FAQ

"Unearthed neutral" is the NORMAL configuration for AC electrical machines, regardless whether they are connected "delta" or "wye". In the case of delta, there is no neutral connection available. In the case of wye, the neutral point is physically located somewhere within the machine winding - but is not brought out to the world at large.

"Unearthed" neutral systems are the PREFERRED network for marine installations (particularly shipboard), since it is disadvantageous to pass curr ...

For a surface mounted PM, the air gap flux density should be as close as possible to the value of the max BH product (energy) of the PM material. Other choices could be taken in case of special working condition has to be considered (overloads, high temperature of magnets, etc...).

If the PM has a Br of 1.2T, you will never be able to have an airgap flux density of 1.2T because in the magnetic circuit, the airgap is a "load" and the magnet is able to achieve the Br only in "no load ...

Induction motors are selected on torque requirements at a specific speed not kilowatts. The mechanical power is the rated power of the motor at the shaft not the input of the electrical energy. The difference between the two is the efficiency. The torque is the mechanical output power in kW x 9950 divided by the speed in rpm. When the induction motor starts the speed is zero and the current maximum. Power of the flux interaction causes the shaft to move slightly. This small number is divided ...

This is a typical example of the gap between disciplines. As a process engineer / automation and control technician you're probably aware that a P&ID does not contain enough information to build a control system and as such is not sufficient to act as a 'control specification'. It should however at least has the information to extract a 'sensor and actor list' from it, containing all electrical properties of all the instruments. It might even show the control loops between sensors and act ...

Reactive power is a result of current and voltage waveforms not being "in phase" with each other. If the reactive power is required by the load, the load is considered "lagging" (current lags voltage; load appears as an inductive component). If the load can be over-excited, it can produce reactive power and is referred to as "leading" (current leads voltage;, load appears as a capacitive component).

The only machines ...

Every motor is to be protected with back up MCB / fuse and overload and single phasing protection. The motor is to be earthed properly. Once protective relays are connected in the system the system get tripped when the live terminal of any phase get earthed. Once tripping happens proper Megger check to be carried out for cable and Motor, to find the cause of tripping. The tripping can be due to Earth fault.

First, the motor body should have a "hard" connection to ground to keep the ...

This question is for developer or those who are master in PID control & would like to save cost in certain application. For speed control, it's no longer used PID methodology by programmer. Now PID control is integrated into variable frequency drive control. For example, if you want to stabilize the speed at 1500rpm, no matter load changed, via an advanced VFD, PID is itself tuning to keep it stable at 1500rpm.

I like the auto tuning function on rotating equipment that has hig ...

All AC machines (synchronous and induction) have a window of opportunity for reclosing. The basic resolution for reclosure (also known as "bus transfer") is either "fast" or "slow".

Typically, "fast" reclosure efforts occur within a few cycles (think less than 8, and often less than 6). In terms of actual time elapsed, it will certainly be faster than 0.12 seconds. If you're attempting this on a synchronous machine, it MUST have brushless excitation, since it can only be done with ...

There is a type of constant current load, once used for street lighting. Going back in time when electric utilities first started providing street lighting, there was a system that wired the luminaires in series instead of parallel. Each luminaire had a transformer wired in series with the hot leg, and the low side was connected to the bulb. Since the bulbs, all identical, were effectively connected in series, the current delivered to the circuit was a constant regardless of the number of bul ...

Over speeding the motor with a variable frequency drive will depend a lot on the existing load on the motor. If it is a fan load and you are currently at 100% of NP rating, you have no head room left to play with. If you have a roll spinning lightly loaded you will have much more head room. In some applications we run 240vac motors on a 480vac VFD and over speed from 60 Hz rated to 90 Hz- and develop 1.5 x the HP at rated torque. If you have a 480vac ...

SYNCHRONOUS: means "turns at a speed proportional to applied frequency independent of load".

For this to occur, the magnetic field on the rotor must be powered separately from the stator magnetic field. As Hector pointed out - the rotor field may result from permanent (e.g. rare earth) magnets, or from an electromagnet.

If the rotor field is electrically created, the current has to come from somewhere. One way to do this is to use a separate DC supply and supply power th ...

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 ...

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 ...

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 ...

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 ...

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 ...

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.Aircraft 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 ...

A fault on an electrical system will continue until either a protective device operates to isolate the fault, the fault burns itself clear or the power source fails due to the load imposed by the fault, which can occur when the fault is supplied by local generators.

If the circuit has a properly adjusted protective relay and circuit breaker operating are: the relay processing time + breaker opening time + arc extinction. In the case of an unprotected circuit time will be the protec ...