Lab_1_Voltage_Sags_and_Harmonics

e = 0 Q1: What does happen if we change two currents? a. Q2: What does happen if we have a three-phase four poles machine? Q3: What does happen if we have a two-phase two poles machine? e = 0 Q4: What does happen if we apply a capacitance in phase b and then use same voltage for both phase. Dr. Ali Ki. pw --

In the system shown in Figure 1, the transformers are connected star-star with both star points grounded and the generators are connected in star with thier star points grounded. The system base is 15 MVA. The transformers all have reactances of 0.04 p.u. on this 15 MVA base. The reactances of all other elements are given in Table 1 (in 2) and the voltage levels are given in Table 2. p.u. G1 p.u. T1 jö Per-Unit Convert all values to p.u. on a 15 MVA base. Xa= p.u. Xc₂= XL = V BABE G1 2 X 9 T3 Figure 1: A section of the distribution system T1 L Table 1: Sequence reactances (2) 3 G1 L G2 0.3 0.59 0.01 4 L 9/10 10 Fault Voltage What is the voltage at bus 3 (in Volts) after the fault has occurred? Vp= V T2 5 T2 34 10/4 Table 2: Voltage bases (kV) G2 4 T3 10/9 | G2 Fault Current A three-phase fault with a fault reactance of 0.01 p.u. occurs at bus 3. Calculate the fault current flowing at the fault point in KA. Ip=-j KA So

Q2\ Two generators G1 & G2 are rated 15 MVA, 11 kV and 10 MVA, 11 kV respectively. The generators are connected to a transformer as shown in the following figure. Find the sub- transient current in each generator when a three-phase fault occurs on the high voltage side of the transformer. A/Y 15 MVA, 11 kV, X"gl=j0.10 pu G2 15 MVA, 11/66 kV, Xr-j0.06 pu 10 MVA, 11 kV, X"g2-j0.10 pu

Lighting arresters are used in power system to protect electrical equipment against a. Direct stokes of lightning b. Over-voltages due to indirect lightning stroke c. Power frequency over-voltages d. Over-currents due to lightning

The maximum flux density is the core of a 3000/240-V; 50Hz single phase distributiontransformer is 1.25 Tesla. If the voltage induced per turn is 8 volts, determine the crosssectional of the core in cm2

A docs.google.com/f 0 :D welding purpose is a shunt generator Indicate whether the following - * statement are true or false False True In a dc machine for the same value of Z, N, O armatūre, e.m.f. is more with wave winding than with lap winding

(a) Explain briefly what is fringing effect and leakage flux. (b) A ferromagnetic core is shown in Figure 1. The depth of the core is 10 cm. The other dimensions of the core are as shown in the figure. By assuming the magnetic leakage to be negligible and relative permeability of the core is 800. Calculate the total reluctance and find the value of the current that will produce a flux of 0.01 Wb. With this current, calculate the flux density at the top of the core 20 cm 40 cm 10 cm, 30 cm 500 turns 30 cm 30 cm Figure 1

3. What are the classifications of Core Loss and Copper Loss?

A transformer has primary and secondary turns of 1250 and 125 respectively. It has core cross-sectionof 36 cm2 and its rms flux density is to be limited to 1.4 T (to prevent core saturation). Whatmaximum 50 Hz voltage can be applied on the primary side and the corresponding open-circuitsecondary voltage?The core has a mean length of 150 cm and its relative permeability can be assumed to be 8000. Whatwould be the rms exciting current when the transformer’s primary winding is excited at a voltage ascalculated above? Also calculate the magnetizing susceptance as seen from primary and secondarysides.If the transformer were to be excited at 60 Hz, 1. What should be the maximum primary voltage for thecore flux density limit not to be exceeded? 2. What would be the magnetizing susceptance as seen oneach side in this case?

2. Why the core losses varying with the load?

10. In a transformer, the leakage flux of each wind- ing is proportional to the current in that winding because (a) Ohm's law applies to magnetic circuits (b) leakage paths do not saturate (c) the two windings are electrically isolated (d) mutual flux is confined to the core. 11. In a two-winding transformer, the e.m.f.per turn in secondary winding is always.........the induced e.m.f. power turn in primary. (a) equal to K times (b) equal to 1/K times (c) equal to (d) greater than. 12. In relation to a transformer, the ratio 20: 1 indi- cates that (a) there are 20 turns on primary one turn on secondary (b) secondary voltage is 1/20th of primary voltage (c) primary current is 20 times greater than the secondary current. (d) for every 20 turns on primary, there is one turn on secondary.

a core type transforem is constructed with 0.014-in. thick laminations having a uniform width of 2.75 in. If the maximum flux and flux density are, respectively, 6.2 X 10' maxwells and 8.2 X 10 maxwells per square inch and the air spaces between laminations occupy 8 per cent of the stacked core, calculate the number of laminations in the transformer. I

Explain the concept of power quality and the impact of voltage sags, harmonics, and other issues on electrical equipment.

For dc machines, the series field windings have many turns of fine wire true False

Q.4/ choose true or false: 1. The reluctance of any core is proportional directly with the length of it and inversely with both the permeability and the cross-section area of it. 2. The number of parallel paths in wave windings is equal to twice of the number of poles. 3. In dc machines with same values of Z, N, Ø, the emf for wave winding type is more than emf of lab winding type. 4. If we insert a current in such a conductor subjected to a constant magnetic field, a movement will achieved giving the principle of electric generator.

1. Why do we represent leakage flux in a transformer by inductive reactance? 2. What will happen if transformer in parallel connection have different voltage ratio?

Machine  Transformers

The hysteresis coefficient of the core material of a power transformer is 110J/ m3. The eddy current coefficient is 132.87J/m3. The volume of the core is 0.005m3, the thickness of the iron is 0.07 m and the maximum flux density is 1.12T. If the supply frequency is 50 Hz:   (a) Determine the hysteresis loss   (b) Determine the eddy current loss   (c) Determine the core loss of this transformer.   (d) Explain how the eddy currents are generated. Suggest one method to minimise this loss.   (e) Illustrate the hysteresis losses using a fully labelled hysteresis loop.

What is phase angle of voltage induced in primary and secondary windings of transformers due to mutial flux?

What are the conditions for the parallel operation of 1-phase transformers?

a)Why are transformers generally connected in parallel at a substation?b)What conditions must be met for two transformers to be paralleled?c)Draw the phase relationship and connection diagram for Dd0 connection andYy6

In the single-phase, three- winding, transformer, the primary current is equal to lo at the condition of ints there is no load on tertiary windings the current in secondary windings equal to zero the resistances (R1, R2, and R3) in transformer windings are equal the inductances (L1, L2, and L3) in transformer windings are equal.

(a) different number of turns (b) same size of copper wire (c) a common magnetic circuit (d) separate magnetic circuits. 10. In a transformer, the leakage flux of each wind- ing is proportional to the current in that winding because (a) Ohm's law applies to magnetic circuits (b) leakage paths do not saturate (c) the two windings are electrically isolated (d) mutual flux is confined to the core. 11. In a two-winding transformer, the e.m.f.per turn in secondary winding is always.........the induced e.m.f. power turn in primary. (a) equal to K times (b) equal to 1/K times (c) equal to (d) greater than. 12. In relation to a transformer, the ratio 20: 1 indi- cates that (a) there are 20 turns on primary one turn on secondary (b) secondary voltage is 1/20th of primary voltage (c) primary current is 20 times greater than the secondary current. (d) for every 20 turns on primary, there is one turn on secondary. 13. In performing the short circuit test of a trans- former (a) high voltage side is…

A solenoid has a magnetic reluctance of 2.2 x 10-3. It has 300 turns and a core area of 5 sq. cm. What is the flux density when the current flowing is one (1) ampere? a. in terms Sl unit b. in terms of CGS unit

What are the constant losses in electrical transformers?

16 *Q)-Indicate whether the following statements are true or false False True The value of flux involved in the e.m.f equation of transformer is average value