0
Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
How many lumen in a 25 watt incandescent light bulb?
a 100W incandescent lamp emits 120 candela.
lumen is the unit for luminous intensity per steradian ,an lamp emits in all direction
therefore a 16.25watt lamp contains 19.5 lumen
Answer
The lumen is the SI unit for luminous flux -which describes the output power of visible light expressed in photometric units. The ratio of a lamp's output luminous flux to its input power is termed 'efficacy', expressed in lumens per watt. The efficacy for incandescent lamp varies from 5-15 lumens per watt. So the output of a 16.25-W incandescent lamp will be between 80-245 W.
Can circuit breaker isolate circuit?
That's just what a circuit-breaker is designed to do - Isolate a circuit from the rest of the system.
AnswerNot necessarily. A circuit breaker is a protective device, designed to disconnect circuits in the event of an overcurrent due to overload or short circuit. While a low-/medium-voltage circuit breaker, of course, can be used to open a circuit, it does not necessarily provide isolation. In general, isolation requires a visible break in the circuit; as a circuit breaker's contacts are enclosed, a visible break is not possible.
In the case of a high-voltage circuit breaker, the device is used to open a circuit but does not isolate that circuit from the supply. Isolation must be provided using separate,usually non-loadbreaking devices (i.e. devices which are not designed to open a live circuit) called isolators (UK term) or disconnector (US/Canadian term), which provide a visual break in the circuit. The exception to this is a racking-type circuit breaker which, after it has been opened, can be racked down from the circuits to provide a visual disconnection.
What is the maximum current unbalance of a 3 phase motor?
No standard prescribes permitted unbalance in current for induction motors. IEC 892/2002 however, specifies permitted unbalance in voltage as 1% at the motor terminal. It is deduced that 1% unbalance in voltage will result in 6% to 9% unbalance in current. This is, therefore, grid caused activity. However, there are load related activities, such as parallel connected single phase loads or shunt capacitors that may also influence unbalance in current across the main contactor. In large motors, sometimes, unbalance in current can be seen if the air-gap eccentricity is seen. In such cases the PF in 3 phases will be unbalanced.
What combination of units is equivalent to the amperes?
The unit of measure for voltage is volt. Ohm measures resistance.
What is mutual coupling in transformer?
It stands for how does the primary and secondary winding magnetic fields connected firmly without much of leakage flux.
How does time inverse over current relay work?
Over Current (Inverse Time) Over current relay function monitors the general balanced overloading and has current/time settings. This is determined by the overall protective discrimination scheme. There advantage over definite time relays is that they can have much shorter tripping times can be obtained without any risk to the protection selection process. These are classified in accordance with there characteristic curves, this indicates the speed of the operation. Based on this they are defined as being inverse, very inverse or extremely inverse. The typical settings for these relays are 0.7-2In (normal or rated generator current) in 1-10 second. Inducing a calibrated test current through the normal load current tests this relay.
Self inductance of a given coil by Andersons method?
Anderson's Bridge is an AC bridge. It is used to measure self inductance of a coil using a capacitor and resistors. The bridge continuously balances itself by a steady current through a moving coil galvanometer replacing a headphone and a battery replacing an A.C. source. The resistance is adjusted until the currents two specific resistors in the center of the arrange are the same. Then inductive balance is achieved by using the A.C. source and headphone in their respective positions.
Why does wiring batteries in a series makes bulbs glow brighter then if they were wired in parallel?
If two light bulbs are connected in the same series circuit, each one will glow dimmer
than it would if it were the only one in the circuit with the same power supply.
How is the reading on an ammeter be affected when one of the parallel resistors is removed?
decrease to half of its original value
Why transformer is rating kva?
the short answer: to distinguish as an AC transformer, as opposed to a DC transformer.
The long answer:
A Kva stands for Kilo-Volt-Amps. The transformers mounted on telephone poles work with hundreds of thousands of volts so rather than 750,000 V, we use the abbreviation kilo, being the metric prefix for thousand and write 750 kV. As for 'VA' some high school physics tells us Voltage*Current=Power. voltage being measured in volts (V), current in amperes or amps for short (A), and power being Watts (W). However alternating current is a very fickle beast and the voltage and current vary in a wave like fashion causing the power to reverse direction. Other factors come into play such as power sag, types of electrical loads, and wasted energy, the equation soon becomes very messy. at times the power is actually negative and is flowing away from your house! so to simplify things they use Volt-Amps to represent the maximum amount of power as an absolute value that the electricity can deliver. as opposed to the USEFUL amount of power which is lower due to resistances in the wires and other loses. Engineers have to worry about the KVA when designing a system so it can handle everything thrown at it, keeping the wires from melting and that transformer from blowing up!
How many window ac can run with 1 KVA generator?
I have never seen a window A/C unit which runs on 1000 Watts and 1KVA is essentially 1000 watts. To run an A/C unit depending on the size you need a much bigger generator and not sized for the rated wattage of the unit but sized extra big to be able to kick the compressor motor over. Motor draw huge amounts of current when they first start typically unless you have a very late model with a VFD in it.
Why the filter used in rectifier circuit?
Filter capacitors smooth out the pulsating DC. Without the capacitors, the pulsating DC drops to zero at the AC crossing point, unless it is a three phase rectifier. Sometimes, that is sufficient. Sometimes, they are followed up with a regulator circuit that further stabilizes the DC.
Explain in detail about construction woking of single phase wattmeter?
Wattmeter
Definition
The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit.Electric power is measured by means of a wattmeter. This instrument is of the electrodynamic type. It consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. The fixed coils are made up of a few turns of a comparatively large conductor. The potential coil consists of many turns of fine wire. It is mounted on a shaft, carried in jeweled bearings, so that it may turn inside the stationary coils. The movable coil carries a needle which moves over a suitably marked scale. Spiral coil springs hold the needle to a zero position.The figure below shows the circuit of a simple wattmeter.
Why secondary winding and metal core earthed at one point?
generally tertiary wndng is delta
.if one point of this delta is earthed(through a CT) then it is not a earth fault. thansformer will operate normally. now if a second point(or any point on the delta winding) is earthed (earth fault) then the fault current will be sensed by the said ct.and Transf will tripped. Avradeep Das. email id: avra.wbsetcl@gmail.com
How can you connect a 120 volt motor to run with 240 volt?
Use one leg of the 240v and the neutral wire. Most electric dryers run the motor this way. The heating element is 240v but the motor is 120v.
NO, THAT IS DANGEROUS ADVICE because a 240 volt service has a circuit breaker which is sized for the current draw of a large 240 volt appliance, so it would have a rated amperage that is too high to protect a 120 volt motor running on its own.
Only 240 volt appliances such as dryers, air conditioners, etc. are safe to use on 240 volt circuits.
<><><>
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.
How do you increase the current produced by coils?
to increase the turn of the coil
ANSWER: Nobody can increase the current of a coil it actually losses power because of IR drop. from the source to the final output will always be less unless the current is amplified by an active device like a current amplifier where the power is from another source.
What is the definition of insulator in engineering?
the definition for an insulator changes from dictionary but they all mean the same thing and that is...
What is the formula of 2 phase power?
The formula which are needed for making of a single phase transformer
i.e o/p voltage,watt,current,turn,core size,coil number,bobin size etc
How do you convert kwh month to mwh?
1 kwh is 1000mwh
Answer:
1 kWh is one kilo Watt hour = 1,000 Watt-hours.
1 mWh is a milli Watt-hour = 1/1,000 Watt-hours.
Therefore the answer is 1,000 x 1,000 or 1,000,000 mWh.
How can you get 230v single phase from 240v single phase supply?
Most modern homes have 240 Volts supplied. The 240 volts are measured between the two main busbars in the electric panel. The way the panel is organized you just need a 240 breaker that spans both busbars. They are double the height of a 120 V breaker. If you have an electric dryer, stove or whole house air conditioner you are likely already using 240 V. If for some strange reason you don't already have 240 V then you would need a transformer rated to your intended use.
What are uses of series and parallel capacitor combination?
Capacitors may be connected in series to provide a capacitance with an effective
working voltage higher than that of any of the individual units, (but the effective
capacitance is less than that of any individual.)
Capacitors may be connected in parallel to provide an effective capacitance value
greater than that of any of the individual units, (but working voltage is equal to
the lowest among the individuals).
How can amperage in a low voltage circuit be measured?
The question should be, "How should electrical current measured?"
Current is measured in Amperes using an Ammeter placed in series with the conductor of the current. This is impractical, so most ammeters have windings of wire that pick up the field generated around the conductor in question. This winding, or coil, is very carefully sized and the meter very carefully calibrated to yield correct readings of current without a direct connection.
How to calculate the resistance to step down DC voltage?
Connect a variable resistance across DC source (fixed ends of variable resistor or Rheostat) and take decreased DC output across its one fixed terminal and other variable terminal of variable resistor.
Other method is connect variable resistor in series with DC output and load, vary the resistance and take decreased DC voltage as required.
Why 3ph motor will work in reverse direction?
no
Under most conditions the answer would be no, however I experienced this very occurrence myself. This is the condition it happened under: Wiring a three phase power band saw with a hydraulic pump. The pump was used to clamp the work in place and raise the cutting head. One of the wires for the pump motor had come out of the factory installed terminal strip. When the saw was started the pump ran in reverse, we changed the rotation at the disconnect. Started the pump again, the pump again ran in reverse. Thinking we had reconnected it incorrectly, we again changed the phasing. Started the pump again, again it ran in reverse. We started looking the wiring over and found the wire out of the terminal strip, corrected this problem and the motor ran in the right direction. Why did this happen? A three phase motor will run with only two phases connected as long as there is no load on the motor. The pump only loaded the motor when it was turning in the right direction and pumping oil. The pump provided no load when turning in reverse and the motor could easily turn it.
