FAQ

More heat means reduced insulation life, accelerated wear of metallic (and some non-metallic) parts, and increased likelihood of personnel injury. There is an optimization required between all factors of machine performance: transient and steady-state torque output, thermal "loading", electrical source variability, initial cost, operating cost, time-to-delivery, mass/weight, availability of spare parts, ease of use, etc.

At normal wither temperature when electrical current pass thr ...

For a 3 phase induction motor, say rated 110 kW, that uses to drive a high inertia centrifugal fan. If we stop the motor, the induction motor still rotates due to load inertia. So is it harmful to run the induction motor again while it's running by load inertia?
Induction motor for centrifugal fan
This will lead to induction generation. Voltage will be induced in stator. Now ...

The efficiency of the induction motor can be improved by controlling the air-gap flux. The flux level varies with load torque i.e. at light load torque the flux required is less than the flux required as the load increases. When the motor is operating at a particular operating point defined by speed and torque, an infinite pair of impressed voltage/frequency can achieve this operating point. However only one particular pair of voltage/frequency will result in the minimum losses and maximum ef ...

I am in the process of designing a harmonic filter for a client and to tell the truth, if you never done this before, it is much more complicated than it seems.

You have to know if the source of harmonic is a voltage or current source. The best is to know the equipment generating them and be able to estimate precisely the amount of harmonic present in the system. If you are lucky it is a current source and you may wish that your filter will not change the amount of harmonics. Then, ...

To properly answer this question, we would need to have the actual motor ratings and operating load conditions, I.e.; nameplate voltage, frequency, amperes & service factor. Actual operating conditions would be; operating voltage, operating amperage & type loading (constant, cyclic/constant etc.). Generally, a motor with a nameplate rating of 3ph 230 volts can operate as low as 3ph 207 (+/-10%) system volts. However, if the operating conditions are a heavy load at or near nameplate fu ...

Let's look at the question in another light and see if it makes sense.

For some reason, you have access to perhaps 5 separate vehicles - different manufacturers (possibly), different makes and models (almost certainly). You install a dash cam on each vehicle, and wire the cam AND the controls (steering, brakes, accelerator) to a wireless robotic controller that gets its input from a single remote source.

The vehicles are in different parts of the city - or maybe even jus ...

Assume that when you changed the frequency from 50 to 60 Hz that you mean the rated frequency but you then ran the motor at the same speed. By doing this you have altered the motor set up calculations that could have changed two items giving a different resistance.

The first is that the slip speed would be different that gives different equivalent rotor resistance values when referred to the stator. The equation is actual rotor resistance / slip. The other is that the skin effect f ...

"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 ...