Answer Posted / engr. l. o. osuji

Hi questioner,
Earthing T/F or T/Fs are not required in distubution S/S.
For example, here in Nigeria the distribution volage for
the T/F is either 11/0.415kV or 33/0.415kV detla-star.
However, in Transmission S/S where there are 132/33kV star-
delta connected T/F or T/Fs earthing T/F or T/Fs are
necessary. The earthing T/F is connected on the 33kV side
of the main T/F while the star-point of earhing T/F is
connected to ground to provide an artificial star-point for
the main T/F. This so because 33kV distribution ground-
fault current must flow back to the main T/F. Earth fault
protection for the main T/F must sense this current and
isolate the main T/F otherwise the earthing T/F will roast
i.e. burn.

grr resistance & contrator malt continuous

2123

---

1. A 380 / 220 V r.m.s. 3-phase 4-wire circuit carries loads of 8 + j8.1 ohm; 4 + j4.1 ohm; and 2 +j2.1 ohmin the three phases respectively. The length of the circuit is 100 m, and the resistivity of the phase conductors is 0.0005 Ω/m. The neutral conductor is of the same size as the phase conductors. a) Select a reference angle 0for the first phase. Then write down the three phase voltages in both polar format and complex number format. b) Make appropriate assumptions, and take temperature effects on resistance is insignificant. Calculate the currents in the three phases. (Note: Determine conductor resistance, and apply Kirchhoff’s Voltage Law) Based on the result, suggest a main switch rating for the circuit. c) Show your preferred direction of neutral current in a diagram, and then determine its value. (Note: Apply superposition principle, and Kirchhoff’s Current Law) Use its magnitude to show that in this circuit, the unbalanced load may increase the voltage drop in some of the phases. (Note: Also observe the common volt drip in neutral) State your assumptions, if there are any. d) Suddenly the neutral wire of the circuit is broken. Estimate the new currents in the first phase, i.e. Phase L1. State your assumptions, if there are any.

2013

---

L.A. (Lightening Arrester) is located at a place from where transmission line enters the transmitting substation. So L.A. (Lightening Arrester) is the first equipments which has to encounter with lightening, high voltage surges and switching surges. It has to absorb energy of lightening, high voltage surges, and switching surges. L.A. (Lightening Arrester) is made up of layers of semiconductors. If these layers can not tolerate energy released by lightening, high voltage surges, and switching surges the L.A. (Lightening Arrester) blasts.

1086

---

how to find out cable size if load is 2800 watts, 230 volts AC supply and load distance is 1800 meters

1596

---

what is the difference between 50 hz freq. and 60 hz freq.? which is better and economic in them ?

2271

---

In EDO ACBs what is a purpose of closing coil and motor, what is the operation of these devices are they inetconnected. means if we give supply to motor and by BCS we charge Closing coil,what exact is operation is and how it charge a spring of ACB. Sir if anybody has an wiring diagram please send me the link to operate and EDO breaker.

2144

---

Match the following a)(X'+Y') b)X'Y' C)XY 1)NAND 2)NOR 3)Carry

1905

---

Hi everyone. Some Generators uses 3-Pole breakers with extra contactors for Neutral. Some uses 4-Pole. Why so? What is the idea behind this? Thanks in advance for the solution. Kr.

2048

---

what is the basic need of domestic loads 1- voltage 2- current

2085

---

what is formula for calculate thermal overload in new numiricalrelay( not in bimetal relay)?

2292

---

What is domestic transformer? Draw the connection of domestic transformer.

2291

---

What is the difference between a Root Locus plot and a Bode plot?

1257

---

how to measure earth resistance of a substation

3305

---

Define peak overshoot.

1249

---

why does a dc machine has high efficiency while working as a generator than as a motor ..

1980

---