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What is the only case that makes the single line-to-ground fault bigger than the 3-phase short circuit fault?

The L-G fault current will exceed the 3Ø fault current whenever you are near the terminal of a D-Y transformer. The Delta winding effectively blocks the zero sequence impedance contributed by the source. Thus Z0 source is zero and the only Z0 contribution to the impedance is the transformer impedance. As you move out from the transformer, the zero component should qu ...

Step 1: Determine the resistivity per unit length for the material of the conductor (you will probably have to look this up on a table of some sort - if you are using some type of cable instead of bus, chances are good the cable manufacturer has a good number to use somewhere on their website.)

Step 2: Convert the actual length of your conductor run to the same units as the resistivity measurement and multiply to obtain the actual resistance.
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While reading a generator AVR operation description: "When a transformer is used to boost the generator voltage, the transformer impedance provides the DROOP characteristic (voltage drop) and so compensates for any reactive cross current flow. In these circumstances, the AVR does not provide a DROOP characteristic".

AVR of generator has a circuitry which senses reactive component & hence called quadrature droop compensation. When we operate multiple generators in parallel exci ...

You should not mix voltage sags (caused by transmission/distribution faults) and voltage fluctuations (starting large motors), voltage transients, switching disturbances or fault disturbances (resulting in sags) ect. are different events.

Every time you speak about voltage sags, we are starting a discussion on power quality and reliability and the definitions, events and for identifying voltage profiles (profiles, durations...) the causes and for providing safe and reliable power s ...

There are several ways:
The most basic and fundamental one is based on series LC circuit with high Q factor: Harmonic trap. The circuit resonates at a specific harmonic frequency and is essentially a short circuit in this specific frequency.

More advanced technique is based on switched LC filter. I recommend looking at ABB's Static VAR compensator as an example.

APF is based on the traditional bridge-rectifier circuit, with boost converter.
The switch on/off s ...

A very common problem affecting submersible motors is over-temperature. Causes for over-temperature include pumping hot water, overloading of the motor by the pump, loss of cooling flow past the motor, ochre or scale buildup and frequent motor starts and stops.

Submersible motors somehow must cool themselves. This is accomplished almost universally by transferring the motor's internally generated heat to the water that is flowing past the motor and into the pump. Most standard wate ...

I'm an EE with almost 30 years' experience and I just looked up the same thing a couple years ago because zig-zags are used extensively in wind farms (for now anyway, not really required anymore). I used them over the years but just assumed they worked. Take the standard WYE phasor diagram with a-phase at zero degrees and divide each phasor in two. The part attached to the origin is the positive sequence.

The second part of the phasor has the polarity reversed and is the negative s ...

As per IEC 62271.1, the rated short circuit current has a time constant of 45ms (approximately X/R=14.1 at 50 Hz). If your application requires a higher time constants, you may purchase a breaker designed to operate on short circuit currents with a time constant of 120ms. Thus if you assume that the relay takes 10mS to detect the fault and actuate circuit breaker shunt trip, it will be interrupting more DC current if the time constant is 120mS, while the AC component remains same.

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Power Transmission lines are usually very long, EHV Transmission lines used for wheeling of power. They are strung on very high lattice Towers. The transmission lines are of ACSR or AAAC conductors of appropriate current carrying capacities. In case of wheeling of large currents at say 400kV level, bundle conductors are used. They don't need any kind of insulation or jackets etc. as the ambient air serves as Air insulation. Thus maintaining requisite flash over distance vis'a vis, EHV voltage ...

Why do we need to Split the Stator of Single Phase A-synchronous (Induction Motor) unlike the 3 Phase Induction Motor?

A 3 phase induction motor has 3 different currents flowing through it... these 3 cause 3 different magnetic fields that are oscillating at 120 degrees (ideally) apart, the interaction of these 3 magnetic fields in the air gap causes a rotating magnetic field, this magnetic field rotates at a speed we call synchronous speed, which is also the maximum speed the motor ca ...

Since there are several electrical standards: by frequency 50/60Hz, by low voltage (residential / commercial) use: 120-220-240-277-380-480V. and we could unify between European/American/Asian use changing all to DC 12Volts, which is used by cars. DC Green technologies are now present in power sources (solar panels) and most loads could be served in DC (led illumination, TVs and all electronic appliances) using USB c ...

Q: I know what is forward synchronization and reverse synchronization. But in the article I read its mentioned that reverse synchronization is dangerous.

1) Why is reverse synchronization dangerous?
2) What are the differences in parameters in auto synchronization for both types of synchronization?
3) If there is no auto sync relay, is there any difference when synchronized manually?

A: In the old days when you had mechanical governors with a lot of droop (the ...

When there is a phase to ground fault on the system and maintenance crew are trying to determine the source of the fault, they are even more danger considering first of all they are working on an energized system and the potential to having a phase to phase fault before resolving the first, can be potentially dangerous to life and the electrical system as a whole, also considering the heavy wear and tear of the insulation on the system and the shutdown time and cost if a fatally occurs. Why a ...

I wonder what is criteria for this test, which reasons important when design transformer for this test? Axial, radial forces or distance between low voltage and high voltage coils or other things?

The meaning of the short circuit proof design of a transformer is easy to understand: in case a short circuit happens in your grid and the damages are repaired, you don't really like to find after you switch on the power again that your transformer fails after short time.

IEEE C57.12 ...

What are some factors in choosing a Four Wire Delta System over a Four Wire Wye System or Visa Vera?

In the 4 wire delta or center tap delta there is usually limits of 5-7.5% of total kVA on the single phase loading. It was meant for control power for the 3 phase load only. I have found most do not get this and overload the center tap capacity. You can tell easily when you take off the cover and Center coil is cooked black and outside coils look good.
3-phase 4-wire wye: In the U ...

What are some other considerations that go into choosing a Three Wire Delta System rather than a Three Wire Wye System other than budget?

Basically, 3-wire 3-phase systems save one conductor, the neutral, in overhead construction.
In a service (600 volts and under) the source transformer winding is a delta or an open-delta. In California, if the voltage is 240V, then one of the corners is grounded. If it is 480V then it is ungrounded.

As a distribution system, the sou ...

Over sizing generators is guzzling energy (higher fuel), money (higher cost) and larger space (high footprint). By applying Harmonic Filter, that depending upon load types, say metal, rolling mills, or much easier loads like buildings, textile plants etc., one can load the Generator and Engine by nearly to 100% of its capacity sustainably. In the past few decades, we have done over several hundreds, if not thousands, of jobs applying Harmonic Filter with generators, both LT (415/ 433/ 440V) a ...

The people have described the single phase 120/240v system that is used in the USA, Canada, and Mexico, with the center-taped transformer. Japan uses a similar system but the voltage is lower: 100/200v. Most North America appliances work in Japan. Commercial and industrial systems in the USA run on three phase 208Y/120v or 480Y/277v. Canada uses higher voltage, typically 600/347v. These are all 60 Hz frequency.

Most of the rest of the worl ...

Aircraft electrical components operate on many different voltages both AC and DC. However, most of the aircraft systems use 115 volts AC at 400 hertz or 28 volts DC. 26 volts AC is also used in some aircraft for lighting purposes, where the power is generated by a commutator which regulates the output voltage of 28 volts DC. AC power, normally at a phase voltage of 115V, is generated by an alternator, g ...

Someone told me the appliances for United States 240v, are combined with TWO 120v hot wires, a neutral, and a ground wire, like refrigerator? If yes, can it be power by one 240v hot wire (single phase), and neutral, ground wire?

There are very few appliances in the US that are 240v, most are 120V, with only the high current ones such as a dryer, stove/range, and some air conditioners. However it is unwise to assume that all 240v appliances only utilize 240v, many older units utiliz ...