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Motors are sized based on the application requirements.
High starting torque (required for a high inertia load) usually translates into light loading at rated speed and voltage. The driving factor is NOT the efficiency under the loaded condition - it is the ability to start the process in the first place.

Environmental conditions also affect design choices - high ambient temperatures, high altitudes, and presence of hazardous (e.g. combustible or flammable) materials will nece ...

Technically an Inductive Load has the current through it lagging the supply voltage across it by 90° and a Capacitive Load will have the current through it Leading at 90° in Advance of the supply voltage across it.

However, this is where the typical expression is wrong.
When most people mention Inductive or Capacitive Loads, they really imply a Resistive Load, with some element of Inductance or Capacitance. That is why others above, refer to the phase angle as being l ...

They can be very "black box"-ish, design in easily and work for decades without a squeak. Or, they can be a nightmare of unanswered questions and inexplicable failures.

It is vitally important to ensure that relays are selected which are appropriate for the current, voltage, atmosphere/environment and use, as many have mentioned. Sometimes, research pays off handsomely if it starts before specification.

For instance, contact shape and composition can have unforseen effec ...

In a star connected motor, if the voltages are equal, and if the impedance of all the phases is equal, the star point will have a zero potential, and it won't matter if you connect it to earth. However, in case of unequal voltages or unequal impendences, there will be some current flowing continuously through the earth conductor connected to the star point, which is not a desirable condition.

There is a world of difference between a 3 Phase motor and a transformer. For a start tge ...

According to standard BS 7821 part 4: A distribution x-former supplying non-sinusoidal load would end up with few percent of overloading with respect to same amount of sinusoidal load which is usually reflected in X-former sizing procedure by a k-factor, I suppose. However, taking up to 20% of spare capacity in distribution x-former sizing, this will hardly result in over temperature trip out unless in case of very marginal sizing design or poorly filtered non-sinusoidal loads e.g. variable f ...

If there is no name plate, you won't be able to know the rated voltage too. In that case, you may have to guess the approx. HP depending upon the size of the motor, select appropriate auto transformer and then run at no load by slowly increasing the voltage till it reaches steady state. I am however still not sure if this will give you the correct rated voltage. There are standard ratings of three-phase 380V, 415V & 440V. I do not know if differentiation between these is possible, because ...

ProfiBus is on a 2 wire RS485 platform with different protocol communication layers that actually define ProfiBus. It's widely used in Europe & Asia for industrial applications. Field communication bus, allows you to enhance the number of devices controlled by for example a PLC. It can be described as a serial network were every device connected to it has an ID number, and a range of inputs and outputs, these ranges are normally defined when creating your hardware configuration, and the d ...

50Hz vs 60Hz in operating speed

The primary difference between 50 Hz (Hertz) and 60 Hz (Hertz) is, well, 60Hz is 20% higher in frequency. For a generator or induction motor pump (in simple terms) it means 1500/3000 RPM or 1800/3600 RPM (for 60Hz). Lower the frequency will be the iron losses and eddy current losses. Lower the frequency, speed of induction mo ...

Basically, there are two types of chillers - constant speed and variable speed. The demand on the chiller varies all over the map depending on several factors that are beyond your control. Suffice to say that the load can range anywhere from 25-100 percent of rated capacity.

With a "constant" speed chiller design, we can either cycle the chiller more frequently or close the valve for light loading conditions requiring less flow. This is inherently less energy efficient than a "var ...

If the rotor of 3 phase induction motor is locked and stator is free to rotate, then would stator rotate? If yes then in which direction?

In normal conditions, it cannot happen. If the load on the shaft of an induction motor would be such that the motor cannot start, and if there would be no protection of the induction motor, then the stator winding would just burn down.

BUT if the induction motor would run at full (rated) speed and if the rotor would be blocked instant ...

Harmonics cause overvoltage, through resonance and amplification. Zero sequence harmonics are commonly known as triplens and add in the neutral of a 4-wire 3-phase system causing neutral overload and heating. Negative sequence harmonics cause additional losses and heating in motors by producing a magnetic field that rotates in the opposite direction to those driving the motor (positive sequence).

Harmonics is a frequency domain interpretation of a time domain reality, distortions i ...

If you choose a NEMA contactor, you choose a size greater than the full load amps FLA. You must derate if you have frequent starts, or jogging duty.

If you choose an IEC contactor, you need to consult the tables on expected life when you size based on FLA.

Now you need to select what type of overload relay you want. Bi-metallic or electronic, manual or automatic reset? Choose the rating based on the directions for what you choose.

If you are placing the cir ...

For a transformer to work, the current in one coil has to somehow make current flow in the other coil and the circuit it's connected to. A DC current in one coil will make a magnetic field on the other coil, but a magnetic field by itself won't drive any electrons around. A CHANGING magnetic field, however, does create an electric force which will accelerate those electrons in the other coil into carrying a current. This process is described by Faraday's law of induction. You get a changing f ...

There are two very basic ways of determining the correct point at which the control gear should change the winding configuration from 'star' (starting mode) to 'delta' (running mode). Both methods determine the point at which the rotor has achieved it's maximum speed in star, and therefore the point at which the starter should change to delta.

One is by current measurement: Firstly, set the delta timer to it's maximum setting. Put a clip on (tongue tester) ammeter on one of the li ...

This question is a little more complex than it seems on the surface. Let's start with understanding the reason you believe you need to provide some form of braking in the first place. Do you need to stop very quickly under either normal or emergency stop conditions? Does your process need to be able to decelerate quickly when changing from a higher speed to a lower speed? If none of these conditions exist you may not need to provide any form of braking at all. The system friction and windage ...

If the motor manufacturer has done the job correctly, there is a permanent match-mark (typically like a chisel or scribe line) on both the supporting ring that stabilizes the brush arms and some "fixed" point on the machine, usually at or near one of the clamping positions where the support is held steady. Line these up and you _should_ be at the best commutation setting. NOTE - This does NOT mean you are necessarily at the neutral axis; the rigging may be intentionally offset to accommodate ...

100% stator ground fault means 100% of the stator winding is protected against ground faults and that includes from the generator terminals all the way to the stator neutral. For 95% stator ground protection means only 95% of the stator winding is protected against ground faults and the remaining 5% which is the neutral part of the generator is not protected against ground faults. Detecting the ground faults at the remaining 5% of the stator winding which is the neutral can be very difficult ...

MOTOR is defined as "a machine giving, imparting, or producing motion". This means the output of an electric motor is a mechanical force; the input is voltage.

GENERATOR is defined as "a machine for converting mechanical energy into electrical energy". This means the input of a generator is a mechanical force; the output is voltage.

The purpose of a commutator is to provide the switching action in the current waveform to allow the magnetic field developed by the rotor ...

For example whether to select 24V DC system or 48V DC system or 110V DC system. What factors are to consider for this selection of like UPS or solar power system?

The same thing that made Edison's DC system a loser, Ohm's Law and voltage drop. Remember Ohm's Law tells us that for a given load the higher the applied voltage the lower the current through the wires. So for a given conductor size higher voltage means more power delivered for the same ampacity of the wire. As an enginee ...

First - Rotor copper losses: Measure the resistance of the main rotor field winding, recording the temperature at which you made the measurement, then calculate the I^R losses at the operating temperature (Use the temperature coefficient of resistance of copper) and operating current. This is straightforward as long as you can access the main field windings and you have an accurate microhmmeter. If it has slip-rings - which I assume it will - then it is very easy. You can eve ...