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What is Constant Current Load?

Wednesday, May 18, 2016

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 ...

Overspeeding Motor with Variable Frequency Drive

Thursday, May 12, 2016

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 ...

How to increase the motor speed?

Tuesday, May 10, 2016

There are two things to consider when looking at increasing the shaft speed of a motor (by whatever method).

First: mechanical. Can integrity of rotor design be maintained? (Typical max safe speed is NP * 1.25 which does NOT mean it operate at that speed, but only that it will not come apart and cause injury.) Will bearing and/or lubrication handle the increased speed? (There's going to be more heat.) How about vibration? (Typically, faster speeds require smoother operation to prev ...

What is synchronous motor and why it needs exciter?

Sunday, May 8, 2016

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 ...

Dynamic Balancing of 3000 RPM Rotor

Friday, May 6, 2016

Is there any problem in conducting dynamic balancing of rotor with lower rpm than the rated rpm of the machine? For e.g. for a 3000 rpm motor rotor if we are doing the dynamic balancing @ 750 rpm will it create any vibrational problems. If it is so what is the acceptable speed limit for doing the dynamic balance of 3000 rpm rated motor rotor.

As a minimum, the equipment really should be balanced at operating speed. The "acceptable" capability limit of the facility performing dynami ...

What is the protection system of the motor terminal?

Wednesday, May 4, 2016

There is more than three protections methods for this case.
1-You can use overload with phase failure detection function this device monitor the current at the three phases if there is no current at one phase the device stop the motor.
2-You can use a sensitive phase failure relay with unbalance detection function and adjust the action time to 0.1 second and the rate of unbalance to less than 5% when one phase loss a high current pass through the other two phases that make drop down ...

Generators in parallel with high current on Neutral

Monday, May 2, 2016

I have two generators 125kW that when they are in parallel and the power is perfectly shared with 60+60kW @PF=1 (resist load) I have 10Amps on neutral. When I unbalance the load (I want remove from grid one Generator) I saw current over 100Amps on neutral, and when the generator is close to have 0kW, current on neutral is over 300Amp.
What's the cause of this problem?

If you have 10kVAR, you have reactive power. Circulating currents have nothing to do with load power factor. Is t ...

Comparing a Repaired Versus New for an Electric Motor

Saturday, April 30, 2016

We have done several years of research on recycling rotating electric machines. We have tried to identify new guidance on this matter. We conclude:
1. There are cases where a rewound motor is better than a new one. We have the opportunity to design the winding tuned to the application. The result in this case might be an upgraded motor.
2. The biggest problem we identify in our research has been mentioned by several discussions. The magnetic core might suffer degradation during repa ...

How to Solve Micro-master 440 Fault F090

Thursday, April 28, 2016

Q:

I have a trouble with a Siemens Micro-master 440 AC converter equipped with the encoder module. Sometimes, not regularly, the axis stuck giving the fault F090 (encoder loss) but everything seems to be OK. I've checked cables, connections, encoder, increased the thresholds and so on, but the problem still appears. Anyone have kind of experience with such trouble?

A:
If has been working for years, it must to be a hardware problem. I would suggest the following:
* al ...

Choosing Vector Group of Generator between YNd11 & YNd1

Tuesday, April 26, 2016

The power plant project is 163MW CCPP and the owner want to select Generator Converter vector group between YNd11 & YNd1. Which vector group should be chosen?

The following will tell you the suggestions with reasons.

Basically this vector group arrangement will define the physical displacement of the generator shaft and the electrical phase of the network. Both solutions can work, the decision depends on the environment in which the generator and the converte will work. I ...

How can We Manage VFD Torque Control?

Sunday, April 24, 2016

How can I control through the VFD Torque for a motor as I have a pump motor of 110 KW of rated current 200A controlled by Soft Starter and during the actual operation it consumed only 65 KW with 98A so I want to change this motor with another one lower in KW with VFD to control at the new motor Torque, so how to do that?
If the new motor is large enough to provide the load requirements then reducing the motor size will not affect performance. It is the load that dictates torque required ...

Difference between LV motor and MV motor

Friday, April 22, 2016

More specifically, a low voltage (LV) motor is normally <1000 V or <600 V, depending on who you ask. They are usually wound with round enamel-covered wire. This is called random-wound or mush-wound coils. Medium voltage (MV) motors, with voltages up to 13.8 kV or even higher, are wound with rectangular cross-section copper wire with enamel or mica tape insulation, depending on the voltage level. This is known as form-wound coils.

Because form-wound coils must be individually ...

Accelerometer for Measuring Motor Vibrations

Wednesday, April 20, 2016

During a discussion with a colleague, I came to know that for motors with antifriction bearings, you only need one accelerometer to measure the vibrations, whereas for motors with sleeve bearings two accelerometers are needed (one for measurement in X direction and other for measurement in Y direction).

ALL bearings are "anti-friction", otherwise they would not be bearings.

There are basically two types of bearing: non-contact (e.g. magnetic) and contact. The contact typ ...

Single line-to-ground fault & 3-phase short circuit fault

Monday, April 18, 2016

What is the only case that makes the single line-to-ground fault bigger than the 3-phase short circuit fault?

The L-G fault current will exceed the 3Ø fault current whenever you are near the terminal of a D-Y transformer. The Delta winding effectively blocks the zero sequence impedance contributed by the source. Thus Z0 source is zero and the only Z0 contribution to the impedance is the transformer impedance. As you move out from the transformer, the zero component should qu ...

How to calculate voltage drop for 50 Sq.mm?

Saturday, April 16, 2016

Step 1: Determine the resistivity per unit length for the material of the conductor (you will probably have to look this up on a table of some sort - if you are using some type of cable instead of bus, chances are good the cable manufacturer has a good number to use somewhere on their website.)

Step 2: Convert the actual length of your conductor run to the same units as the resistivity measurement and multiply to obtain the actual resistance.
...

Voltage Drop Control

Thursday, April 14, 2016

While reading a generator AVR operation description: "When a transformer is used to boost the generator voltage, the transformer impedance provides the DROOP characteristic (voltage drop) and so compensates for any reactive cross current flow. In these circumstances, the AVR does not provide a DROOP characteristic".

AVR of generator has a circuitry which senses reactive component & hence called quadrature droop compensation. When we operate multiple generators in parallel exci ...

Causes of Voltage Sag

Tuesday, April 12, 2016

You should not mix voltage sags (caused by transmission/distribution faults) and voltage fluctuations (starting large motors), voltage transients, switching disturbances or fault disturbances (resulting in sags) ect. are different events.

Every time you speak about voltage sags, we are starting a discussion on power quality and reliability and the definitions, events and for identifying voltage profiles (profiles, durations...) the causes and for providing safe and reliable power s ...

How harmonic filters reduce harmonics and regulate reactive power?

Sunday, April 10, 2016

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 ...

What are the reasons for motor terminal block burn of submersible pumps?

Friday, April 8, 2016

A very common problem affecting submersible motors is over-temperature. Causes for over-temperature include pumping hot water, overloading of the motor by the pump, loss of cooling flow past the motor, ochre or scale buildup and frequent motor starts and stops.

Submersible motors somehow must cool themselves. This is accomplished almost universally by transferring the motor's internally generated heat to the water that is flowing past the motor and into the pump. Most standard wate ...

Neutral achieved by a Zig-Zag transfomer under normal balanced conditions?

Wednesday, April 6, 2016

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 ...