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UPS power and diesel generators

Calibration of diesel generator unit power

Diesel generating set is made up of internal combustion engine and a combination of synchronous generators, internal combustion engine allows the use of the maximum power of restricted by parts of the mechanical load and thermal load, therefore, needs the maximum power regulation allows continuous operation, called nominal power. The internal combustion engine should not exceed the rated power, otherwise it will shorten its service life and may even cause accidents.

1.1 calibration power of diesel engine

According to national standards, the calibrated power on the internal combustion engine designation can be divided into the following four categories:
Stray 15min power: the maximum effective power of an internal combustion engine that allows continuous running for 15min.
Fuck 1h power: maximum effective power of an internal combustion engine that can run continuously for 1h.
The maximum effective power allowed by an internal combustion engine to operate continuously for 12 hours.
Continuous power: the maximum effective power that the internal combustion engine allows for continuous operation.

For a unit, the output power of a diesel engine is the mechanical power of its crankshaft. Civil power calibration of 12 h power of diesel engines, the diesel engine in the atmospheric pressure of 101.325 kPa, the environment temperature is 20 ℃, relative humidity of 50% standard working conditions, diesel engine at rated speed for 12 h during normal operation to achieve effective power.

1.2 rated power of ac synchronous generators

The rated power of ac synchronous generator refers to the rated power output during long-term continuous operation at rated speed.

According to the operating environment and technical requirements of the unit, the rated power output of the unit is calculated from the following formula:

PH = K1. K2k3neh-np (kW)


Rated power output of ph-synchronous alternator (kW);
Rated power output of NeH- diesel engine (ps);
K1-unit transformation coefficient (i.e., kW/ps) K1 = 0.736;
K2- diesel engine power correction factor;
K3- environmental condition correction factor;
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, denoted by K, that is:

K = NeH/PH

The value of K is affected by local atmospheric pressure, environment, temperature and relative humidity, etc., and the value of K is usually 1.6 for units with general requirements used in the plains. The K value of the unit with higher requirements is set at 2.

2. Matching relation between output power of UPS power source and generator set

UPS power enters by diesel generator power supply brought about by the special one of the problems is: due to the power of the diesel generating set is sent out by itself not only large voltage distortion (big) waveform distortion, and its internal resistance is far bigger than the mains electricity grid resistance. In addition, with the reduction of rated output power capacity of diesel generator set, the contradiction of increasing internal resistance is more prominent. When we use a diesel generator with a resistive load, the effect is not noticeable, however, if we use a diesel generator

Rectifier and filter type load (for example: computer and communication equipment, fluorescent lamp, all kinds of control cabinet phase shift speed regulation and control equipment), often meet very big trouble. The reason is that the above nonlinear load will reflect a large amount of high-order harmonic current to the diesel generator unit, especially the 5 and 11 harmonics which are more serious to the operation of the diesel generator.

Follow UPS design practices. The current UPS power supply, due to the different structure of the input "rectifier filter", will have a great difference in the frequency and size of the current harmonic component transmitted to the generator. The harmonic current components that may have the greatest negative impact on the normal operation of the generator present 5 and 11 harmonic current components with the working characteristics of "negative sequence current". Based on the above reasons, when the user chooses the generator for generating set "four stroke", in order to ensure the reliable generator driven to connect the UPS power supply system, the need to select the rated output power of the generator with the ratio of the standard process of UPS power output (currently more general empirical data) as follows:

UPS with 6-pulse rectifier technology:
Pg = 2.5 3 pu;

UPS with 12 pulse rectifier technology:
Pg = 1.6 2.2 Pu;

UPS using high frequency pulse width modulation rectifier technology:
Pg = 1.5 2.4 Pu;

Single-phase UPS using single-phase rectifier technology: Pg = 3-4pu;

UPS using input filter +6 pulse rectifier technology:
Pg = 1.8 2.3 Pu;

UPS using input filter +12 pulse rectifier technology:
Pg = 1.5 2 pu;

Pg represents the nominal output power of the generator and Pu represents the nominal output power of UPS.

In conclusion, in order to reduce the investment cost, the ratio of the capacity of the generator to the UPS capacity should be reduced. There are two methods:

Chinese-select generator with good dynamic characteristics of output voltage;
UPS power supply system with low harmonic current component reflection is adopted. .