Current transformer manufacturer: The relationship and calculation of current transformer ratio and number of turns
May 16, 2024
Regarding the relationship between the number of core turns and the transformation ratio of a current transformer, this question mainly involves the core-type transformer. According to relevant experiments, it is known that the ratio of its primary current and secondary current is equivalent to the number of primary turns. Inversely proportional to the secondary turns ratio. In other words, if the number of core turns of this transformer is 1 turn, its transformation ratio is 500/5; if the number of core turns is 2 turns, the transformation ratio becomes 250/5. The transformation ratio changes with the change in the number of core turns.
Based on this relationship, we can also calculate the current of the current transformer, which can be used to control the size of the current transformer based on the current to prevent the equipment from being burned due to excessive current.
The relationship and calculation of current transformer ratio and number of turns
Calculation of current transformer ratio and number of turns
Some current transformers have lost their factory nameplates during use. When the user's load changes and the current transformer ratio must be changed, the transformer must first be tested to determine the maximum primary rated current of the transformer, and then the ratio change must be carried out as needed. and calculation of turns.
For example, a current transformer with a maximum primary rated current of 150A needs to be used in a 50/5 transformer application. The formula is converted into the number of primary core turns = the maximum primary rated current of the current current transformer/the primary current of the transformer to be converted. =150/50=3 turns, which is converted into a 50/5 current transformer, and the number of core turns at one time is 3 turns.
The maximum primary rated current can be calculated for this purpose. For example, the transformation ratio of the original current transformer is 50/5 and the number of core turns is 3. If you want to convert it into a 75/5 transformer for use, you should calculate it first. Output the maximum primary rated current: Maximum primary rated current = primary current in the original application × original number of core turns = 50 × 3 = 150A, the number of core turns after conversion to 75/5 is 150/75 = 2 turns That is, when the original 50/5 current transformer with 3 core turns is converted into a 75/5 current transformer, the strain stress of the core turns is 2 turns. Another example is that the original 50/5 current transformer with 4 core turns needs to be used as a 75/5 current transformer. We first calculate the maximum primary rated current as 50×4=200A. After conversion, The number of turns for threading the core should be 200/75≈2.66 turns. When threading the core, the number of turns can only be an integer, either 2 turns or 3 turns.
When we pass through 2 turns, the primary current has become 200/2=100A, resulting in a 100/5 transformer, which causes a deviation. The deviation is (original transformation ratio - current transformation ratio) / current transformation ratio = (15-20)/20=--0.25, which is -25%. In other words, if you still calculate the electricity consumption according to the 75/5 ratio, you will undercount the electricity consumption by 25%. And when we use 3 turns, we will eventually overcount the customer's electricity consumption. Since its primary current becomes 200/3=66.66A, a 66.6/5 transformer is produced, and the deviation is (15-13.33)/13.33=0.125, that is, 12.5% is overcalculated when measuring the electrical energy based on the 75/5 transformation ratio. of electricity. Therefore, when we do not know the maximum primary rated current of the current transformer, we cannot casually replace the ratio, otherwise it may cause errors in measurement verification.
The relationship between the current transformer ratio and the number of core turns
The relationship between the current transformer ratio and the number of turns. For a core-type transformer, the ratio of its primary current to the secondary current is equivalent to the inverse ratio of the ratio of the primary turns to the secondary turns;
Transformer, with 1 turn through the core, the transformation ratio is 500/5; with 2 turns through the core, the transformation ratio is 250/5;
Primary current/secondary current=500/5=100/1=number of secondary turns/number of primary turns (number of secondary turns is 100 turns);
There are 2 turns in the core, the number of secondary turns/the number of primary turns = 100/2 = primary current/secondary current, the secondary current is 5A, and the primary current can be calculated to be 250A;
In other words, if the number of core turns changes, the applied transformation ratio changes, but the transformer itself does not change, and its secondary turns number does not change, it is still 100 turns;
Another optimization algorithm is:
Primary current × number of core turns = primary current when the core turns 1 (here 250A × 2 = 500A)
If the factory nameplate only says 150/5, it means that the primary side of this transformer (one wire across the transformer) can only allow a current pass of no more than 150 amps. If it exceeds, the transformer will be burned. However, in actual applications, the current on the primary side may not necessarily meet the current standard of 150 A, but the requirement of 150 A current magnetic induction can be obtained based on calculations, such as 75/5, 50/5, 30/5.150/5. The current on the primary side is 150 A, and the secondary output is 5 A. The transformation ratio is 150 divided by 5, which is equivalent to 30 times, 75/5, 50/5, 30/5 and so on. 75 requires 2 loops; 50 requires 3 loops; 30 requires 5 loops. In other words, to meet the requirement of outputting 5 amps on the secondary side, the primary side must have a current induction of 150 amps. If the primary side can only be 75 amps, then after two turns, 75*2 will satisfy the primary side. The 150 A current is magnetically induced, and so on for the others.
It can be seen that knowledge in these aspects is very important. If it can be mastered very well, it can have a certain maintenance effect on the current transformer. If you need to know more about this and obtain such products, please contact Hemei Electronics Company.