1. Principles of selection and testing of current transformers
1) The rated voltage of the current transformer is not less than the rated voltage of the installation point line
2) Calculate the current transformer change according to the current IC calculation
3) Select the accuracy of the current transformer according to the requirements of the secondary circuit and verify the accuracy
4) Verify the dynamic stability and thermal stability.
2. Current transformer variable current ratio selection
The ratio of the primary rated current I1n and the secondary rated current I2n of the current transformer is called the rated converter current ratio of the current transformer, and Ki=I1n/I2n≈N2/N1. Where N1 and N2 are the turns of the primary and secondary windings of the current transformer.
Current transformer primary side rated current standard ratio (such as 20.30, 40, 50, 75.100, 150 (A), 2Xa / C) and other specifications, the secondary side rated current is usually 1A or 5A. 2Xa/C means that the same product has two current ratios. It is realized by changing the connection mode of the connecting piece outside the oil conservator at the top of the product. When connected in series, the current ratio is a/c, and the current ratio in parallel is 2Xa/C.
In general, the current transformer current ratio of the metering should be chosen such that the primary rated current I1n is not less than the load current in the line (ie, the calculation IC). If the load calculation current in the line is 350A, the current transformer's converter ratio should be 400/5. The current transformer for protection can be selected to be larger in order to ensure its accuracy.
3, good or bad measurement method
Common answer:
First answer
For the high-voltage current transformer: the secondary circuit of the current transformer can only have a small impedance, so in the normal operation, the short-circuit state, the sound is small, and the sound is loud when the fault occurs. The grounding should be good, and the lead wire of the primary winding of the primary current of the capacitive current transformer should be reliably grounded. Oil-immersed transformers should not see oil seepage. In addition, when the secondary winding or circuit of the current transformer is short-circuited, the ammeter and the power meter indicate zero; when the secondary circuit of the current transformer is open, the terminal of the fault point will break through the fire.
Make the following measurements: 1. Insulation resistance of the windings;
2. Dielectric loss; measured values ​​should comply with relevant regulations
Second answer
1, appearance: current transformer housing, insulation, coils, etc. whether there are signs of aging, electric shock, burnt, etc. The following refers to the current transformer below 500V, with 500V megohmmeter check.
2, the primary coil path, can not be broken.
3, the secondary coil path, can not be broken.
4. The primary coil and the secondary coil cannot be accessed.
5. Check the insulation resistance with a 500V megger. The primary and secondary coils are insulated from the outer casing by more than 0.38 megohms.
6. Use the current clamp meter to monitor whether the current ratio is correct. (Mainly check if there is a partial short circuit between the turns inside the coil).
If you have a clamp meter and an ammeter, it is easy to use the universal meter to measure whether the coil is short-circuited or not. The circuit is connected to the circuit. The current transformer output is directly connected to the 5A ammeter. The actual current of the busbar is measured with a clamp meter, and the current of the ammeter is compared. Know that the multiple of the transformer multiplied by the ammeter should be similar to the clamp meter, and the error is too big.
Waterproof Wireless TWS Earphones
Bluetooth Earphones,True Wireless Earbuds,Waterproof Stereo Earphones In-Ear,Ultra-Light Earbuds
Shenzhen Focras Technology Co.,Ltd , https://www.focras.com