Ques:- Keeping in view of parallel operation which of the 3 phase transformer connection are possible?a)delta-delta to delta-star b) delta-delta to star-delta c)star-star to delta-delta d) delta-star to star-delta
Ques:- How can we calculate the power factor of an electrical appliance ?Is there any formula ? Is there any meter around to calculate it ? And how to use that meter ? thanks
Asked In :-
Right Answer: To calculate the power factor of an electrical appliance, you can use the formula:
**Power Factor (PF) = Real Power (P) / Apparent Power (S)**
Where:
- Real Power (P) is measured in watts (W).
- Apparent Power (S) is measured in volt-amperes (VA), which can be calculated as Voltage (V) × Current (I).
Yes, there are power factor meters available to measure it directly. To use a power factor meter, connect it in series with the load, ensuring it is set to the correct voltage and current settings, and then read the power factor value displayed on the meter.
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Right Answer: The current carrying capacity of a conductor can be calculated using the formula:
[ I = frac{K cdot A cdot (T_{max} - T_{ambient})}{R} ]
where:
- ( I ) = current (in Amperes)
- ( K ) = a constant that depends on the material and installation conditions
- ( A ) = cross-sectional area of the conductor (in square meters)
- ( T_{max} ) = maximum allowable temperature of the conductor (in degrees Celsius)
- ( T_{ambient} ) = ambient temperature (in degrees Celsius)
- ( R ) = resistance of the conductor (in Ohms)
The diameter of the cable or conductor is related to its current carrying capacity because a larger diameter increases the cross-sectional area ( A ), which in turn allows more current to flow without overheating.
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Ques:- AVR is used for the Voltage regulation of the Generator using the feedback signal by exciting the field winding of the generator.But how the field winding will be excited & using what?
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Right Answer: The field winding of the generator is excited using a DC supply from the generator's own output or an external power source, typically through a rectifier circuit that converts AC to DC. The Automatic Voltage Regulator (AVR) controls this excitation by adjusting the current supplied to the field winding based on the feedback signal from the generator's output voltage.
Ques:- If power factor comes in leading & showing -0.95. Is thereany effect on electrical system? if yes, then please tell mewhat would be the effects. & how long we keep power factorin leading.Keeping power factor in leading shows more KW & less KVA isit correct or not.
Asked In :-
Right Answer: Yes, a leading power factor of -0.95 can have effects on the electrical system. It can lead to issues such as overvoltage conditions, increased losses in transformers and capacitors, and potential resonance problems. Keeping a leading power factor is generally acceptable, but it should be managed carefully to avoid these issues.
Regarding the relationship between KW and KVA, a leading power factor does not show more KW and less KVA; rather, it indicates that the system is supplying reactive power back to the grid, which can affect the overall power quality.
Right Answer: A differential relay will act when there is a difference in current between the primary and secondary sides of the transformer or HT motor, indicating a fault such as an internal short circuit or winding failure.
