Electrical Troubleshooting

Transformer power is given by P=V*I which takes the unit of KVA while that of KW has energy term which is not produced by the transformer.It only steps up or down the voltage.

Answer:

In a pure D.C. circuit, KW = KVA. However, in any A.C. circuit, there is real power {KW} and apparent power {KVA}, due to the voltage and current being out of phase. Power Factor is the ratio of KW to KVA. Transformers are rated in both KVA and PF. Multiplying the transformer KVA rating times the PF will yield KW.

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A transformer has separate ratings for maximum voltage and maximum current. Multiply the two together and that is called the VA rating, or kVA for larger transformers. So the transformer rating is independent of the power factor of the load.

Any transformer uses a minimum of two windings to change the voltage value. The primary side of the transformer is usually connected to the existing voltage. The secondary side of the transformer is usually connected to the load, who's voltage could be higher or lower voltage than the primary voltage.

If the secondary voltage is increased the transformer is known as a step up transformer and if the secondary voltage is decreased the transformer is known as a step down transformer.

The transformer terminal markings for the primary are H1 and H2 on a single coil primary and H1 to H4 on a dual voltage primary winding. Like wise the secondary terminal markings are X1 and X2 on a single coil secondary and X1 to X4 on a dual voltage secondary winding.

I'm assuming you want to check to see if the motor works.

In other words, if the motor isn't working you want to know if the motor is bad or the capacitor is bad.

Turn on power to the motor, and carefully attempt to start motor rotation in the correct direction by manually rotating the shaft or the load connected to the shaft.

If the motor will maintain its motion once you get it started, the problem is most likely a capacitor. Check the capacitors for bulging and replace any defective parts.

If the motor will not spin at all, or will not maintain any momentum, the motor is likely the problem. You can replace it or try to reduce the rotating friction by lubricating the bearings, etc.

IF YOU'RE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

If you do this work yourself, always turn off the powerat the breaker box/fuse panel BEFORE you attempt to do any work AND always use a meter or voltage indicator to insure the circuit is, in fact, de-energized.

There are basically two types of meggers, an electronic one and the old-fashioned hand-cranked type. On the whole megger testing is non-destructive.

What happens is a DC voltage is applied to the device or winding under test. It is basically an insulation test to see if the insulation has been injured in any way to cause a short circuit when normal power is applied to it.

On some meggers there are 3 ranges 300V, 750V, and 1000 volts. Applying the proper voltage is essential to avoid damaging the device you are testing.

Working voltages up to 240 volts should use the 300 range. Working voltages up to 600 volts use the 750 volt range and working voltages above 600 use the 1000 volt range.

If you used the 1000 volt range on a device that had a working voltage of only say 24 volts, you could damage the insulation of the device just by testing it! So meggering a device is only non-destructive if you use the tester as its instructions tell you to.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

You need to ensure that each line conductor is correctly identified. If you replace them in the wrong sequence, then the new machine will run backwards when you energise it! It may be necessary to use a phase-sequence meter to confirm the phase-rotation before restoring supply to the new motor.

<><><>

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.

A transformer is a device in which two circuits are coupled by a magnetic field that is linked to both. There is no conductive connection between the circuits, which may be at arbitrary constant potentials. Only changes in one circuit affect the other. The circuits often carry at least approximately sinusoidal currents, and the effect of the transformer is to change the voltages, while transferring power with little loss. Sinusoidal excitation is not necessary, and transformers may handle arbitrary signals, in which the action can be considered as a transformation of impedances. The magnetic field coupling the circuits can be in air, but is usually in a ferromagnetic material, the core, in which the field can be thousands of times greater than it would be in air, making the transformer efficient and small. The transformer is an honorary electrical "machine" in which the flux changes occur by variation in currents with time, instead of by motion.

Most transformers with iron cores can be considered as ideal when you use them. An ideal transformer has no losses, an aim that is closely attained in practice, so the energy transfer from the primary circuit to the secondary circuit is perfect. The diagram represents such a transformer, showing the core with magnetic flux φ, the primary winding of N1 turns, and the secondary winding of N2 turns. The reference directions for the voltages and currents at the terminals are shown. All of these quantities are to be considered as phasor amplitudes, varying sinusoidally with time. Note the dots at one or the other of the terminals of each winding. Currents entering the dotted terminals produce flux in the same direction, the direction shown. The current and voltage ratios are equal to the turns ratio. This means that the power factor (cosine of the phase angle), and the power, are the same at input (primary) and output (secondary). These things you probably already know, and we will not explore their consequences further.

The diagram shows the usual schematic way to represent a transformer. In an actual transformer, the windings are wound on top of each other, not on separate legs, to reduce leakage flux. In the usual shell-type transformer, both primary and secondary are on one leg, and are surrounded by the core. A core-type transformer has windings covering the core legs.

In order to design a transformer, or to examine in more detail how it departs from ideality, it is necessary to understand how a transformer works, not just how to express its terminal relations in an approximate way. It is also important to know how the properties of the iron core affect the performance of the transformer. A real transformer becomes hot because of losses, and the ouput voltage may vary with load even when the primary voltage is held constant.

The mutual flux φ is the means of transfer of energy from primary to secondary, and links both windings. In an ideal transformer, this flux requires negligibly small ampere-turns to produce it, so the net ampere-turns, primary plus secondary, is about zero. When a current is drawn from the secondary in the positive direction, ampere-turns decrease substantially. This must be matched by an equal increase in primary ampere-turns, which is caused by an increase in the current entering the primary in the positive direction. In this way, the back-emf of the primary (the voltage induced in it by the flux φ) equals the voltage applied to the primary, as it must. This fundamental explanation of the operation of a transformer must be clearly understood before proceeding further.

An electrical arc, or spark, is caused by a sudden jump of electrons* across a gap or space, from a higher charged, to a lessor charged object. This is why it's wise to keep fingers, metal, water, and other conductive materials away from electrical outlets. Close proximity, not actual physical contact, is what allows arcing and the electric shock associated with it.

*Note: An object cannot lose or gain protons.

kW is the unit of real power & kVA is the unit of Apparent power.

Apparent Power= real power + reactive power

Besides this,the ratings which we write on a motor or generator is KVA & not KW. B'coz there are two types of losses in a motor or generator- core losses & ohmic losses. Core loss depends upon the voltage applied & ohmic losses depend upon the current flowing & none of these losses depend upon the power factor i.e. Cos@. As we know that

KW power = V * I *Cos@.

But as the losses are independent of the power factor hence we need to calculate only KVA = V*I.

Apparent power is the vector sum of real power and reactive power, not the sum.
KVA is the unit of apparent power and KW is unit of active power.

KW is kilowatts, and KVA is kilovoltamps. KW is the apparent power that a normal power meter would measure, while KVA is simply the maximum of the instantaneous product of volts and amps divided by 1000. The difference between these two terms is due to phase angle, which is due to the reactance of the load to an AC power source.

KW (kilowatts) is apparant power, while KVA (kilovoltamps) is true power. They are different when the phase angle between voltage and current is not zero, i.e. when the load is reactive, such as in a motor. The ratio of KW over KVA is Power Factor, and is the cosine of the phase angle between voltage and current. It is zero at a phase angle of 90 degree, which occurs for purely (ideal) inductive or capacitive loads with no resistance in the source or conductors, and it is one for purely resistive loads.