Calculate the capacitive reactance

Assignment Help Electrical Engineering

Reference no: EM13806208

1. For the following distribution feeder systems shown in FIGURES 3(i), (ii) and (iii) determine the load voltage levels.

2040_Determine the load voltage levels.png

2. The following phase schematic diagram (FIGURE 4) shows an 11 kV, 50 Hz, 3-phase, short line feeding a load. By calculation or constructing the phasor diagram (use a scale of 1 mm = 2 A) for the load cuntnt with VR as reference, determine the capacitive current and
• calculate the capacitive reactance/ph such that the load power factor is increased to 0.98 lag

• calculate the percentage reduction in line current with this value of capacitive reactance in circuit.

647_Determine the load voltage levels1.png

3. (a) A short 3-phase II kV line delivers a load of 4.1 MW, 2.6 MVAr lag. If the series impedance of the line is (72 + j12.1) LI/ph, calculate the sending end voltage and load angle.

(b) Develop the receiving end performance chart for the above line and load to a 3-phase power scale. (Use a scale of 10 mm = 1000 V and 30 nun = 4.1 MW.)

4. Using the chart you produced in Question 3, determine:

(a) the real and reactive power when

(i) the transmission angle remains unaltered and the sending end 'oltage is increased by 28%

(ii) the original sending-end voltage is reduced by 15% and the transmission angle increased by 9°. (Use the same scale as that for Question 3 (b))

(b) the real power limit for the sending voltage in (ii) above (i.e. when reduced by 15%). FIGURE I shows four generators feeding into a sectionalised busbar with a fault limiting reactor.

5. Figure 1 shows four generators feeding into a sectionalised busbar with a fault limiting recactor.

2286_Determine the load voltage levels2.png

Each generator is rated at II kV and 30 MVA and has a reactance of 02 p.u.

Calculate the value of the reactance to limit the fault level on a feeder to 500 MVA.

6. Compare FIGURES 2 and 4 with those of FIGURES I and 8 and state briefly why they are similar.

2398_Determine the load voltage levels3.png

7. FIGURE 2 shows the sectionalised busbar of a two generator power station connected to the national grid.

1953_Determine the load voltage levels4.png

Calculate, using a 40 MVA base, the fault level for a 3•phase symmetrical short circuit on the 11 kV feeder.

8. An 11 kV, single phase system is protected by a scheme using 1000/5 CTs and an IDMT relay having a plug setting of 150% and time multiplier setting of 0.68 (FIGURE 3).

Using the standard PSM/time characteristic, find the relay operating time (TMS = I) for a 236 MVA fault.

932_Determine the load voltage levels5.png

The circuit breakers CB,, CB2, CB3 and CB, are part of a scheme which uses 1000/5 as and IDMT relays.

If the maximum fault current capability is 6700 amps, clearance of which must be initiated in 225 secs, select, using the standard characteristic:

(i) plug setting multipliers for CB, at plug settings of 100% and 50%

(ii) the time multiplier setting of each IDMT relay to afford effective discrimination of 0.4 sec at a plug setting of 50%.

Reference no: EM13806208

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