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Yes you can do it but need to exercise some precaution: The LV winding that was intended by design to be the secondary winding, will serves as the primary & the value of the magnetizing inrush current actually will be greater than expected. When a transformer is reverse fed, the taps move to the output side and so their operation is reversed. Taps will control the output voltage so chances of over excitation will be there. This is not serious concern till the input voltage variation is wi ...

Most UPS's are sized for the client load requirements. However in cases of smaller UPS systems won't comply with electrical regulations!
Why?
Let's consider a client needs a 30kW supply, to 2 100amp distribution boards. One 20 meters from the UPS and one 80 meters away. Each DB has some 32amp circuits up to 20m long. The distribution circuit is protected by 63amp BS60947 devices and the final circuits are 32amp BS60898. Specifically for a UPS system, what is going to define your UPS ...

There are 2 different scenarios that occur. One is a circulating current that can occur, mostly through the fact that the rotor is not perfectly formed (you can think of it as not being perfectly round) which creates a circulating current. Insulating one bearing will stop this circulation. The second scenario occurs when a motor is on a VFD (variable frequency drive) and especially a PWM VFD. This produces a charge on the rotor which wants to discharge, and the easiest path is almost always t ...

First, there is the (NO) maintenance approach. This is essentially "run until done" style. Kind of like never changing the oil in the car engine or replacing tires and expecting infinite life. If lucky, the damage that occurs is mild and repairable (at relatively high cost) - if unlucky, complete replacement of machinery required (EXTREMELY expensive proposition, since it also has to include potentially lengthy delay in acquiring new equipment and unanticipated loss-of-production)

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In a position feedback PID controller the integrator component is the sum of all the position error. You could call it the hysteresis, or history of error. Regardless, it is like a running average error and tells your control system how consistently off the mark it is in general. Typically the integrator gain is small to keep a stable system, so that you don't have a strong P or D response to the I induced response itself (the gains reacting to each other's reactions is a source of instabilit ...

Question: How can I control through the VFD Torque for a motor as I have a pump motor of 110 KW of rated current 200 A controlled by Soft Starter and during the actual operation it consumed only 65 KW with 98 A, so I want to change this motor with another one lower in KW with VFD to control at the new motor Torque, so could you help me how can I do that?

Answer: If the new motor is large enough to provide the load requirements then reducing the motor ...

I have an interesting dilemma at work. We have never had the ability to monitor each individual feeder emanating from the substations. I recently installed a modern recloser on one circuit which allows detailed measurement of line characteristics and discovered that we have 1) a serious imbalance among the phases, and 2) a terrible power factor on this feeder - .33 on one phase, and .65 or worse on the other two. The meter that monitors the overall bus reads a combined power factor for the tr ...

Neutral is the normal return path for current coming out of the live terminal and through the load. Ground is a safety wire that (all being well) should not be carrying any current. It is connected to the chassis etc. If some goes wrong inside the box and a live wire touches the chassis, the ground connection should prevent the metal parts going to high voltage. In this pathological case, the ground wire will carry a (possibility very large) current, at least until the fuse blows or the circu ...

UPS modules are no different to other high impedance sources such as generators, they need special consideration that some or most professional design software don't do accurately. If you're an electrical engineer you should have the ability to make suitable decisions based on experience, qualifications and information.

Do your homework, double check any digital calculations and don't expect a lot of help from manufacturers. I have tried and they don't want to assist or can't. The ...

In substation there is Line Matching Unit (LMU) where the equipment impedance and line impedance matching is done, it is connected below coupling capacitor CC, and we have studied in network theory maximum power transfer thermo where impedance matching term is used. It is used for maximum communication signal can pass to other end with reduced loss.

This is the first part of the theory which is maximum power transfer. This is basically figuring out what should be the line impedance ...

The 3rd harmonic currents are not in phase with each other, they are just at 150 Hz but still 120 degrees apart relative to their period now being 6.67 ms instead of 20 ms - i.e. the zero crossings on each phase now occur every 3.33 ms instead of every 10 ms and are spread apart as a normal 3-phase set of waveforms.

But that does not mean that the A phase @ 150 Hz is in phase with the B phase and in phase with the C phase.

Remember what a delta is doing - we generally re ...

We know the equation kva= kw/power factor. When power factor reduces, kva increases. The substation authorities have to pay a penalty if demand indicator (kva) increases over an integrating period. How the maximum demand (kva) is being calculated in substations. Are there any ways to avoid load shedding of critical loads in substations if the maximum demand indicator goes over a maximum value when power factor is reduced?

In a Tr ...

This power inverter is designed for 12v DC, but also can be connected to 24v DC, my goal is 800 watt, strive to 1000 watt pure sine wave output. The inverter overall structure is, downside is a large cooling plate, upside is a power board with same size as the cooling plate, length 228mm, width 140mm. 4 power tubes of voltage boost portion, 4 power tubes of H-bridge and 4 TO220 packed fast diodes are screwed on the cooling plate ...

First of all, a DOL controlled motor may run in Fwd only, or in Fwd and Rev, depending upon the load and process (quad 1 or quad1 & quad 3 operation) - you simply switch it on/off via a contactor and it accelerates/decelerates between 0 and full speed, through its designed torque/slip curve. There will be no generation in these quads, the contactor is open, therefore the electrical supply to the motor windings is OFF and the motor will simply slow and stop in a load defined time (instanta ...

A soft starter is NOT a replacement for a VFD (variable frequency drive) if you have to start a high inertia load. A soft starter works by reducing the RMS value of the voltage supplied to the motor by delaying the firing of the output SCR's (or IGBT's etc.) until later in the half cycle after the zero crossing. To all intents and purposes, it is an oversized lamp dimmer that will reduce the motor starting torque (saves the mechanical drive) and ...

Situation
I have recently encountered a fairly unusual installation where a YNyn0 transformer has been used to supply a low voltage pump installation incorporating a large VFD.
The transformer was initially chosen to offset harmonic distortion with an adjacent Dyn11 supplying an identical VFD.
The transformer has been installed with the primary neutral connection floating in an effort to prevent zero sequence currents from causing nuisance tripping at the su ...

We were called in to replace an old imperial frame 180 kW motor on a circular saw because they needed a faster cutting speed. Shipping a motor of that size to a remote location was expensive, plus all the mounts and pulleys would have to be changed (imperial to metric and smaller frame size.). Instead we changed the VFD, the forced cooling fan and made some changes to the programmed cutting cycle.

With an older motor you often get more copper, and a lower efficiency. But you do get ...

Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor's. The rotor speed will be always slower than the stator speed, we call it slip. Without the slip, the squirrel cage induction motor doesn't have torque. Even without load the motor has slip. It increases with the load, according to the current x torque curves you can check it out ...

VFD and IMO are not going to be competitors in the same market. The benefits of VFD are various depending on the intended use. Bigger the motor (from kW to MW), bigger the benefit. They can act as soft starters therefore reducing the stress caused to the motor during the startup. With the VFD you do not go above nominal current (if you do not want).

VFD for fan and pump applications will considerably increase efficiency of the system as reducing 10% the top speed, the power absorbe ...

BLDC motors are usually in small capacity ratings, and it is universally adopted principle across word to use star connection (either internal or external) in small HP motors. Anyway, Star or delta connection matters only in case of motor with 6 leads and operating with star-delta starter, which is never a case with BLDC motor.

Star/Delta connection matters only when there are six leads and starter ...