transformer protection "over current &differential protection"?
141129
Transformer is an AC machine rated in terms of Voltamperes and Primary and Secondary voltages. The primary and secondary windings are thus rated to carry a certain amount of current. To protect the transformer windings from overcurrent due to overloading an overcurrent relay is used to sense the overcurrent and trip the breaker feeding the transformer.Overcurrent protection of transformers are usually met by utilising relays with Inverse Definite Minimum Time characteristics like, Normal inverse/Very inverse. That is the relay takes some time to operate depending on the extent of overloading.Relay operates faster for more overloading and slower for lesser overloading.The relay picks up only if the transformer is loaded more than 110% of it's rating.\n\nDifferential protection is used for instantaneous tripping when a fault takes place inside a transformer winding.The relay does not operate for overloading.Differential protection is a zone protection. The transformer primary and secondary windings are covered in the differential zone using differential current transformers on both primary and secondary sides. The differential relay compares the currents on both primary and secondary sides and acts on imbalance over a given set value.Hence relay does not operate for normal or overloading.However for a fault in zone, there will be a major imbalance in the circulating current which will operate the differential relay.
79642
Those guys (arc welding power supplies) have high voltage inside, but they output low voltage at high current.\nTry old neon transformers, oil burner ignition transformers (but you need some high-voltage diodes for DC), a discarded TV set (but very dangerous, HV can be stored in various places when you open it). \nFor battery ops you might be able to gin something up with an ignition coil and some sort of primary current interrupter but you'll get pulses, not DC. If you're into DIY, you can rip the flyback transformer from a TV and follow the directions in the ref. Many more such projects if you google High Voltage Inverter". Good luck.
834597
No \nThere are no optimal frequencies for a transformer.
702129
I've found a good site introducing and explaining the voltage and phase relationships between delta and wye 3 phase transformers. Try www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm\nI hope that this proves useful for your research.
391098
i am assuming you are trying to minimize losses in a utility distribution system...when i was a system engineer at a utility..the quickest payback items were 1)correcting power factor as close to unity as possible with switched capacitor banks 2)have a policy of sizing distribution transfomers properly in relation to the load (i.e not oversized) to miminimize NL (no load) losses and not undersized too much either to minimize LL (load losses).\n3)size distribution feeder conductors to miminize both NL and LL losses.  The correct point at which you achieve max savings has a good bit to do with your %rate of capital as well as your cost of power both KW and KWH rates.
1081595
This is not recommended, but in the past we shocked fish with a generator. We just hooked a cable up to it and threw the exposed end in the water. I don't know if the new generators have GFCI's on them, but if they do you may have a problem
97466
there is a metal strip inside that the current flows through. If too much current flows, the strip is actually made of two metals one that expands dirfferently than the other, then it will bend enough to cause the circuit to trip mechanically.\n\nThe GFI part measures the current out and the current back through the neutral with electronics. If they do not match by more than something like 4 miliamps then the current is flowing through ground. This is bad if you happen to be between ground and the circuit so to protect you it trips the breaker.
656571
b) and c)\n\nthe transformer works in such a way that electric current flows through the secondary circuit only when the electric current in the primary circuit is changing.\n\nwhen you close the switch the electric current in the primary circuit suddenly rises from 0amp to some value\nwhich causes electric curent to flow through the secondary circuit\n\n.. b) is true\n\nwhen you open the switch the electric curent in the primary circuit changes from the maximum value to 0amps thus electric curent flows through the secondary.\n\n.. c) is true\n\nbut \n..a) is false\n\nsicne a battery is a dc source wich means that as long as the switch is closed it supplies a steady amount of electric current through the primary. thus ther will be no current through the secondary.
192726
No, that's not a good idea - neutral may not be the same as ground (0 volts).\n\nThink of it this way - the neutral wire provides a return path for the electricity to get back to the power company.  The ground is there to act as a shield, to protect the device from radio interference (if it's an electronic device like a computer).  If there's a ground fault, and you connect neutral to ground, the device may still work OK, but there may start to be "flakey" intermittent failures, like bad signal or data loss, because the neutral voltage is sending interference signals throught the device ground, instead of being shielded by the ground.
664737
Hehe, the utility company inspector will be pretty mad at you the next time he comes around.  I assume from your description that a 220->9V transformer is installed before the meter, but then a 9->220V transformer is placed after the meter to get the voltage back up to normal for your home.  Is this right?\n\nThe step-down transformer will not slow down your meter (there is no free lunch in power consumption).  What will happen is that at the 9V side of the transformer, you will have about 24.5 times the amount of current under the normal setup.\n\nMost meters have coils that sense the voltage and current and mechanically sum up the power.  So, you would be dropping the voltage but raising the current in the same proportion (the power readings will be close to the same as if you left things alone).\n\nPractically, the meter might be damaged since it was probably not designed to handle the higher current and lower voltage.  Also if the transformers you install are not rated correctly, bad things will happen.  The transformers you will need will likely cost a whole lot.  Finally, your meter might actually speed up a little since the transformer after the meter will certainly have some power losses associated with it.\n\nTo sum it up: not a good idea.
144988
If lightning was the problem, no surge supressor or UPS can provide sufficient protection. If you know that a thunderstorm is on the way, the best protection is to shut down the computer and unplug it from the wall.
42027
you shouldn't have to rewire anything.  a(n AC) motor is a generator and a generator is a motor.  physically they are the same thing!  attach the motor contacts to a multimeter or oscilloscope, crank on that bad boy and watch what happens!
171777
I think it's worth it - a surge protector or even a UPS. Sometimes you can get deals on free power strips with surge protection. A UPS will only cost $30-$50 bucks at most, I think.
206554
1 amp (1000 millamps) is the maximum rated operating conditions for the transformer.  You may be able to get more current than that from the transformer, but the rest of its specifications (such as output voltage, operating temperature, efficiency, etc) are no longer guaranteed to be accurate.\n\nIt would be a good idea not to exceed this current draw if you want the transformer to last, and not pose a fire danger.  Consider using a fuse in your circuit to prevent overcurrent conditions.
972206
For computer to do it, I would have been thinking a short in the PC's power supply, for two, no way. I am guessing your computers are connect via the same point of double adapter somewhere and have a suspision that there is a break in the Earth within the cables or adapter somewhere.\n\nThis means the chasis of your computer will not discharge and slowly creap up to high voltages over time, even though the PC's are not on.
379234
Hi! A transformer works on the principle of mutual induction which is valid only when the voltage (or EMF, to be more appropriate) on one of the coils of the transformer is changing with time, as in the case of A.C. voltage. As the magnitude of the voltage changes on one of the coils, the corresponding flux on the other coil also changes, thus giving rise to a voltage on the other side.\n\nAn AA battery provides a constant voltage, as a result of which there is no change in flux and no voltage on the other coil (120 V side, in this case).\n\nHowever, there will be a flux change for a very short duration of time as the current in the 24 V side rises from 0 to its full value after the battery has been connected. During this time, a voltage will be induced in the 120 V side and you'll get an A.C voltage on this side. But this would be for a very short time duration.\n\nSo, the answer: After some time, there is no voltage (A.C. or D.C.) on the 120 V side.
732893
we know that for power, P=IV. we also know that whatever power goes into the transformer comes out of the transformer(conservation of energy). this means that V is inversely proportional to I. or I is inversely proportional to V.\n\nif you already know how much V was stepped up, then just step down the I by the same ratio. for eg, if 110V 10A was transformed to 220V, then the step up ratio is 2. therefore current is stepped down by 2. so current will be 5. try equating 110x10 with 220x5, it is constant.\n\nall of this assumes that the transformer is 100% efficient. if there are losses due to heat, then you multiply the exit current by the efficiency factor. eg, if the trans is said to be 80% effiecient, then the actual exit current would not be 5A but 4A. voltage is not affected by effiency issues.\n\nby the way transformers only work with AC, the guy who mentioned direct currents is thinking of current rectifer not transformer.