Electrical Engineering

In a three phase system, connected wye, neutral is the common return, and it is grounded. In a delta connection, there is no neutral.

Frequency, as regards voltage, is a term applied to changes in the voltage per unit of time. As the voltage of the DC (direct current) supply does not change, it does not "cycle" like an alternating current (AC) supply. The frequency of oscillation of the voltage is zero cycles per second, or zero Hertz.

By adding capacitors or inductors in series (typically lower power) or parallel (higher power power factor correction); the choice of capacitor or inductor depends on whether the reactive resistance is "leading" or "lagging". A capacitor is modelled 1/jCw, where w = frequency in rads; an inductor is modeled jLw. If you know the reactive resistance, and the system frequency, you can calculate how much capacitance/inductance is needed.

Iron losses are due to energization of the transformer; they do not depend on the loading of the transformer. They will vary depending on the voltage applied to the transformer. The best model of this is a parallel connection to the ideal transformer winding.

Voltage = Current * Resistance

ANSWER: 1000V = 1000 I = 1000 Ohms does not compute

It is a relationship that states if there is 1 ohm and 1 volt there will be =1 amperes flowing. The number can change but the relation ship will not

Find it out yourslef

For a three-phase, four-wire, system, the line voltage is measured between any pair of line conductors, while the phase voltage is measured between any line conductor and the neutral conductor.

For a three-phase, four-wire, system, the line voltage is numerically-equal to the phase voltage, and both are measured between any pair of line conductors.

cable size for the 90kW motor is 3CX150sqmm aluminum cable

It will probably run but not correctly. Low voltage will cause the motor to draw less amps than it's designed to. It will not reach its rated RPMs and such slow operation may shorten its operating life.

The electric force that makes current flow in a circuit is related to the resistance.

A transformer has input and output connections, a primary winding (with or without taps) and a secondary winding or windings (with or without taps). It also includes a core and appropriate wrappings, and (perhaps) a housing. Some kind of accommodation will have to be made for mounting it mechanically.

A synchronous generator generally requires DC power supplied to the rotor winding to make it into an electromagnet. As the rotor spins, a voltage will be induced in the stator windings (the stationary windings).

A synchronous generator needs something to supply this initial DC power to the rotor, so it may be deemed to not be "self starting". "Self starting" may have several different interpretations, though. A "black start" generator could be deemed as being self starting, even though this initial power is (usually) supplied by a set of batteries. Many generators pull this power from the power grid, so if the grid is not energized (black start conditions), these generators cannot start until at least part of the power grid is put back in service with another generator.

To correctly size a lighting circuit, you must know the total power that the circuit will draw, in watts. For example, if there is 7 lights on a circuit, each light consumes 100W, that gives you a total of 700W on the circuit. Then you must know the voltage that is being supplied to the circuit. For this example, 120VAC will be used. To calculate the current needs for sizing the breaker, use the formula P=E*I, where P=watts, E=voltage, I=current/amps. So, in this example, P=700, E=120, I is unknown. After working the formula, you have an answer of 5.83 A. Breakers generally come in sizing increments of 5A.....5A, 10A, 15A, 20A, etc. The answer for this example was 5.83A, so the 5A breaker is obviously not enough. The next size is 10A, which is more than the calculation, but you must also consider that breakers are designed to operate at 80% capacity for periods of time over about 3 hours. So for an office atmosphere where the lights will definitely be on for longer periods of time than residential (in most cases), you would need to make sure that the total Amps needed is equal to or less than the 80% of the breaker size you have chosen. A 10A breaker is only designed to provide 8A of capacity for longer periods of time. So for this example, a 10A circuit breaker would be properly sized. You must also abide by the NEC code for maximum number of fixtures on any particular circuit. Refer to NEC for that information. If you were to change the light fixtures to a larger size, such as 200W each, you would then find that you need to also change the breaker and possibly the wire size that is run through the circuit, to maintain compliance with NEC.

The 12V battery connected to the 2.4 Ohm combination will supply 12/2.4 or 5A. The individual currents will be 12/3 or 4A for the 3 Ohm resistor, and 12/12 or 1A for the 12 Ohm resistor. The 2.4 Ohm parallel combination is obtained from a simple product-over-the-sum calculation.

All areas of engineering are heavy in math. For a typical BSEE (Electrical Enginerring) degree, you are required to take three semesters of Calculus and one semester of Differential Equations.

You really need to know the line voltage (VL) involved. Provided the load is balanced, to find the line current, you need to divide the load (in watts) by (1.732 x VL). Incidentally, the correct symbol for kilowatts is kW, not Kw!

A) Outlet plug

B) Ground-Fault Circuit Interrupter (GFCI)

C) Electricity Read Monitor

D) Current Path Detector

In general no, it might do some damage to both the equipment and the power supply. In certain specific cases it might be all right if you are able to measure the current to make sure it is 500 mA or less, and you can also ensure that the appliance can withstand 15 v.

If you have a large power transformer that is leaking oil, do NOT touch it! Older transformer oil contains PCB's which are extremely toxic!! Get a licensed firm to test the oil for PCB's and repair or replace the transformer. Don't fool around with this! PCB's are a serious danger to you and others. Do not let this go. Get it fixed right away!

On the whole megger testing is a non destructive test. What happens is a DC voltage is applied to the device or winding under test. It is an insulation test to see is the insulation has been injured in any way to cause a short circuit when normal power is applied to it. On my megger there are 3 ranges 300V, 750V, and 1000 volts. Applying the proper voltage is essential to not damaging the device you are testing. Working voltages up to 240 volts should use the 300 range. Working voltages up to 600 volts use the 750 volt range and working voltages above 600 use the 1000 volt range. As you can see if you used the 1000 volt range on a device that had a working voltage of say 24 volts you could damage the insulation just by testing it. So meggering a device is non destructive if you use the tester as its instructions tell you to.

An ac generator produces ac, a dc generator produces dc, it all depends on the generator.

Power = E times I = (24 x 2) = 48 watts

This difficulty arises due to the fact that the IC fabrication techniques are layer oriented which typically involve processes which are applied to multiple horizontal surfaces in a sequential fashion. However the inductive circuits has a "non-planar" configuration which typically has a continuous spiral shape. This particular spiral configuration thus prevents the IC fabrication to integrate the inductive circuits as part of the IC devices.

• parallel circuit, a circuit containing two or more subcircuits connected across each other allowing current flow to divide between them, the voltage across all of these subcircuits is identical
• series circuit, a circuit containing two or more subcircuits connected inline with each other allowing the voltage to distribute across them, current flow through all these subcircuits is identical
• open circuit, a circuit with a break (or opening) in it, preventing current from flowing
• closed circuit, a circuit with no breaks (its fully closed) in it, permitting current flow
• short circuit, a circuit having an unintended low impedance path (or shortcut path) somewhere in it causing current flow to bypass one or more subcircuits within the circuit; this often causes excessive current flow and damage, unless a fuse melts or a circuit breaker pops to create an open circuit and thus protect things