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For a transformer, the turns ratio always applies between its primary and secondary windings. So the turns ratio for a three-phase transformer is the ratio of primary to secondary phase voltages, not between line voltages.
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The transformer is called a passive device since it cannot generate power. Its input power Ein x Iin. must equal its ouput power Eout x Iout, with the exception of internal power losses in the transformer itself. This equality can be used to derive a relation for the current transformation properties of a transformer, namely,In other words, if the output voltage increases, the output current must decrease proportionately, to keep the output power constant. The quantity Np/Ns is called the turns ratio.
It depends on the voltage on line side. KVA is simply thousand volt-amps, so you need to know voltage in order to calculate amperes.Another AnswerThe rated primary current is the rated apparent power of the transformer, divided by the rated primary current. However, the actual primary current is determined by the actualsecondary load current in proportion to the reciprocal of the turns ratio.
Turns ratio test is very important in order to find out that the transformer has the right ratio corresponding on its rated voltage in primary and secondary. For example, three phase transformer is subjected to turns ratio test when each phase has equal turns ratio then the transformer is balance.The test is performed to ensure that overheating or overcurrent conditions have not shorted turns in the transformer windings, which would distort the desired output or input voltage. This test is particularly important for instrument transformers, i.e. CTs and PTs which are connected to protective relays. These relays are extremely sensitive, and operate on very small fluctuations in secondary voltage or current. Shorted turns in these transformers can lead to big problems if they cause the relay to operate abnormally, or not at all.
Yes
The primary current on a loaded transformer depends on the secondary current, which is determined by the load. So, if you know the secondary load current, then you can use the turns ratio of the transformer to determine the primary current:Ip/Is = Ns/Np
It's approximately the inverse of the voltage- or turns-ratio:
Transformer turns ratio
RATIO ERROR The secondary current is less than the expected value. The secondary is less in magnitude. This diffence is known as ratio error. PHASE ERROR The angle between the expected and actual secondary current is known as phase error.
A current transformer is just a transformer designed to dutifully give an output related to turns ratio 1:xx.
Transformer turns ratio is the ratio of voltages between two windings. For instance, a 24VAC control transformer that runs on 120VAC will have a turns ratio about 5 to 1.
A transformer. it steps up / down voltage, and steps down / up current.
'CT' is used to designate current transformers, and 'PT' is used to designate potential transformers. A current transformer provides a ratio of primary current to the secondary. A potential transformer provides a ratio of primary voltage to the secondary. A power transformer (step up or step down) resembles a PT more than a CT.
Power flowing into a transformer must match the power flowing out (minus losses which are minimal). If this is not the case, there's something wrong. Differential protection monitors current only; Current flowing into one side of the transformer will be equal to current flowing out the other side scaled by the turns ratio of the transformer. Since the turns ratio is equivalent to the voltage ratio, this is easily set.
The primary current is determined by the secondary current, not the other way around. For example, a step up transformer will step up the primary voltage in proportion to the turns ratio of the transformer. Any secondary current is then determined by the secondary voltage and the load, NOT by the primary current. The primary current is then determined by the secondary current in proportion to the reciprocal of the turns ratio.
The ratio of output windings to input windings determines the ratio of output voltage to input voltage. The ratio of current is the inverse.