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What else can I help you with?
Why must do the insulation testing in circuit?
Insulation resistance testing involves applying a voltage across a dielectric, and measuring the resulting current and resistance. However, in order to get a proper reading, any electrical charge still within the system needs to be taken out, so as not to mess with the readings.
What is the formula to calculate AC resistance if the DC resistance is known?
AC resistance is the term used to describe the elevated value of resistance due to the reduction in a conductor's effective cross-sectional area due to the the skin effect caused by an alternating current. The skin effect describes how AC current tends to flow towards the surface of a conductor, rather than being distributed across the entire cross-sectional area as is the case for a DC current.For 50/60 Hz supplies the skin effect is not great and, so, there will not be a great difference between the DC resistance and AC resistance of a winding. Accordingly, it will be very difficult to calculate the winding's AC resistance, as its value is likely to be masked by experimental error and the accuracy of the instruments.In theory, by using a wattmeter and an ammeter, the resistance of a load -in this case a winding- the readings can be inserted into the equation: R = P/I2. Using a DC supply will reveal the (DC) resistance value, and using an AC supply will reveal the AC resistance value. As explained, a combination of experimental error and instrument accuracy is very likely to mask any actual difference between the two resulting values.So, at mains' frequencies, the difference between AC resistance and actual (DC) resistance would be very difficult to determine with any degree of accuracy.
What will be change in resistance of a wire if you stretch it?
If you stretch a wire, it would become longer, and therefore thinner. The cross sectional area will decrease and so the resistance will increase. in the real world, if it's stranded wire, the strands will likely break. Solid wire would not stretch evenly, and in either case insulation will tear, so I wouldn't recommend stretching a wire.
What will happen if DC supply is given to the transfomer?
A capacitor resists a change in voltage. Initially, a capacitor given a DC voltage will appear to have very low resistance, but as current flows and time goes by, the resistance will increase as the voltage approaches the applied voltage. At equilibrium, the voltage across the capacitor will be equal to the applied voltage, the current will be zero, and the resistance will be infinity.
What happens if resistance decreased in earthing?
It will work properly! The resistance and impedance of the earth lead must be low, though the corollary is that it must be capable of passing any likely fault current safely.
Is the earth fault close to neutral end of an wye connected winding very common?
Probably not, because the potential (with respect to earth) of a point on the winding, close to its neutral end, will be relatively low. Accordingly, it is less likely that the insulation will fail -the most common cause of electrical faults.
Why must do the insulation testing in circuit?
Insulation resistance testing involves applying a voltage across a dielectric, and measuring the resulting current and resistance. However, in order to get a proper reading, any electrical charge still within the system needs to be taken out, so as not to mess with the readings.
Identify one item that needs to be disconnected prior to carrying out insulation resistance tests?
The voltage source needs to be disconnected prior to carrying out insulation resistance tests. Disconnect any electronic devices like Variable Frequency Drives, Soft Starters etc. These devices are likely to get damaged if meggar test is done keeping them in circuit.
What will happen to the transformer if rated voltage is applied to the winding during short circuit test?
If rated voltage is applied to Transformer during S/C test, The secondary winding will burn out due ta heavy current flow through the winding. During S/C test the secondary winding is short circuited so the impedance between phase and neutral is very low(only winding resistance). But the voltage across the secondary winding is rated hence heavy current flows through the winding, as I=V/Z. it depends which rated voltage is applied. if you are talking about primary winding voltage, transformer should withstand the primary rated voltage it's been designed for (OR it has been poorly designed). Otherwise, if rated voltage is the insulation voltage between a winding and earth OR winding-to-winding, you just have to check if: 1 - it is higher than the maximum primary winding voltage the transformer can withstand (could be, could not be..). Then, you can guess if your transformer is likely to burn or not. 2 - your test setup (usually a HV generator connected between primary and secondary winding) can deliver the requested current for the setup. I guess this won't be the case, since HV testers are usually designed to generate high voltages, but very small output currents.
What is the formula to calculate AC resistance if the DC resistance is known?
AC resistance is the term used to describe the elevated value of resistance due to the reduction in a conductor's effective cross-sectional area due to the the skin effect caused by an alternating current. The skin effect describes how AC current tends to flow towards the surface of a conductor, rather than being distributed across the entire cross-sectional area as is the case for a DC current.For 50/60 Hz supplies the skin effect is not great and, so, there will not be a great difference between the DC resistance and AC resistance of a winding. Accordingly, it will be very difficult to calculate the winding's AC resistance, as its value is likely to be masked by experimental error and the accuracy of the instruments.In theory, by using a wattmeter and an ammeter, the resistance of a load -in this case a winding- the readings can be inserted into the equation: R = P/I2. Using a DC supply will reveal the (DC) resistance value, and using an AC supply will reveal the AC resistance value. As explained, a combination of experimental error and instrument accuracy is very likely to mask any actual difference between the two resulting values.So, at mains' frequencies, the difference between AC resistance and actual (DC) resistance would be very difficult to determine with any degree of accuracy.
Which type of winding would most likely be used in a high output alternator?
delta
What is a health hazard an insulation worker is likely to encounter on the job?
Abestos
What happen if primary of transformer connected to dc?
Nothing noticeable. DC power is not transmitted between the coils of a transformer. There would be no current on the other side of the transformer, unless the power of the source was constantly modulated. bescause flux does not change its state.after some time excessive heat is produced and winding may burnAnswerA transformer's primary winding presents two forms of opposition to current flow. The first is resistance, which is dependent upon the length, cross-sectional area, and resistivity of the wound conductor. The second is reactance, which depends upon the inductance of the winding and the frequency of the supply. Resistance opposes both AC and DC currents, while reactance opposes only AC current. In the case of a transformer's windings, the resistance is relatively low while the reactance is very high. When an AC voltage is applied, the reactance is sufficiently high to limit the value of AC current flowing through the winding. However, the resistance is so low that a large current would flow if an equivalent DC voltage was applied instead. This current would likely overheat the winding's insulation, resulting in its breakdown, causing a short circuit(s) which could severely damage the transformer.
Will homeowners insurance pay for mold removal if it was caused by insulation in crawl space?
mold cannot be caused by insulation - likely location of insulation and cause of moisture will need to be determined for coverage analysis - contact your agent
What causes a melting plastic or wax smell from car?
The problem is most likely electrical. Wires could be bare and burning their insulation off. You should probably get your vehicle checked by a mechanical. If the wired continue to burn, it could start a fire that could burn your entire vehicle.
What hormones do you test for osteoporosis?
That depends - usually a TSH (thyroid) and vitamin D are checked. Others can be checked if special circumstances make them likely.
What is the maximum insulation resistance for a 230 volt 50hz domestic circuit if there is one Explain your answer?
This maximum insulation resistance is in the order of Mega-ohms there's a good chance the insulation resistance tester (Megger) will max out it's display to look similar to this: >99MΩor whatever your display can show. The one we used frequently in work did. It was calibrated regularly to Irish electrical standards.*Warning* If you leave lamps in place or don't disconnect electrical equipment from the wall socket you risk pumping high voltage into your device and destroying it. You must also disconnect your main earth from the board you are testing or you will back-feed to the mains incomer transformer where the Earth is neutralised and it will show a false short circuit. It goes without saying do not remove the earth if the board is live. In this case remove the earth belonging to the circuit you are testing.So, the meter tests the insulation resistance, and it does this by V/I=R or Ohm's law.Important: Voltage here is not 230vThe meter should have selectable voltages dependent on what you need to meter. But it is generally 250/500/1000 volts. For this problem we'll use 500 volts to test our cables.I (the current flowing between insulation sheaths of 2 cables, which is hopefully incredibly low, otherwise you have a short circuit) hence500/some really small number =R =Insulation Resistance500/.0001 =5,000,000 Ω5 million ohms won't register on any meter properly so you end up with the maxed out scale as discussed.Check your local Regulations for details on what is considered a pass/fail in your location. In Ireland the current Regulations say the test is fail when producing a result lower than 0.5MΩ or 500,000ΩIn theory the answer to your question is this:Infinity is the maximum insulation resistance for any circuit, however that is based on absolutely no flow of current between the two cables, which will never happen, so You'll have to do with MΩ.The only time you should be worried about insulation resistance test values is wherethe meter starts to properly register them. The smaller the final resistance, the worse the insulation is on your cable and the more likely you have a problem. Approaching 0Ωresistance it becomes clear there is a short circuit.
