Armature Resistance? [′är·mə‚chər ri′zis·təns] (electricity) The ohmic resistance in the main current-carrying windings of an electric generator or motor.
How do you calculate armature resistance? V − O = I a R a ∴ I a = V R a . As the resistance of a motor armature may be less than an ohm, then the armature current at starting if the armature applied voltage were 230 V would be in excess of 230 A.
What is armature resistance in a DC machine? Armature Winding resistance is the ohmic resistance of the copper winding wires.
How do you calculate armature resistance of a DC generator? Essentially, i have to calculate the Armature Resistance (Ra) of a D.C. self-excited shunt generator. I know the e.m.f is 420V, using E = V + (Ia x Ra). So, in the e.m.f calculation, E = V + (Ia x Ra), i know that Ia x Ra = VD = 12V.
Why is armature resistance low in DC motor?
The armature produces a back EMF depending on its speed, which bucks the supply voltage. The armature current then will depend on the difference between the supply voltage and the EMF. So the armature resistance must be low enough to allow sufficient current to flow even with this reduced voltage.
What is armature reactance?
[′är·mə‚chər ‚rē′ak·təns] (electromagnetism) The inductive reactance due to the flux produced by the armature current and enclosed by the conductors in the armature slots and the end connections.
What is armature winding?
The armature winding is defined as the conductors which are housed and protected within the armature slots are connected properly. These windings are arranged in the armature slots. The helpful e.m.f will be encouraged in this winding which is received across the brushes.
How is armature resistance measured in a dc motor?
A practical way to measure the winding resistance is to use the Ohm’s law: Resistance = Voltage / Current. If you apply a power source to the windings and measure the voltage and current flowing through them, a simple division will yield an accurate value for the resistance.
What is the permissible value of armature resistance in a DC Machine?
To deliver maximum power armature current must be high and the shunt field current is minimum. So, shunt field resistance of DC Machine is very high value around 50Ω to 500 Ω. , it can be concluded that for high resistance length of the coil is to be large and area to be small.
What is armature inductance?
Armature inductance — Armature inductance Inductance of the conducting portion of the motor. If you do not have information about this inductance, set the value of this parameter to a small, nonzero number.
What is the emf equation of DC generator?
As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb.
What is the critical resistance in a DC shunt generator?
The critical field resistance is defined as the maximum field circuit resistance (for a given speed) with which the shunt generator would just excite. The shunt generator will build up voltage only if field circuit resistance is less than critical field resistance.
What is the effect of armature resistance in DC generator?
The adverse effects of armature reaction: Armature reaction weakens the main flux. In case of a dc generator, weakening of the main flux reduces the generated voltage. Armature reaction distorts the main flux, hence the position of M.N.A. gets shifted (M.N.A. is perpendicular to the flux lines of main field flux).
Why shunt field resistance is high?
More no of turns used in Shunt field winding intentionally to reduce the starting current. The cross sectional area of the wire is thin so that it possess high resistance. Longer winding is used to produce very strong magnetic field..
What will happen if field resistance is decreased?
What will happen if field resistance is decreased? Explanation: When field resistance is decreased, it will increase field current by Ohm’s law. Thus, field resistance line will lie below the older line of field resistance. Eventually, it’ll intersect OCC afterwards causing increase in no-load voltage.
Why does the armature winding possess reactance?
This leakage flux will set up an emf because of self-inductance. This emf is known as reactance emf, which leads the armature current I by 900. Thus, the armature winding is said to possess a leakage reactance XL. The voltage drop due to this reactance is IXL.
What is armature reaction in alternators?
Armature Reaction in Synchronous Generator When the alternator is loaded, the armature currents are set up which produce the armature flux. This armature flux modifies the main flux in the air gap of the machine. This action of armature flux is called armature reaction.
What is armature reaction proportional to?
Armature reaction drop is the effect of a magnetic field on the distribution of the flux under main poles of a generator. This effect is known as armature reaction and is proportional to the current flowing in the armature coils.
What is the difference between armature winding and rotor winding?
In a generator and a motor, a rotor rotates and the stationary part of the motor is known as a stator. Similarly an armature carries current while field windings produce the magnetic field needed to excite the generator and the motor.
What instrument measures armature winding?
Answer. The windings resistance can be directly measured with an ohmmeter.
What is armature winding and field winding?
The armature is the winding to which the load is connected. In small generators, the field windings are often on the stator, and the armature windings are on the rotor. Most large machines, however, have a rotating field and a stationary armature. A synchronous motor is virtually identical to a synchronous generator.
How do you calculate winding resistance?
Current Voltage Method of Measurement of Winding Resistance In this method of measurement of winding resistance, the test current is injected to the winding and corresponding voltage drop across the winding is measured. By applying simple Ohm’s law i.e. Rx = V ⁄ I, one can easily determine the value of resistance.
How do you neutralize an armature reaction?
The effect of armature reaction can be neutralized by use of compensating winding. It is always placed in series with armature winding. The armature ampere conductors under pole shoe must be equal to compensating winding ampere conductors which will compensate armature mmf perfectly.