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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.
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.
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.
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.
If it's a step up or step down transformer and you know the secondary side current, multiply the secondary current by the turns ratio. If you know the power in the secondary winding but not the current, divide the secondary power by the secondary voltage to get the secondary current and then multiply the secondary current by the turns ratio to get the primary current. The turns ratio is the number of turns on the secondary winding divided by the number of turns on the primary winding. For a step up transformer, the turns ratio will be greater then one. If it's a step down transformer, then the turns ratio will be less than one. If you don't know the turns ratio, divide the secondary voltage by the primary voltage to get the turns ratio.