Electrical Engineering

Nitrogen purging means to inert the atmosphere of hydrocarbon vessels and lines. In other words to limit the oxygen contents so that it cannot react with the hydrocarbons and make some explosive mixtures.

Nitrogen Purging in Gas Well: (Oil & Gas Industry Terms, Well Activation)

Generally for gas well activation air compressors are used. Air compressor puts in oxygen into the Hydrocarbon system in the well, this results in explosive mixture (as hydrocarbon & oxygen can explode by a single spark). To reduce oxygen content in the well, Nitrogen is circulated at high pressure @ 80-100 Kg/cm2 from annulus (casing) and returns of gases are taken out from tubing of the well.

The Nitrogen purging job brings down chances of explosion / explosive mixtures.

What is an ELCB?

An Earth Leakage Circuit Breaker was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI) . The original type of ELCB or GFCI was designed only to detect a current flowing in the safety "ground" or "earth" wire.

If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the "hot" or "live" wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety "ground" or "earth" wire.

It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's "hot" or "live" wire should only return to the power station via that same circuit's "neutral" wire.

So, as a result of that basic fact, if any current isflowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently. Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would "trip" - meaning "operate" - to break the current supply to the circuits for which they were installed to protect.

The original type of ELCB or GFCI did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the "missing current" may actually be flowing to ground via someone's body!

When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give. In the US and Canada such devices are still commonly known as "GFCIs" or "GFIs" even though they have the additional "residual current detector" functionality, whilst in Europe and elsewhere the more accurate name of "Residual Current Detector" or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.

What is an MCB? A Miniature Circuit Breaker. An MCB is a device designed to protect a circuit's wiring from the serious damage which would be caused if it has to carry a current which is too high for the diameter of its wires. Such a current could easily heat up the wires so much that their insulation melts. If that situation were allowed to develop further it would soon cause the wires in a cable to short out and to burn so hot that they could easily cause a house fire.

Before circuit breakers were invented, simple wire fuses were used: the wire in the fuses was deliberately made much thinner than the wires in the circuits they were intended to protect. Thus, if a fault condition occured, as the current in the circuit grew higher and higher, a point would be reached at which the thin wire of the fuse would get so hot that it would melt - all safely contained within the body of the fuse - and thus break the flow of current in the circuit it was protecting. The problem with fuses is that - depending on their design, as some are faster-acting than others - it can take a significantly longer amount of time for them to operate compared with today's very-fast-acting circuit breakers. That fact means that, if a circuit overload current fault condition occurs, considerable damage can still occur both to the circuit wiring and/or to the unit it is supplying with power. Then, after the fault condition has been fixed, the melted or "blown" fuse wire in a rewireable type of fuse has to be replaced or - if it is a "disposable cartridge" fuse - the blown fuse cartridge has to be thrown away and replaced by a new one. A circuit breaker, if it is still in good condition, only needs to be reset.

It is no joke to say if it is still in good condition...! One more fact needs to be mentioned: a significant design feature built into today's circuit breakers is their ability to "self-destruct on a crowbar fault ". A "crowbar fault" is a very serious overload condition, so bad that it would cause many thousands of amps to flow, just as if someone had thrown down a heavy metal crowbar tool onto power lines to connect both hot and neutral wires... Such a fault condition can only be stopped by what is the ultimate fail-safe function of all modern circuit breakers: by using electro-magnetic technology similar to that of a simple relay, they are designed to self-destruct at least as fast as - if not faster than - the fastest acting fuses!

In brief, wherever electrical equipment - and the wiring which supplies it - need to be protected from overload current fault conditions then: a) if the physical space available allows circuit breakers to be installed, and

b) if the higher initial costs of deploying circuit breakers can be afforded

then it is significantly better to deploy circuit breakers instead of fuses.

For more information on all these topics see the answers to the Related Questions shown below.

(a) It reduces the amount of current.

(b) Any current that does pass the resistor will lose some power; this lost power is converted to heat in the resistance.

Internal resistance acts to reduce the terminal voltage of the voltage source when it supplies a load. This is due to the internal voltage drop caused when the load current passes through the internal resistance of that source. The greater the load, the lower the resulting teminal voltage.

By definition, a voltage source's electromotive force is equal to the sum of the voltage drops, including the internal voltage drop, of the circuit supplied.

Yes it will run. That said you will be shortening the life of the motor due to the excessive heat generated at the higher voltage. The insulation of the motor winding is related to the voltage that is applied to the motor. With excessive heat comes insulation breakdown. Once the insulation breaks down, the winding will start to short circuit. With a short circuit on the motor winding copper wire is lost. Think of a welder when an arc is struck. Once this happens to a motor it becomes non operational and a rewind is the only way that the motor is going to become operational again.

Install a Buck & Boost transformer rate for the HP of the motor that will Buck the supply voltage for the motor down to 230 volts. This is the recommended way and the only way it should be done. Any good commercial electrical supply house can help you properly size the transformer that you will need.

Read more: How_do_you_run_a_motor_208_volts_ac_in_a_230_volts_suply

A micro-strip antenna works on the principle of resonant cavity (short circuit walls on top and bottom, open circuit walls on the sides).

A resonant cavity stores energy unlike transmission lines or wave guide which transmits electromagnetic energy from one part to another. A R.C is equivalent to LC device at low frequencies.

Whichever way it is connected, no matter whether it is in a star configuration or in a delta configuration, a 3-phase motor's start-up current can be more than 4 times its normal running current.

If the star configuration is used when first switching-on power to a 3-phase motor, a much smaller "start-up surge" is forced onto the power lines than if it were switched-on directly in the delta configuration.

So "using star for start-up" achieves very worthwhile purchase cost savings because smaller circuit breakers and thinner 3-phase line wire sizes can be installed to supply power to the motor.

However, leaving it running in star has a major disadvantage: the motor can never deliver as much power and torque as when it is running in delta.

For that reason a 3-phase motor was usually started in star mode and then - after reaching a steady speed - switched over to run in delta mode to achieve its maximum power output.

The explanation for this is easier to understand if you draw a sketch of the wirings and their connections, but unfortunately we cannot use diagrams when giving an answer here! Anyway, if you draw the circuit diagram for the windings connected in a "star" or "Y" configuration, it should look like a three-pointed star, with a phase input power line attached to each point of the star.

Thus, when a 3-phase motor's three windings are connected in a star configuration, the current from each individual phase power input line goes directly into one winding and is then series-connected to both of the other two windings via the star's "center-point".

If you draw the circuit diagram for a delta configuration, it should look like a triangle with a phase power input line attached to each point of the triangle.

Thus, when a 3-phase motor's three windings are connected in a delta configuration, each winding is effectively connected directly to two phase supply lines. The third phase supply line is also connected to that winding, but indirectly via the other two windings. They are connected in series to one another, and that series pair is connected in parallel across the first winding, to form the "delta".

The much lower starting current is the main reason why a three-phase motor was usually started in star mode and then - after gaining a steady speed - was switched over to run in delta mode to achieve its maximum power output.

Update: Electronic motor-control systems, which offer soft-starts in DELTA configuration, are now replacing the use of manual or semi-automatic star-delta starters.

Technical explanation

When the windings of a 3-phase motor are connected in STAR:

• the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA.
• the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.
• so, because of the Power Law V [in volts] x I [in amps] = P [in watts],

  the total output power when the motor is connected in STAR is:

  PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3 )] = PD x (1/3) [one third of the power in DELTA]

  where:

  VL is the line-to-line voltage of the incoming 3-phase power service

  ID is the line current drawn in DELTA

  PS is the total power the motor can produce when running in STAR

  PD is the total power it can produce when running in DELTA.

• a further disadvantage when the motor is connected in STAR is that its total output torque is only 1/3 of the total torque it can produce when running in DELTA.

For more information please see the answers to the Related Questions shown below.

answ2. An RF transmitter generates radio frequency waves in its circuits, and to this 'carrier signal', it adds the information part by modulating the carrier signal. This composite signal (carrier plus information) is then fed to an antenna (aerial).

The aerial induces a corresponding signal into the atmosphere, by altering the Electric and Magnetic fields at (obviously) the same frequency.

The impedance of 'free space' is few tens of Ohms to a few hundreds of Ohms.

[Impedance may be considered analogous to resistance, but with reactive properties as well.]

The power emitted by the transmitter can vary from a megawatt or so (for VLF signals) to a few watts for handheld devices.

An Rf receiver receives the signal from the atmosphere, from its own aerial.

The receiver aerial is often quite simple, and the signal level is typically of a few microvolts.

This it tunes in (gets rid of unwanted signals and amplifies only the wanted ones).

The receiver circuits then strip the information part of the signal from the carrier part, and amplify this to a useful level for audio or video.

The actual signal into the loudspeaker will be a few tens of volts. In spite of the inefficiency of loudspeakers, (often only a few %) the signal eventually appears at a level that may be heard. A background radio will be a few milliwatts of power.

Even a very loud sound is only a few watts of radiated (sound) energy!!