What is meant by active and reactive power?
In the process of generating, transmitting, and utilizing AC electric energy, the portion of energy that is converted into non-electrical and magnetic forms is known as active power, while the portion of energy used for the exchange of electric and magnetic fields in the circuit is known as reactive power.
Active power, also referred to as average power, is not a constant value for alternating current instantaneous power. The average value of power in one cycle is known as active power, representing the power consumed by the resistive part of a circuit and its output power for a motor. It is expressed by the letter P, with the unit of kilowatts (KW).
Reactive power is found in an inductor (or capacitor) circuit, which converts energy from the power source into that of magnetic Fields (or electric fields) and stores it for half a cycle of time. Afterward, it returns the stored energy of the magnetic (or electric) field to the power source in another half cycle of time. Reactive power only exchanges energy with the power source, and does not truly consume energy. The amplitude value of the energy exchange with power supply is referenced as reactive power (Q), with unit of kilovolt-amperes (Kvar).
Apparent power is described as the product of voltage and current in a circuit with resistance and reactance, and is represented by the letter S or symbol P, with the kilovolt-ampere (KVA) as the unit. The relationship between active power, reactive power, and apparent power can be conveyed with a power triangle.
What is the parallel engineering of generator sets?
Multiple generators in parallel function as a high-power generator to supply power to the load. Depending on the size of the load, a decision can be made on how many machines to turn on (considering the lowest fuel consumption rate under 75% of the rated load) to achieve fuel savings and reduce the cost of power generation. Moreover, uninterrupted power supply is necessary to protect the factory’s normal production. When a unit is converted to use, the standby unit can be integrated into the operating system, and the load can be switched to the standby unit in operation. Then the original unit in operation can be stopped, enabling the system to continue running without any power failure during the switching process.
What is the reason for the diesel generator oil pump not supplying oil?
To determine the actual working conditions and combustion degree of a diesel engine, it’s common practice to analyze the exhaust temperature, pressure, and smoke color of each cylinder. Based on this analysis, adjustments can be made to the oil supply amount and timing for each cylinder to ensure the injection pump supplies oil to each cylinder in accordance with the principle of distribution according to demand. This helps to eliminate differences between the cylinders and optimize engine performance.
There are several reasons why the oil pump of a diesel generator may not turn on:
- Poor assembly or incorrect installation of the oil pump.
- Loose oil pump shell that allows air to enter.
- Air leakage in the oil drawing pipe system.
- Blockage in the oil suction line.
- Loose stuffing box of the oil pump.
- Blocked oil filter or malfunctioning oil suction check valve.
- Insufficient oil quantity in the oil tank.
To address these issues, the following steps can be taken:
- Inspect and repair the oil pump.
- Clean and repair the oil filter, oil suction valve, and oil suction pipeline.
- Ensure tightness to prevent air leakage.
- Fill oil to discharge air in the oil suction pipe and oil pump.
- Maintain a certain oil level in the oil tank.
What is the role of temperature sensor in diesel generator?
To ensure proper operation of the diesel generator, it is necessary to monitor the coolant and fuel temperatures inside the generator set during operation. This requires the use of temperature sensors.
The coolant temperature sensor in diesel generators is typically located on the right front side of the cylinder. Its function is to control the fan rotation, adjust the starting fuel supply, control the injection timing, and protect the engine. Diesel generators typically operate within a temperature range of -40 to 140°C. If the temperature sensor fails, it can result in lower engine speed, power drop, difficult starting, and ultimately, generator shutdown. Most coolant temperature sensors in diesel generators use thermistors.
The fuel temperature sensor in diesel generators is typically mounted on the top of the inner housing of the fuel filter. Its function is to control the fuel heater and protect the diesel generator through temperature sensor signals. If the sensor fails, it can also impact engine performance.
Why do generators start with excitation power?
To establish the initial voltage of the generator, the first step is to add excitation to the rotor by starting the excitation power supply, which forms a rotor magnetic field. According to the principle of electromagnetic induction, the movement of a conductor in a magnetic field induces a current. As the rotor rotates, current is induced in the stator, which is the moving conductor relative to the rotating magnetic field. Once the generator outlet voltage reaches the normal excitation voltage, the excitation power supply automatically exits and the excitation thyristor rectifier switches automatically.
If there is no exciter but an excitation transformer, the start-up power supply should be used first. Since the generator and the excitation transformer have no power at the beginning, a little power and excitation current should be given using the start-up power supply. After a while, the starter power supply can be thrown off. The excitation power supply is very small and only needs a little to enable the generator to generate electricity. If the shutdown time is short, the generator can be started by residual magnetism and generally does not require the excitation power supply unless it is necessary for major repairs.
What is non-contemporaneous juxtaposition, and what is the harm of non-con temporaneous juxtaposition?
When synchronous generators fail to meet the quasi-synchronous paralleling conditions, they are paralleled with the system in an asynchronous manner. This is known as asynchronous paralleling. Asynchronous paralleling is a critical issue in power plants and can cause significant damage to related equipment such as generators, series-connected transformers, and switches. In severe cases, the generator windings may be burnt and the ends may be seriously deformed. Even if the equipment is not immediately damaged, it can pose serious hidden dangers. In terms of the entire power system, asynchronous paralleling of a large unit can have a significant impact, potentially causing power oscillation between the generator and the system, severely disrupting the normal operation of the entire system, and even leading to a collapse.
After the generator set starts normally, the voltage is high (three-phase 600V) and there is no voltage for about ten seconds?
Q: Is your connection correct?
A: Yes.
Q: Is your No. 7 line properly connected to the generator set’s zero line?
A: Yes.
Q: Are your No. 6/8 lines connected to the L1 and L2 lines of the generator set?
A: Yes.
Q: In that case, you can adjust the RMS potentiometer slightly in reverse.
A: I adjusted the RMS potentiometer, but the voltage (320V) disappeared after about ten seconds.
Q: In that case, adjust the OVER V potentiometer clockwise.
A: I adjusted the OVER V potentiometer. If the voltage is high (three-phase 410V), it cannot be adjusted down, but it can be adjusted up.
Q: Does your unit have an adjustable resistor? It would be helpful if it didn’t have one.
What is the so-called reverse power transmission of the generator? What are the two serious consequences?
The scenario in which a self-provided generator sends electricity back to the city network is referred to as reverse power transmission. This can lead to two serious consequences:
a) If there is no power outage in the city network, the power supply from the city network and the self-provided generator will be paralleled asynchronously, which can damage the unit. If the capacity of the self-provided generator is significant, it can also cause disturbances in the city network.
b) In case the city network experiences a power outage and is being repaired, if the self-provided generator sends electricity back, it can electrocute the maintenance personnel of the power supply department.
What is the meaning of floating charge of generator charger？
The principle of float charging for generator chargers and cell phone chargers is similar. Float charging is a mode of battery pack power supply (discharge), where the battery pack is connected in parallel to the load circuit and the power lines. Its voltage is mostly constant, only slightly higher than the battery pack break voltage. A small amount of current is supplied through the power lines to compensate for the loss of the battery pack, which allows it to maintain a charged state without overcharging. As a result, the battery can be charged and discharged in sync with the fluctuation of the power line voltage. When the load is light and the power line voltage is high, the battery pack charges, and when the load is heavy or the power supply is accidentally interrupted, the battery pack discharges and shares part or all of the load. In this way, the battery pack acts as a voltage stabilizer and remains in a standby state.
How to check the real useful power of diesel generators?
To determine the actual useful power of the unit, you can follow this method: Multiply the rated power of the diesel engine by 0.9 for 12 hours to obtain a value in kilowatts (kW). If the rated power of the generator is equal to or less than this value, then the rated power of the generator is considered as the actual useful power of the unit. However, if the rated power of the generator is greater than this value, then the value obtained through the calculation must be taken as the actual useful power of the unit.
What harm does a short circuit do to the generator and system?
The damage caused by a short circuit to a generator can be significant. Firstly, the end of the stator winding may be exposed to a large electromagnetic force, which could potentially damage the outer insulation of the wire. Secondly, the rotor shaft may experience a significant electromagnetic torque. Additionally, the short circuit may cause the stator and rotor windings to overheat.
When it comes to the power system, a short circuit can also have negative consequences. It may lead to damage of electrical equipment, and it may also disrupt the stable operation of the system due to low voltage.
What are the advantages and disadvantages of several methods of parallel generators?
There are two types of methods for parallel connection of generators: quasi-synchronization method and self-synchronization method.
- Advantages of quasi-synchronization method:
(1) No inrush current is generated when the generator is closed.
(2) No impact on the power system.
- Disadvantages of quasi-synchronization method:
(1) If there is a large inrush current due to some reason, it may be twice as large as the three-phase short-circuit current at the machine end.
(2) It is difficult for the operator to accurately determine the timing of the parallel operation when using manual quasi-synchronization.
- Advantages of self-synchronization method:
(1) The operation method is relatively simple, and the automation of the closing process is also simple.
(2) Quick closing in case of an emergency.
- Disadvantages of self-synchronization method:
(1) There is an inrush current, which may have an impact on the system.
(2) The voltage of the system may decrease momentarily at the moment of closing.
How to diagnose and deal with the difficulty of engine hot start?
- Diagnostic Reasons:
The main reason is the severe wear of the injection pump plunger and injector needle valve. When the car is hot and needs to start, the high temperature of the injection pump and fuel filter causes the fuel viscosity to drop. Coupled with the low starting speed, most of the diesel fuel leaks from the worn gap, resulting in insufficient starting oil, which makes it difficult to start the car.
- Diagnosis and Treatment Method:
① Emergency exclusion method: Put the car in gear and start it by towing it with another car. Use the speed of the car to rotate the engine at high speed, so that the diesel fuel does not have time to leak and ensure sufficient starting oil supply. However, this method is not recommended because the cylinder pressure of a Cummins supercharged engine is relatively high, and the impact of trailer starting on the connections is large, which affects the service life of the vehicle.
② If the plunger or needle valve is severely worn, it should be replaced with new products after inspection and confirmation on the injection pump test bench.
Can the battery charger use the power from the generator to charge the battery?
Yes, battery chargers typically come equipped with automatic float charging and other features. Generator set users can utilize the generator to directly supply electricity for charging purposes, while also ensuring that the engine operates at a low speed (idle speed).
What conditions need to be met for the generator to be paralleled?
The requirements for parallel generators to meet are as follows: (1) voltage must be equal at the same time, (2) voltage phase must be the same, (3) frequencies must be equal, and (4) phase sequence must be the same.
When we say voltage is equal, it means that the voltage of the generator and the system are in close proximity, with a difference that generally does not exceed 10%. If the voltage is not equal, a circulating current of reactive power may occur between the generator and the system.
Consistent voltage phase means that the generator voltage phase angle is close to the system voltage phase angle, with a difference that generally does not exceed 20 degrees. If the voltage phase is inconsistent, it may cause a large inrush current, leading to generator burnout or damage to the end due to the action of huge electric power.
Equal frequency means that the generator frequency is close to the system frequency, with a difference that generally does not exceed 0.5HZ. If the frequencies are not equal, a beat voltage and a beat current will be generated. The torque generated by the active component of the beat current on the generator shaft will cause the generator to produce mechanical vibration. When the frequency difference is large, even the generator cannot be synchronized after being merged.
Finally, the generator needs to be connected to the grid through the synchronization device, which can be either manual quasi-synchronization or automatic quasi-synchronization. The generator voltage and frequency need to be adjusted to meet the grid connection conditions.
What is the reason for the high water temperature of the generator set?
High water temperature in a generator set is a common phenomenon in the United States, but there are many causes.
Firstly, it is important to ensure that the unit’s ventilation conditions meet the standard.
Secondly, the load should be checked to ensure that it is not excessive.
Thirdly, it is important to check whether the thermostat return pipe is blocked. If it is blocked, it needs to be cleared.
Fourthly, the water tank should be checked for any oil blockages or loose fan belts. Most importantly, the internal blockage of the water tank should be investigated.
Secondly, it is important to check whether the water pump is functioning properly.
Of course, high exhaust temperature caused by oil nozzle atomization or valve leakage can also result in high water temperature, but the chances of this are relatively low.
What is the relationship between the speed drop of the generator governor and the load distribution?
When multiple units are operating in parallel, it is important to ensure that the transfer rate is positive. However, it is also acceptable for a backbone unit to have a transfer rate close to zero. If all transfer rates are zero, each unit will have to compete for the load, resulting in unstable operation. In reality, due to the speed regulation dead zone of many units, the situation of load
What is the maximum speed of the generator governor can be set?
The maximum setting for the engine speed is 1800 rpm, with an overspeed value of 1750 rpm. The normal range for engine speed is between 1475-1575 rpm. Shutdown values can be adjusted as needed, and the maximum engine speed is limited by the oil pump. These specifications make the engine suitable for high-speed generators.
Regarding the voltage of four 12V generator chargers connected together, the voltage will still be 12V (with a float voltage of 13.7V). However, the charging current will increase. If the chargers were connected in series, the voltage would be U=4*12V=48V.
The engine idle speed is too high, how to diagnose and deal with it?
The engine’s idle speed being too high means that when the accelerator is released, the engine speed remains higher than the specified idle speed.
⑴ Possible reasons for this include:
① The throttle lever is not properly adjusted.
② The accelerator return spring is too soft.
③ The idle speed limit stop or adjustment screw is out of balance.
④ The idle spring is too hard or the preload is adjusted too much.
(2) Diagnosis and treatment methods:
High engine idle speed is a relatively easy fault to troubleshoot. First, check if the throttle has returned to the minimum position. If not, check the throttle adjustment and throttle return. Adjust the throttle cable limit screw. If the throttle still cannot return, check if the throttle return spring is too soft. If a fuel injection pump has recently been repaired and calibrated, consider whether the idle speed adjustment is correct and whether the idle speed spring preload adjustment is too large. If the spring has been replaced, check if it is too hard.
What is the working principle of generator float charging?
Float charging operates on the principle that when a battery is fully charged, the charger continues to provide a constant voltage with a very small current to balance the natural discharge of the battery. This is because if the charger stops charging, the battery will naturally release electrical energy. Float charging is commonly used in generators or small UPS systems.
If the generator is only magnetically regulated at 1500 rpm, can it be magnetized at 1200 rpm?
In principle, it is definitely possible. If it cannot be adjusted through magnetization, it suggests that the magnetism is insufficient and requires magnetizing.
Why do generators still need generator chargers to charge?
Prior to starting the generator, it is necessary to rotate it and establish a magnetic field in order to generate electricity. In cases where the residual magnetism of the excitation system is insufficient, it is necessary to charge it using a charger. In this context, charging refers to charging the generator battery, which provides power to the excitation system and builds up the residual magnetism.
What conditions need to be met for the generator to be paralleled?
The requirements for parallel generators are as follows:
The voltage must be equal at the same time. This means that the voltage of the generator and the system should be close, with a difference generally not exceeding 10%. If the voltage is not equal, there will be a circulating current of reactive power between the generator and the system after being connected in parallel.
The voltage phase must be consistent. This means that the generator voltage phase angle should be close to the system voltage phase angle, with a difference generally not exceeding 20 degrees. If the voltage phase is inconsistent, it may cause a large inrush current, leading to generator burnout or damage due to the action of huge electric power.
The frequencies must be equal. This means that the generator frequency should be close to the system frequency, with a difference generally not exceeding 0.5Hz. If the frequencies are not equal, it may generate a beat voltage and a beat current. The torque generated by the active component of the beat current on the generator shaft may cause mechanical vibration. When the frequency difference is large, the generator may not even be synchronized after being connected in parallel.
The generator needs to be connected to the grid through a synchronization device, which can be manual quasi-synchronization or automatic quasi-synchronization. The generator voltage and frequency must be adjusted to meet the grid connection requirements.