Regulation of a Transformer MCQ Quiz in తెలుగు - Objective Question with Answer for Regulation of a Transformer - ముఫ్త్ [PDF] డౌన్లోడ్ కరెన్
Last updated on Mar 9, 2025
Latest Regulation of a Transformer MCQ Objective Questions
Top Regulation of a Transformer MCQ Objective Questions
Regulation of a Transformer Question 1:
A transformer can have regulation closer to zero on __________.
Answer (Detailed Solution Below)
Regulation of a Transformer Question 1 Detailed Solution
Voltage regulation:
Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.
E2 = no-load secondary voltage
V2 = full load secondary voltage
Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.
Voltage regulation \(= \frac{{{E_2} - {V_2}}}{{{E_2}}}\)
It can also be expressed as,
Regulation \(= \frac{{{I_2}{R_{02}}\cos {\phi _2} \pm {I_2}{X_{02}}\sin {\phi _2}}}{{{E_2}}}\)
+ sign is used for lagging loads and
- ve sign is used for leading loads
Hence voltage regulation can be negative only for capacitive loads
In a transformer, minimum voltage regulation occurs when the power factor of the load is leading.
The voltage regulation of the transformer is zero at a leading power factor load such as a capacitive load.
For zero voltage regulation, \({E_2} = {V_2}\)
\( \Rightarrow IR\cos \phi = IX\sin \phi \) (negative sign represents leading power factor loads)
\( \Rightarrow \phi = {\tan ^{ - 1}}\left( {\frac{R}{X}} \right)\)
\(\cos \phi = \cos {\tan ^{ - 1}}\left( {\frac{R}{X}} \right)\)
This is the leading power factor at which voltage regulation becomes zero while supplying the load.
Regulation of a Transformer Question 2:
The voltage regulation of a transformer having 2% resistance and 5% reactance at full load, 0.8 pf lagging is
Answer (Detailed Solution Below)
Regulation of a Transformer Question 2 Detailed Solution
Concept:
In transformer voltage regulation is given by,
Voltage regulation = x (Rpu cosθ ± Xpu sinθ)
Where x = fraction of load
Rpu = resistance in pu (we can use % resistive drop in fraction)
Xpu = reactance in pu (we can use % reactive drop in fraction)
+ for lagging load
– for leading load
Calculation:
Given that, transformer is working at 0.8 lagging power factor at full load
⇒ cos θ = 0.8, sin θ = 0.6
x = 1
Rpu = 2%
Xpu = 5%
%V.R. = 1 × (2 × 0.8 + 5 × 0.6) = 4.6%
Regulation of a Transformer Question 3:
Calculate the regulation of the transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage, when the power factor is 0.8 leading
Answer (Detailed Solution Below)
Regulation of a Transformer Question 3 Detailed Solution
Concept:
Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.
E2 = no-load secondary voltage
V2 = full load secondary voltage
Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.
Voltage regulation \(= \frac{{{E_2} - {V_2}}}{{{E_2}}}\)
It can also be expressed as,
Regulation \(= \frac{{{I_2}{R_{02}}\cos {\phi _2} \pm {I_2}{X_{02}}\sin {\phi _2}}}{{{E_2}}}\)
Regulation = %R cos ϕ ± %X sin ϕ
+ sign is used for lagging loads
- ve sign is used for leading loads
Where %R = ohmic drop
%X = reactance drop
Calculation:
Ohmic loss (%R) = 1%
Reactance drop (%X) = 5%
Power factor = cos ϕ = 0.8 leading
∴ sin ϕ = 0.6
Regulation = %R cos ϕ ± %X sin ϕ
= 1 (0.8) - 5 (0.6) = -2.2%Regulation of a Transformer Question 4:
In a short circuit test with LV side shorted, a 230 V/115 V, single phase transformer required 20 V to allow full load current at ϕsc = 60°. Its voltage regulation at full load, 0.707 lagging is ________%
Answer (Detailed Solution Below) 8.3 - 8.5
Regulation of a Transformer Question 4 Detailed Solution
Percentage voltage regulation,
\(\% \;Reg = \frac{{{V_{sc}}}}{{{E_2}}} \times \cos \left( {{\theta _{sc}} - \theta } \right) \times 100\)
Vsc is the voltage applied for the short circuit test-high voltage
E2 is the high voltage side voltage
θ is the load impedance power factor angle.
Given that, Vsc = 20 V, E2 = 230 V
cos θ = 0.707 ⇒ θ = 45°
θsc = 60°
\(\% \;Reg = \frac{{20}}{{230}} \times \cos \left( {60 - 45^\circ } \right) \times 100\)
= 8.39%Regulation of a Transformer Question 5:
If transformer is working at leading power factor then the voltage regulation can be
Answer (Detailed Solution Below)
Regulation of a Transformer Question 5 Detailed Solution
Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.
E2 = no-load secondary voltage
V2 = full load secondary voltage
Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.
Voltage regulation \(= \frac{{{E_2} - {V_2}}}{{{E_2}}}\)
It can also be expressed as,
Regulation \(= \frac{{{I_2}{R_{02}}\cos {\phi _2} \pm {I_2}{X_{02}}\sin {\phi _2}}}{{{E_2}}}\)
+ sign is used for lagging loads and
- ve sign is used for leading loads
From the above formula, we can observe that voltage regulation can be negative only for capacitive loads or leading loads.
And voltage regulation can be positive and zero also for the leading power factor.
Regulation of a Transformer Question 6:
What is the representation of the effective resistance of the transformer (R01) as referred to primary?
Answer (Detailed Solution Below)
Regulation of a Transformer Question 6 Detailed Solution
Concept:
Consider a two winding single phase transformer as shown below,
N1 = primary winding turns
N2 = secondary winding turns
V1 = primary winding voltage
V2 = secondary winding voltage
I1 = current through the primary winding
I2 = current through the secondary winding
Transformation ratio: It is defined as the ratio of the secondary voltage to the primary voltage. It is denoted by k.
\(k = \frac{{{N_2}}}{{{N_1}}} = \frac{{{V_2}}}{{{V_1}}} = \frac{{{I_1}}}{{{I_2}}}\) ....... (1)
Where R02 = Effective resistance referred to the secondary side of the transformer.
R02 = R2 + R1' ........ (2)
R1' = Primary winding resistance as referred to the secondary side.
R1' = R1 × k2 ......... (3)
Similarly, the effective resistance referred to the primary side of the transformer is given as,
R01 = R1 + R2' = R1 + R2/K2
R2' = Secondary winding resistance as referred to the primary side ( equivalent secondary resistance which is specified as primary)
Regulation of a Transformer Question 7:
The regulation of a two winding transformer is 5% at full load unity power factor. At full load 0.8 power factor lagging the regulation would be:-
Answer (Detailed Solution Below)
Regulation of a Transformer Question 7 Detailed Solution
Concept:
In transformer voltage regulation is given by,
Voltage regulation = x (Rpu cosθ ± Xpu sinθ)
Where x = fraction of load
Rpu = resistance in pu (we can use % resistive drop in fraction)
Xpu = reactance in pu (we can use % reactive drop in fraction)
+ for lagging load
– for leading load
Calculation:
Given that, transformer is working at unity power factor at full load
⇒ cos θ = 1, sin θ = 0
V.R. = x (Rpu cosθ + Xpu sinθ) = 1(Rpu × 1 + Xpu × 0)
0.05 = Rpu
Now the load is changed to 0.8 power factor lag (at full load ⇒ x = 1)
⇒ cos θ = 0.8, sin θ = 0.6
(V.R.)new = x (Rpu cosθ + Xpu sinθ) = 1(0.05 × 0.8 + Xpu × 0.6)
(V.R.)new = 0.04 + 0.6 Xpu
Normally the reactance of a transformer is greater than resistance.
So, (V.R.)new > (V.R.)
∴ (V.R.)new > 0.05 = 5%
Alternate Method
Voltage regulation curve of a normal transformer
From the graph, it can be concluded that
- VR is minimum at leading power factor.
- VR is maximum at the lagging power factor.
- VR is positive for the unity power factor.
- While moving from unity power factor to lagging power factor the VR increases.
So, if the voltage regulation is 5% at unity power factor than at 0.8 lagging power factor the voltage regulation will be more than 5%.
Regulation of a Transformer Question 8:
Determine the regulation of a transformer in which ohmic loss is 1% of the output and the reactance drop is 5% of the voltage when power factor is unity.
Answer (Detailed Solution Below)
Regulation of a Transformer Question 8 Detailed Solution
The correct answer is option 1): 1%
Concept:
Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.
E2 = no-load secondary voltage
V2 = full load secondary voltage
Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.
Voltage regulation \(= \frac{{{E_2} - {V_2}}}{{{E_2}}}\)
Regulation = %R cos ϕ ± %X sin ϕ
Calculation:
Ohmic loss (%R) = 1%
Reactance drop (%X) = 5%
Power factor = cos ϕ = 1
sin ϕ = 0
Regulation = %R cos ϕ ± %X sin ϕ
= 1(1) + 0
= 1
Regulation of a Transformer Question 9:
The voltage regulation of the transformer will be negative when the power factor angle (φ) is :
Answer (Detailed Solution Below)
Regulation of a Transformer Question 9 Detailed Solution
Voltage Regulation
Voltage Regulation of single-phase transformers is the percentage (or per unit value) change in its secondary terminal voltage compared to its original no-load voltage under varying secondary load conditions.
The voltage regulation is given by:
% \(VR={V_{nl}-V_{fl}\over V_{nl}}\times 100\)
Voltage regulation curve:
Explanation
The voltage regulation is calculated by:
\(VR=IR \space cos\phi \space + \space IX \space sin\phi\)
For negative voltage regulation:
\(IR \space cos\phi \space + \space IX \space cos\phi \space <0\)
\( sin\phi \space <{-R\over X}\space cos\phi\)
\( tan\phi \space <{-R\over X}\space \)
\( tan\phi \space >{R\over X}\space \)
\(\varphi>\tan ^{-1}\left(\frac{R}{X}\right)\)
Regulation of a Transformer Question 10:
Voltage regulation and efficiency of four transformers A, B, C & D are as given below:
A - 5% regulation & 94% efficiency
B - 2% regulation & 96% efficiency
C - 5% regulation & 97% efficiency
D - 2% regulation & 97% efficiency
The transformers that is good working conditions is:
Answer (Detailed Solution Below)
Regulation of a Transformer Question 10 Detailed Solution
Concept:
Voltage regulation:
The percentage of voltage regulation (VR) of a transformer is defined as the ratio of voltage drop from no load to full load to no-load voltage.
\({V_R} = \frac{{No\;load\;voltage - full\;load\;voltage}}{{no\;load\;voltage}} \times 100\)
Good voltage regulation means minimum regulation i.e. less fluctuation in full load voltage compared to no-load voltage.
Efficiency: Efficiency (η) of a transformer is the ratio of output to input.
Output = Input – losses
\(\eta = \frac{{output}}{{input}} \times 100\)
The transformer with fewer losses gives high efficiency. So, the transformer with higher efficiency is desired.
Application:
Among the given transformers, transformer D has lower voltage regulation and higher efficiency. So, transformer D is in best working condition.