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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 are brushes with reference to DC motors?
Bushes, with reference to DC motors is a brushed DC motor which is a motor that designed to run from a direct current (DC) power source. This type of motor is an internally committed electric motor.
What is the purpose of a high voltage transformer?
if the transformer is distributing transformer then we shoud have to give more prefer to the high volatage to reduce losses
if we distibute power at low volage there is more current which causes more losses
and in hv system there is high volage and low is current so the losses are also low
Is a step up transformer a Ynd or a Dyn?
Whether a transformer is 'step up' or 'step down' has nothing to do with the way its windings are connected, so it could be wye-delta or delta-wye.
How do you calculate rated kva of a circuit breaker?
You don't calculate the rated kV.A of a circuit breaker; it's determined by the manufacturer. It's important that a circuit breaker's rated kV.A exceeds the fault level kV.A at the point where the circuit breaker is located, otherwise it may fail to interrupt a fault current and, possibly, self destruct.
How can you identify which one is step up or step down transformer?
A transformer has two windings, termed the 'primary winding' and the 'secondary winding'. The primary winding is the winding connected to the supply, while the secondary winding is connected to the load.
The secondary voltage of a 'step up' transformer is higher than the primary voltage; the secondary voltage of a 'step down' transformer is lower than the primary voltage.
The simplest way to determine whether a transformer is a step up or step down, is to measure the primary and secondary voltages. If you are simply looking at a transformer, then the transformer's insulated bushings will give you a clue -the higher voltage bushings are much bigger than the lower voltage bushings. If you have access to the inside of the transformer, then the higher voltage windings are thinner and have a greater number of turns than the lower-voltage winding.
What are the reasons why a current is induced in a coil?
Current is not induced into a coil. It's voltage that is induced into a coil. If the coil is connected to a load, or even short circuited, then a current will flow as a result of the induced voltage -but it's the voltage, not the resulting current, that's induced!
Voltage is induced into a coil because the the changing magnetic field, due to the change in current (0 to Imax or vice versa) applied to that coil. The process is called 'self induction'.
What is pg clamps in transmission line?
pg clamp is known for parallel groove clamp,especially used in transmission line to hold transmission conductors in parallel.
How can an ammeter loading effect the circuit under test?
Since internal resistance of the ameter will increases the resistance of the circuit. Thus decreasing the current giving an errorenous reading.
Is the torque output of a DC motor directly proportional to armature current?
In dc shunt motor,base speed is 500 rpm and its field current is 17A, top speed is 1200 rpm and field current is 5.6 A.But 600 rpm it has reduced by 10A It is normal? How
Why is a starting current in a DC motor very high?
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
The relation between resistance R, Current I and voltage V is:
R= V/I
Therefore: 60 = 12 / I <=> I = 12 / 60 = 0.2 amp
How do you prevent shock by capacitors?
Discharge the capacitor, normally with a resistor accross the terminals (Calculated size)
Why do you represent leakage flux in a transformer by inductive reactance?
A transformer is often represented by an equivalent circuit, in which the transformer itself is considered to be 'ideal', and its basic losses are then represented as resistance and reactance in series with both the primary and secondary windings for a loaded transformer, or just on the primary side for a transformer on open circuit.
The transformer's primary flux comprises two components: the main flux, which links the primary and secondary windings, and a leakage flux which links just the primary winding. The leakage flux is considered arising from a self inductance in series with an 'ideal' primary winding. The reactance of this inductance is termed the primary leakage reactance. The voltage drop across this reactance will lead the primary no-load current by 90 degrees which, when added to the voltage drop across the resistance of the primary winding, acts to reduce the back emf of the primary winding below the value of the applied voltage and cause it to lag.
A similar explanation accounts for the an inductance and resistance in series with the secondary winding, when the transformer is loaded.
The term 'house earthing' is used in the electrical wiring of a structure in order to ground the house against electrical leakage which can cause increased power usage and the possibilty of safety concerns involving electrical shock.
Why may copper losses be neglected in the open circuit test of a transformer?
Because the magnetising current is very small, so the primary losses are insignificant, while there is no secondary current, so there are no secondary losses.
What is the difference between off load tap changer and on load tap changer?
An on-load tap-changer must not break the supply to the transformer's windings while the transformer is on load. So it has a 'make-before-break' arrangement with its contacts -i.e. one contact moves to the second tap setting, before the second contact moves away from the first tap setting, while a reactor balances the load currents when the contacts are on different tap settings. An on-load tap changer is motor-driven, and can be operated automatically or manually.
An off-load tap-changer does not require a make-before-break arrangement, because it is designed to be operated when the transformer is disconnected.
How do you calculate the rpm of a motor with a known number of poles and a frequency of 60 Hrtz?
A synchronous motor will spin at the system frequency. 60 Hz translates into 60*60 = 3600 direction changes per minute. If this is a two pole motor (one north and one south), it will spin 1 rotation per direction change. If it is a four pole motor (two north and two south), it will spin 1/2 rotation per direction change.
If this is an induction motor, it will spin at a frequency slightly less than an equivalent synchronous motor; this frequency difference is referred to as slip.
WHAT TYPE OF transformers has secondary current of the same order as the magnetising current?
A one to one, i.e. isolation, transformer.
CommentIt might be worth pointing out that the secondary current is determined by the load, and the primary current is then determined by the secondary current. The questioner appears to think that the secondary current is determined by the primary current.
Can LED lights flash on and off?
yes i think so
Yes, there are flashing l.e.ds. An ordinary l.e.d. can, of course, be flashed on and off by interrupting the current through it. There are products such as the LED-FLASHDIM available from LED-SUPPLIES.COM that will enable you to control how LED strip lighting flashes and at what speed and brightness levels
What is a disadvantages DOL or direct online starter?
it can not be use for heavy duty motors as well as it requires a high starting current.
Why 3 phase are called as r y b?
In the UK, the letters, 'R-Y-B', stand for 'red-yellow-blue' which are the colours used to identify the lines (not phases) of a three-phase transmission or distribution cable. The colours are also used, in some cases, to identify the corresponding bushings for transformers, circuit breakers, voltage transformers (potential transformers), etc., in substations. The sequence of these letters/colours also correspond to the normal phase sequence of the three-phase system.
In UK residential, commercial, and industrial installations, these colours have now been replaced by the EU harmonisation colours: brown-black-grey.
Other countries use different methods of identifying line conductors, including 1-2-3, A-B-C, R-S-T, L1-L2-L3, etc., or various combinations of these methods.
What is shunt and series motor?
A series motor is one in which the field windings are in series with the armature windings. So the torque is proportional to the square of the supply current.
'Shunt' is an archaic term for 'parallel'. So a shunt motor is one in which the field winding is in parallel with the armature windings. So the torque is proportional to the supply current.
What happen when you reverse the direction of rotation in a separately excited dc generator?
When reverse the direction of a seperately excited DC generator,only polarities has been reversed,i.e., (+) becomes (-) and (-) become (+).
