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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
The resistance of earth wire is?
The recommended resistance that one should strive to obtain is zero.
A polarity test is used to find out the electrical polarity (positive or negative) of the voltage at a given point within a circuit relative to some other point. Most multimeters, including digital multimeters, can do this.
Answer regarding alternating current
In the context of an a.c. supply, a polarity test is done to ensure that the line and neutral conductors are connected the correct way around at, for example, electrical sockets, Edison-screw lamp holders, etc.
Why and how does insulation depend on voltage?
Where you find wire insulation with ratings of 300 volts, 600 volts and 1000 volts, these are the highest allowable voltages that can be applied. A wire that is rated for 300 volts is good for 120 volts, 240 volts and 277 volts. At test research facilities, insulation on a wire is tested to destruction. The label that is given to wire's insulation, as a result of the tests, is the highest safest voltages that can be applied to that particular wire. So when you see a wire that has a label stating that it is rated for 300 volts it means that any voltage under and up to 300 volts is safe to apply.
Why Current Transformer Placed Between Power Transformer and Breaker in Substation?
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.
Additional Answer
Current transformers are widely-used in substations to (a) allow the measurement of currents in the high-voltage lines, and (b) to operate protective relays. There are many different types of protective relays, and their function is to disconnect faults by (a) detecting them, and (b) tripping the appropriate circuit breaker(s).
Can step down transformer be used as a step up transformer?
If the transformer has two separate windings, then, YES a step-down can be used as a step-up, and vice-versa.
It is more correct to say you are reversing the high and low sides.
By definition Primary is the "IN" side and Secondary is the "OUT" side.
The Primary could be the high voltage side if it is a step-down,
or it could be the low voltage side, if it is a step-up.
Care must be taken when reversing the operation of a step-down transformer to insure that it does not exceed the ratings of the transformer. For example, let's say we have a 12 VA step-down transformer that takes 120Vac in and is rated to provide 12V at 1 amp at the secondary. If we were to reverse it and apply 12Vac to the new primary (the old secondary), we would have 120Vac at the new secondary, but to keep within the original ratings it could only be loaded to 0.1A @ 120Vac.
As long as you treat the output rating of the step-down transformer as the input rating as a step-up transformer, and don't try to draw current beyond what would normally have been applied to the high voltage primary, you should be fine. Potentially one could push up the voltage on such a transformer beyond what its stated application specified, while making sure not to exceed the power rating of the transformer and not exceeding the breakdown voltage of the transformer's insulation, for example driving the above transformer at 24V to get 0.05A @ 240Vac. It is important to realize though that the rated input voltage for a step-down transformer will likely not be a safe input voltage if you use it as a step-up transformer - for example, applying 120V to the above transformer with the windings reversed would generate 1.2KV!
One important point to remember when reversing a three-phase transformer to a step-up is what kind of windings it has. Most three-phase transformers use a "delta" configuration on the primary side. This means that there are three "hot wires" and a ground, but not a neutral. (The white wire in a circuit). On the secondary side, transformers are usually wired up in a "Wye" (sometimes called a "star" configuration. Doing this allows the transformer to create a Neutral connection. If a step-down transformer is reversed to make it a step-up, the high (output) side will not have a Neutral connection. If one is not needed, say for a three-phase welding machine, this would not be a probem. However, if a Neutral IS needed ,say for lighting, reversing this transformer would not work. In this case, a listed step-up transformer will be needed. One final thing, if a step-down transformer is used as a step-up, a Neutral wire is not required to be connected to the input side.
Why cooling oil is used in transformers?
The oil in a transformer has two functions: Oil is a better electrical insulator than air is, so high voltage parts can be placed closer together, saving space and materials. Also, oil is more efficient at cooling the transformer. The oil circulates inside the transformer, removing heat from the internal core and transferring it to the cooling radiators or the surface. In small transformers, this occurs naturally, by convective currents. In large transformers, there are thermostatically controlled pumps to assist this cooling cycle.
What does the size of a current depend upon?
One way to determine current is to measure it, with an ammeter. Another way is to calculate it using Ohm's law: current = voltage / resistance.
What is the maximum current carrying capacity of 16 sq mm copper wire?
the current carrying capacity of 16sq.mm copper conductor is as below:
For Single phase A.C or D.C is - 76 amperes (VIR insulated) and that
For Three phase A.C or D.C is - 66 amperes. (rubber insulated)
What is power factor significance in calculating the AC power?
Power Factor is one of most significant parameter in calculating AC Power. As we know it is cosine of angle between AC Voltage and Current it comes in picture while calculating power in AC circuits Power In AC (P) = Voltage (V) X Current (V) X Power Factor
Let us take an example of Power with Power factor and without power factor for same circuit.
Let Us assume
V = 125 Volts
I = 1 Amp
Power Factor = 1
Then
P = 125X1X1= 125 Watts
But for any circuit when Power factor is below 1, to execute same power, Circuit has to draw more current. for example
P = 125X 1.25 X 0.8 = 125 Watts
In first example power factor of the circuit was unity = 1 and in that condition current of the circuit was 1 amp whereas in second example power factor of the circuit is 0.8 due to which current of the circuit increases to 1.25 amp to execute the same power. Now due to increase in current of the circuit many factors are affected like heat loss, Conductor's specification , Class of insulation etc.
Thus it can be concluded after going through above explanation that power factor play a significant role in AC power calculation as well as in actual practices.
Cheaper to run 2 110 air conditioners or 1 220?
Whoever wrote this answer has the math correct, I will admit it. 220 volt circuit is two 110 volt circuits put together. 110+110=220. As seen below in the following equation, the 220 unit and 110 unit use the same amount of wattage, if you double the 110 volts amperage use. 220 volt circuits are used with major appliances such as air conditioners, dryers and electric oven/ranges for this reason. The amount of current they draw (amperage). The reason behind using a 220 volt circuit verses the 110 is the wire size needed to carry the amount of current used. It comes down to the cost of wiring and that is it. In the equation below the 220 volt/10 amp unit would only use 14 gauge wire. The 110 unit would have to use a larger gauge wire to perform the same function with 12 gauge wire. The larger the gauge number, the smaller the wire, thus less the cost. Sorry to say there is no cost difference to operate a 110 A/C to a 220 unit. Unlike the statement made below, it will take you forever to see the cost difference in your electric bill as you will be using the same amount of power for both. If the fellow below does not believe me, try this on for size. Take amp meter to L1 and view the use. Then take a second amp meter and view the use of L2. Now that you have simotaneous readings, add them together. See, no savings at all. A 220 Volt appliance uses half of the current that a 110 Volt appliance does. Your house power starts with 220V with neutral phase grounded. 110V is obtained from either one of the 220v wires and neutral. Your meter measures current at the 220V rate. If you use a 220V appliance your meter will record power used. If you use the half voltage of 110V you will have to double the current to obtain the same power output. Your meter will record double what you are actually using. Your circuit panel is laid out for two 110V circuits and their combined 220V. Orginal layout of your house wiring was a gusse at trying to pair 110V devices that may be on simultaniously. This helps ballance the two 110V circuits and gives a truer reading on the meter. In addition to this meter error are current losses. The more current the more loss! example: 220V X 10A = 2200W or 110V X 20A = 2200w So the 220V appliance is a winner in both cases. DEFINETLY ENERGY EFFICIENT ! The catch is you need a 220V outlet installed. Depending on your cost for the outlet it may take an few extra months to realize a savings.
How the change a 220 volt generator to 380 volt 3 phase?
The motor has to be a dual voltage motor for this operation to happen. This will be a six coil motor. Each motor coil will be rated for a 220 volt drop across it. For the high voltage connection the motor's coils are connected in series between L1 and L2, L2 and L3, and L3 and L1. For the low voltage connection the motor's coils are connected in parallel between L1 and L2, L2 and L3, and L3 and L1.
See sources and related links below. Look on page 76 and 77.
What components are present in every nuclear power plant that generates electricity?
(Nuclear reactor) creates heat
Water heated to create pressurised steam (Boiler)
Pressurised steam released via turbine chamber (Steam Turbine) translating motion to turbine shaft.
Turbine shaft windings rotate inside magnets to generate electricity (Generator)
What is a capacitive reactive circuit?
A circuit that has only a capacitor in it. Or the net reactance is below zero, making it capacitive. The current leads the voltage in a negative (capacitive) reactive circuit.
How many amps will a 20VA transformer provide?
To answer this question a voltage is needed. I = 20/E.
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Each device powered by the transformer will have a rating of draw also in VA. So many for a t-stat, so many for zone valve or damper etc... add em up, make sure transformer is over and you re good. 20 VA is not very big. door bell transformers are around that size. most hvac systems need 30, 50, 70 or more VA.
DYn1 = Delta connected highside winding, Wye connected lowside winding, neutral brought out, lowside lagging by 30 degrees
DYn11 = delta connected highside winding, Wye connected lowside winding, neutral brought out, lowside leading by 30 degrees
In a DYn1, the lowside A phase is coupled to the highside A-B leg. In a DYn11, the lowside A phase is coupled to the highside C-A leg. So to convert one to another, you must physically change this coupling, which would require rewiring the internal connections of the transfomer delta.
The formula we need to use is called "Ohm's Law":
E = I x R
which can also be stated as:
R = E / I
or as:
I = E / R
where I = current (amps), E = potential difference (volts) and R = resistance (ohms),
"x" means "multiply by" and "/" means "divide by".
So, using the values stated in the question, the current I = 120 volts / 15 ohms = 8 amps.
How do you draw a circuit diagram with a series connected to a parallel?
--------------[res 1---]------------|-----------------|
| | |
| [res 2] [res 3]
| | |
| | |
--------------------------------------------------------
res 1 is in series with a parallel connection of res 2 and 3. This is just one example.
Remedies for Armature reaction?
Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows in the coils. This field is at right angles to the generator field, and is called cross magnetization of the armature. The effect of the armature field is to distort the generator field and shift the neutral plane. The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines. This effect is known as armature reaction and is proportional to the current flowing in the armature coils.
The brushes of a generator must be set in the neutral plane; that is, they must contact segments of the commutator that are connected to armature coils having no induced emf. If the brushes were contacting commutator segments outside the neutral plane, they would short-circuit "live" coils and cause arcing and loss of power.
Armature reaction causes the neutral plane to shift in the direction of rotation, and if the brushes are in the neutral plane at no load, that is, when no armature current is flowing, they will not be in the neutral plane when armature current is flowing. For this reason it is desirable to incorporate a corrective system into the generator design.
These are two principal methods by which the effect of armature reaction is overcome. The first method is to shift the position of the brushes so that they are in the neutral plane when the generator is producing its normal load current. in the other method, special field poles, called interpoles, are installed in the generator to counteract the effect of armature reaction.
The brush-setting method is satisfactory in installations in which the generator operates under a fairly constant load. If the load varies to a marked degree, the neutral plane will shift proportionately, and the brushes will not be in the correct position at all times. The brush-setting method is the most common means of correcting for armature reaction in small generators (those producing approximately 1000 W or less). Larger generators require the use of interpoles.
Is ac current dangerous or DC current?
Both will kill you easily ;)
But medium/high voltage, high current DC is generally considered 'more dangerous' as it tends to make people clamp onto the cable rather than being thrown away from it, so fault current is suffered for longer as a result.
Hope this helps.
Paul.
ANSWER : NOT TRUE VOLTAGE DOES NOT KILL current however will even a 'D' cell can kill you [able to deliver 2 amps] Now which is more dangerous DC for sure it is continuous AC WILL PASS TROUGH ZERO AT TIMES ENOUGH MAYBE TO DISCONNECT
Why did scientists think lime was an element?
because they could not separate it which required electricity which wasn't in tuse as they didn't know how to harness it.
Can you use ac volt on a DC volt?
There is no such thing as a d.c. transformer; all transformers work on a.c.
So, what you are probably referring to is a power supply: the type of thing you would use, for example, to run a small radio or to charge a battery.
In that case, no, you cannot plug a a.c. appliance into a power supply that has a d.c. output.
What is the main difference between star and delta connection for 3-phase machines?
The difference is where they are grounded in the supply transformer. If you're the same guy that continues to ask questions regarding delta and star or "Y" connections, then you probably already know the answer.
High voltage transmission lines supply power to step down transformers to supply buildings. The power will likely go through a switchgear to control overcurrent and distribute the electricity to a number of transformers. Those transformers will typically step down the voltage through a "Delta" (primary) and "Y" secondary.
The Delta primary is grounded at a mid-point between two of the three phases, this creates the so called high leg out of the third phase. The Y secondary is grounded at the center of the Y.
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For more information see the answers to the Related Questions shown below.
It is always desirable to run any equipment or device at maximum efficiency for that matter, not only the power transformer.
Power transformer maximum efficiency occurs when copper loss is equal to iron loss. (or no load loss equals to load loss). This does not necessariliy mean that maximum efficiency occurs at maximum or full load.
Generally the maximum efficiency occurs at relatively less than full load of the transformer.
What are difference between electrical and electronic?
Electric device means a device which works by using electric power or current and it's working principle or working area is shown whoever sees it. Where as electronic device means it can work by consuming electric power or battery power, but we can not see the working principle , i.e , how it is working ,and just we see the result. Electronic devices are preprogrammed and it consists of chips (which are small pieces, encapsulation of programs.
Why you are using on load tap changer in primay of transformer?
The primary windings are bigger In size and it will be more accurate to tap it than tapping the smaller size secondary windings. Answer
A tap changer is installed on the high-voltage side of a transformer, regardless of whether that transformer is a step-up or a step-down type. So, it isn't necessarily installed on the primary side of the transformer. The reason for this is that the current on the high-voltage side of the transformer is lower than on the low-voltage side, and the make/break contacts can be smaller.
Also there are more turn on the high-voltage side so a finer degree of adjustment can be achieved.
