What Are The Consequences Of A Generator Operating At Too Low a Voltage?

1. What are “analog quantity” and “switch quantity”?

Answer: Analog quantity – displays the unit speed, stator and rotor current, voltage and temperature of each guide bearing, water pressure, oil pressure, and other analog values, as well as line and bus voltage, frequency, line current, active and reactive power and main transformer temperature The numerical value of the equivalent analog quantity;

Switching quantity—displays the opening and closing of the unit’s main unit’s circuit breaker, knife switch, and excitation switch, the increase or decrease in active power, and the operation and withdrawal of each solenoid valve.

2. What is a closed-loop control system?

Answer: Any control system whose output signal can have a direct impact on the control function of the system is called a closed-loop control system. The speed regulator system and microcomputer excitation regulation system of the unit are both closed-loop control systems.

3. What are the causes of generator oscillation?

Answer: a. Static stability damage is mainly caused by changes in operating mode or excessive time to remove the fault point;

b. The impedance connecting the generator and the system suddenly increases;

c. The power in the power system suddenly changes, and the balance between supply and demand is seriously lost;

d. There is a serious shortage of reactive power in the power system and the voltage drops suddenly;

e. The generator speed regulator fails.

What Are The Consequences Of A Generator Operating At Too Low a Voltage?插图

4. Why does the generator need to be equipped with an air cooler?

Answer: When the generator is running, due to the existence of a current and magnetic field, iron loss and copper loss will inevitably occur. This loss is transmitted to the stator winding and iron core in the form of heat, causing the winding temperature to rise and reducing the generator’s efficiency. In addition, On the one hand, it will also cause the generator stator winding and iron core insulation to burn out, causing the generator to catch fire. The air cooler can turn the hot air in the generator into cold air, and the heat will be taken away by the cooling water.

5. What is the large shaft grounding brush and what is the function of the large shaft grounding brush?

Answer: The large shaft grounding brush is a carbon brush connected to the main shaft of the generator, and its other end is grounded. The function of the large shaft grounding brush is:

a: Eliminate the shaft current and introduce the shaft current into the earth;

b: Monitor the generator rotor insulation and use it as one-point grounding and two-point grounding protection of the rotor. When a large current flows through the grounding brush, it can be judged as insulation damage and grounding;

c: Measure the positive and negative voltages of the generator rotor to ground.

What Are The Consequences Of A Generator Operating At Too Low a Voltage?插图1

6. What is the danger of axial current?

Answer: Due to the existence of shaft current, small arc erosion is generated between the journal and the bearing bush, causing the bearing alloy to gradually stick to the journal, destroying the good working surface of the bearing bush, causing the bearing to overheat, and even melting the bearing alloy. Due to the long-term electrolysis of the shaft current, the lubricating oil will also deteriorate and turn black, which will reduce the lubrication performance and increase the bearing temperature.

7. What types of main valves are there? What is the function of the butterfly valve?

Answer: The main valve is divided into a ball valve, used for water head above 200 meters; butterfly valve, used for water head above 200 meters. Widely used gate valves and butterfly valves:

a: As backup protection for unit overspeed;

b: Reduce the amount of water leakage when the unit guide vanes are fully closed;

c: Convenient for inspection and maintenance. When one unit is inspected or malfunctions, closing its main valve will not affect the normal operation of other units;

d: For a power station with a long water diversion pipe, when the unit is out of operation or for maintenance, it can only close the main valve and not the dam inlet gate, so that the water diversion pipe is working and waiting for water filling and saves the waiting time for water filling.

e: The butterfly valve can only be opened by static water, but can be closed by moving water;

f: The butterfly valve only has two states: fully open and fully closed. It is used to cut off the flow of water and cannot be used to adjust the flow rate.

8. What is the function of the bypass valve?

Answer: When the water head is high or the valve diameter is large, to reduce the door opening force and prevent the butterfly valve bearing from being worn due to force on one side, before opening the butterfly valve, open the bypass valve first, manually or automatically. Make the pressure on both sides of the butterfly valve reach equilibrium before opening the butterfly valve.

9. What is the function of the air valve?

Answer: The air valve is installed on the connecting pipe behind the butterfly valve. When the water in the pipe section behind the valve and the volute is emptied, air is supplied or when the water is filled, the air is discharged. When the butterfly valve is closed due to an accident, the air valve is also used to supply air, so that the valve The rear tube section, and the volute will not be damaged by vacuum.

10. What is the reason for the increase in unit-bearing temperature? What is the setting value of the temperature of each bearing of the unit?

Answer: Reasons for the increase in bearing temperature:

a. The thermometer malfunctions, causing the signal to be sent incorrectly;

b. The cooling water volume decreases and the water pressure decreases;

c. Oil level decreases or oil quality deteriorates;

d. The vibration and swing of the unit increase;

e. The cooler is blocked and the ambient temperature rises;

f. The lubricating oil pressure drops or is interrupted, and the oil flow is not smooth.

The thrust bearing, engine bearing, and water guide bearing of the unit sends out high-limit signals at 60°C. At this time, inspection and treatment should be carried out according to the bearing temperature rise fault. The thrust bearing, engine bearing, and water guide bearing of the unit sends out high-limit signals at 65°C. At this time, inspection and treatment should be carried out according to the bearing temperature overheating accident. The thrust bearing uses metal plastic tiles. The oil temperature of the bearings is not allowed to exceed 50°C. The temperature is not allowed to exceed 65℃.

11. What are the effects of too high or too low DC bus voltage?

Answer: If the DC bus voltage is too high, electrical components that are regularly operated with power, such as instruments, relays, indicator lights, etc., are easily damaged due to overheating. On the other hand, if the voltage is too low, the protection may malfunction or refuse to operate. Generally, the allowable voltage is stipulated. The variation range is ±10%

12. What are the consequences if the generator operating voltage is too low?

Answer: a: When the voltage is lower than 90% of the rated voltage, the stator core will operate in an unsaturated state, making the voltage unstable. If the excitation changes slightly, the voltage will change greatly, and even cause out-of-synchronization, destroying system stability;

b: Too low voltage will worsen the working condition of the factory motor;

c: If the generator capacity is kept constant when the voltage is too low, the stator current must be increased, and the stator winding temperature will increase, otherwise the generator will operate with low capacity.

13. How are the hot and cold air temperatures of the generator regulated?

Answer: The cooling air temperature of the generator is 35°C. The maximum inlet air temperature shall not exceed 50°C. The temperature difference between the hot and cold air at the inlet and outlet shall not exceed 25°C. The minimum cold air temperature shall be based on the fact that the cooler does not produce condensation droplets, which is usually around 30°C.

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