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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
Why do power companies use high voltage transmission lines?
1 .to reduce I2R( power) losses
2. it is economical to transit at higher voltages through transformers, rather than generate them
AnswerFor a given load, the higher the supply voltage, the lower the resulting load current.
There seems to be a widely-held myth that the main reason that electricity is transmitted at high voltage in order 'to avoid energy losses (I2R losses) along the line'. While it is certainly true that energy losses are reduced, the primary reason is to reduce the otherwise-enormous voltage drop along the line which would make it impossible to transmit electricity at lower voltages. The secondary reason is to ensure conductors of practical size and weight can be used.
The voltages produced by alternators (a.c. generators) is limited to around 30 kV, due to the physical limit to the number of windings that can be installed in the machine, so transformers are used to step up the alternator voltages to very high levels (400 kV in the UK, for example).
Can all receptacles in a bedroom be on the same circuit?
yes
Answer for UK SystemThe answer is yes, as all the outlets will be supplied from the same ring main.
RCT is Secondary resistance of Current transformer it depends on Design.
In an electric circuit what provides the push?
You could consider the Voltage as the pushing force in a circuit. It drives the current.
Why is the meter to measure current called an annmeter?
It's called an ammeter, because it measures amperes.
A:
The inductor does not allow ac signal to pass through. It blocks ac and passes dc. If the switch is open, then the ac signal wont pass. If the switch is closed, then the ac signal will pass through the switch.
Answer
It is incorrect to say that an inductor 'does not allow' the passage of an alternating current. An a.c. current will pass through an inductor, although the inductor will limit the value of that current due to the inductor's inductive reactance. Inductive reactance, which is expressed in ohms, is directly-proportional to the inductance of the inductor and to the frequency of the supply. The value of the current is determined by dividing the supply voltage by the inductive reactance of the inductor.
If the switch is connected in parallel with the inductor, then closing the switch will apply a direct short circuit across the inductor, and the resulting short-circuit current will cause the circuit's protective device (fuse or circuit breaker) to operate.
Difference between two phase and three phase welding machine?
Three phase uses a safety circuit away from the machine, two phases uses you as the safety circuit
What happens when you apply DC directly to a capacitor?
When you apply DC directly to a capacitor, it charges to the value of the DC potential, and then there is (nearly1) zero current flow through the capacitor. If the capacitance is large enough, though, and the DC source has a low enough impedance, the current flow can be quite substantial, damaging things.
The reason the equilibrium current is zero is that a capacitor resists a change in voltage, proportional to current and inversely proportional to capacitance...
dv/dt = i/c
... which makes the capacitor essentially a high pass filter, and a DC blocker.
1 The equilibrium current is "nearly" zero because, in our non-ideal world, every capacitor has some leakage current. Practically, the current is zero - from a purist perspective, it is not.
An oscillation is a term we could use to refer to a single cycle of a cyclic or repeating motion. Let's just take one example (so we don't run it into the ground) and see how it applies. And we'll use that familiar pendulum clock. The pendulum on a clock will be driven by a spring. We swing the pendulum up, release it, and gravity and the spring do the rest. The spring, as you have guessed, adds just enough energy to offset the friction loss in the system. When we lift the pendulum and release it, it is pulled down (accelerated) by gravity. It passes through a point where it is at the "bottom" of the swing (having achieved maximum velocity), and then heads up on the other side. It's decelerating here under the influence of gravity - that same gravity that accelerated it. I continues to slow, it stops, and then accelerates back down and across the "middle" or "bottom" again. Up it goes to the top of its arc on the other side, and it returns to its starting point. It has completed one cycle of its oscillation. It has performed one oscillation. Simple, and easy.
What is the definition of octopus splice?
In electronics, an octopus splice refers to a cable that has been split into different branches, like the tentacles of an octopus. These branches each have a connector on the end.
Can you use a 15a 220v fuse for a 15a 32v FUSE?
If it fits you are fine. You are at the same current and the voltage rating is higher.
Why you choose rms value of voltage and current for calculations?
Because peak to peak measurements are only accurate if the wave is nearly perfectly sinusoidal and without excessive sideband spurs. An average measurment wheather it be done by a gizzmo that did the math for us or an o-scope where we have to divide what we see by 2.828 for the RMS value. A digital voltmeter simply averages all of the voltage changes into "a number" that agrees with what the predicted mathematical value should be. these devices always have frequency limitations. You should slways check the specs of your measuring device before you start to make sure it is capable of making an accurate enough measurement at the freqyency you have in mind.
AnswerAll a.c. voltages and currents are expressed and measured in rms values, unless otherwise stated. So it follows that any calculations would be done using these values.
Do higher watt inverters drain batteries more than lower watt?
The inverter draws little current on its own. It is the load that is connected to the inverter. If there were no load on the inverter you could use an ampmeter to determine the no load current. One thing to consider is that a higher wattage inverter would have larger gauge wire which is of lower resistance. This could make the no load current lower for the higher wattage inverter. Bottom line is you would have to measure or have a specification on the no load current.
since the volt amphere turns in secondary neautralises the primary voltamphere turns making the magnetic flux in the core remain constant
What are the dis advantages of turbo generators?
they are quite a maintenance problem
lots of pitting and cavitation on the blades
low speed turbines ( water wheels ) are easier to get to and dont have near the problem and are easily inspected
Can you run a 7 volt battery on a 6 volt portable radio?
The increase in current (assuming resistance is the same and increase in voltage will lead to an increase in current) will fry your portable radio.
Your question reveals a misunderstanding of how a transformer works.
The primary current of a transformer is determined by the secondary current, not the other way around. When the secondary voltage is applied to a load, a secondary current flows, and its value is determined by the secondary voltage and the load impedance. This secondary current then determines the value of the primary current.
Why use a suspension insulator on 11kv electric power lines?
Suspension insulators are glass 'dish' insulators that are designed to take longitudinal strain -i.e. strain in the direction of the conductors. They are so-called, because they are suspended below the pole's crossarm. Suspension insulators, therefore, are used on terminal poles where the main strain on the crossarm is in the direction of the conductors, or on angle-poles where there is a sharp change in direction of the power line.
No. Fuse is a protective device.
A fuse is part of a circuit and does not act as a load and does not cause a voltage drop unless more than the rated current passes through it and it heats up (using up some power and causing a voltage drop) and melts or switches off breaking the circuit.
Why does your bathroom or kitchen extractor fan run when the switch is turned off?
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A fan unit which has a timer in it must have two separate "hot" wires feeding it:
- A "non-switched hot", which is permanently fed with power from the breaker on the main supply panel. After the fan has been switched on using the "switched hot" wire described below, this "non-switched hot" wire keeps the fan running for the length of time the timer has been set for.
- A "switched hot" wire which should be connected to the on/off switch that controls the fan.
Depending on the actual design of the control circuitry inside the fan unit, if the above two "hots" have been connected to the fan unit the wrong way round, the result can be that the fan will "stay on and running" all the time, regardless of the position of the on/off switch for its circuit.
The solution is to switch off all the power at the main breaker panel and, after you have checked that no wires are still "hot" or "live", re-wire the "hots" on the fan unit the other way round:
- You must ensure that the "switched hot" connection on the fan unit is no longer connected to the permanent hot feed wire coming from the breaker on the main supply panel. (It should now be connected to the switched hot wire from on/off switch that controls the fan.)
- The "non-switched hot" connection on the fan unit isconnected to the permanent hot feed wire from the breaker on the main supply panel. (Instead of to the switched hot wire from the on/off switch that controls the fan).
More details:
If the fan stays on after it has been switched off there is probably a timer inside the fan unit which will turn the fan off after a set time. If the fan does not go off after 2 hours from switching it off then either the fan unit has no timer but has been wired up incorrectly - so that it is not controlled by the on/off switch (see above) or the timer may have been set to stay on continuously.
Sometimes a fan may come on when the switch for a light in the same room has been turned on but, if the fan has a timer, that timer will keep the fan running even after the light has been switched off.
Sometimes a fan may have its own on/off switch, separate to another switch controlling a light in the same room. In that situation you might switch off both the light and the fan but, if the fan has a timer, the timer will still keep the fan running even after the light has been switched off.
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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.
The ampere is one of the seven SI base units, and is used to measure current.
It is defined in terms of the force between two parallel conductors due to the magnetic fields set up around those conductors.
An ampere is a unit of electrical?
The Ampere (capitalized because its name came from a person) is the basic unit of electrical current.
In general, a DCS or PLC, handles numerous discrete I/Os. One common I/O module (board) is used to supply 8, 16 or more points. Discrete output circuits from a DCS typically use low power level signals (transistors, micro relays) which cannot be sent directly to the field devices such as electromagnetic valves or motor control circuits. That is why interposing relays are often necessary.
These relays play an important role by amplifying the current capacity of the contact signal of the I/O module allowing larger current flow. In addition, discrete input circuits normally can handle only dry contacts or wet contacts of low voltage, which also require interposing relays.
For example, let's say the relay of a PLC can only accommodate 0.5A at 220 VAC, but the solenoid which is to be connected to the relay requires 1.2A at 220 VAC. In this case, an interposing relay with contacts rated for operation at 1.2A at 220 VAC would be used as an interposing relay "between" the PLC relay and the solenoid. The coil of the interposing relay should require less voltage and current than the driving relay is rated for, and the contacts of the interposing relay must be rated to handle the requirements of the load (solenoid, light, contactor, motor, etc.).
