Current transformer winding and ampoule conversion method - Database & Sql Blog Articles

inductance

The principle of current transformer is based on the principle of electromagnetic induction. The current transformer consists of a closed core and a winding. Its primary winding turns are few, and it is in the line of the current that needs to be measured. Therefore, it often has all the current flowing through the line, and the number of turns in the secondary winding is relatively large, and is connected in series in the measuring instrument and the protection circuit. The LMZ-0.5 low-voltage core-through current transformer is commonly used in the reconstruction of rural power grids. However, there are still a few comrades in the construction. The primary winding method of the current transformer, the conversion ratio of the ratio and the number of turns are wrong. Discuss with you on the above issues.

Correct winding method

We should first determine the multiplier ratio according to the size of the load, and then wew the primary line from the center of the transformer as required. Note that the number of turns around the outer ring should not be the number of turns, and should be inserted into the current transformer. The number of turns in the standard shall prevail. For example, a current transformer with a maximum current ratio of 150/5 has a maximum rated current of 150A. If it is to be used as a 50/5 transformer, the wire should be wound around 150/50=3匝, that is, the inner ring is wound. 3匝, at this time, the outer ring is only 2匝 (that is, no matter how many inner rings, as long as you wear from the inside to the outside, then the number of turns in the outer ring is always one less than the inner ring, of course, if the wire is from the outside In the case of internal wear, the opposite is true. At this time, if the number of turns in the outer ring is 3, the actual number of turns in the inner ring is 4匝, and the converted primary current is 150/4=37.5A, which becomes 37.5/5. The current transformer has a magnification of 7.5. In the meter reading, the staff calculates the electricity with a current transformer of 50/5 and a magnification of 10. The error is: (10-7.5)/7.5=0.33 Electricity 33.

Conversion ratio and number of turns

Some current transformers are lost in use. When the user load changes, the current transformer ratio must be changed. First, the transformer should be tested to determine the highest rated current of the transformer, and then the ratio and number of turns should be adjusted as needed. Conversion. For example, a current transformer with a maximum rated current of 150A should be used as a 50/5 transformer. The conversion formula is the number of core through turns = the highest rated current of the current current transformer / the primary current of the transformer to be converted = 150/5=3匝 is transformed into a 50/5 current transformer, and the number of core passes is 3匝. It can be used to calculate the highest rated current. For example, the ratio of the original current transformer is 50/5, and the number of core turns is 3匝. To use it as a 75/5 transformer, we first calculate the highest. Primary rated current: highest rated current = primary current in original use × original core winding number = 50 × 3 = 150A, after the conversion to 75/5, the number of core windings is 150/75 = 2, that is, the original core When the 50/5 current transformer with 3 turns is converted to a 75/5 current transformer, the core strain is 2匝. Another example is the current transformer with 50/5 of the original core winding number, which needs to be changed to 75/5 current transformer. We first find the highest rated current of 50×4=200A, and change the wearing after use. The number of core turns should be 200/75≈2.66匝. The number of turns in the actual core can only be an integer, either 2匝 or 3匝. When we wear 2 ,, its primary current has become 200/2=100A, forming a 100/5 transformer, which produces an error, the error is (original ratio - current ratio) / current ratio = (15-20) / 20 = - 0.25 is -25, which means that if we still calculate the electricity according to the ratio of 75/5, we will count less than 25 power. And when we wear 3 ,, we will definitely count the user's power. Because the primary current becomes 200/3=66.66A, a 66.6/5 transformer is formed, and the error is (15-13.33)/13.33=0.125, which is calculated by the ratio of 75/5. Electricity. Therefore, when we do not know the highest rated current of the current transformer, it is not possible to change the ratio arbitrarily, otherwise it is likely to cause measurement error.