATION END-OF-LIFE.
What is the effect of low frequency on the voltage?
The frequency would decrease the gain and increase the output voltage
How do you convert 220V two phase to 220V single phase?
A standard household AC mains power supply, either 220-240 Volt 60 Hz or 50 Hz, is already a single-phase supply so it will not need to be converted. For more information please see the answers to the Related Questions shown below.
What is the total power in a circuit with a current of 4 A and a resistance of 12 ohms?
In DC circuits, V = I / R, and P = V*I
You can use these to get P = I^2 * R = (4)^2 * 12 = 192 watts.
Does a capacitor reduce electricity?
Absolutely not, if you are a residential consumer. Capacitors, when used for power-factor correction, reduce the supply current but NOT the amount of energy consumed and you pay for energy, NOT current! Energy meters measure the supply voltage and the in-phase (resistive) component of the supply current, so power-factor correction is irrelevant to residential metering. The video referred to in the original answer shows current being reduced but, as explained, this has absolutely no relevance to your electricity bill. In fact, the video is complete and utter nonsense! Capacitors used in this way are a complete scam.
Power-factor correct ONLY applies to large commercial and industrial consumers because they are penalised for unnecessarily-low power factors because the resulting unnecessarily-high currents require the utility companies to install larger transformers, switchgear, and cables.
Another Answer
Yes, if you are a big customer and you are paying a premium on your power charges through having a poor power factor on the site. Otherwise a capacitor does not reduce the kWh consumption of your appliances, but it might reduce the current you draw, but your meter measures energy used and not the current. For a domestic customer power factor correction will almost certainly notreduce your charges.
Can a circuit be a combination of series connections and parallel conections?
Yes. There are also more complicated circuits, that can't be described ONLY as a combination of series and parallel circuits - basically, circuits that contain several loops.
What are the important components of a nuclear power plant?
There are other complication to nuclear power, importantly that there must be a neutron source, and so, for example, uranium must be enriched to increase the number of neutrons, as its neutron source is uranium-235, which is not present in sufficient quantities in naturally occurring uranium.
Interview question answer for electrical power plant?
Question; If you were to ask the operator in a power plant to tell you how many mega watts the plant is generating; how would you ask?
Answer: How much load are you carrying?
Power plants do not generate electricity -- they carry load.
Can transformer develop three phase power from a single phase source?
To do this, you will need to phase shift the single phase power supply into three distinct phases that are 120 degrees out of sync with each other. Phase shifting transformers can be used for this, but there might be other ways as well.
What is the phase difference between three phase supply?
First, consider single-phase 120/240 service like you would find in a house. the two hot wires are said to be 'in phase'.
Think of it this way. Imagine a ruler12 inches long. Put your finger on the six inch mark, the center. How far to each end? Six inches. Both ends are on the same line, just in opposite directions. So if you go six inches one way, and six inches the other way, the total distance is 12 inches.
120/240 volt systems are like that voltage-wise. The middle of the ruler is the neutral, and each end is a hot wire. When one hot leg is going positive, at the exact same time (that's the 'in phase' part) the other leg is going negative. Same line only opposite directions, like our ruler. So the two 120 volt legs just add up to 240.
Now, here's the important part. Since one leg goes positive while the other leg goes negative, they are said to be 180 degrees apart, 360 degrees making up one complete AC cycle (2 X 180 = 360). In three phase power, there are, not two, but THREE hot wires. Since there are three, they can no longer be 180 degrees apart. They are 120 degrees apart (3 X 120 = 360). So, when phase A peaks, phase B has not yet peaked. it is at some intermediate voltage between zero and maximum. The two phases cannot just be added up because of this fact.
Back to our ruler. Break the ruler in half. bend the two halves so the ruler is no longer straight (180 degrees) but bent at an angle of 120 degrees. Draw a line from end to end. See how we have formed a triangle? See also that the line we drew is not 12 inches long, but is shorter (the two ends are closer together)? That's why the voltages in a three phase system do not appear to add up.
Lets make our ruler 240 inches long. If we bend it into the 120 degree angle and measure end-to-end, we will find the length to be about 208 inches, not 240! In a 120/208 three-phase system, each hot leg (phase) measures 120 volts to ground, BUT phase-to-phase measures 208 volts. This is true whether you measure A to B, B to C, or C to A.
The math guys call this a vector sum. The vector is the angle at which the phases are in relation to each other (120 degrees) and the sum is the distance between the two bent ends (phases).
To figure the phase-to-phase voltage, multiply the phase-to-neutral voltage by 1.73 (the square root of 3). Thus: 120 X 1.73 = 208, 277 X 1.73 = 480, etc.
To figure the reverse, divide the phase-to-phase voltage by 1.73. Thus: 480 / 1.73 = 277, 208 / 1.73 = 120, etc.
You trig people see how this relates to our triangle example using the cosine rule.
It should be noted that the use of the term phase above, as in "phase to phase" is not strictly correct, although a common usage. Each hot conductor in a 3-phase system is correctly called a "line", so the correct terminology would be "line to line", "line to neutral", etc.
How do we Calculate Kwh to Kvah?
To convert 'kwh' to 'kvah' you first need to measure the length of time. You will then convert this amount to hours by dividing by 3,600. You will then divide this amount by the length of time.
