POLYPHASE POWERLINE REVIEWER

premopremo remo · 75問 · 2年前

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問題一覧

In a balanced 3 phase wye connected generator the line to line voltage is

1.732 times the phase voltage

In a balanced three phase star connected system, the line voltage is

the phasor difference of two phase voltages

In a star connected system, the line current is

equal to the phase current

In delta connected system the line is

1.732 times the phase current

Power in three phase star system is equal to

√3 x Vl x Il x power factor

In a balanced 2 phase system. The neutral current is

1.414 x Iph

When the phase sequence at the three phase load is reversed

Phase current are changed in angle but not in magnitude

The voltage phasor of a three phase balance voltage system are Vab = 230 cis 30 deg volts and Vbc = 230 cis 270 deg volts. What is the phase sequence of the voltage system

ABC

In a balance three phase voltage, Van=120<-30°, What is Vcn using ABC sequence?

0+j120

The wye connected three phase ABC voltage source has Vc= 230 Vrms with 150 degress angle. Find the magnitude and angle of voltage between line A & line B.

199.2+j345 volts

A balanced three phase wye connected source has using ACB phase sequence, Vab=381 V rms with 30 degrees angle. Determine Van

110+j190.5 V

* A symmetrical three phase 240 V supplies a balanced delte connected load of 6-j8 ohms per phase. What is the line curren?

25+j32 A

In a 3 phase 4 wire system the line voltage is 400 volts. What is the line to neutral voltage?

230 volts

** What is the actual voltage of the high-leg (middle) for the three phase, four wire delta grounded system 240/120V secondary voltage?

208 V

The posistive phase sequence of a yhree phase load is abc, the negative sequence would not be________

cab

Three 90 ohms resistance are connected in delta across 220 V, 3 phasesupply. What is its equivalent wye connexted resistance?

30 ohm

** Three equal impedance Za= Zb= Zc = 4-j7 ohms are connected in wye, find the equivalent impedance in ohms if these imoedances are connected in delta

12-j21

The load on a three phase wye connected 220 volt system consists of three 6 ohms resistance connected in wye and in parallel with three 9 ohms resistance conencted delta. Calculate the total power

24.2 kW

Three 100 ohm resistor are connected in wye across 480 volts, 3 phase source. If one of the resistor is open, what is the power absorbed by the remaining resistor?

1,152 W

Three identical resistance connected in wye carry a line current of 100 amp. if the same resistance are connected in delta across the same supply, what is the line current?

300 A

A balanced star connected load is supplied from a symmetrical thre ephase 440 V system. it draws current of 40 A at 0.866 power factor lagging. The total power taken by the load will be

26.4 kW

A 170 kV 3 phase electric source delivers 200 MVA to a balanced load which has a power factor of 90% laggkng. What is the line current?

679 A

Three impedance of 3+j4 ohm are connected in ∆ to a 220 V, three phase line. Find the complex power using current conjugate methid

17.4+j23.2 kVA

A three phase line has an impedance of 2+j4 ohm. The line feeds two balanced three phase loads that are connected in parallel. The first load os wye connected and has an impedance of 30+j40 and the second is delta connected load and has an impedance of 60-45 ohms. The line is energized at the sending end from a balanced supply of line voltage 207.85 Volts. Calculate the voltage across the loads.

193.65 V

The type of ac distribution system commonly used to supply both light and power is the

three phase star system with nuetral wire

In a three phase supply floating nuetral is undesireable because it give way to

unequal line voltages across the load

A 3 phase 4 wires 400/230 V feeder supplies 3 phase motor and an unbalance ligthing load. In this system

neutral wire will carry current only with lighting load is switched on

The primary of 34.5 kV/13.8 kV, 50 MVA transformer is wye grounded. The three primary currents are Ia=720 cis-30°

42.39 cis 17.34°

The power is to be measured for a balanced delta connected load whoseteeminals cannot be opened. How many wattmeters do you need?

two

If the readings of two wattmeter in 2-wattmeter method if power measurement are 4.5 and 3.5 kW respectively and the latter readingnhas been obtained after reversing the current coil of the wattmeter. What will be the totsl power in kW?

Two wattmeter connected to measure the power input to a balanced 3 circuit indicate 2500 W and 500 W respectively.What is the power factor?

0.655

What is the minimum number of wattmeter/s required for measuring power of a three phase balamced load

one

What is the minimun number of wattmeter requiered to measure unbalanced power of a three phase system

two

The least number of 1 phase wattmeter required to measure the totak power consumed by an unbalanced load fed from 3 phase 4 wire system is

three

A three phase system delivers 50 MVA of a balanced delts load of power factor 78%. Determine the size of capacitor bank necessary to raise the power factor to 90%

12.4 MVAR

What will be the rating of a phase advancing plant in kVA if it improves the power factir from 0.8 lsgging to 0.95 lagging?. The consumer load is 500 kW and the current tsken by phase advancer lead the supply voltage at power factor of 25%

200 kVA

Given the floowing sets of per unit sysmmterical component of phase A current, determinenthe ohase B current Iao=1.0 cis 75 deg Ia1= 1.0 cis 15 deg Ia1=1.0 cis (-45deg)

0.259 + j0.966 p.u

A three phase unbalanced current are Ia=10 cis(-30°) Ib=0 Ic= 10 cis 150°

5.77 cis 249° A

** Given the following phase current phase current La= 3.5 + j3.5 Ib = j3 and Ic = -2.5 + j1.5. Determine the negative sequence current of phase A

0.313 + j 0.678

In two wattmeter methid the readings of the wattmeter will be identical when

power factor is unity

In a balanced 2 phase coktage system the phase voltages are 120 volts what is the line to line voltage?

170 volts

In a balanced 2 phase system. The total load power is

1.414 x VL x IL x power factor

The power factor angle of a balanced 3 load is the phase angle between

phase voltage and phase current

In a star wye connected balanced voltage system the angle between line voltage and phase voltage is ________ degrees

In a balanced 3 phase voltage generstor the different phase voltages are ________ degree apart

120

A balanced three phase wye connected source has using posistive phase sequence, Vca= 230 Vrms wIth 90 degrees angle. Determine Vbc

-199 - j115 V

The wye connected three phase ACB voltage source has Vcn= 230 Vrms with 45 degrees angle. Find the magnitude and angle of line voltage Vbc

400 cis(-105°) V

In a balanced dleta connected load with ACB sequence the line A current is 17.32 + j 0 amp. Find the current at phase A

8.66-j5 amp

In a balanced delta connected load with ABC sequence, the phase BC current is 20 cis20° amperes. Find the current at line C

-22.27-j26.54 amp

The three phase rural distribution system has a phase to neutral voltage is 40,000 volts, what is the line to line voltage?

69,000 volts

The secondary of a 3 phase transformer bank is connected delta, the line to ljne voltage is 230 V, the midpoint of the winding between terminal A & B is grounded. What is the voltage across terminal C & the ground?

199 volts

Three 100 ohm resistor are connected in wye across 240 volts, 3 phase source. What is the power absorbed by the resistor?

576 W

Three capacitors, each having a capacitance of 75 uF are connected in star to a 400 V, 3, 50Hz supply. Calculate the delta equivalent capacitance so that when they are connected in the same supply the line current will remain the same.

25 uF

Three equal resistor are connected in delta across 240 volts 3 phase lines. To what value should the line voltage be changed to obtain the same power with the residtor wye connected?

416 V

A balanced delta connected load of 4+ j3 ohms per phase is connected to a 3 phase 230 V supply. What is the line current

80 A

A 100 kW three phase delts connected motor works on a supply of three phase 3.3 kV. The motor efficiency is 92% and the power factor is 90%. The line current drawn by the motor will be

21 A

Three impedance esch 4-j3 ohm are connected in Y to a 280 V three phase line. Find the line current

24 A

A balanced delta connected load drawns 10 amp line current and 3 kW at 220 V. The reactance of eaxh phase of the load in ohms is?

23.5

A 25 kVA delta connected balance load is supplied from 239 volts 3 phase source. What is the impedance?

6.3 ohms

A balanced 3 phase load consumes a total power of 100 kW at a power factor of 0.6 lagging. the line voltage bieng 1000 V. Determine the values of the impredance components per phase assuming delta connection of resistance and reactance in series.

10.8+j14.4

A balanced 3 phase source supplies three loads. Load 1 is 15 kVA at 75% pf lagging. Load 2 is 10 kW at 90% pf lagging. and Load 3 is unknown. if the geenrator deliver 35.52 kVA at 80% p.f lagging, what is the unknown load?

9.7 kVA at 73.8% pf lagging

A delta connected load of 9+j12 ohms per phase is supplied by a 3 phase balance source of 239 volt rms through a line with an impedance of 0.06+j0.12 ohm. Find the phase voltage at the load

224 volts

A delts connected load has a per phase impedance of 10+j 10 phms. It is supplied by a wye connected balance source through a 3 phase line with 1.0 ohm resistance snd 1.0 ohms inductive reactance. The voltage sequence is given by Va = 120<-30° Vb=120<-150°Vc=120<90°. What is the line A current?

5.07 - j 18.93 A

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