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

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

Answer :

No, logically prevented.  
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Related questions

During unit operation, can we parallel UT & SUT continuously?

Description : During unit operation, can we parallel UT & SUT continuously?

Last Answer : No, due to switchgear limitation.  

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. 

In the illustration, the component labeled 'EXC' is _______. EL-0003 A. a separate class II regulated DC generator for critical direct current loads B. a generator feeding the FLD winding through the voltage regulator. C. the controller to drive the governor for turbogenerator speed. D. the electronic driver for the switchboard metering circuits

Description : In the illustration, the component labeled 'EXC' is _______. EL-0003 A. a separate class II regulated DC generator for critical direct current loads B. a generator feeding the FLD ... to drive the governor for turbogenerator speed. D. the electronic driver for the switchboard metering circuits

Last Answer : Answer: B

The purpose of 'R6' in the winch circuit shown in the illustration is to _______________. EL-0102 A. maintain dry conditions within the winch brake box B. keep the series field current at a low value during 'fourth and fifth point lowering' C. act as the armature dynamic braking load to assist the winch in stopping D. limit the armature current during lowering operation with heavy loads

Description : The purpose of 'R6' in the winch circuit shown in the illustration is to _______________. EL-0102 A. maintain dry conditions within the winch brake box B. keep the series field current at ... to assist the winch in stopping D. limit the armature current during lowering operation with heavy loads

Last Answer : Answer: C

Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV?

Description : Why UT, SUT secondary is rated for 6.9kV where as bus voltage is 6.6kV? 

Last Answer : The no load secondary 6.9kV voltage level adequately takes into account voltage drop during loaded condition to cater station buses at 6.6kV level. 

In the illustration, the contacts between terminals 26 and 27 should be closed when _________. EL-0046 A. using one generator in isochronous mode only B. using two or more generators in parallel only C. the prime mover speed is to remain constant through varying loads in parallel or single operation D. the circuit breaker is closed for that generator

Description : In the illustration, the contacts between terminals 26 and 27 should be closed when _________. EL-0046 A. using one generator in isochronous mode only B. using two or more generators in ... through varying loads in parallel or single operation D. the circuit breaker is closed for that generator

Last Answer : Answer: C

What are the protections for UT?

Description : What are the protections for UT?  

Last Answer : a) Differential protection b) LV restricted earthfault protection c) LV back up earthfault and over current protection d) Buchholz and high oil, winding temperature protection. 

Why REF is provided in the LV side of SUT and UT?

Description : Why REF is provided in the LV side of SUT and UT? 

Last Answer : The LV sides of the two transformers are earthed through the resistance. This will limit the flow of current in case of LV earth fault. Hence the differential protection may not act for a LV earth fault. Hence ref protection is provided. 

Why the neutral is earthed through earthing resistance in case of UT and SUT?

Description : Why the neutral is earthed through earthing resistance in case of UT and SUT? 

Last Answer : This is done to limit the earth fault current.  

What is the vector group of GT, UT, SUT?

Description : What is the vector group of GT, UT, SUT?

Last Answer : Yd11 Dy1 Yy0 

Why main generator/UT is not provided with separate overfluxing protection?

Description : Why main generator/UT is not provided with separate overfluxing protection?

Last Answer : Since GT is provided with overfluxing protection, it is adequate to protect main generator / UT also. Main generator can withstand higher degree of overfluxing. If a generator CB is used, separate overfluxing protection is essential for main generator. 

What is E/F current limit for SUT and UT?

Description : What is E/F current limit for SUT and UT?

Last Answer : 400a limited by 10 ohms resistor.  

Purpose of standby E/F protection in SUT/UT?

Description : Purpose of standby E/F protection in SUT/UT? 

Last Answer : Back up for LV winding, LV neutral CT- CDG 12 – resistance earthing – relay set high time delay to discriminate with LV feeder and trip transformer if sustained E/F, also protects neutral earthing resistor.

Where fault level is more, whether in generator bus duct or UT bus duct? Why?

Description : Where fault level is more, whether in generator bus duct or UT bus duct? Why?

Last Answer : Fault level is more in UT bus duct. Because the fault currents fed by the both generator and GT adds up within UT bus duct in case there is a fault in UT bus duct. 

During unit operation, can we parallel 2 SUT?

Description : During unit operation, can we parallel 2 SUT? 

Last Answer : No, due to switchgear limitation. 

Can we trip GFB from control room during unit operation?

Description : Can we trip GFB from control room during unit operation?  

Last Answer : No only if generator breaker is off.  

What are the types of cables used in 6.6 kV and 415 V system voltages?

Description : What are the types of cables used in 6.6 kV and 415 V system voltages? 

Last Answer : In 6.6 kV system AC (unearthed) grade having stranded aluminium conductors cables are used. Their insulation's are as follows. 1. XLPE - Crossed linked polyethylene insulation. 2. FRLS PVC - Fire ... V grade copper or aluminium stranded cables are used. Their insulations are HR PVC and FS type. 

What are the interlocks between 415 V and 6.6 kV switch gear?

Description : What are the interlocks between 415 V and 6.6 kV switch gear? 

Last Answer : 6.6 kV Breaker closed cannot rack in or out. Service lever cannot move while breaker closed. Breaker cannot be closed in in-between position. 415 V Breaker door cannot be opened when breaker is ... . Breaker cannot be closed in in-between position. Breaker closed cannot be rack in or out. 

What is the difference between lockout of 6.6 kV and 415 V CB’s?

Description : What is the difference between lockout of 6.6 kV and 415 V CB’s?

Last Answer : Voltage levels. Manual / auto reset. Lockout relays of 415 V breakers are all Electro-magnetic type. There is no mechanical latch. But in 6.6 kV it is of mechanical latch type relays.

What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?

Description : What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?

Last Answer : Closing coil and Trip coil 2 supply from one source. Trip coil 1 supply from one source. Protections supply from one source. 

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?

Last Answer : a) To avoid relay mal-operation due to CT saturation b) Better sensitivity is got. c) High pickup and TMS avoided in IDMT earth fault relay. 

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?

Last Answer : I – Trips 6.6 kV breakers only. It gives primary protection for 6.6 kV bus bars. I1 – Trips the both HT and LT breakers. It acts as a backup to ref and also acts as backup to bus bar earthfault relay. 

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

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

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

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?

Description : What type breakers are provided in 6.6 kV buses?

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

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

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

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. 

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

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

Last Answer : Minimum 80% of rated voltage.

The voltage at the two ends of a transmission line are 132 KV and its reactance is 40 ohm. The Capacity of the line is (A) 435.6 MW (B) 217.8 MW (C) 251.5 MW (D) 500 MW

Description : The voltage at the two ends of a transmission line are 132 KV and its reactance is 40 ohm. The Capacity of the line is (A) 435.6 MW (B) 217.8 MW (C) 251.5 MW (D) 500 MW

Last Answer : (A) 435.6 MW

Why the earthing transformer primary voltage is 16.5 kV rated in main generator even though actual voltage during the E/F is root 3 times less?

Description : Why the earthing transformer primary voltage is 16.5 kV rated in main generator even though actual voltage during the E/F is root 3 times less?

Last Answer : The transformer should not saturate during E/F otherwise it will cause ferroresonance with the GT winding capacitance. Dangerous O/V and neutral shifting will occur. During loss of load or field ... saturation. Saturation can also occur due to point on wave of application causing flux doubling. 

If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

Description : If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

Last Answer : A. As we know the Voltage & current relation for transformer-V1/V2 = I2/I1 We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps. By putting these value on Relation540/11000= I2/2334 So,I2 = 114.5 Amps

If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

Description : If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

Last Answer :  As we know the Voltage & current relation for transformer-V1/V2 = I2/I1 We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps. By putting these value on Relation540/11000= I2/2334 So,I2 = 114.5 Amps

Overhead system can be designed for operation up to (a) 11 kV (b) 33 kV (c) 66 kV (d) 400 kV

Description : Overhead system can be designed for operation up to (a) 11 kV (b) 33 kV (c) 66 kV (d) 400 kV

Last Answer : (c) 66 kV

Overhead system can be designed for operation up to (a) 11 kV (b) 33 kV (c) 66 kV (d) 400 kV

Description : Overhead system can be designed for operation up to (a) 11 kV (b) 33 kV (c) 66 kV (d) 400 kV

Last Answer : (c) 66 kV

A 20-MVA, 6.6-kV, 3-phase alternator is connected to a 3-phase transmission line. The per unit

Description : A 20-MVA, 6.6-kV, 3-phase alternator is connected to a 3-phase transmission line. The per unit positive-sequence, negative-sequence and zero-sequence impedances of the alternator are j0.1, j0.1 and j0.04 respectively. The neutral of ... the fault is  (A) 513.8 V (B) 889.9 V (C) 1112.0 V (D) 642.2 V

Last Answer : A 20-MVA, 6.6-kV, 3-phase alternator is connected to a 3-phase transmission line. The per unit positive-sequence, negative-sequence and zero-sequence impedances of the alternator are j0.1, ... line. The voltage of the alternator neutral with respect to ground during the fault is 642.2 V

What is the mystery greene discusses and why does he say ut is something we should all care about?

Description : What is the mystery greene discusses and why does he say ut is something we should all care about?

Last Answer : Feel Free to Answer

Answer: e The role of nutritional support in the cancer patient remains an important component of overall therapy. Preoperative nutritional support should be given only to those patients who do not require an emergency operation and who have severe weight loss (> 15% of pre-illness body weight) and a serum albumen < 2.9 mg%. Preoperative nutrition (enteral or parenteral) should not be given for longer than 7 to 10 days. Enteral nutrition is always the preferred route of feeding cancer patients if the GI tract is functional. There are several benefits of using the bowel lumen for nutrient delivery. The trophic effects of enteral feeding on small bowel mucosa have been well described. The integrity of the mucosal lining is maintained and it may provide an effective barrier to intraluminal

Description : Answer: e The role of nutritional support in the cancer patient remains an important component of overall therapy. Preoperative nutritional support should be given only to those patients who ... of bowel rest; this atrophy is not reversed by currently available total parenteral nutrition solutions

Last Answer : Which of the following hormones can be expected to be released as part of the stress response? a. Antidiuretic hormone (ADH) b. Aldosterone c. Insulin d. Epinephrine nswer: a, b, d ... This hormone has the exact opposite effect of insulin, which promotes glucose storage and uptake by the cells

Why do we use 3 phase power supply for heavy loads?

Description : Why do we use 3 phase power supply for heavy loads?

Last Answer : With a single phase, the voltage drops to 0 every half-cycle. Therefore, the amount of power you can get out of the line is not constant over time; it has a very large 120-hz ripple. With ... this can be accomplished, but in every case there are drawbacks that are not present in the 3-phase system

The dielectric strength of a vacuum or dry air is approximately ________________. A. 450 volts/inch B. 1000 volts/inch C. 20-kv/inch D. 50-kv/inch

Description : The dielectric strength of a vacuum or dry air is approximately ________________. A. 450 volts/inch B. 1000 volts/inch C. 20-kv/inch D. 50-kv/inch

Last Answer : Answer: C

Why 1.1 kV grade cables used for 415V?

Description : Why 1.1 kV grade cables used for 415V?

Last Answer : To take care of the both earthed / unearthed systems.  

What are the levels of SF6 gas in 220 kV breaker and their significance?

Description : What are the levels of SF6 gas in 220 kV breaker and their significance?

Last Answer : 7 kg/cm2 - normal pressure 5.2 bar - alarm 5.0 bar - closing/tripping operation blocked. 

What is the type of 220 kV circuit breaker?

Description : What is the type of 220 kV circuit breaker? 

Last Answer : 220 kV, SF6 breaker, single pole, puffer type. 

What are the main parts of 220 kV Circuit Breaker?

Description : What are the main parts of 220 kV Circuit Breaker? 

Last Answer : Pole column filled with SF6 Pneumatic drive system with compressed air circuit Control cubicle unit 

Give the details of switchyard 220 kV CB, Isolator, CT, CVT and lightning arrestor.

Description : Give the details of switchyard 220 kV CB, Isolator, CT, CVT and lightning arrestor.  

Last Answer : 220 kV SF6 Circuit Breaker 1. Make - ABB 2. Air pressure blocking a. Close Block - 17.3 bar. b. Open block - 16.7 bar. c. Auto reclose block - 19 bar. 3. SF6 pressure block a. Alarm - 5. ... , storage and erection. Rated voltage : 216 kV rms. Operating voltage : 184 kV rms. 

Why resistance grounding preferred for less than 33 kV and more than 415 V?

Description : Why resistance grounding preferred for less than 33 kV and more than 415 V?

Last Answer : a) To limit the earth fault current for equipment safety else, high short ckt forces dislocate in windings/bus bars etc, b) Over voltage due to arcing ground reduced c) Permits earth fault protection (not possible in ungrounded system)

Why neutrals are solid grounded above 33 kV?

Description : Why neutrals are solid grounded above 33 kV? 

Last Answer : a) Less transient over voltage due to arcing grounds. b) Voltage of phases are limited to phase to ground voltage. (No neutral shifting) c) Allows graded insulation of transformer (low cost) d) Fast E/F protection. 

In 220 kV switchyard why lightning arrestor should be properly grounded?

Description : In 220 kV switchyard why lightning arrestor should be properly grounded?

Last Answer : a. During lightning, surges should be discharged to ground, otherwise it will puncture the equipment insulation and it is possible only when lightning arrestor is grounded properly.  b. In order to make it effective ... kV. Soil resistivity a should be minimum and may be it is 3.5 ohm per meter.