Alternator Voltage Regulation MCQ Quiz in मल्याळम - Objective Question with Answer for Alternator Voltage Regulation - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Normally for voltage regulation calculation, we use the following methods.

1. Synchronous impedance or emf method
2. Armature turn or mmf method
3. Zero PF or Potier method
    

Synchronous impedance method:

• The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called as the EMF method.
• The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction by an imaginary reactance.
• This method gives result which is higher than the original value. That's why it is called the pessimistic method.
• For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic and the short circuit characteristic.

Armature turn method:

It is also known as MMF method. It gives a value which is lower than the original value. That's why it is called an optimistic method.

To calculate the voltage regulation by MMF Method, the following information is required. They are as follows:

• The resistance of the stator winding per phase
• Open circuit characteristics at synchronous speed
• Field current at rated short circuit current

Potier triangle method:

• This method depends on the separation of the leakage reactance of armature and its effects.
• It is used to obtain the leakage reactance and field current equivalent of armature reaction.
• It is the most accurate method of voltage regulation.
• For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.

Concept:

Normally for voltage regulation calculation, we use the following methods.

1. Synchronous impedance or emf method

2. Armature turn or mmf method

3. Zero PF or Potier method

Synchronous impedance method (EMF Method):

• The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called the EMF method.
• The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction with an imaginary reactance.
• This method is not accurate as it gives a result that is higher than the original value. That's why it is called the pessimistic method.
• For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic, and the short circuit characteristic.

Armature turn method:

It is also known as the MMF method. It gives a value which is lower than the original value. That's why it is called an optimistic method.

To calculate the voltage regulation by MMF Method, the following information is required. They are as follows:

• The resistance of the stator winding per phase
• Open circuit characteristics at synchronous speed
• Field current at rated short circuit current

Potier triangle method:

• This method depends on the separation of the leakage reactance of armature and its effects.
• It is used to obtain the leakage reactance and field current equivalent of armature reaction.
• It is the most accurate method of voltage regulation.
• For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.

Normally for voltage regulation calculation, we use the following methods.

1. Synchronous impedance or emf method

2. Armature turn or mmf method

3. Zero PF or Potier method

Synchronous impedance method:

• The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called as the EMF method.
• The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction by an imaginary reactance.
• This method gives result which is higher than the original value. That's why it is called the pessimistic method.
• For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic and the short circuit characteristic.

Armature turn method:

It is also known as MMF method. It gives a value which is lower than the original value. That's why it is called an optimistic method.

To calculate the voltage regulation by MMF Method, the following information is required. They are as follows:

• The resistance of the stator winding per phase
• Open circuit characteristics at synchronous speed
• Field current at rated short circuit current

Potier triangle method:

• This method depends on the separation of the leakage reactance of armature and its effects.
• It is used to obtain the leakage reactance and field current equivalent of armature reaction.
• It is the most accurate method of voltage regulation.
• For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.

The following assumptions are made in this method.

• The armature resistance is neglected.
• The O.C.C taken on no-load accurately represents the relation between MMF and voltage on load.
• The leakage reactance voltage is independent of excitation.
• The armature reaction MMF is constant.

Concept:

The voltage regulation of an alternator is defined as the ratio of the rise in voltage when full-load is removed (field excitation and speed remaining the same) to the rated terminal voltage.

% voltage regulation \( = \frac{{{E_0} - V}}{V} \times 100\)

Where E0 is the no-load voltage

And V is the rated voltage

Calculation:

Given: no-load induced emf (E0) = 230 V

Rated terminal voltage (V) = 200 V

Voltage regulation \( = \frac{{230 - 200}}{{200}} \times 100 = 15\% \)

Voltage regulation: The voltage regulation of an AC alternator is,

Percentage voltage regulation \(= \frac{{{E_{0}} - {V}}}{{{V}}} × 100\)

E0 is the internally generated voltage per phase at no load and it is given by,

E₀ = V + I_aZ_s

V is the terminal voltage per phase at full load

Voltage regulation indicates the drop in voltage from no load to the full load.

There are three causes of voltage drop in the alternator.

• Armature circuit voltage drop
• Armature reactance
• Armature reaction
   

The first two factors always tend to reduce the generated voltage, the third factor may tend to increase or decrease the generated voltage. The nature of the load affects the voltage regulation of the alternator.

Voltage Regulation Curve at different Power Factor:

From The curve:

• Voltage regulation at the lagging power factor will be more than the voltage regulation at the unity power factor.
• Negative voltage regulation and zero voltage regulation occur at the leading power factor.
• Positive voltage regulation occurs at both unities as well as lagging power factors.
   

Illustration:

Phasor Diagram at Unity Power Factor:

At unity power factor the value of phase angle will be zero and hence, phasor can be drawn as,

∴ E₀ = V + I_aR_a .... (1)

Phasor Diagram at 0.8 lagging Power Factor:

Given, cos ϕ = 0

∴ ϕ = 36.86°

Now, R_a = Z cos ϕ & X_s = sin ϕ

Phasor diagram can be drawn as,

From Phasor, the value of E₀ given by

(E₀)2 = OA² + AB² = (OD + DA)² + (AC + CD)²

(E₀)² = (V cosϕ + I_aR_a)2 + (V sin ϕ + I_aX_s)² .... (2)

Proof:

Let consider,

V = 200 volts (single phase)

R_a = 0.06 Ω

X_s = 0.8 Ω

Since. X_s >> R_a

I_a = 50 A

At unity Power,

E₀ = V + I_aR_a = 200 + (50 × 0.06) = 200 + 3 = 203 volts

∴ Change in voltage = 203 - 200 = 3 volts

At 0.8 Lagging Power factor,

cos ϕ = 0.8 → sin ϕ = 0.6

Now, V cosϕ = 200 × 0.8 = 160 volts

V sin ϕ = 200 × 0.6 = 120 volts

I_aR_a = 3 volts

I_aX_s = 50 × 0.8 = 40 volts

From equation (2),

(E₀)2 = (V cosϕ + I_aR_a)² + (V sin ϕ + I_aX_s)²

(E₀)2 = (160 + 3)² + (120 + 40)² = 163² + 160²

∴ E₀ = 228 volts

∴ Change in voltage = 228 - 200 = 28 volts

Hence, Voltage regulation at 0.8 lagging power factor will be more than the voltage regulation at unity power factor.

Concept:

Voltage Regulation:

• The voltage regulation is defined as “the rise in voltage at the terminals, when the load is reduced from full load rated value to zero, speed and field current remaining constant”.
• With the change in load, there is a change in the terminal voltage of an alternator or synchronous generator. The magnitude of this change not only depends on the load but also on the load power factor.
• It is also defined as “the rise in voltage when full load is removed divided by the rated terminal voltage when speed and field excitation remains the same.” It is given by the formula,
  ​

\(V.R=\frac{E-V}{V}\)

Where,

E is no load voltage

V is the terminal voltage

Case 1:
E > V: Then V.R will be positive and the power factor will be lagging or unity.

Note: V.R under unity power factor is less than voltage regulation under lagging power factor,

Case 2:
E < V or E = V: Then VR will be negative and zero respectively and the power factor will be leading.

Conclusion:

From the above concept,

Curve D represents V.R at leading power factor.

Curve C represents V.R at a somewhat unity power factor.

Curve A and Curve B represent V.R at lagging power factor.

Concept:

Voltage Regulation:

• The voltage regulation is defined as “the rise in voltage at the terminals, when the load is reduced from full load rated value to zero, speed and field current remaining constant”.
• With the change in load, there is a change in the terminal voltage of an alternator or synchronous generator. The magnitude of this change not only depends on the load but also on the load power factor.
• It is also defined as “the rise in voltage when full load is removed divided by the rated terminal voltage when speed and field excitation remains the same.” It is given by the formula,
   

\(V.R=\frac{E-V}{V}\)

Where,

E is no load voltage

V is the terminal voltage

Case 1:
E > V: Then V.R will be positive and the power factor will be lagging or unity.

Note: V.R under unity power factor is less than voltage regulation under lagging power factor,

Case 2:
E < V or E = V: Then VR will be negative and zero respectively and the power factor will be leading.

Conclusion:

From the above concept,

Curve D represents V.R at leading power factor.

Curve C represents V.R at a somewhat unity power factor.

Curve A and Curve B represent V.R at lagging power factor.

Normally for voltage regulation calculation of alternator, we use the following methods.

1. Synchronous impedance method

2. Armature turn or mmf method

3. Zero pf or Potier method

The Synchronous impedance method or EMF method gives a result which is higher than the original value. That's why it's called the 'Pessimistic Method'.

The Armature turn or MMF method gives a value which is lower than the original value. That's why it's called the 'Optimistic Method'.

The most accurate method of voltage regulation is the Potier method. This can be done using the no-load or OCC curve and Full load ZPF curve (not SCC). It is based on the separation of armature leakage reactance drop and the armature reaction effects.

Additional Information

Potier triangle method:

• This method depends on the separation of the leakage reactance of armature and its effects.
• It is used to obtain the leakage reactance and field current equivalent of armature reaction.
• It is the most accurate method of voltage regulation.
• For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.​

ΔDEF is Potier triangle which is a right angle triangle 

DE = armature MMF (Fa) or field current which compensates armature reaction  

DF = IaXal = armature leakage reactance

The following assumptions are made in this method.

• The armature resistance is neglected.
• The O.C.C taken on no-load accurately represents the relation between MMF and voltage on load.
• The leakage reactance voltage is independent of excitation.
• The armature reaction MMF is constant.

Synchronous impedance method:

• The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called as the EMF method.
• The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction by an imaginary reactance.
• It gives a result that is higher than the original value. That's why it is called the pessimistic method.
• For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic, and the short circuit characteristic.

Armature turn method:

It is also known as the MMF method. It gives a value that is lower than the original value. That's why it is called an optimistic method.

To calculate the voltage regulation by MMF Method, the following information is required. They are as follows:

• The resistance of the stator winding per phase
• Open circuit characteristics at synchronous speed
• Field current at rated short circuit current

• The synchronous impedance method of calculating voltage regulation of an alternator is called the EMF method.
• The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction with an imaginary reactance and does not account for magnetic saturation.
• This method is not accurate as it gives a result that is higher than the original value. That's why it is called the pessimistic method.
• For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic, and the short circuit characteristic.

Determination of Voltage Regulation Using the Potier Method

• The MMF method suffers from a few limitations; that is, it does not take into account the leakage reactance drop.(X_al) and the armature resistance drops.
• While the field excitation corresponding to rated O.C. voltage takes saturation into account, the S.C. test does not as it is conducted with less excitation.
• All these shortcomings are overcome with the potier method where the machine supplies rated current to a purely inductive load at rated voltage (ZPF lag) and thus the magnetic circuit is in saturation while supplying the demagnetizing ampere-turns to overcome armature reaction.
   

Potier Method: It lays down a procedure to account for the moves that correspond to the Armature Reaction voltage drop (I_aX_a), leakage reactance voltage drop (IaXal), and resistive voltage drop (I_aR_a)

Explanation: Curve X shows the O.C.C. with saturation effect and Curve Y shows ZPF characteristics considering purely inducting load with purely demagnetizing armature reaction effect. ZPF characteristics are obtained by subtracting Leakage reactance drop from O.C.C. shown by vertical distance FD or (PQ).