What you say is not correct. This is the current practice in many situations, but it is not actually the most scientific. According to weighing various situations, there are advantages and disadvantages, but after weighing, your point of view. , the most reasonable grounding method is to adopt a three-phase three-wire system at the end of the generator, that is, the neutral point is not grounded.
Failing to ground can reduce the generation of harmonic currents in generators and transformers.
However, the problem caused by not being grounded is how to implement grounding protection? Generally, protection is obtained after detecting a large short circuit current after a short circuit. Indeed, at this time, protection that detects the three-phase voltage to earth can be used. Or other protection againstzero sequence voltage, etc.
The neutral point of the generator cannot be grounded here. The main reason is that the generator here does not provide power directly, but the transformer does. Therefore, even if the generator has a three-phase, three-wire system, if a single-phase short to ground occurs in the stator, which will cause the phase voltage of the other two phases to increase, you will be fine , because the phase voltage of the generator is not transmitted to the single-phase load at all. Don't be afraid of damaging single-phase loads. There is also no problem with the user's personal safety.
So you have to analyze it yourself and stick to what you think is a reasonable point of view. What most others say is not necessarily true. On this issue, many people have written articles on the Internet. and I discussed it. It's my point of view. VYou can check it yourself.
Why must the neutral point of the generator transformer be grounded?
The 700 kW low voltage generator set requires neutral point grounding, which is a necessary electrical safety measure that can effectively protect the safe and stable operation of the generator and equipment electrical it contains. Neutral point grounding refers to bonding the neutral point (i.e. neutral line) of the electrical system to ground via grounding, so that the electrical system is in a status of good safety performance.
The main functions of neutral point grounding are:
1. Protect personal safety: If a series of faults causes electrical equipment to leak or short, grounding the neutral point can bypass the leak. current over time, effectively reducing the risks ofelectrical shock.
2. Prevent equipment surges: When a power outage exceeds the equipment voltage limit, neutral point grounding can limit the surge value through the grounding resistor.
3. Reduce the maximum system impact value: When the AC system causes impulse current due to equipment short circuit and other faults, grounding the neutral point can minimize the value maximum impact and effectively protect the equipment.
In short, for generator sets of any power, neutral point grounding is a necessary electrical safety measure to ensure the stable and safe operation of electrical equipment.
The generator center point grounding transformer is a single-phase transformer. The primary side rated voltage is the generator phase voltage multiplied by 1.05 (taking into accountof the increase in voltage). usually 100V.
If a resistor is to be connected on the secondary side (as a high-resistance ground at the center of the generator), the secondary winding voltage should be selected according to the resistor's rated voltage . But at that time the transformer should haveA third winding with a rated voltage of 100 V is used for measurement and protection. ?
One end of the primary winding of the grounding transformer is connected to the center point of the generator and the other end is grounded.
Depending on the design, either the secondary winding is connected to a resistor or the secondary winding is connected to protection and measurement.
The resistance of the load resistor connected to the secondary side of the grounding transformer is very small, but the converted resistance to the primary side is very large (several thousand d'ohms). Therefore, the neutral point of the generator is actually a high-resistance ground, which can effectively limit the capacitor current.