Main technical performance of diesel generator set1. Basic parameters
As a user and maintainer of diesel generator set, it is necessary to understand and master the main technical parameters of the unit. The main technical parameters of diesel generators are as follows:
Proportional rated power P(kW) or S(kVA) : P is the active power output from the generator (P= square root of 3IVcos), S is the apparent power of the generator (S= square root of 3IV).
In general, the rated voltage V: is 400V/230V, that is, the rated voltage of three-phase is 400V, and the rated voltage of single-phase is 230V.
As per the national standard, the power frequency unit is 50Hz and the intermediate frequency unit is 400Hz.
Automation rated current I: refers to the current size of the stator winding of a generator that allows for a long time to pass.
The three-phase generator is 0.8(lagging), while the single-phase generator is 0.9(lagging) and 1.0.
Derive rated speed n: the speed of the generator rotor at the rated power. At present, the three-phase generating set is mostly used at 1500r/min, while the single-phase generating set generally USES 3000r/min.
Ir: dc current passing through the excitation winding of ac generator under rated load condition.
Voltage Vf: the dc voltage applied to the excitation winding when the current is rated.
The power supply that provides the excitation current is called separately excited from the outside of the generator, and is called self excited from the generator itself. He and self - excitation are collectively called excitation modes. Different excitation modes are divided into parallel excitation type and compound excitation type. Self-excitation modes can be divided into salient pole type reverse magnetic field excitation, ac exciter excitation, reactance phase shift phase complex excitation, resonant phase complex excitation, three harmonic excitation, thyristor excitation and so on.
Evaluation reliability index MTBF: gjb235a-1997 general specifications for military ac mobile power stations stipulate that the average time between failures of diesel engines is 500h, 800h and 1000h.
2. Performance indicators of generating units
(1) voltage setting range
Voltage setting range refers to the range of maximum and minimum voltage that can be reached by adjusting the manual or automatic voltage regulator on the control panel when the generator is running at no-load rated speed. In general, the no-load voltage setting range is 95%~105% of the rated value.
(2) steady-state voltage regulation rate
Steady-state voltage regulation rate is the rate of change of steady-state voltage of a synchronous generator under all load conditions from no-load to rated load.
Where :U is the rated voltage or the rated voltage of 95;
U1 is the stable voltage after load change, and the average value of three-phase line voltage is generally taken.
The state I, Ⅱ, Ⅲ plant technical requirements is delta u = + (l ~ 3) %, technical requirements for Ⅳ class power station is the delta u plus or minus 5 or less.
Under normal circumstances, the steady-state voltage adjustment rate of synchronous generators is different under different load conditions. When the inductive load is added to the generator, the steady-state voltage value after load change is lower than that of no-load setting voltage. When adding capacitive load to the generator, the steady-state voltage value after load change is higher than that of no-load stable voltage. No-load setting voltage deviation depends on the size of the automatic voltage regulator (AVR) adjustment ability, in general, the higher the voltage regulator adjusting precision, no-load setting voltage deviation is small, and the smaller the steady-state voltage regulation.
(3) transient voltage regulation rate
Transient voltage regulation rate refers to the rate of change of instantaneous voltage in the process of sudden addition or negative load reduction when the speed and voltage of a generator are at no load and reach the rated value.
Where :U is rated voltage;
Us is the maximum or minimum value of instantaneous voltage when the load is suddenly changed. In general, the average value of three-phase line voltage is taken.
(4) voltage stability time
Voltage stability time refers to the time required for the generator to be in no-load condition and when the voltage reaches the rated value, from sudden load to voltage stability within a specified range, denoted by s. The provisions of the state I, Ⅱ, Ⅲ power plant for voltage stability of 0.5 ~ ls, Ⅳ class power station for 3 s.
(5) voltage fluctuation rate
Voltage fluctuation rate refers to the voltage fluctuation degree of a synchronous generator when the load is constant.
Where :UBmax is the maximum voltage when the load is constant;
UBmin is the minimum voltage at constant load.
UBmax and UBmin take the maximum and minimum voltage values of the same observation time under the same load.
(6) steady-state frequency adjustment rate
The steady-state frequency adjustment rate refers to the ratio of the difference between the frequency stability of synchronous generators and the rated frequency before and after the load change.
Where :f is the rated frequency of synchronous generator;
F1 is the maximum or minimum value after the frequency stabilizes when the load changes.
F2 is the frequency before the load changes.
(7) transient frequency adjustment rate
Transient frequency adjustment rate refers to the ratio between the difference between the instantaneous change frequency and the rated frequency before the change of load and the difference between the instantaneous change frequency and the rated frequency of the generator set during the sudden addition or reduction of negative load.
Where :f is the rated frequency;
Fo is the stable frequency before sudden addition or negative load reduction;
F1 is the maximum or minimum frequency of sudden addition or reduction of negative load.
(8) frequency fluctuation rate
The frequency fluctuation rate refers to the frequency fluctuation degree of the generator set when the load is constant.
Where :fBmax is the maximum frequency when the load is constant;
FBmin is the lowest frequency when the load is constant.
The maximum and minimum frequencies of fBmax and fBmin should be taken at the same load and at the same observation time.
(9) frequency stabilization time
Frequency stability time refers to the time required for the generator to stabilize from sudden load to frequency within a specified range when no load and frequency are rated. Regulations of the state, I, Ⅱ, Ⅲ frequency stability of the power station time is 2 ~ 5 s' Ⅳ class power station at 7 's.
(10) the sine wave distortion rate of no-load line voltage
The output voltage waveform of generator unit under normal condition should be sine wave, but it is found that there are three or more high harmonics in the induction electromotive force of generator. Due to the existence of high harmonics, the voltage waveform of generator output will appear sinusoidal distortion. When the voltage sinusoidal waveform distortion rate of no-load line is too large, it will cause the generator to overheat and reduce the insulation performance.
In general, the line voltage sinusoidal waveform distortion rate of the generator set at no-load voltage should not be more than 5%.