What are the advantages and disadvantages of three dark lamps method of synchronizing?

What are the advantages and disadvantages of three dark lamps method of synchronizing?
by

1 Answer

Answer :

Advantages:
·  The synchronous switch using lamps is inexpensive
·  Checking for correctness of the phase sequence can be obtained in a simple manner which is essential especially when the Alternator is connected for the first time or for fresh operation after disconnection
Disadvantages:
·  The rate of flickering of the lamps only indicates the frequency difference between the bus-bar and the incoming Alternator. The frequency of the incoming Alternator in relation to the bus-bar frequency is not available.
by

Related questions

What are the advantages and disadvantages of estimating the voltage regulation of an Alternator by EMF method?

Description : What are the advantages and disadvantages of estimating the voltage regulation of an Alternator by EMF method?

Last Answer : Advantages: · Simple no load tests (for obtaining OCC and SCC) are to be conducted · Calculation procedure is much simpler Disadvantages: · The value of voltage regulation obtained by this method is always higher than the actual value

How synchronoscope is used for synchronizing Alternators?

Description : How synchronoscope is used for synchronizing Alternators?

Last Answer : Synchronoscope can be used for permanently connected Alternators where the correctness of phase sequence is already checked by other means. The rotation of pointer is proportional to the difference in ... alternator is running slow. If the difference in frequency is large the pointer will oscillate

What is synchronizing?

Description : What is synchronizing?

Last Answer : The operation of connecting an alternator in parallel with another alternator or with common bus bars is known as synchronizing.

What happens in all dark lamp method ?

Description : What happens in all dark lamp method ?

Last Answer : If frequency and phase difference of incoming alternator and busbar are not same then lamps connected across incoming alternator will flicker. The flickering decreases as frequency will become near to each other by adjusting the speed by prime mover.

An AC generator panel is fitted with both synchronizing lamps and a synchroscope. When the synchroscope pointer reaches the noon position, one synchronizing light is bright and the other is dark. This means _____________. A. there is a ground on the phase with the dark lamp B. the phase sequence is incorrect C. the phase sequence is correct D. the generator breaker may be closed

Description : An AC generator panel is fitted with both synchronizing lamps and a synchroscope. When the synchroscope pointer reaches the noon position, one synchronizing light is bright and the other is dark. This ... sequence is incorrect C. the phase sequence is correct D. the generator breaker may be closed

Last Answer : Answer: B

While paralleling two (2) AC generators using synchronizing lamps only, both lamps will go dark when the generators are ____________. A. running at the same speed B. grounded C. of the same polarity D. in phase

Description : While paralleling two (2) AC generators using synchronizing lamps only, both lamps will go dark when the generators are ____________. A. running at the same speed B. grounded C. of the same polarity D. in phase

Last Answer : Answer: D

What are the advantages of salient pole type of construction used for synchronous machines?

Description : What are the advantages of salient pole type of construction used for synchronous machines?

Last Answer : 1. They allow better ventilation. 2 The pole faces are so shaped radial air gap length increases from the pole center to the pole tips so that flux distribution in the air gap is ... 3 Due the variable reluctance, the machine develops additional reluctance power, which is independent of excitation.

Why synchroscope method is more better compared to others?

Description : Why synchroscope method is more better compared to others?

Last Answer : It is very accurate as it doesnot require personal judgement

Why is the MMF method of estimating the voltage regulation considered as the optimistic method?

Description : Why is the MMF method of estimating the voltage regulation considered as the optimistic method?

Last Answer : In this method the actual value is more than the result obtained.

What are the test data required for predetermining the voltage regulation of an Alternator by MMF method?

Description : What are the test data required for predetermining the voltage regulation of an Alternator by MMF method?

Last Answer : Data required for MMF method are : · Effective resistance per phase of the 3-phase winding R · Open circuit characteristic (OCC) at rated speed/frequency · Short circuit characteristic (SCC) at rated speed/frequency

In what way does the ampere-turn method differ from synchronous impedance method?

Description : In what way does the ampere-turn method differ from synchronous impedance method?

Last Answer : The ampere-turn /MMF method is the converse of the EMF method in the sense that instead of having the phasor addition of various voltage drops/EMFs, here the phasor addition of MMF required for the voltage drops are carried out. Further the effect of saturation is also taken care of.

Why is the synchronous impedance method of estimating voltage regulation considered as pessimistic method?

Description : Why is the synchronous impedance method of estimating voltage regulation considered as pessimistic method?

Last Answer : Compared to other methods, the value of voltage regulation obtained by the synchronous impedance method is always higher than the actual valuei.e actual value is lower than the results obtained and therefore this method is called the pessimistic method.

When paralleling two alternators using three synchronizing lamps, the flickering of all three lamps becomes progressively slower and slower. This means the ______________. A. frequency of the incoming generator is approaching that of the bus B. frequency of the incoming alternator is less than that of the bus C. phase rotation of the incoming alternators is opposite to that of the bus D. terminal voltage of the incoming alternator is approaching that of the bus

Description : When paralleling two alternators using three synchronizing lamps, the flickering of all three lamps becomes progressively slower and slower. This means the ______________. A. frequency of the incoming ... the bus D. terminal voltage of the incoming alternator is approaching that of the bus

Last Answer : Answer: A

State three important features of turbo alternator rotors.

Description : State three important features of turbo alternator rotors.

Last Answer : 1. The rotors of turbo alternators have large axial length and small diameters. 2. Damping torque is provided by the rotor itself and so there is no necessity for additional damper winding. 3. They are suitable for high speed operations and so number of poles is usually 2 or 4.

Attempting to parallel an AC generator which is out of phase with the bus will result in which of the following problems? A. The breaker should trip. B. The KVA will decrease. C. The synchronizing lamps will burn out. D. The power factor will be unitized.

Description : Attempting to parallel an AC generator which is out of phase with the bus will result in which of the following problems? A. The breaker should trip. B. The KVA will decrease. C. The synchronizing lamps will burn out. D. The power factor will be unitized.

Last Answer : Answer: A

A current-carrying conductor makes accidental contact with a wiring conduit. This will be indicated by a _____________. A. low switchboard wattmeter reading B. high switchboard wattmeter reading C. darkened switchboard ground detecting lamp D. darkened switchboard synchronizing lamps

Description : A current-carrying conductor makes accidental contact with a wiring conduit. This will be indicated by a _____________. A. low switchboard wattmeter reading B. high switchboard wattmeter reading C. darkened switchboard ground detecting lamp D. darkened switchboard synchronizing lamps

Last Answer : Answer: C

When paralleling two alternators, the synchronizing lamps remain lit as the synchroscope pointer approaches the 0°. This indicates the _____________. A. incoming alternator is running too fast B. alternator voltages are 180 degrees apart C. synchroscope is defective or broken D. alternator power factors are in phase

Description : When paralleling two alternators, the synchronizing lamps remain lit as the synchroscope pointer approaches the 0°. This indicates the _____________. A. incoming alternator is running too fast B. alternator ... apart C. synchroscope is defective or broken D. alternator power factors are in phase

Last Answer : Answer: C

When paralleling two alternators the synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. This indicates the ____________. A. alternator voltages are 180° apart B. incoming alternator is running too fast C. incoming alternator is in phase with the bus voltage D. synchroscope pointer is defective or broken

Description : When paralleling two alternators the synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. This indicates the ____________. A. alternator voltages ... alternator is in phase with the bus voltage D. synchroscope pointer is defective or broken

Last Answer : Answer: C

You are paralleling two alternators. The synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. This indicates that the ____________. A. alternator voltages are 180° apart B. circuit breaker can be closed C. incoming alternator is running too slowly D. synchroscope is defective or broken

Description : You are paralleling two alternators. The synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. This indicates that the ____________. A. alternator ... be closed C. incoming alternator is running too slowly D. synchroscope is defective or broken

Last Answer : Answer: B

Discuss how the ventilation and cooling of large high speed alternator is carried out.

Description : Discuss how the ventilation and cooling of large high speed alternator is carried out.

Last Answer : For high speed alternator two cooling methods are available and they are conventional cooling and direct cooling. In conventional cooling methods, radial and axial ventilating ducts are provided in the ... oil or hydrogen are circulated in the ducts to remove the heat directly from the conductors.

How does increase in steam input of the Alternator connected to infinite bus-bars affect this operation?

Description : How does increase in steam input of the Alternator connected to infinite bus-bars affect this operation?

Last Answer : KW output power of alternator increase with increase in steam input keeping excitation constant.

How does increase in excitation of the Alternator connected to infinite bus-bars affect this operation?

Description : How does increase in excitation of the Alternator connected to infinite bus-bars affect this operation?

Last Answer : Increase in excitation level of the synchronous generator will effectively increase the reactive power supplied by the generator keeping steam input constant.

What steps are to be taken before disconnecting one Alternator from parallel operation?

Description : What steps are to be taken before disconnecting one Alternator from parallel operation?

Last Answer : The following steps are to be taken before disconnecting one Alternator from parallel operation · The prime-mover input of the outgoing generator has to be decreased and that of other generators ... delivered by the outgoing generator is zero, it has to be disconnected from parallel operation.

What happens if speed of prime mover is changed keeping excitation of alternator constant?

Description : What happens if speed of prime mover is changed keeping excitation of alternator constant?

Last Answer : If speed of prime mover is changed, the speed of alternator also changes hence frequency also changes. The frequency increase with increase in steam input and hence speed and vise versa.

What happens if excitation of alternator is changed keeping speed of prime mover constant?

Description : What happens if excitation of alternator is changed keeping speed of prime mover constant?

Last Answer : The emf induced will be changed and hence terminal voltage will also change. The terminal voltage will increase with increase in excitation and vise versa.

List the factors that affect the load sharing in parallel operating generators?

Description : List the factors that affect the load sharing in parallel operating generators?

Last Answer : The total active and reactive power delivered to the load, connected across the common bus-bars, are shared among Synchronous generators, operating in parallel, based on the following three factors ... characteristic/input · Excitation level and · Percentage synchronous impedance and its R/X ratio

What is a synchroscope?

Description : What is a synchroscope?

Last Answer : Synchroscope is an instrument, which shows the phase relationship of emf of the incoming alternator. It also indicates whether the incoming alternator is running slow or fast.

What are the methods of checking the phase difference?

Description : What are the methods of checking the phase difference?

Last Answer : 1. All Dark lamp method 2. Two bright one dark lamp method 3. Synchroscope

What is meant by infinite bus-bars?

Description : What is meant by infinite bus-bars?

Last Answer : The source or supply lines with non-variable voltage and frequency are called infinite bus-bars. The source lines are said to have zero source impedance and infinite rotational inertia.

State the condition to be satisfied before connecting two alternators in parallel

Description : State the condition to be satisfied before connecting two alternators in parallel

Last Answer : The following are the three conditions to be satisfied by synchronizing the additional Alternator with the existing one or the common bus-bars. · The terminal voltage magnitude of the incoming ... incoming Alternator voltage must be the same as the bus-bar voltage. . Zero phase difference

What is need of parallel operation of alternators?

Description : What is need of parallel operation of alternators?

Last Answer : 1. Optimum utilization of alternators as most of the power stations are interconnected by grid. 2. Reduced operating cost: number of alternators operating at a time can be changed depending on ... demands. 3. Easy maintenance: Alternator may be shut down for maintenance 4. Continuity and reliability

Name the various methods for predetermining the voltage regulation of 3-phase Alternator.

Description : Name the various methods for predetermining the voltage regulation of 3-phase Alternator.

Last Answer : The following are the three methods which are used to predetermine the voltage regulation of smooth cylindrical type Alternators · Synchronous impedance / EMF method · Ampere-turn / MMF method · Potier / ZPF method

What is the necessity for predetermination of voltage regulation?

Description : What is the necessity for predetermination of voltage regulation?

Last Answer : Most of the Alternators are manufactured with large power rating , hundreds of kW or MW, and also with large voltage rating upto 33kV. For Alternators of such power and voltage ratings ... performance like voltage regulation then can be predetermined at any desired load currents and power factors.

Define the term voltage regulation of Alternator.

Description : Define the term voltage regulation of Alternator.

Last Answer : The voltage regulation of an Alternator is defined as the change in terminal voltage from no-load to load condition expressed as a fraction or percentage of terminal voltage at load condition ; the speed and excitation conditions remaining same.

An Alternator is found to have its terminal voltage on load condition more than that on no load. What is the nature of the load connected?

Description : An Alternator is found to have its terminal voltage on load condition more than that on no load. What is the nature of the load connected?

Last Answer : The nature of the load is of leading power factor , load consisting of resistance and capacitive reactance.

What is meant by load angle of an Alternator?

Description : What is meant by load angle of an Alternator?

Last Answer : The phase angle introduced between the induced emf phasor, E and terminal voltage phasor , U during the load condition of an Alternator is called load angle.

Why synchronous generators are to be constructed with more synchronous reactance and negligible resistance?

Description : Why synchronous generators are to be constructed with more synchronous reactance and negligible resistance?

Last Answer : The presence of more resistance in the Synchronous generators will resist or oppose their synchronous operation. More reactance in the generators can cause good reaction between the two and help the ... to remain in synchronism in spite of any disturbance occurring in any one of the generators

What is meant by synchronous impedance of an Alternator?

Description : What is meant by synchronous impedance of an Alternator?

Last Answer : The combination of armature resistance and synchronous reactance is known as synchronous impedance

What is synchronous impedance?

Description : What is synchronous impedance?

Last Answer : It is the combination of synchronous reactance and armature resistance.

What is synchronous reactance?

Description : What is synchronous reactance?

Last Answer : It is the combination of leakage reactance and armature reactance

What are the causes of changes in voltage in Alternators when loaded?

Description : What are the causes of changes in voltage in Alternators when loaded?

Last Answer : When alternator is loaded the armature carries load current. Due to this load current the voltage drops occur in alternator. Hence terminal voltage decreases due to following voltage drops: 1. Voltage ... the leakage reactance of the winding, Xl 3· Voltage drop due to the armature reactance, Xa

Explain armature reaction of an alternator and its effect on main flux at various power factor.

Description : Explain armature reaction of an alternator and its effect on main flux at various power factor.

Last Answer : 1. zero lagging pf: armature flux lags main flux by 180 . Hence effect is demagnetizing i.e the main flux is reduced 2. lagging pf: it has 2 components demagnetizing and cross magnetizing ... 5. zero leading pf: Armature flux is in phase with main flux. Effect is completely magnetizing.

What is meant by armature reaction in Alternators?

Description : What is meant by armature reaction in Alternators?

Last Answer : The effect of armature flux on main flux

Why alternators are rated in KVA?

Description : Why alternators are rated in KVA?

Last Answer : The KVA rating of ac machine depends on the power factor of the load. The power factor in turn depends on the operating conditions. The operating conditions differ from place to place. Therefore the KVA rating is specified for all ac machines.

Why are Alternators rated in kVA and not in kW?

Description : Why are Alternators rated in kVA and not in kW?

Last Answer : The continuous power rating of any machine is generally defined as the power the machine or apparatus can deliver for a continuous period so that the losses incurred in the machine gives rise to a ... generator , the Alternators have only their apparent power in VA/kVA/MVA as their power rating.

Which type of winding is preferred for armature windings of alternator? Why?

Description : Which type of winding is preferred for armature windings of alternator? Why?

Last Answer : Double layer, short pitched and distributed type of armature winding. It eliminates high frequency harmonics hence it makes induced emf more sinusoidal.

Write down the formula for distribution factor

Description : Write down the formula for distribution factor

Last Answer : Kd = sin (mβ/2) / msin(β/2) where m - number of slots/pole/phase Slot angle β - angle between adjacent slots in electrical degree =180/(slots/pole)

what is slot angle β?

Description : what is slot angle β?

Last Answer : The phase difference contributed by 1 slot in electrical degree is called slot angle. Slot angle β - angle between adjacent slots in electrical degree =180/n =180/(slots/pole)

Define distribution factor or winding factor or breadth factor or spread factor

Description : Define distribution factor or winding factor or breadth factor or spread factor

Last Answer : The distribution factor is defined as the ratio of vector sum to arithmetic sum of emf induced in the conductor of one phase spread. OR It is ratio of resultant emf induced when coils are distributed to the resultant emf induced when coils are concentrated.