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If a current transformer (CT) has its secondary winding left open-circuit whilst there is current in the primary winding, the magnetic core will saturate, large eddy currents will occur in the core causing the core to heat up rapidly, the voltage in the secondary will rise to dangerously high values and the current transformer will fail catastrophically. To further describe why this happens, consider an "ideal" transformer (which has no losses at all - a reasonable assumption because Transformers are generally very efficient), therefore, power in equals power out. Power can be calculated by multiplying the voltage by the current (amps using the symbol I) in each case. Therefore: Pin = Pout, or Vin x Iin = Vout x Iout, or again Vprim x Iprim = Vsec x Isec (where prim refers to the primary or input winding and sec refers to the secondary or output winding). The primary winding of current transformer is connected in series with the load, therefore the current in the primary winding is fixed by the load. Thus if the secondary winding is open circuit, the secondary current is zero, and the voltage will rise to a very high value in trying to balance this equation. It will exceed the breakdown value of the insulation and will cause an arc because the insulation will never withstand an infinite voltage! In addition to this if the secondary is open circuit, there is no magnetic flux from secondary winding current, to balance and negate any of the magnetic flux from the primary winding current as occurs in power and voltage transformers. This is the reason for magnetic saturation of the core, and the rapid heating effect of the current transformer which affects the ability of the insulation to withstand the high voltage described above. The failure of current transformers under these conditions can be explosive and highly dangerous.
Wiki User
∙ 15y ago
Wiki User
∙ 12y agoTo prevent the operator being exposed to dangerously-high voltages.
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What does the word load mean in science?
it means a current as in an electrical current
Why is ammeter connected in series with the load?
A ammeter will tell you how much current draw the load is drawing
What stops the current flowing in a circuit?
Current will cease when either or both the potential difference across the load is Zero or when the load, itself, is Infinite in resistance or impedance.
Is it possible to connect two transformers together?
The PT's (VT's) primary is connected between any two line conductors (or line to neutral). It's secondary is connected directly to the burden (e.g. voltmeter). If used together with a CT for the purpose of measuring power or energy, then its polarity markings must be observed.
What is the difference between a full-load current rated current?
no load voltage means there is no connected devices operating on the circuit. usually the voltage reading will reflect the normal or highest voltage reading in the circuit. full load voltage is measured when all devices in the circuit are operating at the same time. initial load startup will usually drop the voltage somewhat, but it should recover in a short period of time
What is the no load current of 1600 kva transformer?
No load current depends on the design of the transformer, and what voltage it is energized at. It will typically be below 1% of full load, and can be significantly below 1% for utility sized transformers.
Why alternating current is use for electrical system?
The transmission of electrical energy requires very high voltages (for a given load, the higher the supply voltage, the lower the load current). To increase/reduce these voltages, you need transformers. Transformers are AC machines; they do not work with DC.
Why PT Burden is always higher than CT Burden?
PTs are high voltage, low current transformers and so need a relatively high impedance (or burden) load to function accurately. CTs are high current, low voltage (if not open circuited!) transformers and so need a very low impedance load to function accurately.
Differentiate step-up transformers from step-down transformers?
Step up transformers increase the voltage, while step down transformers reduce it. Higher voltages are better for electricity transmission/distribution, because, for any given load, the higher the voltage, the lower the resulting current. This means the supply conductors can have a lower cross-sectional area and the resulting saving in copper makes the installation cheaper. A lower load current also means lower line (energy) losses.
What is the difference between no load current and no load voltage?
What does the question refer to? Induction motors? Transformers? For transformers, the no-load voltage is the voltage -- across the secondary or primary -- when there is no load attached to the secondary, that is, when there is no current in the secondary. No-load current really only makes sense when talking about a motor, because current is flowing in the device even when it's not under load. A rule of thumb is the no-load current is about a third to one half the full-load current.
Why no load current in transformer small?
No load current is energizing current. This is effectively "lost" power, power used in the transformer to energize the core. It, therefore, should be small!
Is transfomer output voltage designed to full load?
Transformers are designed to run at specific voltage levels, and they are designed to handle a maximum load (known as "full load"); this load is usually based on the amount of current that can be pushed through the transformer without overheating, so if 1/2 voltage is applied, full load would be 1/2 of normal. Some "complicated" transformers may have other limitations (dual voltage transformers may have two different full loads specified, and they may not be directly proportional relative to voltage).
What is a current of transformers?
The current rating of transformers vary widely as well as the types (step-down, etc.....). So depending on the use, the primary power, and the secondary power, the amp load will change. More in general current is amps, if your transformer has say 1Kva on it then that tells you the apparent power the transformer can handle. As a side note a lot of transformers are rated in VA or KVA and that is a combination of volts and amps (apparent power).
WHAT TYPE OF transformers has secondary current of the same order as the magnetising current?
A one to one, i.e. isolation, transformer.CommentIt might be worth pointing out that the secondary current is determined by the load, and the primary current is then determined by the secondary current. The questioner appears to think that the secondary current is determined by the primary current.
Why LV side is shorted in short circuit test?
Transformer short circuit tests are used to determine the impedances (positive and zero sequence) of the transformer. A simple explanation: to do this one winding is shorted, and voltage is applied to another winding to circulate the normal full load current of the transformer. The impedance of the transformer is the applied voltage divided by the induced current. If one winding was not shorted, the voltage divided by induced current would not give the impedance of the transformer - the induced current would be much lower, giving a much higher impedance measurement that would be essentially meaningless.
Is wattmeter reading under no load test is equal to iron loss of the transformer?
Yes; that is the principle used in no-load tests on transformers. The current in the copper windings is zero on the secondary and low on the primary, so the copper loss is negligible.
How does load current varies with the load resistance?
Load current is related to load resistance by an inverse relationship. The load current increases linearly as load resistance decreases. Remember, the less resistance, the more current.
