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Technical conditions and performance of diesel generators

(1) working conditions of the unit

The working condition of a unit is that it can output rated power under specified operating conditions and can work continuously reliably. The working conditions of a power station (unit) as stipulated by the national standard are mainly determined by altitude, ambient temperature, relative temperature, whether there is mould, salt mist and inclination of placement. According to the national standard of gb2819-81, power stations should be able to output rated power under the following conditions and operate reliably.

Class A power station: 1000 m altitude, temperature 40 ℃, relative humidity 60%;

Class B power plant: 0 m altitude, temperature 20 ℃, 60% humidity.

Power plant should be able to work reliably under the following conditions, is no more than 4000 m altitude, temperature upper and lower limit, respectively: upper limit is 40 ℃, 45 ℃; Lower limit is 5 ℃, 25 ℃ and 40 ℃ -; The relative humidity is 60%, 90% and 95% respectively.

(2) the main technical performance indicators of the unit

Technical performance index of the unit, it is to measure the main basis of the power supply quality and economic indicators, the main technical performance are usually from 0.8 ~ 1.0, according to the unit power factor in three-phase symmetrical load (0 ~ 100) % and (100-0) % rating within the scope of gradient or mutation, should reach the performance are:

1. Steady-state voltage regulation rate U (%)

The delta U100 %

Where, U1 -- the maximum (or minimum) of stable voltage after load change;

U - no-load voltage setting value.

Delta U Ⅰ ~ Ⅲ class unit as + (1 ~ 3) %. Ⅳ class unit delta U is not more than plus or minus 5%.

2. Steady state frequency adjustment factor f (%)

The delta f

Type of f1 ­ ­ - load steady frequency after gradient maximum (or minimum);

F2 -- frequency at rated load; F -- rated frequency.

Ⅰ ~ Ⅲ class sets the delta f (0.5 ~ 3) %. Delta Ⅳ class unit f less than 5%.

3. Voltage stability time (s)

The time required to stabilize a voltage from a sudden change in the load is usually measured by an oscilloscope.

Ⅰ ~ Ⅲ class unit for voltage stability time (0.5 ~ 1) %. Ⅳ class unit stability time of 3%.

The time required to stabilize the frequency from the time of load mutation is usually measured by oscilloscope.

Frequency stability Ⅰ ~ Ⅲ class unit time (2 ~ 5) s; Ⅳ class frequency stability time of 7 s unit.

4. No-load voltage setting range

The set voltage of the unit shall be adjustable and stable within the range of 95~105 % of the rated value. For example, for a unit with rated voltage of 400V, its no-load voltage can be adjusted between (380~420) V.

5. Stability of line voltage under three-phase asymmetric load

Power supply unit under the asymmetric three-phase load running, if each phase current shall not exceed the rating, and the electric current shall not exceed the rating of 25%, the difference between the voltage of each wire and the difference between the average value of three-phase voltage should not exceed 5% of the average three phase line voltage.

6. Parallel performance of the unit

Two three-phase units of the same specifications and models should be able to operate in parallel in a stable and parallel manner within the range of (20~100) % rated power charge under the power factor of frontal guest. In order to improve the distribution precision and operation stability of the active power and the reactive power reasonably, the diesel engine governor in the unit is required to have a device which can adjust the steady speed within (2~5) % range. The voltage regulator in the control box (screen) can adjust the steady voltage regulation rate within 5% range.

In addition, there are volatility, the overload operation time limit of voltage and frequency, transient voltage, frequency regulation and the ability to directly start the no-load asynchronous motor, such as performance, with the development of technology, the domestic and the introduction of the performance of the unit also has other special, there is not much.

(3) the automation performance of the unit

With the development of communication, the popularization and application of modern communication equipment, power supply requirements for the ac power is becoming more and more high, some communication equipment don't allow ac power instantly interrupted, which requires the unit must have the function that automation, promote power equipment centralized monitoring technology is now gradually also calls for the unit must be automated. Because the degree of automation of the unit is different, therefore, the national standard has definite provisions. According to the national standard gb4712-84, the unit automation is divided into three levels, which are described below.

1. Performance of first-class automatic unit.

(1) the unit shall automatically maintain the emergency readiness operation state, and the diesel engine shall be automatically pre-lubricated before starting;

(2) when the unit needs to start operation, it can start automatically according to the automatic control instruction or remote control instruction. If the unit needs to stop, it can also stop automatically according to the automatic control instruction or remote control instruction.

(3) during the operation of the unit, the abnormal conditions such as overload, short circuit, overspeed, overfrequency, high water temperature and low oil pressure can be automatically protected.

(4) the unit shall be equipped with a sound and light signal system indicating normal operation and abnormal operation, which indicates the operation condition of the unit.

(5) the unit should be able to run continuously for 4 hours without being on duty.

2. Secondary automatic unit

In addition to meeting the requirements of the first level automation unit, such units should also meet the following requirements:

(1) the unit shall have the function of automatic replenishment of fuel oil, oil and cooling water.

(2) the unit can run continuously for 240h without anyone on duty.

3. Three-level automatic unit

In addition to meeting the requirements of the first and second level automatic units, the unit must also have the following functions:

(1) when the self-start fails, the self-start control program system should be able to automatically transfer the start instruction to the next standby unit.

(2) the unit can automatically merge and disassemble two units of the same type according to the automatic control instruction or remote control instruction.

(3) when the unit is running parallel, it should be able to distribute the active power and reactive power output automatically.

(4) in addition to the protection of the primary and secondary automatic units, the unit should also have the function of reverse power protection.

Calibration of unit power

Oil engine generator unit is composed of internal combustion engine and synchronous generator. The maximum allowable power of an internal combustion engine is limited by the mechanical load of the parts and the heat burden. Therefore, the maximum allowable power for continuous operation needs to be specified, which is called calibrated power.

The internal combustion engine should not exceed the rated power, otherwise it will shorten its service life and may even cause accidents.

1. Calibration power of diesel engine

According to national standards, the calibration power on the nameplate of internal combustion engine falls into the following four categories:

(1) 15-minute power is the maximum effective power that the internal combustion engine can operate continuously for 15 minutes. It may overload operation and require calibration power with acceleration performance in the shortest time, such as the calibration power of internal combustion engines such as automobiles and motorcycles.

(2) one hour power is the maximum effective power that the internal combustion engine can operate continuously for one hour. Such as wheel tractors, locomotives, ships and other internal combustion engines calibrated power.

(3) 12-hour power is the maximum effective power that the internal combustion engine can operate continuously for 12 hours. For example, the calibration power of internal combustion engine for power station unit and engineering machinery.

(4) continuous power. The maximum effective power that an internal combustion engine can operate continuously.

For a unit, the output power of a diesel engine is the mechanical power of its crankshaft. According to gb1105-74, the power of the diesel engine used in the power station is calibrated to 12 hours. The diesel engine in the atmospheric pressure of 101.325 kPa, the environment temperature is 20 ℃, relative humidity 50% standard working conditions, diesel engine at rated speed 12 consecutive hours during normal operation, to achieve effective power, expressed in Ne.

Cummins NT series diesel engine in the United States, its power is divided into continuous power and standby power, the ratio of the two power is 0.91:1, which is equal to China's 12 hour power and continuous power.

2. Rated power of ac synchronous generator

The rated power of ac synchronous generator refers to the rated power output when running continuously for a long time at the rated speed, expressed by PH. According to the operating environment and technical requirements of the unit, the rated power output of the unit is calculated by the following formula:

PH is equal to K1 times phi (k2k3neh-np) (kW)

Where, PH -- rated power (kW) of synchronous alternator output;

NeH -- rated power output of diesel engine (PS);

K1 -- unit transformation coefficient (i.e. KW /PS) K1=0.736;

K2 -- power correction factor of diesel engine, as shown in table 1-2;

K3 -- correction coefficient of environmental conditions, as shown in table 1-3 and table 1-4;

The efficiency of the synchronous alternator;

Np - mechanical power consumed by diesel fans and other accessories (PS).

In general, the ratio of the rated power (PS) of diesel engine output to the rated power (kW) of synchronous alternator output is called the matching ratio, which is denoted by K, i.e

The development of the modern internal combustion engine

With the development of technology, the emergence of new materials, the application of new technology and new technology, the technical level of internal combustion engine from design to manufacture has been greatly improved.

(1) development trend of internal combustion engine

1. Improve the single engine power of internal combustion engine

The main ways to improve the power of a single engine of an internal combustion engine are to increase the working volume of the cylinder (that is, increase the cylinder diameter and cylinder number), increase the rotating speed, and increase the average effective pressure. For example, cummins K series diesel engines have 6 cylinders, 8 cylinders, 12 cylinders and 16 cylinders. Their power ranges from 450HP to 1800HP.

2. Improve economic performance

Modern internal combustion engine adopts supercharging technology, improving combustion process and improving mechanical efficiency to reduce fuel consumption and improve economy.

3. Improve reliability and extend service life

Modern internal combustion engine manufacturers widely adopt new materials, new technology and new technology, constantly improve the design and production process to improve its reliability.

4. Improve test methods

Modern internal combustion engines are increasingly widely used in electronic computer, automatic control, regulation, measure and record in terms of monitoring and testing, radioactive isotope is used to determine the wear parts, crankshaft, connecting rod is measured by laser holographic photoelasticity method, the stress of the piston and the body parts, such as situation, to check the quality of the machine.

5. Improve environmental pollution

The modern internal combustion engine is constantly improving in reducing the harmful components, odor and noise in the exhaust gas to reduce the environmental pollution when the internal combustion engine is running.

Restrictions on development

The development and progress of science and technology have promoted the development of production and the improvement of equipment manufacturing technology. However, in the process of development, it will be restricted by materials, manufacturing technology and other aspects, which will restrict its development. The development of internal combustion engines is currently subject to the following limitations:

1. Increase the limit of single machine power and cylinder diameter. In recent years, the maximum cylinder diameter of a large low-speed two-stroke diesel engine is kept at 1060mm, and the single engine power is maintained at 48000HP. The reason is that the machine weighs 1700t, and its resizing is limited by manufacturing, installation, transportation and maintenance factors. Therefore, the maximum cylinder diameter of the high-power medium-speed machine is stable around 650mm. The maximum cylinder diameter of modern gasoline engine should not exceed 108~117mm.

2. Increase the speed limit. The average speed of the piston of a modern internal combustion engine is 11~12m/s. If it is greater than 12~13m/s, it is restricted by factors such as inertia force, vibration, friction and wear of parts. If the internal combustion engine rotates too fast, its combustion process will deteriorate and its economy will be reduced. To this end, many manufacturers to increase the internal combustion engine speed, shorten the piston stroke, shorten the piston and the connecting rod length, improvement of fuel supply system, reduce the number of piston ring, improve parts of stiffness and strength of a lot of improvement measures.

3. Limit the average effective pressure of internal combustion engine. The internal combustion engine supercharger is an effective way to increase the average effective pressure, but the strengthening measures such as supercharging are limited by the thermal stress and mechanical stress of parts. Many manufacturers use cooling piston, piston, piston variable compression ratio, bimetal thermal regulating piston, secondary injection and secondary pressure, reduce the compression ratio, with high strength alloy steel parts, and high quality lubricating oil and other measures to improve the mean effective pressure.

In a word, the development of things will always be restricted by some objective factors. If these constraints are breached, science and technology will take a big step forward.