What is the minimum voltage required for starting of 6.6 kV motors?

What is the minimum voltage required for starting of 6.6 kV motors?
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1 Answer

Answer :

Minimum 80% of rated voltage.
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What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?

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How 6.6 kV-bus supply was chosen?

Description : How 6.6 kV-bus supply was chosen?

Last Answer : 11 kV was rejected in view of the high insulation cost with 11 kV motors. 3.3 kV was rejected, since max motor size with 3.3 kV bus is limited to 2 MW. But we are having the motors having rating more than 2 MW, which cannot suit to 3.3 kV bus. 6.6 kV bus we can start upto 5 mw size motor. 

Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Description : Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

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Why 2 types of earth fault relays in 6.6 kV side of transformers?

Description : Why 2 types of earth fault relays in 6.6 kV side of transformers?

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What is the design basis of 6.6 kV aluminium bus bars?

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Last Answer : a) Temperature rises not exceed 90 ºC. b) Withstand short ckt stresses. c) Take care of thermal expansion. 

During unit operation can we have one UT feeding both unit 6.6 kV loads?

Description : During unit operation can we have one UT feeding both unit 6.6 kV loads? 

Last Answer : No, logically prevented.  

Why 6.6 kV transformer is resistance grounded by 10 ohms and current limited to 400 A?

Description : Why 6.6 kV transformer is resistance grounded by 10 ohms and current limited to 400 A?

Last Answer : a) To reduce burning and melting in faulted switchgear or machine. b) To reduce mechanical stresses in equipment. c) To reduce the electrical hazards by stray ground fault currents in the ground ... screen in 6.6 kV XLPE (cross-linked polyethylene). Therefore the cost of the cable decreases. 

What is the difference in action of lock out pressure signal on 6.6 kV and 220 kV breakers?

Description : What is the difference in action of lock out pressure signal on 6.6 kV and 220 kV breakers?

Last Answer : When lock out signal comes to 6.6 kV breakers the breaker will trip. Where as in case of 220 kV breakers the breaker will not trip. If the breaker is open it will be open only and can not be closed. If it is in closed condition it will be closed.

What type breakers are provided in 6.6 kV buses?

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Last Answer : ABB. Make, SF6 gas, 1250A and 2000A capacity circuit breakers are provided in 6.6 kV buses. 

List some important loads to 6.6 kV buses.

Description : List some important loads to 6.6 kV buses. 

Last Answer : a. Auxiliary transformers. b. PHT motors. c. BFP motors.  d. CEP motors. e. CCW motors. f. Chiller motors. g. Pressuring pump motors. 

What are the main sources of power supply to 6.6 kV buses?

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Last Answer : a. Unit transformer which steps down the generated voltage to 6.6 kV from the generator. b. Start up transformer, which steps down the grid voltage to 6.6 kV. 

How do split-phase induction motors become self-starting?

Description : How do split-phase induction motors become self-starting?

Last Answer : By using combinations of inductance and capacitance to apply out-of phase currents in starting windings.

A direct online starter is used for starting motors?

Last Answer : A direct online starter is used for starting motors up to 5 H.P.

Synchronous motors are generally not self-starting because?

Last Answer : Synchronous motors are generally not self-starting because the direction of instantaneous torque reverses after half cycle.

The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Description : The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Last Answer : (c) 7.0 m

The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Description : The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Last Answer : (c) 7.0 m

cables are used for 132 kV lines. (a) High tension (b) Super tension (c) Extra high tension (d) Extra super voltage

Description : cables are used for 132 kV lines. (a) High tension (b) Super tension (c) Extra high tension (d) Extra super voltage

Last Answer : (d) Extra super voltage

For transmission of power over a distance of 500 km, the transmission voltage should be in the range (a) 150 to 220 kV (b) 100 to 120 kV (c) 60 to 100 kV (d) 20 to 50 kV

Description : For transmission of power over a distance of 500 km, the transmission voltage should be in the range (a) 150 to 220 kV (b) 100 to 120 kV (c) 60 to 100 kV (d) 20 to 50 kV

Last Answer : (a) 150 to 220 kV

For transmission of power over a distance of 200 km, the transmission voltage should be (a) 132 kV (b) 66 kV (c) 33 kV (d) 11 kV

Description : For transmission of power over a distance of 200 km, the transmission voltage should be (a) 132 kV (b) 66 kV (c) 33 kV (d) 11 kV

Last Answer : (a) 132 kV

Transmission voltage of ll kV is normally used for distances upto (a) 20—25 km (b) 40—50 km (c) 60—70 km (d) 80—100 km

Description : Transmission voltage of ll kV is normally used for distances upto (a) 20—25 km (b) 40—50 km (c) 60—70 km (d) 80—100 km

Last Answer : (a) 20—25 km