Open Circuit Test of a 3-Phase Alternator
Equipment:
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Three phase power supply
VFD (Variable Frequency Drive)
DC Field voltage
Procedure:
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Three Phase generator
Ammeter
Voltmeter
Circuit Diagrams:
Open Circuit Test
Calculation:
Open Circuit:
In Amps
In Volts
Graph:

Plot Field Current (If) V/S Open Circuit Voltage (Voc) and explain the results.
Result/Conclusion:
What is importance of open circuits test in power generation system?
Short Circuit Test of a 3-Phase Alternator
Equipment:



Three phase power supply
VFD (Variable Frequency Drive)
DC Field voltage
Procedure:



Three Phase generator
Ammeter
Voltmeter
Circuit Diagrams:
Short Circuit Test
Calculation:
In Amps
In Amps
Graph:

Plot Field Current (If) V/S Short Circuit Current (Isc).
Result/Conclusion:
What is importance of Short circuit test in power generation system, does it
relate to any losses?
To find Regulation of a 3-Phase Alternator by Open
Circuit and Short Circuit Tests
Equipment:
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

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Three phase power supply
Tachometer
DC Motor as prime mover
Three Phase alternator
Ammeter (AC, DC)
Voltmeter (AC, DC)
Procedure:
1. Use the readings of O.C and S.C tests to synchronous impedance Zs.
2. The next step is to find synchronous reactance Xs.
3. Find the Voltage Regulation using formulas and conclude the results.
Calculation:
The open circuit characteristic (O.C.C.) and short circuit characteristic (S.C.C.) are drawn
on the same curve sheet as shown in figure 01. Determine the value of Isc and field current If that
gives the rated alternator voltage per phase. The synchronous impedance Zs will then be equal to
the open circuit voltage divided by the short circuit current at the field current which gives the
rated e.m.f per phase.
For the same value of field current, the synchronous reactance is found as follows:
√
Sr.no.
Zs
Zs (av)
Xs
Xs (av)
Figure 01: Characteristic curves of Open-Circuit & Short-Circuit Test
In figure 01, consider the field current If = OA that produces rated alternator voltage per phase.
Corresponding to this field current the open circuit voltage is AB.
Calculate the excitation e.m.f Eo and voltage regulation for full-load for these three conditions:
1. 0.8 lagging power factor (+ sign is for lagging pf load)
2. Unity power factor
3. 0.8 leading power factor (-sign is for leading pf load)
√[(
)
(
) ]
V = rated terminal voltage per phase of alternator
Phasor Diagram:

Draw phasor diagrams for above three loads and verify the calculated results.
Result:
Regulation of alternator at full load is found to be:
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At unity pf = -------------------------At 0.8 lagging = ---------------------At 0.8 leading = ----------------------
Synchronous Impedance varies for different values of excitation.
Conclusion:
To synchronize 3-Phase Alternator with Infinite Bus
using Bright Lamp Method
Equipment:
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

Three phase power supply
VFD (Variable Frequency Drive)
Lamp bank
Procedure:
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Three phase alternator
DC shunt motor
Voltmeter & Ammeter
Circuit Diagram:
Circuit (a): Synchronization of alternator (Synchronized)
Circuit (b): Synchronization of alternator (Un-Synchronized)
Result/Conclusion:
To synchronize 3-Phase Alternator with Utility Supply
using Synchroscope
Equipment:
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

Three phase power supply
VFD (Variable Frequency Drive)
Synchroscope
Procedure:
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Three phase generator
Ammeter
Voltmeter
Circuit Diagram:
Result/Conclusion: