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Matching Scheme Between Diesel Generator Set and UPS

Feb. 25, 2019

In the matching use of UPS and generator, only a small number of backup batteries should be configured for UPS to be used when switching. Generator-to-market conversion can be either manual or you can set up an automatic switching device (ATS). When the market power fails, the automatic switching equipment (ATS) will automatically switch to the generator terminal, and the generator will start automatically after a certain time delay (which can be set according to the customer's needs) to provide power protection.

Matching Scheme Between Diesel Generator Set and UPS.jpg


In the practical application, according to the different customer's availability request to the power supply system, the configuration mode of UPS and generator is different, generally speaking, the common way is divided into single machine mode, parallel machine mode and so on, each kind of way has its own characteristics. The following are introduced one by one.


A. Stand-alone running configuration


According to the actual load power, the matching UPS single machine operation is selected. The structure diagram of the power supply system is as follows:

Power supply system structure diagram 1.jpg


The configuration is characterized by


1. Cost-effective, although the availability of power supply systems are common, but the composition of the system is simple and economical.

2. Generally speaking, there is no need to consider the late expansion of the system, do not need to use parallel UPS, equipment utilization.

3. The system has a single point of failure.


The main components of the system are


1. UPS mainframe: the UPS host can provide high quality power to the load regardless of whether the input power is available or not, and there is no output interruption in the conversion between the municipal electricity operation and the battery operation. With the built-in static bypass system, the availability of UPS is improved, and the load power supply during UPS shutdown maintenance is realized with the operation of maintenance bypass switch.


2. Backup battery DC circuit breaker: the backup battery is the energy source of the load power supply after the market power interruption, and the stored energy is supplied to the load after the UPS inverter. The battery circuit breaker mainly plays an overcurrent to the battery pack and protects the circuit break. Avoid battery damage and UPS failure expansion, in addition, circuit breakers in battery maintenance, replacement of man-made disconnection, can ensure the maintenance personnel's operation safety.


3. Diesel generator: In the high-power UPS system, the long backup time requires that the battery configuration required is large and the investment is high, therefore, the scheme of using the diesel generator plus the UPS is often considered; even when the two-way city is electrically introduced, The standby diesel engine can still be used as the final backup means, and the cost performance is higher compared with the large-capacity backup battery pack.


In the conversion between generator and market power, it is possible to manually set up automatic switching equipment (ATS), and the capacity ratio relationship between generator and UPS configuration, which is often due to the interference of harmonic feedback of UPS, sudden change of load current, and so on. The capacity of the generator is 2-3 times the maximum load of the UPS, and the capacity of the generator should be determined by taking into account the factors of the other loads carried by the generator.


4. Other: include related input, output distribution system.


B. Redundant parallel configuration


When the availability of single-machine system can not meet the requirement, two or more parallel UPS systems are often used in parallel operation to improve the reliability of parallel systems. The structure of the power supply system is as follows.

Power supply system structure diagram 2.jpg


Power R, S, T, N are connected to the UPS, and rocked by hand to see if the wire rod is loose and locked. After confirming the R, S, T phase sequence, the R N, S N, T N voltage of 220 V ±25% and the frequency of 50Hz ±1 were measured with a multimeter. Close the machine market power input switch, then close the machine automatic bypass switch, if there is a long sound alarm is the market power input wrong phase, should immediately correct the phase (arbitrary exchange input three phase of which two phase, no long ringing alarm means phase is accurate).


In high-power UPS system, if customers need a long backup time, they often need to configure a large number of backup battery packs. This configuration scheme has some limitations, a large number of backup battery packs need a larger storage space, but also consider the load-bearing problem of the floor, and the backup battery pack has a certain replacement cycle, and also needs a larger investment of funds. In order to solve these problems, the configuration scheme of matching generator with UPS is often considered, and the generator is used as the final backup method.


In the case of UPS and generator matching, only a small number of backup batteries are required for the UPS to be used for switching. The electrical conversion between the generator and the city can be manual or automatic switching equipment (ATS) can be set. When the city electricity fails, the automatic switching equipment (ATS) will automatically switch to the generator end, and the generator will be started automatically after a certain time delay to provide the power guarantee.


When the generator is connected with UPS, there exists the problem of mutual matching. According to the external characteristics of the generator, there are two factors affecting the stability of its frequency and output voltage: the high harmonic component of the load current and the instantaneous start-up of the load. The input power factor of traditional dual-transform UPS is only 0. 8, the high-order harmonic of the input current is more than 30%. When the diesel generator is used for its power supply, the stability of the frequency and output voltage of the engine is bound to be seriously affected. Therefore, the power capacity of the generator must be as high as 2.5 times of the UPS capacity in order to ensure the normal operation of the system.


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